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What Is a Cold-Air Return?

Cold-air return vent near floor.
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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 07 July 2014
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A cold-air return is a vent that sucks cold air into a furnace so that it can be heated and brought back to a room through a furnace register. These vents are seen in many types of furnace systems, although there are alternatives, such as drawing air from the outside or from the area around the furnace. Depending on the design, each room in a house may have a return, or they may be strategically located at various points around the house. A heating and cooling specialist can make recommendations about the number of returns and their optimal placement.

In addition to being used in heating systems, cold-air returns can also be used in cooling systems. In both cases, the benefit is that air drawn from a room is naturally closer to the desired temperature, which means that less energy is required to heat or cool it to the necessary level. Furnaces can also combine a cold-air and main return, a vent on the furnace that brings in air from the area immediately surrounding the furnace.

Typically, this vent is located near the floor; because heat rises, the coldest air will be close to the floor. Locating a vent up high would leave pockets of cool air near the floor, which would be undesirable when the goal is to heat a room. Registers that emit hot air can be located at various heights, depending on the design of the system.

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Often, the interface of a register and that of a cold-air return look identical. People can tell which is which by waiting for the furnace to turn on, and holding a piece of tissue in front of the vents. If the tissue is pushed out, the vent is a register, and if it is pulled in, it is a return. Both returns and registers typically have filters that prevent the passage of dust and dirt, and these filters need to the periodically changed to avoid clogging the vent.

People can control the amount of air moving through the furnace by opening or closing the vents. With the installation of a new furnace system that takes advantage of existing ductwork, people may be told that they need additional or fewer returns, depending on how the system works. In the case of unnecessary returns, they can be capped or simply closed, depending on personal taste.

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anon353182
Post 8

A stuffed animal was thrown into our cold air return. It's a large Carrier brand furnace where the filter is located in the ceiling opening and not on the furnace side. We can't get to the toy. Is this a fire hazard?

anon337961
Post 7

How do I uncover an air conditioning return that someone covered with plywood when they put in a new floor?

anon296811
Post 6

We moved into an apartment. There are five units in our building. We have two vents on the floor and three about six feet off the floor.

We assume the bottom ones are cold air returns, but if we uncover them they pump in cooler air and cigarette smoke from other apartments. Can we cover our bottom vents without worrying about the furnace? It is a very old house.

blue487
Post 4

If a room has a heat duct and no cold air return, will it cause that room to stay cooler or at least contribute to it?

anon150807
Post 3

i have one bedroom in my house that is always cold in the winter. it has heat coming into the room and i am told that there was a cold air return but it was covered up after that room was remodeled. Will the cold air return being covered up cause this room to not get warm?

anon75979
Post 2

I suffered similar problems when I went from an old, very inefficient furnace to a very high efficiency model. The two furnaces worked very differently.

The old one had a burner that looked like the rocket nozzle on the Space Shuttle, only upside-down, and it had a huge fan. The burner was huge, because to work, it was blasting most of its heat up the chimney.

The new furnace had a two-stage burner and a variable-speed motor. This meant that only enough heat was generated to warm the air to the desired temperature.

The old furnace, with its big fan, blasted very hot air up the ducts and into the room below my inefficient, leaky windows. The new furnace gently wafted mildly warm air into the room.

The result was, that while the thermostat said the room was warm, the flow of hot air was not countering the radiant heat loss and drafts from the windows, which are usually far away from the thermostat.

In rooms without cold-air returns (the bedrooms), the problem was worse because the airflow from the registers could no longer blast hot air into the room in spite of the lack of returns. It's like blowing air into a paper bag. Once it is full (of cold air) you can't put any more in. (warm air).

We got in the practice of leaving doors open, which helped a bit. The big improvement came when we put some work into making the house more efficient with new thermal windows, added insulation and lots and lots of caulking. This meant that the temperature was even in all parts of the house, so when the thermostat said it was warm, it actually felt warm.

High efficiency furnaces are not designed to heat leaky houses. Cut the heat loss and you should feel more comfortable.

Keep in mind that tightening the building envelope makes it even more important to have a combustion air source for the furnace, which is what the outside air vent is for. The available outside air helps prevent carbon monoxide backdrafting into the house.

A homeowner.

anon72899
Post 1

I just had a new high efficiency furnace installed but i don't have a lot of heat and a lot of cold air before the heat comes on. I have two cold air returns in my home and now coming in from the outside vent.

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