Furnace Finished

Today's post covers the final steps of completing the furnace in the NewOldHouse. In my last post, we had cut the hole for the intake and lined it with venting. Our no-longer-an-HVAC-guy electrician was coming over to test the system so I needed to solve a couple of things first. Like the exhaust venting.

Exhausted

operational furnace

When I disassembled the furnace last summer, I saved all of the exhaust venting. I figured I could reuse all of it and but whatever pieces I needed after that. When I did my test fit to confirm the angle (minimum is 1/4" per foot or 1" per 4 feet, I did 1" per 3 feet so better than minimum), I determined that I had more than enough pieces, but did not end-to-end assemble it. These double-walled vents are built to twist-lock and they only assemble one way, indicated by the arrow on the sticker on the side. They are kind of like big-boy Tinkertoys. The sections which can turn are an engineering marvel. They can be twisted into all kinds of off-set shapes or simple angles to get the venting to go where you need it to. My needs were simple, however. From the top of the furnace, I turned it 45* towards the chimney, ran a straight segment and then another 45* angle to head straight into the chimney clear-out hole and the liner contained within. I had retained the collar that threads onto the liner and rests in the brick and I had retained the connector at the end of the vent that abuts the collar, and it tightened down with a set screw. I had expected a couple of hours, and assembly of the chimney was less than an hour.

Using stainless steel pipe-hanger strapping, I suspended the chimney from the floor joists in 3 spots, all closer to the chimney than the furnace. I recalled from my angle testing that I needed the exhaust to enter the chimney near the highest point in the hole. So, I started there, pressing the vent up against the hole, and then worked towards the furnace from there. I used screws instead of nails so the straps could not work their way loose from vibration. Before crawling out claiming victory, I grabbed the cloth webbed strapping that I used to suspend the HVAC and supported the gas line from the floor in a similar fashion. Like the exhaust vent, I do not want the gas line to shake itself loose, potentially creating a leak. I chose to use the fabric webbing instead of the stainless because I thought steel-on-steel could either create a spark or slowly cut into the pipe. Cloth don't cut. Content, I contacted our electrician to test things.

Furnace Active

suspending the vent

Our electrician connected the thermostat to the control wire (which was just run out through the big hole in the floor) to test the system. He knew the state of the gas line, the electrical, etc, so I wanted him to run the test. Besides, I wanted a final review of the work too. The review was quick and positive, so he started a test.... shazam (not boom) we have central heat. While the cold air side of the furnace is just an open plenum reaching into the crawlspace, the test was successful. We ran the system for a bit while he checked for leaks and CO. Everything came back perfect, so we just let the furnace run and bring the temperature of the house up from 58*F to 68*F (14.5C to 20C). The following weekend, I returned to the cold air intake.

Return to the Return

With the furnace operational, I could get back to the intake with a little bit of time flexibility. I had the start of the intake from the floor side and I had the plenum jutting out from the intake side of the furnace. I just needed to connect them. I started with what I thought would be the hardest part: the sides from the plenum to the intake. In retrospect, I probably should have started with the floor of the floor-side to keep it square, but it's done now so who cares. Because the furnace is not 100% square to the house, the sides were not exactly the same length. I cut them the same though, so the south side is a little longer, jutting into the floor-side box by an inch or so. Regardless, the installs for the 2 sides were the same: I set the plenum side into the S-clamp, screwed in 2 sheet metal screws and then attached the other end with another pair of sheet metal screws. I shifted to the top and bottoms next.

Because the floor-side is not aligned with the plenum, the top and bottom were parallelogram shaped, with the ends measuring 20" and the sides at a angle around 45*. Again, because the sides were not exactly the same length, one cardboard template did not suffice. In the interest of conserving materials, the top was completed with multiple smaller sections and then seam-taped. The bottom, however, is one shaped piece added after the floor of the rectangle intake was in place.

Last, I got to the rectangle at the bottom of the intake box I built earlier. For this "floor", I cut another piece of sheeting 23 inches long by 16 inches wide and cut 1/2" notches out of each corner. 3 edges were then bent 90*, leaving the edge facing the furnace flat. I set the floor in from below, sealing the seams with tape, before shifting to the bottom of the intake-to-plenum connector.

 

Filtered

I had intended to get clever with brackets and such to hold the filter in place. I abandoned that simply because I ran out of give-a-shit by now and simply wanted filtered air. Since the south-side ran long into the airbox, that provided material to hold the upper corner of the filter. Using a filter to guide the shaping, I bent the overhang into a tang to hold the filter. The other corners simply stay put, and the 16 x 20 opening is perfectly covered with the filter.

where we started

We have been running the furnace since the filter was added and the air in the house is steadily getting less dusty. After all the work that's been done around here, the dust has been considerable. We have run a small portable filter, but it has not been as effective.

