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Pros and Cons of Attic Ductwork?

Posted by firsthome (My Page) on
Tue, Apr 7, 09 at 10:45

My husband and I are looking into Geothermal. We currently live in a 2350sqft 2 story house built in 1976 that has a forced air oil furnace and A/C. In the summer the upstairs gets much warmer and the downstairs is much cooler and the windows get condensation on them from the temperature differences. (we have old storm windows that we will replace in a few years but the 33 old oil furnace is on it's last legs). FYI: Our system has floor vents and no wall/ceiling returns.

I think it is tolerable, but my husband wants to fix the system by doing a split system (whether we go Geothermal or not). Our attic is probably not up to today's insulation standards so I am sure that would need to be improved and our attic does not have any fan so I am sure that should be added as well.

I am curious as to the pros and cons of installing attic ductwork. I am sure the idea of installing cooling systems in the attic is based on the theory that cold air falls down and it would solve our upstairs heat issues. However I am concerned that even if we install better insulation and an attic fan that our attic is not built to handle such a system and doesn't have the proper sealing and ventilation.

My concerns are that an attic system would mean
- the size of the system would have to be increased to compensate for the inefficiencies of our attic
- The system would have to run longer to make up for the losses in the attic ductwork
- Inefficiencies due to the fact that the cooling system is generating cooling in the hottest part of the house
- Installing ducts will make the attic heat migrate down into the house through the ducts making the system have to run longer to cool the warmer air in the house
- And just the opposite in winter, the house heat will rise up through the ducts into the attic and be lost.
- We have very poor access to the attic (through a small closet) and it woudl be difficult to change filters.

Are my assumptions correct? Is there a better way to solve or problem or because we are doing a retrofit is this our only solution? I assume that installing attic ductwork is going to run us an additional $10k ,plus the cost of additional insulation and a fan.

Also does anyone know if a split system geothermal is more expensive than a self contained unit?

Follow-Up Postings:

RE: Pros and Cons of Attic Ductwork?

ductwork should be put in the attic as a last resort only if there is no other option. ductwork should always be inside the conditioned space if possible.

RE: Pros and Cons of Attic Ductwork?

Adding insulation in the attic is a separate issue. It will reduce your heating and cooling costs no matter where your ductwork is installed.

A split system geothermal would be a little more money because you have to run refrigerant lines from the basement to the attic.
Your main problem is from what you said you do not have any high returns on the 2nd floor. Do you have any returns on the 2nd floor? If you could find a way to get a high return you could most likely stay with one system. It would be preferred to have ductwork and the unit within the insulation envelope but there are plenty (maybe most) of houses where this is not the case.

RE: Pros and Cons of Attic Ductwork?

like funnycide said if there was a way to remodel ducts to upper story that would help. but if you really want it nice then i would put a 90+ furnace with air in the attic. Can you go on the out side of the house and put a hatch door in get into the attic. i have done that a lot of times. If you vent the attic good, insulate the ducts real good you will not lose that much to the attic. One problem you have if you remodel with one system is if you are saying you have 2350 sq' on both stores, one furnace will not move enough cfm. of air to do a good job. if the house is that large you need to move over 3000 cfm of air between the 2 'story's to treat the air. later paulbm

RE: Pros and Cons of Attic Ductwork?

make sure if your using the attic for duct work make sure you metal duct work is well insulated cause the cold and the warmness from the duct it will create consedantion and you don't want that plus having the duct work in your attic is an other good thing cause its makes it easier for cleanning your system every 3 years ... yes lots of people don't do it and after a while dust lands on the bottom of your duct work and restrict the flow you wouldn't belive it but it does plus you breath that air that flows in and with dust laying in the bottom and spreads trought the house .

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