This is why I love GT, in a moment a member who designs these things will be in here to answer all your questions.
Till then we laugh about frogs.
OK, imagine your furnace. It burns fuel to heat your house. Imagine all the air it is heating comes directly from outside, you are heating very cold air to room temerature air, using a lot of fuel in the process.
Now instead of drawing intake air from outside, you draw it from inside. You already have some heat energy in the inside air, then you are boosting it as it goes through the furnace again.
Less fuel to do the work.
Oh, you're in TX, your furnace is a baseboard heater.
Its like using the "recirculate" setting on your car air conditioner.