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-