Heating oil and outside temperature

  1. Let's say it is 20 degrees Fahrenheit outside.

    If I have my thermostat set at 60 F, then each time my house dips below that temperature, my furnace should kick on and reheat it to 60 F. And the cycle continues...

    If I have my thermostat set at 68 F, then the scenario remains the same, it's just that the furnace kicks on below 68.

    Does the furnace burn more heating oil to keep the house at 68 than it does at 60?

    Does a house at 68 F lose heat to the 20 F surroundings at a greater rate than does the house set at 60 F?

    If not, is there any savings...that is, after the house initially reaches the set temperature?
     
  2. jcsd
  3. mgb_phys

    mgb_phys 8,952
    Science Advisor
    Homework Helper

    Your furnace is trying to keep the house above the outside temperature.
    The heat loss rate depends on the temperature difference - so the power you need to keep a stable inside temperature is more for a higher temperature, Similairly the rate of heat loss when the furnace turns off is higher for a higher temperature difference.
     
  4. russ_watters

    Staff: Mentor

    To be more specific, it is directly proportional to temperature difference. So on a 20 degree day, the difference between a 60 and 68 degree setpoint is:

    1-(60-20)/(68-20)=17%
     
  5. Russ posted one key fact, the other is that heat loss depends on conduction, convection and radiation. Convection means air circulation losses...on a windy day depending on how air-tight a home is, heat loss can increase substantially due to cold air infiltration....say 20% so fixing cracks, crevices,leaks, can make a big difference.

    There are standard HVAC (Heating, Ventilation and Air Conditioning formulas...and "R" is a standard insulation measure; the higher R the slower heat is lost and the lower are heating and cooling costs...so, for example, different windows have different R values indicating how well they insulate. Windows are a major source of heat loss in many homes in cold climates...and heat gain via sun can add to air conditioning costs in summer...
     
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