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-