Scorching attic trigger furnace blower to activate

Q: Last year we replaced our rock roof with asphalt shingles, and the strangest thing has happened since then. The convection oven in our attic switches on in hot weather. The only way to stop operation is to turn off the circuit breaker in the switchboard. Our house inspector found nothing wrong with the stove, and the roofer says it wasn’t his fault. How can we solve this annoying problem?

A: The new shingles on your roof may absorb more heat from the sun than the old roofs. In this case, additional roof vents will likely be needed.

Inadequate ventilation can cause an attic to overheat during the hot summer months. This can activate the temperature limit switch in your convection oven and turn on the fan. To overcome this problem, two conditions must be met. First have a heating contractor check the heating limit switch in the furnace to ensure that it is set correctly. The switch may be set to a lower temperature than normal, or it may simply be defective and need to be replaced.

Next, on a hot day, put a thermometer in your attic to determine the heat gain. If the temperature approaches 150 degrees it would explain the unexpected activation of the oven fan.

The most effective ways to ventilate an attic without installing mechanical fans are ridge and turbine vents. A roofer or general contractor can advise you on the best approach to the design of your roof and attic.

Q: I have a brick fireplace in my house that has been converted to use gas blocks instead of wood. Now that I am selling the property, the buyer’s home inspector has recommended removing the hatch before we close the escrow. I explained that this would be impractical as an open chimney would allow warm air to escape from the house during the winter months. The inspector agreed, but insisted that flaps are unsafe when fireplaces are fitted with gas burners. This seems to be a conflict of priorities. Is the house inspector right to remove the damper?

A: The house inspector is right about the damper. The safety requirements for chimney flaps were improved in 1991. According to these standards, hatches must either be removed or permanently secured in the open position when gas logs are installed. This requirement is intended to prevent harmful combustion gases from entering the living area. If the gas burner is lit with the hatch closed, combustion gases, including carbon monoxide, can escape into the house.

This is particularly dangerous with gas burners that can be switched on via a switch, as someone could ignite the burner without considering whether the flap is open or closed.

Fortunately, removing the damper is not required for compliance. Instead, the damper can be deactivated by installing a special clamp that is available wherever fireplace equipment is sold. If heat loss from the home is an issue, buyers can put glass doors on the front of the fireplace after they have taken possession of the home.

• To write to Barry Stone, visit him online at www.housedetective.com or write to AMG, 1776 Jami Lee Court, Suite 218, San Luis Obispo, CA 94301.

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