The arrow is always pointing the direction of air flow and should always point toward the furnace. This is the air returning from your house carrying dust and other potential allergens. The filter is used to keep these from getting into the furnace and also to clean the air you breathe. Inexpensive filters mainly help to protect the blower from dust, and the more expensive ones can help you [...]
That is a good question and the primary answer is dependent on your preference. The high efficiency systems have a blower motor designed to be running all the time to filter the air in the home and mix the air to even out hot/cold spots in the home. We recommend leaving the fan switch on “ON” all year but especially in the summer months since it is more efficient for your air conditioner.
You should keep the thermostat set high enough so that the basement is well above freezing in the winter. Pipes are in the basement, so keeping a warm temperature will help prevent pipes from freezing, then bursting. To be safe, you should expect the basement to be about 10 degrees lower than the main level. You should also consider the location of your refrigerator.
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This varies according to the outside temperature. The average humidity level is about 35%. When it is really cold, your windows may have condensation or frost build up on them so the automatic humidistat will bring that number down to prevent that from happening. Here is a chart based on the outside temperature showing what the humidity level should be: