Making fires for heat

For a long time, humans have kept themselves warm by setting fire to the embodied energy concentrated and stashed away by other life forms, such as trees (wood, charcoal), wetland vegetation (peat), herbivorous animals (dung) and ancient marine organisms (oil, coal, and natural gas). 

This is still the way that a lot of us stay warm. Say you live in a house with a furnace. When your thermostat senses the temperature falling below your ideal setting, that furnace kicks on, burning fuel (usually natural gas, but sometimes oil) and heating the air inside it. A fan blows that hot air through your house via air ducts inside your walls, and, eventually, to you. 

There are a few major drawbacks to this process. It’s extremely inefficient and uses much more energy than you get back in the form of heat. Burning that fuel also releases emissions (carbon monoxide, nitrogen oxide, among others) that aren’t great for anyone nearby, which means that these heating systems need to be well vented and carefully maintained.

A better way

But there are other ways to heat your home than just setting stuff on fire. Instead of burning fossil fuels inside your house to release heat, a heat pump uses a small amount of electricity to move heat into your home, and move cold out of it. It’s also more efficient than an old-fashioned electric heater, which doesn’t produce the emissions that a gas or oil heater does, but is still designed to make heat by toasting air and blowing it around, instead of capturing heat from the outdoors and bringing it to you. 

A heat pump is a gnome

While the scientific process at work here is  well-understood, there’s something so extraordinary about a heat pump that even scientists sometimes describe them using magical terms. Like Kevin Kircher, a professor of mechanical engineering at Purdue University, who has explained heat pumps this way: 

A heat pump is a gnome with a bucket running in circles. He runs outside, wrings a little heat from the cold outdoor air, runs inside, pours out the heat, and repeats. He eats electricity to keep up his strength.

The science behind these gnomes is physics. Because heat will always move from a warmer to a colder object (aka, the second law of thermodynamics), a heat pump (gnome) uses its bucket (hyper-cold liquid refrigerant) to capture heat from outside, which is always present in the air, even in subzero temperatures. As the refrigerant absorbs that heat, it converts into a gas, which the heat pump compresses, making it even hotter (more physics, this time Charles’s Law). As that heat flows into your house, the refrigerant cools back into a liquid, carrying the colder air in your house back with it into the outdoors to absorb more heat. 

One example of this magic/science in action is another kind of pump—a bike pump. When you’re pumping air into a tire, you’re compressing it, which means that its molecules bounce off one another more frequently and the air gets hotter. If you pump for a few minutes, and then touch the hose carrying the air to your bike tire, you’ll feel that it’s gotten warm. When you open the valve of your bike tire to release a little air, you’ll notice that the air escaping feels cool—that’s because it’s expanding instead of contracting. A heat pump is doing basically the same thing, but much more efficiently, and with a lot less work on your part. 

The magic continues

The fact that heat pumps can be so efficient is another reason why they feel like magic. 

• They actually give you more energy to use, in the form of heat, than the amount of energy it takes for the heat to reach you. This is peak efficiency (aka magic).

• They’re four times more efficient than a traditional electric baseboard heater or space heater. 

• They’re a way to cool your home as well as heat it. The gnomes/your heat pump also run in reverse, keeping your home comfortable through heat waves as well as cold snaps. Is this more efficient than installing two separate systems for heating and cooling your house? You bet your sweet gnome it is. 

• They’re not only more efficient than an old-fashioned furnace, but easier and less expensive to install (because you don’t have to open walls to install ductwork to push hot air around). 

• They control the temperature of your home room-by-room, by design. This is both magically efficient compared to central heat or air conditioning (which lose 20-30% of the energy that you use just by moving air around your home through ductwork) and wildly luxurious (every person in your house can set the room they are using to their preferred temperature). 

• They are the most efficient way to ditch heating with gas, propane, or fuel oil, as well as the associated health risks. Paired with solar and battery, you can generate your own energy to heat and cool your home.

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