Help, I have a Natural Gas forced Hot Air furnace installed by a previous owner. Just to make sure it was sort of done right Had heating contractor come over to check it out, but he was only a little help, he let me know I needed more return air duct but not how much. How do I figure out how much return ducting in Sq in for a upflow furnace with a 1600cfm 3/4 hp blower or are there a lot more things I need to consider. I know bends and transitions in ducting affect their performance but maybe just a rough idea will help.
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I don't understand, you had the expert there why didn't you ask him?
Becuase this expert was the rudest and most impatient one I have ever met in my entire life,and he was the finest heating and cooling professional in the state and if you dont believe that all you had to do was ask him and he would tell you.
In general, size return ducts at 500 - 800 fpm. For instance, 1600 cfm at 500 fpm would be a 20 x 24, or better yet 4 at 12x10 or 14x8. If you size the ducts at no more than 800 fpm, the turns and bends will be taken care of. The size is important but the location(s) of the return(s) are equally important. Multiple returns, located such that good cross flow is acheived is better than a single return. I have a 4 ton system in my home (1600 cfm nominal cooling air flow, 1200 high fire heating, 1000 cfm low fire heating) and I have 10 separate returns on three levels (two story w/ full basement).
thanks for the hot scoop on the duct sizing I went to the library, HD and every where else I could think of with no luck. I am trying my best to get the best placement for the ducts but this house is 134yrs old with all of the 18" beams and rock walls and small crawl spaces that are in the place its tough.