Post date: Jun 21, 2017 1:13:58 AM
During this hot weather my thermostat (in the living room) has registered up to 82°F. Thinking I will cool the house, I turn on the fan, circulating air under the floor (where it is supposed to be cool).
However, at first the temperature in the house rises. The only possible source of this heat is from the mechanical room itself. That room must get very hot in the afternoon, as it is not so well insulated as the rest of the house.
So, I take my thermometer up onto the mechanical room (on the roof). The temperature inside is about 85°. Not bad, considering that it gets a lot of reflected sunlight off the rest of the roof. And considering that the outside temperature has been 90° for most of the afternoon.
When I return to the living room and check the thermostat temperature it has come down to 79°.
So I conclude that the ductwork (which is not insulated) and the furnace (which is thinly insulated) inside the mechanical room are picking up heat, and that hot air is the first to be blown into the house. Later, when the hot air is displaced by cool air from under the floor, the temperature drops.
So I shall insulate the sheet metal ducts that are in the mechanical room.
After the outside temperature drops I can open a couple of windows. The furnace fan will pull cool air into the house and blow hot air out the exhaust vent. All of the fresh air from the windows will be pulled under the floor slab and cool it for tomorrow.
So, I conclude that the heating system is working as planned, but it will help to insulate the ductwork that is in the mechanical room.