Cold-air re­turn will boost base­ment heat

Winnipeg Free Press - Section G - - HOMES - ARI MARANTZ

QUES­TION: We have a 1,440-square-foot base­ment un­der a full two-storey home heated with a high-ef­fi­ciency gas fur­nace. We have four warm air out­lets in the base­ment with no cold air re­turns. A friend, who used to in­stall fur­naces, told me to cut a re­turn in the cold air re­turn to the fur­nace, near the floor. Is this a good idea and if so what size should the open­ing be? If not, what al­ter­na­tives do I have? Do I re­ally need a cold air re­turn there to in­crease heat and ef­fi­ciency in the base­ment?

Thanks for your time, Wayne Spit­tal

AN­SWER: A lack of re­turn air duct­ing and reg­is­ters in base­ments is one of the most com­mon is­sues I see in older homes. While some of the fin­ished rec-rooms in these base­ments are fairly com­fort­able in the heat­ing sea­sons, oth­ers are not and of­ten have sup­ple­men­tary elec­tric heaters in­stalled. In­stal­la­tion of proper re­turn air duct­ing and reg­is­ters should make the area much more com­fort­able, es­pe­cially with your newer high-ef­fi­ciency fur­nace that should have a much more pow­er­ful fan than the older one it re­placed.

Your friend has given you good ad­vice about in­stal­la­tion of re­turn air for the base­ment, but I don’t think you got the whole story. Ei­ther you mis­un­der­stood his rec­om­men­da­tion, or he was giv­ing you a sim­pli­fied so­lu­tion that may not be the best one pos­si­ble. While in­stal­la­tion of re­turn air for the base­ment will im­prove the air flow to and from the fur­nace, cut­ting a hole in the re­turn air plenum right near the fur­nace may not be ad­e­quate for the en­tire base­ment and may pre­vent proper re­turn air move­ment in your home.

The proper method to achieve what you want is to in­stall one or more ducts di­rectly to the ex­ist­ing re­turn air duct­ing or plenum. These should run to one or more lo­ca­tions near the base­ment floor, but far­ther away from the fur­nace. Also, in­stal­la­tion of proper reg­is­ters over the end of the ducts will pre­vent ex­cess dirt and de­bris from en­ter­ing the duct­ing. In­stal­la­tion of these ducts can be through an ex­ist­ing in­te­rior base­ment wall or other ac­ces­si­ble area. These ducts should not be in­stalled di­rectly against an unin­su­lated foun­da­tion wall, or within an in­su­lated wall, as con­den­sa­tion can cre­ate mois­ture-re­lated prob­lems.

Be­cause of the size of your base­ment I would ex­pect more than one re­turn air would be pru­dent, but if the en­tire area is un­fin­ished, one may do un­til fur­ther walls are con­structed.

A mod­ern forced-air heat­ing sys­tem in a home has two main duct­ing sys­tems, which al­low good air cir­cu­la­tion through­out the build­ing. The warm air duct­ing is typ­i­cally in­stalled be­low the main floor and will ter­mi­nate in reg­is­ters near the ex­te­rior walls on the main and up­per floors. This duct­ing is pres­sur­ized as warm air is blown past the heat ex­changer on the fur­nace by the fur­nace fan, into the duct­ing. This heated air will en­ter in­di­vid­ual rooms in the house through these reg­is­ters and rise to the up­per level of the rooms due to nor­mal con­vec­tive forces.

Once the fur­nace fan shuts down, this air will cool and set­tle to­ward the floor. The re­turn air reg­is­ters and ducts are in­stalled to help col­lect this cool air and draw it back into the fur­nace hous­ing, so that it can be heated and re­cir­cu­lated once the fan is re­ac­ti­vated. With­out re­turn air duct­ing, as in your base­ment, much of this cool air may not be drawn back to the fur­nace, re­sult­ing in stale or damp air in that area of the home.

By cut­ting a hole in the re­turn air plenum right near the fur­nace, you may col­lect some of this cool air from the base­ment, but not from the right lo­ca­tion. If you in­stall re­turn air duct­ing and reg­is­ters at the op­po­site end of the base­ment from the fur­nace, you will then make the air move­ment more ef­fi­cient. The cool air will be col­lected from the lo­ca­tion where it is most sus­cep­ti­ble to be­com­ing stag­nant, at the far end of the home from the fur­nace.

This in­creased air flow will also al­low the ex­ist­ing heat reg­is­ters in the base­ment to more eas­ily re­place the cool air with warm, heated air, fur­ther im­prov­ing com­fort.

I’m glad that you are seek­ing ad­vice from a pro­fes­sional heat­ing tech­ni­cian, even if he is no longer prac­tis­ing, but you should be care­ful about the ap­pli­ca­tion of that ad­vice. While you may be adept enough to do some of the work in the in­stal­la­tion of the new re­turn air duct­ing in your home, this is nor­mally a pro­fes­sional job. Holes in ex­ist­ing duct­ing and at­tach­ment of dis­tri­bu­tion pipes can be dif­fi­cult to ac­com­plish, un­less you have the proper tools and know-how. A trained heat­ing tech­ni­cian should also be able to do mea­sure­ments and cal­cu­la­tions, if nec­es­sary, to de­ter­mine how many re­turn air reg­is­ters are re­quired for your base­ment.

Warm­ing up cool base­ments in the heat­ing sea­son is of­ten some­thing that many peo­ple de­sire but don’t know how to ac­com­plish. One of the sim­plest ways to achieve this goal can be to add proper re­turn air duct­ing to this level of the home. Im­prov­ing air cir­cu­la­tion to the fur­nace, by this method, can be the dif­fer­ence be­tween com­fort and cold in your base­ment. An­other ben­e­fit of im­proved air­flow is to min­i­mize stale air and pre­vent con­den­sa­tion and mould growth, com­mon to base­ments with no re­turn air sys­tems.

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