Technician says I need more return air... is he right?
Last summer I asked an HVAC technician to come out and check on my AC. My house was built in 2005, so the AC is around five years old, and runs pretty much constantly throughout the day on hot days (90+ degrees in northern Alabama). He peeked into the attic and said my return air ducts were too small and quoted me a price on replacing the return ducts and filter box with larger ones. Before I spend the money (because it is quite a lot), I'd like to know if I really do need larger ducts and a larger air filter box. Could some kind soul please offer their opinion?
I have a 2000 sq ft house, single floor with a bonus room above the garage (the bonus room is about 220 sq ft of the 2000).
I have a 3.5 ton unit, which is serviced by two return vents: a 20" x 30" filter box into a 16" flexible duct (~30 ft long) and a 12" x 12" filter into a 10" flexible duct (~5 ft long). Is this sufficient?
Here are the unit models:
outside: Goodman CPLE42-1C
attic a/c: Goodman CHPF042B2C
attic furnace: Goodman GMS80904BNA
If you need any other information, I can try to get it!
how are the flex runs connected to the furnace?
Originally Posted by Nate79
Do they run into a common box on the return side of the furnace? If so what size is that?
Your home must be old and not very tight?
Originally Posted by d_griff
Most technicians arent going around condemning duct work for no reason as it is usually a pain in the ass to replace. Undersized ductwork is a frequent problem where im from. And hard to diagnose.
Im thinking if you had freeze up problems in the past this would correlate with undersized ductwork.
Best bet is to trust your technician on this one. If he is planning on replacing the flex duct especially.
Yes, they run into a common box. Well, actually they both connect to the furnace box; one from the top, the other from the side.
Originally Posted by d_griff
Well, to be honest, the tech did not seem very thorough. He peeked into the attic for less than 15 sec (to his defense, it was really hot up there), saw the duct and we went and sat in the kitchen and he did some napkin calculations. I don't think he really knew the duct dimensions or that even I had a second air return connected (the 12" x 12") when he was doing his calculations. I mentioned the second return and he stated that it really didn't make a difference.
Originally Posted by skr0oface
I'd just like to have more confidence in his opinion before I go and spend the $1800 to change out a return duct.
Without seeing the sytem its hard to say for sure, but it sounds like you have enough return duct to me. Are the ducts sealed up good? A little duct leakage in a attic adds a lot of load to the system. Leaks in the supply are the worst, youre losing the cold air and the hot air from the attic goes through the structure cracks to replace it. In the summer youre losing 60deg air and getting 135deg air in its place.
Get second opinion, attic units often are too short on supply also. Check TD. [18-22]
Nate, three months ago I spent somewhat less than you were quoted on re-doing my cold air return and adding a second return. I don't know if you are having "noise" issues" when the system runs, but my home -- four years old in March-- had a 16 inch single upstairs hallway return and it was choked down to 10 inches.
Noisy... very noisy. Different company fixed the problem and all is quiet and more air is blowing. Temps more even, too. And... no more orange flashing light on the furnace. Second opinion wouldn't hurt.
"Therefore, since we have been justified through faith, we have peace through our Lord Jesus Christ.." (Romans 5:1)
Ask your tech to check the system static pressure.
3 1/2 ton needs 3.5 sq ft of filter. Allowing for the face area of your returns equals 4.19 sq ft. You should be ok as far as the filter sizes. As stated, you need the tech to measure static pressure. The 16in flex may be too small.
+1, and maybe it couldn't hurt if it was a different tech. One thing I will say though, skr0oface's comment has some merit too, especially if your attic is as hot as you say it is. I know I wouldn't want to charge somebody a bunch of money to do something in a scorching hot attic unless I was really sure of my diagnosis of the problem and that the action being taken would make a formidable difference.
Originally Posted by martyinlincoln
Before spending that kind of money I would look into replacing your roofs shingles with the new reflective shingles, and you may get a tax credit for doing it. I've only read a little bit about them, but they look just like ordinary roof shingles but they say they can significantly reduce the roofs temp-thereby reducing the attics temp which will greatly improve your cooling systems capacity.
Maybe look into exterior shading of your windows to cut down the heat gain to your home also.
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Information without understanding is useless.
You can lead a horse to water............