Attic Fans – Use or Not to Use!

MANY YEARS AGO, there were no attic fans in homes. Then someone decided they were necessary and builders started installing them in homes.

Times have changed again and now the consensus is they are not needed.

The reasons constantly change as more information becomes available. Common sense said “move as much air as possible through the attic”.

What was later discovered was that this air movement also pulled the cooler air from within the house. Thereby, increasing your air conditioning cost.

NOWADAYS, the logic is to move enough air to reduce the temperature in the attic and keep the humidity constant.

The cooler air from within your home condenses the moisture in the hotter air. This creates a humidity and mold problem.

Now before you consider installing an attic fan, you need to seal up every air leak you can find.

  • Look in the attic for openings around pipes;
  • electrical outlets and wiring;
  • light fixtures, especially the recessed fixtures; and
  • look for dark areas where the insulation has been filtering the air.

IDENTIFY each leak and seal it.

Be careful not to seal anything such as fireplace flues or the recessed lighting fixtures unless they are rated IC (insulated ceiling).

Anything other than IC MUST have a barrier to protect the fixture from overheating and starting a fire.

Ways of keeping safe while sealing:

The fireplace flues require special procedures to keep them safe. For this you will need to bring in a professional.

Use sheet metal to build a can around the light fixtures.

You can use plywood or sheet metal cut to fit around plumbing, if the opening is larger than 3 inches.

Use expanding foam if the hole is larger than 1/4 inch and not more than 3 inches or caulk if the opening is 1/4 inch or less.

Then cover with blown in or fiberglass insulation.

  • Electrical boxes are the easiest to seal. Pull the insulation back and use caulk to cover the holes and around the outside where it penetrates the drywall. Put the insulation back in place.
  • If your air conditioning/heating ducts are in the attic, seal around them also.While you are at it, check to make sure the seams are good. There should be no air leaks. If there are leaks, make sure to fix them!

Do not use fiber duct tape, use the metal tape.

Also before installing an attic fan:

    • Make sure the soffit vents are open and not blocked in any way. If your house has fiberglass batts, the batts should go to the edge of the wall and NOT into the soffit space.

If you have blown in insulation, there are several ways to ensure the insulation does not intrude into the soffits.

Your house should have a dam of some type to stop the insulation from blowing into the soffit space.I have seen builders use cut out pieces of cardboard wedged in the space and also pieces of form board carefully placed and glued into place.

The dam should be installed right to the bottom of the rafter vents to ensure the insulation does not move around.

We had a house in Florida that was insulated with a bright white cotton looking material, as the winds shifted, so did the insulation, from one side of the house to the other.

The other consideration is to make sure there is plenty of insulation to keep the living space and the attic space in different thermal zones. The EPA thinks most areas should have R 38 (or 10 to 14 inches).
Relatively recent on the scene are solar powered exhaust attic fans. This could be a good idea as they run during the hottest and brightest days. They also will run on sunny cold days.
Another positive fact is that they cost you nothing after the initial installation. An on/off and humidity switch away from the unit would be beneficial.
A Personal Note: I believe attic fans have a place and much depends upon your unique situation.

I would not install a fan until convection vents are in place and insulation is at the maximum levels to keep the attic and the living space as far apart temperature wise as possible.

Then assess the situation to meet your needs.

Dave Altman

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About Attics | My Blog - April 10, 2017

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