Well, that's the end of this epic effort. For a timeline, the furnace was disassembled in August and moved in September, the chimney repaired and lined in early October. The crawlspace patio was dug out, graveled and patio-blocked in late October; a stand attached and the furnace secured in early November. Air distribution was disassembled, cleaned, reassembled and insulated from mid November to early December. Everything else was crammed into the following 2 weeks. This job was quoted to me for $10kUS. If I paid myself $100US per hour, I still would have paid the HVAC company more for this.

 

This effort took place around a music festival, a family wedding, multiple holidays, kitchen planning, prepping and seeding a lawn, gigs, jams, love and life, and of course, my band (shameless plug: Sunkicks) recording, tracking and mixing an EP (release date 2024-Feb-2). Life is full. I expect there will be more construction posts, but Hapy needs some work done so I expect there will be a post or 2 on that, once I get to it. Thanks for following along-

Planning the Intake

Today, I further document the efforts to put heat into this old farmhouse. First, Hapy New Year. I absolutely recognize that it is past Winter Solstice and we have not had central heat since last spring. We have been getting by with small oil-based space heaters, as opposed to the ones with bright orange electrical coils and blower fans. Except for the sub-freezing cold snaps or windy days, the space heaters have been up to the challenge. On those sub-freezing days and nights, we have closed off sections of the house and hung blankets over doorways, etc. It has been an adventure. A couple of weeks ago, we had that which had once been thin gross cellulose insulation in the attic removed. So, what little heat that grot held in was now escaping to atmosphere. If being cold were not enough of a motivator before, it just went up another notch

In my last post, I could see the finish line. The furnace had been moved, mounted on a stand and angle-confirmed for safe exhaust. The conditioned air side had nee disassembled, cleaned, re-assembled and insulated. The gas line had been reconfigured to feed the furnace, with a "T" fitting so we could tap into it for the stove later. The electrical had been completed to the furnace, with an integrated worker-safety switch. The thermostat control cable had been wired into the furnace. So, what remained? Connecting the thermostat to the control cable, the exhaust vent and a cold air return. I started with the cold air intake, but shifted midway once I concluded that we could get the furnace running for a short time without a cold air return, drawing air mostly from the crawlspace.

Best Laid Plans

completed box

My original plan for the cold air intake was, again, to reuse as much of the HVAC stuff that I had removed from the furnace as I could, and add what was needed. When I looked at the pieces above the plenum, though, I decided they were not up to snuff. Whoever built that intake restricted the airflow considerably. Consider that the plenum is 16x20. The intake grate and filter are also 16x20. In between, they built a 90* turn using a 15x15 box. No wonder the furnace made so much noise when it was running; it was begging for more air. Simple math: 16x20 = 320 square inches. 15x15 = 225 or over 30% smaller. When discussing this with our electrician, he indicated that the restriction was probably not as bad as I thought. I never sought to be an HVAC expert; I just want heat and a quiet running system.

My plan was to install the original intake-side plenum and simply reverse it back on top of itself and then route over to the hole in the floor where the furnace used to sit. In theory, this was a great idea. There's an old Yogi Berra quote about theory and practice (In theory there is no difference between theory and practice - in practice there is). I think it applies here. The intake plenum was nearly as big as the conditioned-side plenum, and once attached it took up more than 50% of the space between the floor joists above and the vapor barrier on the ground. There would be no doubling-back on itself. For a moment I thought about having it turn on it's side, but that would route it where the exhaust vent is. We can't have both things in the exact same space.

I could route the cold air intake around the chimney and under the main beam of the house twice to leverage the existing hole where the furnace was. I started to take measurements and discovered that the space between the bottom of the beam and the top of the concrete curb underneath where the furnace used to be... was a little over 12 inches. I can't run a 16x20 rectangle through the 12" space. I could neck it down, but that would decrease air flow, create noise and potentially shorten the life of the fan since the reduction would be, like 25% (16 to 12). We have already suffered a 30% reduction before, and all of the downsides with it. Now, I could create a pass-thru that's like 12 x 26 so we don't restrict air flow, but when I took a minute and considered how long that intake would be, I figured it was time for a new course.

Before I got too wrapped up in the next step, I installed the intake plenum, sheet-metal screws, tape and all and then suspended it from the floor joists with webbing. With the plenum in a fixed location, I could take some measurements and make some plans.

