What takes more energy heat a cold house to 71 or maintain house at 71 degrees, doors open outside temp 55?

Question

My roommate constantly leaves the back door open for "Fresh Air", so when he does I turn off the heat to conserve. So the arguement came up which uses more energy

warming house from a cold temperature or maintaining a constant temperature where the heat is being continuoisly lost.

Answer 1

It depends, how insulated or air tight is the home?  What type of heating system is it?  Different systems require different amounts of energy to heat the same room to a desired temp.  Heat pump, gas, oil, baseboard?  Either way, if your leaving the doors open then turn the heat off and heat it up when u get home.

Answer 2

I assume you're asking whether it takes more energy for a heating system to rapidly warm a house or to maintain a house at a given temperature for a long period of time.  For example, if you're leaving your house, what should you do with the thermostat.

The most energy efficient method is to set the thermostat to a low temperature while you're gone, then have it warm the house just before you return.

If you keep the house at a constant 71°F, you're wasting energy because some of the heat is going to be lost to the outside atmosphere, and the heating system will have to continue to run to replace that heat.  If the system is at a low temperature, you're losing less heat energy to the outside.  Then as it warms over a short period of time, most of the energy is staying inside.

The house wants to be in equilibrium with the temperature outside, and the only thing preventing this is your insulation and your heating system.  So let it come closer to equilibrium (colder temperature) while you're gone, then use the energy to heat up the house when you need it.

Answer 3

I hope Dana will forgive me if I try to make this simple.

Heat flows like water, only from high temperatures to low temperatures.  The greater the temperature difference, the faster it flows.

So, letting the house get cold, slows down the rate of heat flowing out, heat that has to be replaced.  That uses less energy.

Answer 4

It takes more energy to heat a cold house and then to maintain it . It will take less energy just to maintain it .