Can I heat my house with air conditioning?

Although I could have installed a central heating system using natural gas like almost everyone else in my area, I've really wanted to try out a heating system that would be cleaner, easier to maintain, and, if possible - require less pipes, boilers and radiators. Pulling that off would mean a much more cleaner and modern look to my rooms. With that minimalist approach, I was also hoping to minimize the heating costs, because, you know, how many times have you heard in the past that the gas or electricity prices went down?

Important parts of the decision were also the cost of the heating system and yearly maintenance costs. I needed to calculate this right. If I save some money on the monthly gas or electricity bill, but end up spending a ton of money on yearly maintenance and cleaning, then the overall expenses would be much higher. Not to mention I need to take into account the longevity of the boiler or other heating elements. Some gas or electric central heating boilers are very pricey and could rarely last longer than 10 years even with proper care.

When I first mentioned I'm considering heating a two-story house during the cold autumn, winter and early spring days using only an air conditioner - everyone was stunned by such an idea. And they were sure it would never work.

But that's exactly what I did and I've been heating my house this way for the past 6 years. As Larry David would agree, you could say I'm running my spite heating system to keep my house warm and cozy.

Air conditioner unit with no bells and whistles

I'm using a simple entry mid-range AC Daikin unit labeled as a 3,5 kW, or 12.000 BTU of power. It's important to mention that this AC unit has a COP (Coefficient of Performance) of 4, which means that for every 1 kW of electrical energy, it can deliver up to 4 kW of heat energy to the space. This is of course during ideal conditions as labeled by manufacturer, meaning it's 7°C (44°F) outside and low humidity.

The Energy Efficiency Ratio (EER) is the label for the cooling ratio and the Coefficient of Performance (COP) is the label for the heating mode ratio. The higher the EER and COP coefficients, the lower the electricity consumption. In the case of my AC unit, a COP of 4 puts it in the A+ energy class.

See our article Everything you need to know about heating your home with an air conditioner for more technical information.

Although Daikin is one of the more recognized AC unit manufacturers, it's fair to say that even other less popular units would perform the same or close to this unit, given that it's also an inverter unit (which all modern units are), and has similar specifications.

Also, keep in mind that this is an entry mid-level unit that was priced about 800€ at the time. It doesn't have any special features like a special outdoor coil to help with defrosting. It doesn't have an auto-cleaning feature, some special air-purifying filters, nor the WiFi option.

If I installed a more expensive model, I'd get some nice features which would make this heating experiment even more enjoyable. But the point of this scenario case is heating the space with affordable and simple unit.

House layout, location, insulation

The house is located in the continental part of Croatia, southeast Europe. With all outside walls exposed to the cold or hot conditions, there's no help from the supporting objects like auxiliary facilities or other heated apartments like there are in residential buildings.

It's a smaller house, with a floor base of about 50 m² (540 sq. ft) and with an upper floor connected with an open staircase which actually allows hot air to flow to the upper floor. On the upper floor, there are 3 rooms, one of which is bedroom that is not heated directly. By keeping the bedroom door closed and an opened window, I maintain a perfect few degrees lower temperature than in the rest of the house. If I wanted a more warm bedroom, I would achieve that by opening the bedroom door, and closing the window a couple of hours before bedtime.

So the actual square footage that is being heated is about 85 m² (915 sq. ft). Keep in mind that the bedroom is also heated through warm walls, but not directly via warm air flow. I also like to keep a window crack open in the bathroom and in the hallway to let some fresh air circulate. Yes, even with all these opened windows the temperature is high enough to dance around in my T-shirt.

Although with global warming taking visible and measurable effects, there were some colder winters that really put this heating system to the test. Normally, the temperatures during winter nights in December, January and part of February are around 0°C to -5°C (32°F to 23°C), but there were colder winters with temperatures below -15°C (5°F).

