Basement Cold Air Return Placement

[TheKingfish]

First time poster in need of advice. I am in the process of having a new furnace quoted for a northern Michigan part-time residence. The basement area (700 square feet, three rooms) has never warmed particularly well, and I have been told it would benefit from additional cold air return.

In this instance, installing a floor-level return is a physical challenge. Contractor #1 proposes to run a return in two rooms; in each case the return would be in the ceiling located about 7 feet from the ceiling heat vent. Contractor #2 proposes to run a single floor-level return in an area that would generally serve both of these rooms. This contractor has no faith in a ceiling cold air return.

I am wondering if I should insist upon floor-level placement. Best course of action? All thoughts are welcome.
Thank you,
TheKingfish

[tipsrfine]

Is the basement insulated? It should be cost effective to insulate it since you are in a cold climate.

[Shophound]

Is the basement finished? No return should be in a basement if it will have direct line of sight to gas burning equipment, such as a water heater, boiler, or furnace. If these items are in a mechanical closet that is air sealed from the basement but can get combustion air from outdoors, then you're good with a return in the basement (as long as it's not in the same closet with the equipment!).

[BadgerBoiler MN]

A return does not insure warmth. If you have an open door to the upstairs and the doors of the basement rooms are not sealed you likely have an effective warm air return. What you may lack is a separate zone for the lower level. Though most basements have lower heat loads than the upper floors, they usually do not have solar gain, shutting down the furnace for long periods of time and idling off the heat to the basement as well. Warm air rises while cold air naturally fall to the lowest level.

I would look into a basement zone. It works for our customers and in my own house as well.

[TheKingfish]

Thanks to all for your feedback; very helpful. The basement is not insulated and half finished. Safety wise, there would not be a direct sight line from the furnace to the proposed cold air vent. Furnace combustion air is drawn from outside.

A basement heat zone is probably more than I want, given my residential frequency. There is an open stairway to the upstairs. I am leaning toward the proposed single floor-level return vent.
Thanks again,
TheKingfish

[beenthere]

The type of supply register will determine if your going to have a warm basement or not. If the supply just throws the air across teh ceiling and not downward, your basement will be cold.

[vstech]

how much of the basement is below grade?
with an open staircase, you would need to have nearly all the return air drawn from the lowest part of the basement to get decent warm air down there.

in cold climates, I'd invest in radiant floor heating for a basement...

[RoBoTeq]

The return will do best if closer to the floor. With the return close to the floor, the statafied warm air in the basement will be able to move toward the floor rather than be recirculated back to the furnace without warming the air closer to the floor.

It is off course best to get return air in each room, if possible. If there are rooms that are going to be closed off with a door that cannot have return ducting to them, a one inch undercut on the door (1" above flooring. If carpeted, 1" above the carpeting) or a by pass chase in a wall between the room and the common area where the return ducting is will help.

If going with a bypass chase, have a grill installed low in the wall in the closed room and high in the same stud chase of that wall in the common area where return ducting is. Make sure the wall cavity is free of obstructions such as cross braciing.

[jtrammel]

Unless its an extremely small room then a one inch undercut is not sufficient. 1" x 36" = 36sq in. It's usuall more like a 6" undercut which is not feasible. Bypass chase or "jumper" duct is better if you want any privacy

[jtrammel]

Jumper ducts have to be Sized correctly. Much larger than a regular return because you don't have the force of the blower to create pressure

[RoBoTeq]

Unless its an extremely small room then a one inch undercut is not sufficient. 1" x 36" = 36sq in. It's usuall more like a 6" undercut which is not feasible. Bypass chase or "jumper" duct is better if you want any privacy

This is not at all accurate. A one inch undercut of door is usually equivalent to a 6-7 inch round opening, which is more than enough free area for the air being pushed into a room to be allowed out of the room, especially when the area outside of the room is at a lower pressure due to their being a return grill there.

[RoBoTeq]

Jumper ducts have to be Sized correctly. Much larger than a regular return because you don't have the force of the blower to create pressure

The force that pushes air through a jumper duct is based on the amount of air entering the room and the lowered pressure of the air outside of the room. You don't need an open door to have air transfer from a room.

[jtrammel]

The force that pushes air through a jumper duct is based on the amount of air entering the room and the lowered pressure of the air outside of the room. You don't need an open door to have air transfer from a room.

I understand that but the force of pos pressure on a room caused by having supply air with no return is not near as great as the force of having a return that is ducted to the equipment which has the force of the fan to pull the air, therefore if you have a 6" supply forcing air in then you need a larger return than one that would pull ~100 cfm if connected to the return side of equipment via ductwork.