New Plan, New Hole

simple floor grate

I started by determining where the joists were and marked them on the floor above. Since the joists are 16" on-center apart, the usable gap between the joists is about 15". While obviously that is less than 16, it is greater than 12, so I could put a hole anywhere without touching a joist and the neck-down would be significantly better than running it in a big circle around the chimney in the crawlspace. I also figured that the shorter the intake, the fewer opportunities for leaks. Consider that the area of the house above the furnace is our emerging kitchen. We had been making plans accommodating an intake along one wall, making an allowance for a space without a cabinet for that intake. Now that the intake will no longer reuse that big hole, we can reconsider the cabinet plan there, and have that floor fully repaired by our flooring guy (Thomas).

Both Boo and I have lived in older houses before and we both recall having air intakes in random places in the floor. For whatever reason, they seem to usually appear in hallways, so you get to walk on them a lot. Since there doesn't appear to be much reasoning other than have them centrally located, We are going to make the intake run as short as possible, setting the intake alongside the chimney. This will allow for a simple 90* turn at the end of the plenum straight up to the floor. I will add a little bit of ducting to align between the floor joists, but it will be quite short.

Cutting a hole in a perfectly good floor is hard to bring myself to doing. I ultimately asked our general contractor to do it. I figured he could get the cut straight and along the top of the joists on his first try. In the picture on the right, here, you can see the floor grate I got on Etsy from a guy (Doug) who hand makes these in Minnesota. Big fan of Etsy's handmade stuff.

Return

building the box

With the hole cut, I had a clear target for building the rest of the cold air return. My plan was to have a simple straight down, 90* bend to the plenum. At the point where the venting turns, the air filter sits and it is replaced from above, after removing the air return grate. To help hold the air filter in place, I planned to add a small rib an inch to the plenum side of the 90* bend. Last, I added a flip-down tab above the filter so that after the filter was set in, the tab would rotate down to hold it in place. Back to that Yogi Berra quote, the reality, however, was not simply applied theory. I mean the applied Yogi Berra theory would be there's no difference between what you plan and what you build until you start building. In that spirit, I got after it with a stack of 24" by 36" HVAC sheeting.

I started with a simple box that lined the sides of the joists down to the level where the plenum was. The top of the plenum is about 1 inch below the floor joists, so the box was little more than a 3-sided rectangle. With one sheet, I bent the side furthest from the furnace into a wide U, with the center section 22" across. I pre-drilled holes to connect additional pieces and screwed it into the floor joist level with the top of the joist. Adjacent to the shorter sections of the "U", I added 10-1/2" and 12-1/2" sides (also 24" long). The wider of the 2 sides was bent 90* for the final 2-1/2", and that short stretch runs along the furnace-facing side, reducing the aperture from 22" to 20" to align with the size of the plenum. I left an extra 1/2" of HVAC sheeting so I had something to connect the next pieces to. Along that 4th edge, I ran an 8-1/2" strip of HVAC, covering the floor joist plus an inch. That last half-inch was angle bent rear and upwards to provide something to attach to. Once I got this far, I shifted gears over to the exhaust vent so we could get the furnace tested while our electrician was available.

I am going to stop here since things got moving really quickly around the electrician's visit. Thanks, as always, for following along-

Completing the Furnace Conditioned Air

In my last HVAC/furnace post, I had described the conditioned air plenum, and my efforts to create and then attach one. Today, I get on with the rest of the "conditioned air" venting. As before, I call it that so there's no confusion between the venting that has the output from the furnace and the venting that is the cold-air return side that feeds the furnace.

Rectangular Vent Prep

long arm

Recall that the crawlspace in this house had been infested with rodents. I mean it was bad. We had it emptied of rubbish and insulation by a team who seemed borderline hazmat. The work was disgusting, that team was amazing. They replaced some, but not all, of the circular vents with insulated flexible venting, but left the larger rectangular trunk lines. Perhaps they thought those vents were clear and clean or maybe they just wanted to complete the job (not that I blame them). Those vents were unobstructed, but far from clean. I had intended to clean them in-place with a microfiber cloth on an extendable pole. Once I got to really looking at them, I knew this was simply not going to be sufficient, and chose to ignore the fact that these vents were used last winter. Yuck.

ga-ross

To remedy, I dismantled them, and hauled them piece by piece out of the crawlspace into the backyard. Using the highest pressure setting on my hose-end sprayer, I jetted off the worst of the caked on filth, inside and out. Then, with a scrub brush and dish-soap, I cleaned each piece inside and out. Once rinsed, they were set aside to dry and I took one of my most-needed showers ever. The insides are clean, but I noticed a very slight brown staining. I concluded that it's probably from many years of people smoking tobacco in the house. I considered spray-painting all of the inside surfaces, but decided that the off-gassing of the paint was worse than whatever caused a stain (but was now gone). I did, however, spray paint bits of the outside of the venting which had rust or remnants of the old fabric (asbestos-imbedded?) tape which was removed by the hazmat guys.

