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Upgrading the HVAC

20th May 2011


We were almost starting from scratch with the heat and air system. The AC compressor was gone (stolen), the furnace and AC coil housed in the crawlspace were antiquated, and the ducts were missing much of their insulation. The good news was that we could simply retrofit and new HVAC to the existing ducts with minimal changes. We also discovered that the Gas Meter had been recently relocated from the front of the house to the side. All new stainless steel flex gas lines were installed to the furnace and hot water heater. The old gas lines running to each room were left intact, although not hooked up to anything. I started by removing as much of these old lines as I could get to easily.

We decided to go with a packaged heat and air unit. The entire system would be located outside the crawlspace. The existing crawlspace access and concrete pad needed to be enlarged but that was an easy fix.
I used the existing concrete pad and poured and L-shaped extension to form the new pad. I extended the opening through the foundation 20 inches and framed the opening with 2×6 headers and filled the opening above the header with salvaged brick. The electric was already available so all that was required was a short extension to the gas line. There was enough salvaged gas line to accomplish this.

The real work involved supplying the air to the ducts. With the help of a friend who does AC work we came up with a great solution. The plan was to build a plenum out of duct board. From there we would use flexible ducts of various sizes to connect to the existing ducts. This would allow us to build everything out side the crawlspace. Duct board is a great product. You can use special tools to cut perfect miters and lap joints, but I used a regular box knife with great results. Using metal tape and duct starters, I had the plenum built in matter of an hour or two.

Hooking up the system was tedious and time consuming but it all went together just fine. One by one we ran flexible line from the plenum to each trunk line using flex duct.

10 inch line going to upstairs registers

12 inch lines connecting to HVAC unit outside

The final task was to rebuild the air return. Originally the air return was the entire space under the stairs. The previous installer simply cut a hole in the floor to accept the duct line and a filter cover on the wall in the living room. The problem was that the space under the stairs was not sealed very well. Not only would air be pulled through the filter, it would alos be pulled from countless other holes and leaks in this space. To solve the problem i created a box out of duct board and created a tightly sealed air return.

We finished off the HVAC installation by replacing and missing insulation on the old ducts and hooked up the gas electric and new thermostat. The new system worked perfectly first time. I was finally done working under the house. As long as i can keep rodents out and water line from freezing I shouldn’t have to return to the crawlspace for a long time.

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