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Advice on Overhauling Crawlspace Duct HVAC system!

When I come under my house (crawlspace throughout the floorplan) , I am blocked by duct work everywhere. I know that I can remove any segment to get through but I wonder why ? You see, the floor joist has rows and rows of clearance that I can tuck the ducts up neatly and out of sight or that I can move the duct work above the ceiling in the attic space. My gas furnace pulls in air from the ceiling airspace and push air under the entire house through ductwork throughout the crawlspace, so I guess it is better to keep the same configuration as before . The floor register holes are already there orignally. I am cost conscious so I am asking for anyone's advice about how to realign the entire ductwork with most sections tucked between floor joists which is 8 or 10" . I can draw a diagram of how the floor joists are arranged but I dont think it is necessary. My main problem is that the floor joists may cross the path of the original duct branches. I have about 8 or 9 registers mostly floor and a couple of them off the wall a foot or so above the floor like for bathrooms. It looks like I have to make some necessary detours in order to tuck up as much sections as possible following the joist layout. Some sections will still have to be placed under joist in "J" coupling in order to get to the floor joists. All of the floor joists are close to the perimeter of my house. I feel I can move some of the floor registers closer to the central furnace to save on the traveling distance of the heated air toward the floor registers. Some of the duct branches are ridiculously lengthy like 80 or 90 feet between the furnace blower and the floor registers because the furnace is placed at the end of the house instead of center of the house. My goal is to make all registers no longer than 50 foot or so so to cut down on the heat loss. I might eliminate the furthest registers outright so to save on heat loss. Some of the rooms especially bedrooms can be shared with same register on the double side off the wall and the unwanted far-off floor registers capped off. I wonder about regulations and safety . I figure if I use the same number of registers as originally, it should not be a problem. I think I can eliminate a couple branches since my new furnace and blower are more energy efficient as the blower is less powerful than the original one made back in 1970. The original one blew more air than the newer one. I want my crawlspace all cleared of the blocking ductwork . If I tucked most fo the duct segments between floor joists, I can nail 1/4" plywood covering under the joists after stuffing insulation around the duct sections. Am I brilliant or what? Has anyone else done that already ? Eh?

Re: Advice on Overhauling Crawlspace Duct HVAC system!

What belongs between those floor joists is insulation, not ductwork. And welcome to construction where the word for every day is compromise when many things all have to go in one space. They weren't thinking of you when they ran the ducts, they were thinking of what would work best for them.

HVAC installers, plumbers, and electricians all tend to make the most efficient runs for their purposes, however that does not always make it easy for the people coming through later on. Were I you, I'd have a few HVAC contractors look at it and bid a price to reroute the ducts where they will be as much out of your way as possible without reducing system efficiency. Be sure to note exactly what each one wants to do so the prices will be at least roughly comparable.

Be warned that you may not be able to gain much space- sometimes the placement of the other components pretty much dictates where the ducts must go. If the potential airflow in your system is already marginal, adding more twists and turns and length may be more than it can handle efficiently. Then again you may be able to easily relocate the ducts (and possibly the air handler) to open most of the space. Only a well-done drawing with all the system specs and duct sizes and lengths can tell us much here whereas a good contractor can quickly figure all this out on-site.


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