Rectangular Vent Install

cleaned

Once cleaned, partially painted and moved back into the crawlspace, I was ready to start installing. I started at the furnace and worked by way out. First were the bits that connect the plenum to the rectangular vents. These are angled and change shape from one end to the other, converting whatever size hole you had in the plenum to the size of the vent. I found that by bending the lip wide open, the piece fit easily, and then just fold the lip back against the inside of the plenum. With high-end foil tape, I sealed the seams from inside the plenum.

I read about and considered using a brush-on goop to seal the seams but decided that painting goop while army-crawling around a filthy crawlspace just did not sound like a great idea. Consider too, the goop seals as well as tape, for the most part, and it's effectiveness is directly tied to user application. So, again, lying prone (or supine) with a brush of goop sounds like errors would abound. Taping is hard enough when you're lying down.

Once the 2 main bits were connected to the plenum, I first did a 90* turn bit on the smaller distribution arm (8 x 12 rather than 8 x 18) and then shifted to completing the larger arm. This took many hours, even though there were only 4 sections. For each section, I would wrestle the rectangle into the connectors on the end of the one prior. I used another section of HVAC to hold the far end up while I fastened the new piece to the old with sheet metal screws. Then, I suspended the far end from the floor with nylon webbing stapled to the floor joists above. Once free-standing, I sealed the seams with that high-end foil tape and then wrapped the vent with (R8) foil-wrapped closed cell HVAC insulation. I expected the venting to take a little while, but did not anticipate that the insulation step would take maybe twice as long as the venting assembly. I took care to seal up the insulation seams, but the time was consumed by, again, lying down and wrestling large rectangular insulation panels, trying to wrap them around a rectangular vent which had circular vents jutting out of it. I don't know if having the insulation sealed up tight matters much in the grand scheme, but I made sure they were relatively well sealed anyway. I spent probably 8 hours in total getting the larger arm assembled and insulated.

original round vent

Before I moved to the smaller arm, I attached the round vents to the larger arm. I had initially intended to remove the original remaining round vents, believing they were not up to snuff. While I was assembling the larger arm, I looked at the 2 remaining larger circular vents (picture on the right shows what condition they were in) and while there is some dust and more brownish stain, there is no rodent evidence. What I did not expect was just how close the rectangular venting is to it's original location. The round outlets on the rectangular vents are a few inches off center and less than a foot away from the original. So, I placed a short stretch of insulated flexi-venting between, taping both the inner hose and the outer insulation wrap at both ends. I did not capture a close-up picture of that, but I found that these sections were so short that it was actually easier to remove the inner sleeve from the insulation, attach it to both ends and then wrap the flexy-hose with the insulation jacket afterwards.

Smaller Arm

When I changed the vents around on the larger arm, I inadvertently removed the vent intended for the bathroom. I will re-integrate that later. The bathroom floor vent has not been connected since we first got the house. Recall above where I described where I made the cut in the plenum, I removed another vent access, which was direct-connected there, to the bedroom. Since it was not part of the air design plan for either arm, adding it to one or the other could upset the pressure for the other destinations. Since the bigger arm distributes to the west side of the house and the smaller arm goes east, I decided to tie it into the east (smaller) arm simply because that's the side of the house the bedroom is on. As it stands, the smaller arm only had 2 destinations (the kitchen and one main living space) so I felt adding a 3rd there would be less intrusive than adding a 5th destination to the larger arm. Also, I considered that the kitchen is an uninsulated space, cordoned off from the rest of the house with plastic. I decided to connect the bedroom to the used-to-be-kitchen vent in the smaller arm. When the kitchen is ready for a vent, I'll cut a hole and tie it in or I will move the bedroom connection back to the plenum.

short arm completed

The smaller arm took less time, and other than threading new stretches of flex-hose from the arm to the vents, it was a reflection of the larger arm work. Each arm-piece-to-arm-piece connection was metal-screwed in multiple spots, foil-taped and suspended with webbing. The entire arm was insulated with the R8 closed cell stuff, each circular connection was double-taped (inner tube and insulation jacket). The only real anomaly was with one rectangular-to-circular connector not aligning between the floor joists because of the furnace move. To remedy, I simply flipped it upside down (see picture on the right) so it is on the bottom instead of the top. I'm sure some HVAC person somewhere doesn't like this, but it fits, and it's sealed. All told, building the large arm took a weekend while attaching the circular vents to it and doing the entire smaller arm took a second weekend.

