Q&A / 

Why is House Drafty

Stacey lives in a nice house that was built the same year I was born! It's in Winnipeg, Manitoba Canada where it can get bitter cold. Let Stacey tell you what the problem is:

"Hi. I'm in a 1,100 square foot one and one-half story house built in 1952.

During the colder months I feel a draft even when the heat is cranked. The furnace has been checked and works fine.

I've put plastic on my windows and caulked window seals.

I think I have too many or incorrectly placed cold air returns. My hydro bills are $300 +/- and it seems like I am heating my house more than I need to.

All vents are on the wall just above the floor except for the one floor vent specified in the picture."

This is the layout of Stacey's house. You may think the drawing is crude, but I'm here to tell you it speaks volumes. Image credit: Stacey

This is the layout of Stacey's house. You may think the drawing is crude, but I'm here to tell you it speaks volumes. Image credit: Stacey

Stacey, your wonderful drawing tells me all I need to know. Congrats to you for realizing the placement of the heat vents might have something to do with the problem!

One of the reasons your house is drafty is because the heat vents are not located properly.

To get even heat, and cooling if you have AC, the source of the heat / cooling should be on the exterior walls.

This is where the heat loss and heat gain is, so you want to offset the heat or cold by flooding the exterior walls with either heat or cool air (if it's summer).

The return air ducts, in a forced-air system, should be on the opposite wall so the conditioned air is pulled across the room.

If the supply ducts (for both heat and cooling) are down low on the floor or lower portion of the wall, the return air ducts should be HIGH on the opposite wall so the conditioned air travels at a diagonal across the room heating or cooling your body.

If you have a basement and your furnace is located there, you should be able to get the ductwork relocated so the supply ducts are on the outside walls.

It's VERY IMPORTANT that heat loss calculations be done so you put in the correct sized duct and number of registers in each room. 

In other words, if a room has a Btu heat loss of say 2900 Btus, you MUST inject that many each hour for the room to stay at the temperature you want. A good furnace professional knows all about this.

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8 Responses to Why is House Drafty

    • This article has me thinking that perhaps the return air duct setup should be tailored for both the heating and cooling seasons as follows:

      For the cooling season with the air supply coming from the floor vents on outside walls the return air ducts should be on inside walls mounted high up in the various rooms. This is what is described in the article. However, I am thinking that for the heating season the return air duct openings should be low down on the inside walls.

      My reasoning as that the heated air coming in from the floor mounted supply vents will tend to rise and cross the room directly to the high mounted return air ducts while colder air will tend to sit at floor level. With low mounted return air vents the colder air would be sucked into the return air ducts while the freshly heated air would tend to stay in the room until it cools over time.

      I can see achieving this dual functionality by installing extra return vents low down on the walls directly below the current high mounted vents. In the winter I would close off the high mounted vent covers and open the low mounted ones. In the summer I would reverse this with the high mounted vent covers open and the low mounted ones closed off.

      Is there anything wrong with my logic here? The amount of work here is trivial when a wall cavity formed by the space between studs is used as the return air duct.

  1. Here is another part of the heat supply equation that should be mentioned. The source needs to be able to supply somewhat more than (the theoretical 2900 BTUH here) to be able to do an initial warm-up from an unoccupied state. After it's warmed up, in order to maintain the desired temp, it will cycle on/off or ramp up/down as needed if the system has an ECM motor. Definitely agree with the other comment about getting a professional energy audit. That said, beware of grossly oversizing. Oversizing is a common technique done by lazy HVAC installers who don't do a proper Manual J calculation.

  2. I used to own a house with the heat registers high on the inside walls and the cold air returns on the floor under the windows. I moved the cold air returns to the inside walls and left the heat returns where they were. the heat ducts were run in the atic and the cold air returns in the crawlspace. By the time i got done remodling the house it was so insulated,we heated it with a pellet stove. We had a woodstove,but by the time i got done it would overheat the house. I never felt like spending the money to get it routed properly.

  3. My house was built in the late 1920s and also has the heat vents on the interior walls. My theory is this thinking had not moved past the old days of pot bellied stove or fireplaces in the center of the house. Lots of cold spots in this house in the winter. But my theory is not important. What I want to know is how expensive is it to run duct work from the interior wall vents to the exterior walls? Thankfully, the basement, where the furnace is, is an unimproved space with open ceilings.We bought a new furnace two years ago and the techs never said anything about this arrangement, they just replaced the furnace which I estimate was from the '50s.

  4. Interesting information. Our century home only has one outside wall register and one outside and 2 inside air returns. I can't do anything about moving ducts. But I can clear stuff blocking 2 of the returns. So that will be my goal today. We also typically keep our middle dining g room register closed so the furnace works a little harder to heat other rooms. Thermostat is in that room. Thanks.

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