I’m planning to finish my basement. The basement will be divided in 2 rooms, one will have the forced air furnace and gas boiler (300 sqf) and the other one will be living space (400 sqf). Being kind of tall I want to eliminate the air ducts from the middle of the basement to gain some height. I will route the feed duct by the side wall and remove the return duct from the new room. The return air from the house will get in the new basement room go across and sucked by the furnace return closing the circuit. I would prefer to use the return air for cooling and heating in the new room because the basement doesn’t need as much heating or cooling as the house. Also by circulating the air will keep the air basement room dry. Please tell me your professional opinion and any concerns. Thanks

Sorry I'm a bit confused! Forced air furnace and boiler? What's the boiler heat? Having a return in the basement will help the humidity, when heating it will simply send much of the humidity to a dryer upstairs. In cooling the evaporator coil will dehumidify the air, also drive down the efficiency of cooling for 2 reasons. Condensation (water) will remove BTU's from the evaporating refrigerant and cold water will run right down the drain. Heat rises, and if you reduce the cfm going into the upstairs returns you won't remove the heat from the upstairs very well, but the basement might become an ice box. I think you want to rerout the supply trunk in the basement and this may cause so many adverse effects to the airflow balance in the home. Some supply runs will now be very short and athers will be very long. At this point, this is what I've come up with as far as pro's and con's go.

Thanks for quick answer.

Sorry I'm a bit confused! Forced air furnace and boiler? Whats the boiler heat?

The boiler is a water heater for bath and kitchen.

Having a return in the basement will help the humidity, when heating it will simply send much of the humidity to a dryer upstairs.

Increasing humidity in heating season is good for me because in winter usptairs is very dry. I will stop using the humidifier.

In cooling the evaporator coil will dehumidify the air, also drive down the efficiency of cooling for 2 reasons. Condensation (water) will remove BTU's from the evaporating refrigerant and cold water will run right down the drain. Heat rises, and if you reduce the cfm going into the upstairs returns you wont remove the heat from the upstairs very well, but the basement might become an ice box.


In summer is the most humid in the basement and dry air will help. I agree that the efficiency will be reduced but this will be the price to pay for using the ac as dehumidifier. I don't plan to reduce the returns from upstairs. I will leave the ducts in place connected between the rooms and basement. Do you think I should use a blower to add extra suction because I don't want an ice box?


I think you want to rerout the supply trunk in the basement and this may cause so many adverse effects to the airflow balance in the home. Some supply runs will now be very short and athers will be very long. At this point, this is what I've come up with as far as pro's and con's go.

Most of the ducts will be shorter which I think is good. Is just one which will be longer and I intended to use a supplementary blower to help the air flow. This is cheaper than digging a deeper basement.

Thanks again for your comments.

Much of the moisture in a basement or crawl space in the summer time comes from warm, moist outside air leaking in and condensing due to the coolness of the earth. Before finishing the basement, make sure all the joints are sealed tight. Caulk the top and bottom of the band joist, plus between the plate and foundation if it didn't have a layer of foam when the house was built. Caulk around all the pipes and wires too, including the ones going up through the floor above. Some of the gaps can lead clear to the attic allowing warm, moist air to rise to the attic and cause condensation problems.

Make sure the ground slopes away from the house to keep ground water from working its way in. Apply a sealer to the foundation walls and the floor. As Northern Heat said, any moisture from the basement the air conditioner has to remove, reduces its efficiency.

After you have your ducts redone, you may want to check the temperature rise o the furnace and have the blower speed reset.