Should the furnace's cold-air return duct be insulated?

Question

The heating ducts are all insulated. Should we also insulate the cold-air return? All the ducts pass through an unheated crawl space.

I'm up North, in zone 5.

Answer 1

I disagree with the other answerers to your question (so far). The issue is in the details you provide -- all the ducts pass through an unheated crawl space. Normally it would not make sense to insulate a cold air duct. But in this case, you have warm, relatively moist air moving through a cold duct in the winter; and (in the summer) warm, relatively moist air outside a cold air duct. Both situations will cause condensation on the metal duct. In the winter, this will be inside the duct. In the summer, outside. Even galvanized ductwork will eventually rust. Insulate it.

Answer 2

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The number and location of cold air returns are dependent on the square footage and the number and location of heat ducts. You need the system to be balanced, allowing the air to move from the furnace to the room, circulate in the room, and the colder air pushed out of the room back down to the furnace. If you re-purpose a cold air return in a room that will have it's doors closed, such as a bedroom, the heat will not be able to enter the room as much as you may need to maintain a comfortable temperature. So, you can only take out a cold air return (which is also using duct work in most installations) if there is another way for the colder air in the room to find its way back to the furnace in the basement. This would be through other cold air returns in the house, or by traveling down to the basement through open air flow. I'd say this may work in an open area of the house with enough other cold air returns, but create a problem for you in a bedroom or other enclosed space.

Answer 3

You can, but its not neccessary. The cold air return is just pulling room temperature air to the funace for heating. The air is not in the ductwork for long enough to make a difference in cost of heating or temperature rise.

Answer 4

No, it's not necessary. All cold air returns should be located near the floor allowing the cool air to be recirculated to the furnace to be reheated. I'm not trying to be rude but it's Cold air.

Answer 5

you should not insulate because if you have a humidifier installed then you have a sail switch located in the duct work [return] .that judges how much water is in the return air

Answer 6

Unless you live way up north there's little value in it.