Proposed HVAC Summer Cooling Home Modification

Problems related to residential installations.

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Proposed HVAC Summer Cooling Home Modification

Post by thundermasmacho » Thu Apr 09, 2015 9:07 pm

Here's my -
My home is built in an area with a very clay-dominant soil, so my unfinished underground basement stays around 60 degrees F year-round. I'd like to use the main blower (fan) in my furnace to pull cold air from the below-ground basement up into the house during the summer months. The point of this post is to run this idea by someone with a much greater knowledge of HVAC systems than I have, with the hope that they might be able to address possible problems with this idea, and advise me how-best to proceed.

Furnace P/- Goodman GMS80703AXBD
Furnace - Y / W / R / G / C
Furnace Spec. - SEE REPLY
Furnace Parts - SEE REPLY

Thermostat P/- Filtrete (3M) 3M-22
Thermostat - C / B / O / W / W2 / Y / Y2 / RH / RC / G / A
Thermostat Ops. - SEE REPLY
Thermostat Install - SEE REPLY

Here's what I -
I understand that my furnace doesn't have an actual cooling compressor or A/C unit, but rather just a blower fan, and that the Y terminal in the furnace simply controls said main blower, essentially allowing the blower to function like what used to be called a “summer fan”. When the Y terminals are connected between the furnace and thermostat, and the thermostat is switched to “COOL” mode, it controls the main blower in the furnace as-if it were an A/C compressor; it turns the fan on until the temperature drops below the desired setting and then turns the fan off.
Knowing this, my goal is to allow the system to draw cold air from the basement via a convertible intake vent in the basement, rather than via the normal intake on the main floor of my home. I don't see the point of having the system pull relatively HOT air from my house and redistribute it, when it could pull relatively COLD air from the basement instead. I know this won't be as effective as an actual A/C unit, but I feel it will be more effective than my current setup.

Idea of how to accomplish this goal (see image below for reference)-
1. Install a manually switchable damper in the ducting below the main-floor intake. The purpose of this damper will be to close-off the main floor intake during the summer, allowing the system to take-in cold air from the basement, rather than hot air from the house.
2. Install an alternate intake vent in the basement (still aft of the filter), which can be closed in the winter and opened in the summer. The purpose of this intake will be to open it in the summer allowing the main blower to draw-in cold air from the basement and distribute it throughout the house. (It will be closed in the winter, and the damper will be opened, allowing the system to again pull air from the house rather than the basement).

Here are my questions/-
1. Will this even work? / Is it worth the effort?
2. Will the cooling effect of the basement be able to actually continue to cool the air it draws in from outside, or will it simply equalize temperatures eventually making the whole point moot?
3. Can anyone tell me the duty cycle of the blower in my furnace? Will converting it to function as a summer fan over-exert it and cause it to fail sooner than it normally would?
4. I know that I will have to play with the temperature settings on the thermostat in the summer, because it will only really cool the house to a certain point (roughly the average between the basement and the main floor) and that having it set too low, will keep the fan running all the time, and defeat the purpose of having the fan connected to the thermostat anyway. I'll have to set the thermostat to a temperate that is realistically reachable by the system (I suspect 65 degrees, depending of course on how hot it it outside.)

Any help you can provide will be greatly appreciated. Thank you for your time!

Basement -


1. Duct below from Main Floor Intake/Plenum
2. Proposed Damper Location
3. Proposed Summer Intake Location
4. Filter Location/Access Panel
5. Furnace

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- Proposed HVAC Summer Cooling Home Modification

Post by thundermasmacho » Thu Apr 09, 2015 9:08 pm

2nd attempt at image -


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- Proposed HVAC Summer Cooling Home Modification

Post by thundermasmacho » Thu Apr 09, 2015 9:09 pm

Well I give up -- I think I'm far too dumb for this forum. --(

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- Proposed HVAC Summer Cooling Home Modification

Post by LennoxHVAC » Fri Apr 10, 2015 11:06 am

thundermasmacho -
> Well I give up -- I think I'm far too dumb for this forum. -(

Give up the modification project?

Your idea is insightful.
Warm air rises - heavier cool air tends to stay low to the ground.

Opening the return duct in the basement, and then installing a vent or two will change the return air temperature entering the HVAC chamber. How will thermostat adjust to this change?
Will the furnace run longer - burner flame working little more in winter.
Would humidity increase during the summer?

Aside from temp, HOW is the quality of basement air?

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- Proposed HVAC Summer Cooling Home Modification

Post by Freon » Sun Apr 12, 2015 2:46 pm

Your concept will work from a technical point of view. Switching the furnace return to a new one in the basement from the existing one you have will work. However I have concern if you have the heat transfer necessary to accomplish significant cooling in the upstairs.

The basement feels cool and the walls and floor are like thermal batteries. However the BTU/hr you may need to keep the upstairs comfortable may be greater than the BTU/hr you get from the basement battery. The basic heat transfer mechanism in the basement is convective transfer as the air flows over the basement walls and floor. It is natural convection, not forced, so it will likely transfer little energy per hour. You could do some calculations an see if I am correct or just go ahead and try it. Keep it simple in case there is not the required BTU/hr you need.

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