Tuesday, November 7, 2023

Setting the Furnace

Continuing the fun with the furnace today. It being October, of course we had another issue with Hapy not starting so I'll touch on that as well. EDIT: oops. Didn't post on Hapy. Next time, I swear!

Plan and Plan Again
today's end-state
Recall our plan to move the furnace into the crawlspace. We had the work bid by a furnace company and they quoted us $12kUS; we recognized that as a "go away" price and chose to do it ourselves. My biggest considerations are around the combustion exhaust, so I spent some time researching this. According to multiple sources, an 80% efficient furnace needs a double-walled exhaust (check) and it must have an upward pitch of no less than .25" per foot. I thought that was fairly flat, so checked other sources. From this data point, I collected others, like how far from the ground is the bottom/top of the exhaust pipe heading into the chimney, where the exhaust exists the furnace, etc. With these numbers in mind, I set to planning where to set the furnace.

planning a hole
Initially, I planned to put it directly beneath where it had previously been. This would have changed the routing of the conditioned air, gas line, cold intake and exhaust the least. Unfortunately, this would have put the furnace right against a main beam running the width of the house, making seasonal maintenance impossible. Additionally, that spot under the furnace had an unexpected rectangular concrete curb that was smaller than the space we needed cleared. So, the furnace is going to be adjacent to that curb'd rectangle, but because the distance to the chimney is around 3 feet, and I would like an angle of assent that is greater than the minimum, the furnace will need to be almost on the ground. So, a plan that wound have suspended the furnace from the floor joists will be replaced with a plan that has the furnace a-fixed to the ground instead.

Dig Another Hole
hole dug
Obviously, I am not going to simply set the furnace on the vapor barrier on the ground. Beyond the fact that there are safety issues, the furnace needs to be up off the ground height-wise to get the exhaust angle I want and to minimize both the conditioned air and gas line routing. Instead, I decided to dig a foundation and set the furnace on a stand. That sounds so simple until you get down to trying to dig a hole when the headroom between the dirt and the bottom of the floor joists is less than 2 feet. Starting with my tools, I had a 5 gallon bucket for removing dirt, a small-bladed shovel with a broken-off handle, a crescent-moon scraper thing and a 4-prong hoe. I cut 3 sides of a rectangle into the vapor barrier with scissors and peeled it away, leaving a 2 foot by 3 foot rectangle of rough dirt. With the tools I mentioned, I removed probably 60 gallons of dirt, leaving a 2 foot by 3 foot hole nearly a foot deep. This took almost 3 hours since the whole thing was done on my belly.

After taking a break for a few days, I returned and repaired the vapor barrier with thick black garbage bags. Along the cut edges, I made sure the plastic overlapped more than a handful of inches, and I lined the hole with sufficient slack so the additional layers of material would not cause gaps to form. Once satisfied, I added a 1/2 yard of gravel and moved it flat with a garden rake and then my gloved hands. On top of the gravel, I set 6 1-foot-square patio blocks. For each block, I made sure it was flat, and then flat to the adjacent block. As you can imagine for each block, this required multiple install-remove-install cycles and then additional ones to get the overall 6-block space flat. Between the gravel and the blocks, I probably spent 2 hours getting it level. This crawlspace patio will serve as a foundation for a stand upon which the furnace will rest.

Rack It
crawlspace patio
I initially thought I would simply use a pair of hot water heater stands for the furnace. I figured, they could withstand the weight of a full hot water heater so they could definitely hold a 70# furnace. I priced them but the cost and availability was not good. While searching, I found air conditioner stands designed to hold up to 400#. While local availability was again nil, the price was the same as for one hot water heater stand, and they are height adjustable. The rack I ordered was lost in shipping, so I switched the plan again. This time, I ordered a non-adjustable storage rack capable of holding 1000#. While I won't need anything that strong, this rack is also 2 foot by 3 foot in dimensions so it will fit into the hole, and potentially support the furnace better. When the rack arrived, I took the pieces into the crawlspace to consider my options. The rack is only "adjustable" by cutting legs to the height I need them to be. So.. adjust once, really.

prepping the legs
Accordingly, I wanted to be sure of my height, so I considered the exhaust run from where I expected the furnace to be over to the chimney. By suspending a long exhaust run, I could consider the angle of assent and the final destination for that edge of the furnace. From this, I could measure and math to the needed length for the furnace stand legs. You may notice from the pictures that I needed to move a couple of the blocks around too. Once satisfied, I took the rack back out from the crawlspace and cut the legs. Since the stand is really just unbraced legs, I added angle-irons at the bottom so I could mount the stand to the patio block. I then took the pieces to the crawlspace and re-assembled the stand. I set the stand where I planned, marked the holes on the patio blocks and took the stand apart again. Now, I could drill holes and mount the legs to the blocks. With the legs attached to the patio block, but not torqued down, I could set the stand top on, and then torque the concrete screws. I checked level along the way, pleased that all of this amateur work is level. Last, I bolted the legs to the top, using blue locktite so they would not work themselves loose from furnace vibration.

With the rack assembled, I was ready to move the furnace onto the stand. The gas line and the electrical will both enter the furnace from the bottom, and these will need to be routed so the "front" cover can be removed for seasonal servicing. The electrical entry has some wiggle room, but the gas line does not. I needed to account for these as I considered where on the stand the furnace would be placed. The stand is more than large enough to account for that adjustment and the space beneath it has ample room to run gas and electric.

rack installed
The furnace is heavy and the ceiling in the crawlspace is limited. I had feared that pushing and lifting it would be quite the undertaking for me (Boo had to work). My fears were not warranted, it turned out. To prevent the furnace from getting scratched up, I left in place the moving blanket in which we had moved it around under the house. This also reduced the friction as I moved it around. I set the furnace rear-ward of center on the stand, further from the chimney. This aligned with where I had expected it to go, mostly, leaving me with an exhaust run of around 3 feet along the plane, with a slight diagonal turn in it.. when I install it. The picture at the top of the post shows how it is right now, and no, the end furthest away is not touching the ground; it just kinda looks that way.

Once the furnace was in, I spent some time rough-assembling the exhaust. This consisted of taking the old exhaust down to it's most basic pieces and assembling a path that had the correct angles and took a slightly indirect route so I could route the cold air intake without interference. Once roughed-in, I took it back apart so I could easily get to the other side of the furnace. I have a great deal of "conditioned" air work to do, and having the fuller access will make that work easier.

This has gotten super long, and it has covered a few weeks of work. I was able to get another few hours in, but I'll couple that with whatever I get done next weekend into my next post. The calendar says 7-November, so, clearly, the weather is starting to get cold. We were fairly motivated when the daily high temperatures dropped into Autumn temps. We are getting overnight lows below freezing now, so there is no lack of motivation nor pressure. Still, I want to do it right and have a safe space once it is completed. Since I am doing it mostly by myself, it will only go so fast. At this point, I hope to have an operational furnace by the Winter Solstice.

Thanks, as always, for following along-

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