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How much return air do I need?

Posted by robsb123 (My Page) on
Thu, Feb 28, 08 at 18:15

I bought a house at the end of last summer and I have been having problems getting the temperature to balance. Let me start with some background info that may be helpful. The house is 2 stories and about 1500 fininshed sq ft (750 each floor). The furnace is a Rheem Classic 90 plus,high efficiency, natural gas, 60,000 Btu. I do not know how many tons the AC is. Ten year old house with 4 year old double pane windows. I live in Northern KY. There is a single air return vent, high on the wall, on the first floor about 13"x6". The second floor has two return vents. One of the vents is high and the other is low on the wall, both are 23"x6".

When we moved in we were still running the AC. It was always cold on the first floor and hot on the second floor. One of the return air vents on the second floor was blocked with cardboard (I'm pretty sure that it was the top one). I removed the cardboard hoping that I would get more flow from the vents on the second floor. It didn't seem to work.

Now it is winter and the 2nd floor is still hot and the first floor is still cold. Should I be blocking one of the return air vents on the second floor? Which one? Is it typical for the return air vent on the second floor to be so much larger than the first floor?

I thought about running the blower continuously but it is really loud. It is kind of a strange pulsating sound that echoes through the house. I have read in other posts that it is loud because it is high efficiency and has to move a lot of air.

Does anyone have any recommendations on how to balance the temperature in the house. I plan to add to the problem by finishing the basement and tying into the system. I am probably best off just calling an HVAC guy to evaluate the system. How much do you think it would cost to have a consultation? I think that is enough questions for now...


Follow-Up Postings:

RE: How much return air do I need?

the only way to balance the tempature on a two story house with one unit is to zone the system. it dont matter how few or how many returns you have.zoning is the way to go. dont waste your money trying to do this and that because it won't work.

RE: How much return air do I need?

I would try blocking off the return on the first floor, this may draw the conditioned or heated air up to the second floor.

Yes, the heat rises, so the heat rises to the 2nd floor.

When I put a system like this in a new house I always put the return as high up as possible on the second floor.

Can you block off the stairway ? this will keep the hot air from rising and being trapped on the top floor.

Also, I would damper down the first floor registers and make sure the second floor registers are wide open.

To run the fan continuously, you may be able to change the fan speed to the lowest setting where it will be very quiet.
Read the manual.
As far as zoning goes, it may not be possible with your model furnace and it will cost some good money, so try this first.

RE: How much return air do I need?

As someone in the business for 20 years and growing up in a HVAC family I would say your idea to consult a professional is the right thing to do and an estimate on new equipment should be free. A few things I have noticed. First your heater is probably too small to move enough air for the size of your house. This can affect the AC as well. Undersized systems usually affect the place farthest from the indoor equipment. Second the noise is not because of high efficiency. To the contrary it may indicate a problem with the blower system. Third never block air ducts or return air ducts as this reduces the efficiency of your unit and can cause damage. If you are adding onto your house you will need another or a larger system so perhaps adding a second system would be the best bet. My advice get a professional. The money you save in energy costs will be worth it in the long run. Good luck with it.

Here is a link that might be useful: Ra-Jac Air Conditioners and Heaters Texas City TX

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