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-