Additional air-intake upstairs for downstairs A/C unit?

Old 03-14-10, 05:49 PM
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Additional air-intake upstairs for downstairs A/C unit?

My house is ~3000 square feet. It is a two story house. The downstairs is around 2000 square feet and upstairs around 1000. The house has two air conditioning systems. The downstairs is a 5 ton Lennox heat pump. The upstairs unit is not a heat pump and is 2 or 2.5 tons.

The downstairs unit is over 20 years old and I am going to replace it to take advantage of the federal tax credit and state rebate sense it has so much age on it. I am going to get a 5 ton dual-stage Lennox heat pump system.

The contractor said the new system will need additional air intake, so he will need to add another opening to the existing air-intake shaft. The current opening is downstairs on the floor under the thermostat. The air handler is in the attic so that air intake shaft goes from the first floor to the attic.

The contractor is proposing constructing the additional opening mid way up the house next to the stairs (it would be about even with the 2nd floor in an open area of the house.) He says not only will this add more air intake but it will help cool the upstairs by circulating some of the upstairs air.

Does doing this make sense? I am concerned this could cause cooling problems since the additional air intake would be taking warmer air (it would be located on a fairly open are of my house where there is a balcony from the 2nd to 1st story and stairs - this area is probably the warmest part of my house.)

Would it help or hurt efficiency of the downstairs unit? Will this help cool the upstairs by sucking out some of the upstairs air, creating an air flow from the cooler downstairs to upstairs - or would it mess up air flow and cause the upstairs to be even hotter?
Old 03-16-10, 12:19 PM
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Most residential units in my area don't have outside make up air. If your contractor is proposing a economizer for free cooling your looking at an upscale system.
Commercially they Do have a Min Outside air requirement, and will have separate opening to Outside air and also one for exhaust , to prevent building pressurization.
Have never seen it in residential, but then again i am a commercial HVAC tech. Most house don't have this type of system that i am aware of.
Ask him more Questions does this system have a damper that automatically opens and closes. or is it fixed open.
Is this opening connected to the duct work and if so where does it connect to.
I would get at least 3 estimates and be sure they preform a heat load calculation. 5 Tons is alot of cooling. I would rater be slightly undersized then over sized. This is a major mistake people make .
There are a few online calculators for a rough idea tonnage per square foot for different parts of the country.
Old 03-16-10, 04:56 PM
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Return needs to pull air from the area it supply's the heating and cooling.
Old 03-27-10, 08:36 AM
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No, don't do that, you mess up both up and down stair systems. If youhave to open another hole, try to find somewhere downstair and far away from your original in-take. In fact, newer houses have in-take in every room. You may not find a good place easily, but try the best you can, good luck to you..

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