[stevemobile]

Hi. We have a new furnace exact HE replacement for the same unit and a 2 ton AC 1900 sq ft home. No returns. This all seems to work just fine except for rodents getting in the ducts. I wanted to replace the current 6"x13" OD fiberglass ducts (two on both sides) including a crossover, that feed 10 - 5" vents, with a new single round metal duct, center of the crawl space. I have repaired all the ducts temporarily. I do notice that when a window is cracked in15 feet from the furnace supply, a small amount of outside air is drawn in. We leave this open to get regular fresh air. My main goal is to seal the ducts, air tight below, insulated, and keep rodents out. The house has block around the perimeter, so that is sealed from weather conditions. Also the walls have been rebuilt with plywood and extra insulation and are very well sealed. I know that double wide HVAC designs may not be the most efficient, yet or heater does not run too often or seem to overwork. Thank you for any input.:smile:

 

[beenthere]

Going to metal is fine as long as you insulated it.

Might want to go to 6x14 duct for even better air flow.

 

[stevemobile]

Thank you for the reply. I am not sure of sizing for one single round pipe connecting to the eleven 5 inch ducts. I just wonder if anyone has converted a system like this to a single down the middle of the crawlspace, and what might be the standard. It does not need to be perfect, just enough flow. It is about 50 foot run. Thank you for any ideas on this center sizing going to round.

 

[beenthere]

Run the same size or next size larger metal duct as the current flex cross over is. You get much better air flow from the metal duct.


You can convert over to a standard duct system like you suggest. Its been done on double wides on crawlspaces, and full basements.