If you’ve ever watched the news and heard a meteorologist talk about the change in temperature from one week to the next, then you already have a basic understanding of what a temperature differential can mean to you. Outside, you may feel the swings of the weather: 40 degrees and cloudy one week, then 70 and sunny the next. That’s a 30-degree difference in one week!
Inside our homes, we can feel the difference in temperature, too. And thanks to the help of our HVAC systems and insulation, we can walk through the front door on a blustery day and can feel a 30-degree difference in temperature instantly. So what exactly is temperature differential, and how can you use it to your benefit?
NOTE: This article is not about the thermostat temperature differential (the difference between the temperature your thermostat is set at and what it's actually heating/cooling to). For information on that topic, visit our article entitled Thermostat Temperature Differential: Does it Help?
The Physics of Heat Transfer
Since heat is energy, we need something – like fuel – to help create it.
“Heating or cooling – which is actually moving of heat – is directly associated with the electrical or gas energy it takes to provide it, and why we all should be concerned about it. It costs money, and it adds to our collective carbon footprint,” says Keith Hill, technical support manager at Minnesota Air.
Putting it simply, heat is generally measured by temperature, and temperature refers to the intensity of the heat. It moves from hot to cold, and the greater the difference in temperature, the faster the rate of heat transfer occurs, says Keith. That transfer of heat is why you should pay attention to the temperature differential between inside your home and the outside temperature.
“Think of temperature difference like pressure difference. Ever inflate a tire with a hand pump? The greater the pressure in the tire, the harder and slower it is to pump it up,” says Keith. “In home heating, the temperature difference that we are most concerned about is between indoors and outdoors. When the temperature difference is 40°F (for example, 70°F indoors and 30°F outdoors), the home will lose heat at approximately half of the rate it does when the difference is 80°F (70°F indoors and -10°F outdoors). This is why we set back thermostats to save money.”
Does Setting Back The Temperature Really Make a Difference?
The effects of setting back the temperature – or putting your thermostat at a lower setting while you are away or sleeping – comes with some skepticism. Some people believe that setting back doesn’t save money because it takes just as much energy to get back up to the desired temperature later. But this is wrong when you think of it in terms of physics and heat transfer.
“If you set your thermostat back from 70°F to 60°F, that’s 10°F less of temperature ‘pressure,’ so your home will lose heat at a slower rate, saving you money,” says Keith.
He says the energy needed to heat it back up to your desired temperature vs. keeping it at that consistent higher temperature will almost always help you save. Plus, the more you lower the setting, and the longer you have it set there, will help you maximize the savings. Just note that you do need to keep it high enough in the colder months to avoid frozen pipes and house damage.
Keith also warns that there are systems where setting back the thermostat does not make sense – like with in-floor radiant heating, where it takes a long time to recover and get back up to the preferred temperature.
And, if you are looking for maximum savings while using principals of temperature differential, setting back your thermostat when it’s 45°F or 50°F outside won’t result in much savings.
“At those outdoor temperatures, the ‘heat pressure’ is very small to begin with, so setting your thermostat back will have little effect on your energy bill,” says Keith.
For further energy savings, getting a programmable or smart thermostat can help because they can take the human factor out of the equation if you forget to set back or adjust to outside weather conditions. We’ve put together a guide to help you find your home’s ideal temperature here.