At this point, it had grown dark on a Sunday afternoon/evening. So, I picked up my tools and supplies and put everything away. With some scrap paper and a pen, I started contemplating the cold-air supply side. I will start that work next, but I think getting the "conditioned air" / distribution part completed was a significant milestone. Sure, I still need the gas hooked up, the exhaust re-assembled and suspended, the cold air return I just mentioned, the trigger wiring done and, last, the electrical (and walk thru by our electrician / HVAC guy). Yes, that is a lot, but I feel like the largest, hardest part is now behind me. I know... "famous last words".

Thanks, as always, for following along-

Starting to Solve for the Furnace Conditioned Air

If it feels like this furnace saga is unending, it definitely feels that way on my end. Every passing day, the weather gets colder, but I will not short-cut this work. It being correct is too important for health and safety. I do want to stress that our electrician, Gary, owned an HVAC company and did hundreds of furnace installs. He consulted on the plan and will be reviewing my work / confirming everything when he connects the electrical at the end. So, we keep going. Honestly, the hardest part is putting on cold clothes in a cold house to get into an even colder (and, frankly, filthy) crawlspace.

Anyway, today, I am focusing on what I refer to as the "conditioned" air. This is the air that is leaving the furnace, presumably warmer, but on those days we are only running the fan, it will just be filtered. For simplicity, and since this was the way I did it, we are working from the furnace exit to the floor vents. Sadly nothing was as easy as it seemed in my head, resulting in this expanding to cover many weekends. This is just the first part of it.

Furnace Mounted

checking pitch

Before I shift to the new topic, I had a couple of final things I needed to do with the furnace: confirm the pitch and attaching it to the stand. To confirm the pitch, I found a straight bit of hard plastic tubing that was over a meter long. At exactly 1 yard (36 inches or 3 feet), I attached a 1 inch thick piece of scrap wood. Recall the minimum pitch for the exhaust from a furnace installed on it's side is 1/4 inch of rise per foot (or 1 inch of rise per 4 feet). I figured that if I made sure my work was at 1 inch per 3 feet I would have exceeded the minimum and have some wiggle room for the furnace or the ground shifting. I set the plastic tube jig on top of the furnace and set the level on top of that. Bubble between the lines? Yes, so somewhere along the way between my level crawlspace patio and the top of my furnace the world tilted. Glad it pitched the right way for me. I had planned to shim the exhaust-exiting end. Do I want to know why it shifted? Yes, but I think because the furnace is offset rearward (you can see the stand in the lower right corner of the picture), the weight of the burner is causing the tilt.

Feeling fortunate, I grabbed a longer run of that plastic tubing to simulate the exhaust from the furnace to the chimney and set the jig on that. We have good angles, though I will need to add a brace near the chimney end to make sure it doesn't relax downward over time because the exhaust needs to enter the chimney near the top of the hole. To make sure the rest of my efforts don't cause the furnace to move, I sent sheet metal screws through the now-bottom of the furnace into the stand so it is fixed-in-place. I re-checked the pitch, and it is still 1 inch for 3 feet even after sending screws through. On to the conditioned air!

Plenum Pablum

building a plenum

The first thing the conditioned air enters is a box called a "plenum". It acts as a singular junction box for all of the conditioned air, but it does more than that. Consider what happens when your furnace kicks on. The fan starts and very quickly air pressure increases at the furnace outlet. To cushion the system from that large pressure increase, there is the big box (plenum). Secondarily, this box allows the air to flow smoothly and evenly into the ducts. If the box is too small, or nonexistent, the air would not enter all of the vents evenly, leaving some spaces with too much airflow and others getting an old microbus heating system experience (virtually nothing). I am over-simplifying it as there are air dynamics about back pressure from the branch lines, etc. that I really don't understand.

The original plenum to this house was just that. The original plenum, as in it was the plenum when the heat source was something other than gas, we believe. I think it may have been coal based on the soot we have found and then oil since there's an old oil-tank shed in the back of the house. Still, airflow is airflow and if the thing that is pushing the air is heated by coal or wood or geo-thermal fanciness, and the venting beyond the plenum is the same, I would expect the plenum should be relatively the same. Of course, 15 years after the house was built they added 2 rooms to the back, so maybe the plenum has been the wrong size since. I suppose, this could be a recently-added bit, but none of the other metal venting looks remotely new.

furnace entry

The plenum was almost a meter tall and about 2 feet square. From my research, this is excessive, but was unable to arrive at a clear answer as to what size it should be, like with a calculator or simple rubric. The most basic advice seemed to be "make it a little bigger than the outlet of your furnace". I am fairly sure that would lead you to a too-small plenum and poor circulation impacts, but I defer to experts. Regardless, I took all of this and decided that I needed the plenum to fit in the space I had, so if it was smaller, well... we'll just deal with it and worst case I'll make another one later. I simply built what would fit in the space without digging again. 

Plenum Fab-lum?