To be fair, I have to say I had to use a space heater to help heat the house on a couple of occasions when the temperatures hit their low and stayed that way for about 15 days. When you have good insulation, a sudden drop in outside temperature which lasts for a few days isn't much of a big deal, but when it lasts for 5+ days it's getting harder to compensate for the heat lost through the walls, windows and roof.

My house has a medium-solid insulation of brick walls, and a medium insulated PVC windows. The roof if insulated with wool. It's important to emphasize that insulation is the most important factor responsible for this heating system to work. Without proper insulation, it would be hard to achieve cosy temperatures using only an AC unit, and the electricity bill would be much higher. But this is also the case with any other heating system since a lot more thermal energy needs to be produced in order to compensate for the heating losses.

Warm house all day and night

The most important difference compared to other heating systems is a nice and constant temperature all of the time. AC is constantly running and maintaining the same preferred temperature, meaning there are no big temperature oscillations.

Output air from air conditioner is not as hot as air from radiators that circulates through a convection. Because of this, it's important to run AC most of the time to maintain a constant temperature and keep the fan speed at the minimum, thus reducing heating costs.

How much does it cost me to heat a house with an AC unit?

In my case, It's dirt cheap, no easier way to say it. During the coldest winter months, It costs me about 30€ to have the heating running at all times. That means that it's nice and warm even at 2 am if I need to use the bathroom.

In Croatia, the price per kilowatt-hour is about 0,17€. The median price of electricity in Europe is about 0,22€ / kW. The cost of running an AC unit to heat up space will depend on the square footage, insulation and how warm you want it to be. You also need to account the kW price in your country or state.

Needless to say, there's no other heating system that would come even close in terms of costs to this one. Not even wood heating.

Is this the best type of heating then? It has it's pros and cons, read on to find what I've learned in years of using this type of heating and what I like and don't like about it.

Pros - what I really like about heating my house with an AC unit

• It's nice and warm all the time, air conditioner is constantly running and maintaining the same preferred temperature, there are no big temperature oscillations.
• Even if the heating has been of for a few hours or during the day, once the AC is turned on - the whole space gets filled quickly with warm air. With other types of heating it would take longer to achieve a desired temperature.
• The same AC unit used for heating during winter is used for cooling during summer.
• AC units are much less expensive compared to extensive central heating systems.
• AC unit maintenance is cheap and everyone can take the air filters out and wash them every couple week.
• No radiators mounted to the walls. Some rooms would require 2 or more radiators get enough balanced heat. That usually means placing a radiator under every window, and sometimes behind a couch or where it just doesn't look nice. With only an AC unit, there's a minimalist look to all rooms, more space and easier maintenance. You don't need to remove dust from the radiators and painting the walls behind them is a nightmare.

Cons - what I don't like about it but can live with it

• Air conditioners blow warm air when heating, if the indoor unit isn't positioned in the right place - you could have warm air blowing right into you and your guests which is not always pleasant. Central heating, or any heating with radiant heat is much more pleasant.
• Air filters need to be washed every two weeks. While this is a minor inconvenience, since it take just a couple of minutes to rinse and dry the filters, some other heating systems don't require this type of maintenance, such as radiators or space heaters.
• Some noise. Although most modern AC units are pretty quiet, there's still some noticeable noise that the airflow produces. If your AC unit isn't properly mounted, you could also sense small vibrations.

Could you use an AC unit to heat your apartment or a house?

If you live in an area with really cold winters, and / or have a poorly insulated house - the answer straight away is - no. However, if your house has good insulation, a stronger AC unit, or installing more units might be able to do the job. There are AC units designed to handle extreme winters, but the layout of the house needs to be taken into account when opting for such a system because the warm air needs to be able to get to every room in your house. Local companies that sell and install AC units will be able to provide more information and do a calculation based on your specific case.

Do you already have an air conditioning unit you use to cool the room in the summer? Now is the perfect time to test that same unit to heat up the space and find out first hand whether you like it or not.