So, what did I do? The original plenum had the air enter from above and then it routed air sideways out 2 rectangular vents and one round one. In order to keep the orientation of the rectangular outlets, I needed the top covered and a new entry added on one of the other "horizontal" sides. In order for the 1-meter-tall plenum to fit into my not-quite2-feet-high crawlspace, I needed to shorten it too. So, I measured and then cut (with the death wheel) 9 inches down from the top in each of the 4 corners. Then, I folded the sides in like a cardboard box. With a hammer and dolly, I squared the newly folded lines. Content with the shape, I drilled and then pop-riveted the new top in place (upper image). Last, I sealed all of the edges with high-end foil tape.

Plenum added

So, I have a box, but no entry for the furnace. Onto the side which had a circle-vent, I applied blue tape and then measured the dimensions of the furnace exit. Half an inch inside this rectangle I marked the actual cut line. That extra 1/2" will be the lip which will press against the exit "flange" on the furnace. I cut the hole with the death wheel, turned the lip with some pliers and cleaned up the fold with the hammer and dolly again. The circle-vent used to feed the bathroom, which does not currently have a vent. If we re-introduce a vent into that bathroom, I can re-integrate it into the system.

I lowered this new plenum into the crawlspace, army-crawled it past the furnace and attached it to the furnace. It barely fits between the ground and the floor joists, but it does and it did not disturb the angle of the furnace. Once it was in place and the edges sealed, I was ready to look back at the main trunk / vent lines (the big rectangular ones).

As often happens when I get to posting about something, this got very long. This feels like a logical transition point so, I am going to stop here, and pick it up next time. Thanks, as always, for following along-

VW Bus Cold Air Intake

Back when Hapy was getting regular long summer drives, I noticed that the engine bay would get pretty warm. Recall back to the Newberry trip report for example. So, I put together a cold air intake concept to drop the temp going into the turbo inlet. I really do not expect to notice much of a performance difference. While I understand a cold air intake can reduce intake temps, and improve engine performance by a handful of HP, I just don't think what I did will have that kind of impact. Still, it was fun to do.

For someone running the original engine, with the engine tins and surrounding foam in place, this modification makes absolutely no sense. The tins already effectively separate the hot side of the engine from the air intake. If you have lost your tins (or foam), and for some reason cannot replace them -or- you are running a modified engine where tins cannot be fitted, something like this might work for you too to keep the hot side from meaningfully impacting your intake air temperature. This whole bit is triggering memories of that old Burger King advertisement about keeping the hot side hot and the cool side cool.

 

Before I begin, today marks the Ides of March. I am not really sure how to recommend ways to celebrate that. Pay off your debts? Enjoy a celebration picnic with revelry and drinking? Wander out of town in an animal skin? Perhaps we can all just hope Putin will suffer Caesar's fate this day for the inhumanity he is visiting upon our Ukrainian friends. Whatever transpires, in a couple days, it will be St. Patrick's Day. So, I will just get some rest to prepare for that. Hopefully, we can tip a drink within 2 meters of dear friends to celebrate a post-pandemic Spring.

Orientation Thoughts

On topic, consider the VW bay window bus engine bay from the rear hatch (picture on the right is of a '68). Most to the rear on the left is an otherwise unused battery tray. Some folks (like late-bay Westy-drivers) have a luxury battery there to power the fridge when shore-power is not available. On Hapy, there are just a lot of wires, so it's actually not much to look at. The spare tire well hangs down towards the front, meeting the rear tire well. Above to the rear there is a tall open area that eventually reaches the finned ear behind the rear window. Running along the bottom edge, front-to-rear, there is a small lip or perhaps a pinch weld that's about half an inch tall. My thought: wall this in, and create a pass-through for my engine intake, isolating it from the heat generator (engine exhaust and the turbo). Keep the cool side cool.

Parts

My go-to for all things metal fabrication these days (at least for air movement) is HVAC flashing, and this is no exception: I started with some basic 20ga HVAC flashing that I had lying around ($0). Onto the air intake, I need to add a 90* turn ($14US from siliconeintakes.com) so the air filter which used to sit next to the rear end of the spare tire well can instead go into the new cavity. The last piece is pipe flashing (like this) which cost me about $18US to provide safe passage for the aluminum pipe through the HVAC. The air cleaner needs to fit through the hole left in the basic wall when the pipe flashing is removed, so getting one large enough for this purpose was important. I had some HVAC flashing lying around, but at the time I did this, a 4 foot by 3 foot sheet (common size) would have run about $20US. A smaller sheet would cost a little less, but not much. So, all-in this would cost around $50US plus your time.

Cleanup

paper model

I learned along the way that this wall idea is not as straight-forward as it looked. As I started trying to model with a large sheet of brown paper, I realized there were some wiring clean-up items left undone. I tidied up the wiring a little bit, and strung as much as I could into the upper rear corner where the fuel vent line passes into the new cavity, securing them together (and to the vent line) with a cable/zip-tie. Below this bundle of wires, at the rear-most bottom, a couple of wires need to pass as well, so that makes 2 gaps to manage. The front-to-back T-12 cable (See the Chasing the Hapy Electrical Gremlins posts for context) routes into the engine bay where the flat rear meets the upward angle of the rear tire well, so that's a third gap to seal. Last, the stock TDI engine management cable routes into the engine bay from under the center-point of the spare tire well, so that's 4 gaps. Had I planned for this when I did the wiring, I could have potentially cut this list in half, or even reduced it to one. I preferred to not revisit the electrical again this winter, after last winter's adventure. So, I made 4 distinct gaps for wires to pass through. I numbered them in the image of the paper model on the right, here.

Model with Paper

With the wiring bundled, I could start working on the wall... with a model. I started with brown packing paper. These days, so many things ship with large sheets of brown paper as the padding, and that stuff is nice and thick, and sometimes wide enough for things like this. It is also 100% recyclable (unlike the bubble wrap), so I'm doubly a fan. Anyway, I started with a basic measurement: 22 inches deep by 16 inches tall. Of course, I discovered that the hole is not square, and the 22 inch measurement is correct from the bottom of the rear wall to the point where the engine bay curves towards the fuel tank. The top is more than 24 inches from rear to top of fuel-tank compartment. Also, the section is not flat: the bottom curves slightly inwards while the top remains straight.

 

cardboard model 1

Then Cardboard

After a few rounds of test-fit, measure/cut and some added painter tape for strength, or for adding material for sizing, I arrived at an approximate paper model. I transferred the paper model to cardboard with a pencil using some tracing and some angle-square. Consider: the rear wall makes a 90* angle with both the top and the bottom, and (I thought) the rear wall is straight. The top run is straight, though I chose to cut some of the area away which would have been pressed against the spare tire well. I made this choice for 2 reasons: first, the vacuum control valves are mounted there, and I did not want to move them. Second, having a sheet of metal against metal like that would have created rattle noise I would have to solve. With my outline and wire bundle cut-outs defined, I cut the line with a razor blade and cleaned up the edges with scissors.

test-fitting a model

With this stiffer model, I performed another few rounds of test-fit, measure/cut until the cardboard wall completely covered the gap, the wire bundles easily fit through their respective gaps and the edges of the wall were clearly in a place where I could envision mounting. The final cardboard model, in-place in the picture on the right, also eliminated a large triangular shape from the lower front corner which would otherwise have set against the driver-side wheel well. Similar to the cut out from the spare tire well, having a large metal-to-metal contact area would create a vibration-noise opportunity. Looking back, this cardboard wall looked at least as good, if not better than, the final metal wall.

Then Model with Cardboard Again

The front and bottom have a lip I can easily attach to. The top and rear will need some kind thought and some creative drilling. One additional consideration: on the rear pillar, there are grounding points which cannot be disturbed. I decided to add a small tab on either side (above and below) to hold the new wall to the rear. The top will mount directly to the spare tire well for the front 2/3rds. The rearmost section of the top, will not get any treatment at all. I thought about it, and decided that there were already enough planned fastener points to hold the wall stable without adding another hole in the cabin floor. I transferred the cardboard model to another sheet of cardboard after a few repeated fit-attempts. I want to make sure the HVAC, when cut, will fit correctly. Last, I modeled mounting tabs with scrap cardboard and more blue painters tape so I would have them in the right place and the right size when I cut the HVAC. The picture above was taken before I added the mounting tabs to the model.

Plan the Intake Pass-Thru

note imperfect rear line

With the cardboard wall in place, that side of the engine bay looked considerably better... well, it hid what looked bad, anyway. Motivated, I planned the intake route based on the placement of the new 90* aluminum intake pipe. I made a rough cut in that general area of the cardboard wall and put it back in. The 90* pipe is too long on both ends. I needed to remove about 4 inches from the end that juts into the cavity, so there would be room for the air filter (7" tall from rubber grommet to chrome top) without it touching the side of the bus. The filter housing allows for up to 2 inches of pipe before it bottoms out, so there is some wiggle room for my cut on that end. Similarly, the engine-intake end of the 90* pipe needs to be shortened. Again, the silicone collar that attaches the new pipe to the air flow meter on the end of the intake allows for a couple of inches of play. I did not make the actual cuts to the pipe at this point, though.

 

The intake looked about right, so I added in the pipe flashing. I drew the edge of the flashing on the cardboard and then drew another set of lines 3/4-inch to the interior of the tracings. I cut the smaller square out of the cardboard, making a square that was about 6-1/2 inches per side. I tested that I could pass the air filter through that hole. Otherwise, maintenance of the air filter would require removing the entire wall. It fit, but barely, leaving about a quarter of an inch on each side (the widest part of the filter is 6-inch diameter).

Adjustments

HVAC test fit

I transferred the last model above to a sheet of HVAC, but I did not fit properly and had to do another round of cardboard before I was able to get a good HVAC design. The big barrier for me was the location of the vacuum valves (so probably not an issue for anyone else). Ultimately, I removed the valves that were no longer being used (anti-shudder and EGR), and moved the turbo controller to the rear mount. This freed up the front edge of the spare tire well. The second issue will appear for everyone who tries this: I thought that the rear inner wall was perpendicular to the floor and ceiling. It is not. Consider, the contour of the rear of the bus has a slight curve; the inner skin does as well. The picture just above on the right shows the deviation from pure vertical / 90* angle. That picture also shows on the bottom rear corner that the body panels do not have clean 90* transitions either. I cut off that little tab in future efforts. With these considerations, the models were working: showing me how to get to a viable wall.

 

Assemble

prepping the wall

For the second time, I transferred my cardboard model to HVAC flashing, complete with marks for mounting tabs. I cut the HVAC with my tin-snips, and formed the wire pass-thru's with pliers. For clarity, I marked the outline of the hole and then cut crossing lines through the center of that marked area. I folded the triangular bits of HVAC back upon itself to create the opening while also avoiding a sharp edge where the wire bundles would pass. With a hammer and dolly, I smashed the fold-back flat. By doubling the material at the openings, the wall was effectively stiffened; I had not anticipated, but will definitely appreciate that. For the upper rear wire pass-thru, I left a tang or tab nearest the rear wall that I could bend back into place, so the rear edge of gap #1 (visible in the pictures of the installed cardboard model) could get covered up once the wall was in place. Once I drilled the mounting holes in the tabs I set the wall in-place, marked the holes on the bus and drilled them out.

Pipe Flashing

wall installed

At this point, I considered how I would attach the pipe flashing to the HVAC. First, I transferred the square-ish hole from the cardboard model to the HVAC, and cut it. I need to be able to remove this section so I can clean the air filter. I drilled out 4 holes in the pipe flashing, one each per side, where the rubber had dimples for that purpose. I set the pipe flashing in place and marked the HVAC. These spots were within the folded-back HVAC, making the area thick enough to tap. Sweet! So, with a M4 (.75 thread-pitch) tap, I tapped the 4 holes in the HVAC. Into these threaded holes, I sent bolts from the cold-air side with thread-lock so these bolts will act like studs for the pipe flashing. The picture above on the right shows the studs through the HVAC.

Finishing

cold air intake

I moved the wall into place and secured it to the side of the bus with sheet metal screws. I had thought about tapping the holes and using bolts instead. The holes were too hard to access with a tap and I don't think this wall will be coming out with much frequency anyway. Even so, removing some sheet metal screws is not hard. With the wall in, I re-checked my measurements for cutting the aluminum pipe. Once verified with the permanent position of the pass-thru, I cut the pipe down. I pushed the shortened 90* aluminum pipe through the rubber collar and attached the air filter. I sent the air filter into the cavity, and maneuvered the not-filter-end of the 90* pipe through a connecting silicone collar to the rest of the intake. I set the pipe flashing against the HVAC and threaded on the 4 9mm nuts.

 

When I maintain the air filter, the process will be the same as this initial install: remove 4 nuts, loosen the hose clamp and remove the cold air intake assembly. After I clean the air filter, I would re-install by fitting the flashing atop the studs, finger on the nuts, get the pipes connected and then cinch down the nuts.

final install

Now, Hapy has a cold air intake, and the left side of the engine bay is no longer a complete visual downer. Instead, we have a nice clean wall and the engine will get colder air than it used to. This wall does have some small gaps, of course, so the air will not be as cool as it could have been. Perhaps I will circle back later with something on top of the wall to better seal the edges and pass-thru's. Longer term, I may apply a thermal layer onto the engine-bay side to help reduce temperatures even more. The picture on the right, here, shows it in its current (final) state, though a keen eye will see that I had not yet plugged in the AFM (air flow meter) when I took the picture.

 

This took quite a while to actually complete, having started before the 2021 winter holidays. I had other things going on, and this was a lower priority for sure. Also, there were multiple modeling cycles as I figured out the unique puzzles added to the driver side of the engine compartment from adding a TDI (and related vacuum control valves) to the mix.

That's it for today. Thanks, as always, for following along-