Deciding on what size heat pump you need comes down to the size of the area you want to heat/cool in your home.
While bigger may be better in muscle cars, it isn’t so with heat pumps. In fact, too big of a heat pump in too small a space can cost you more money or worse, cause a freeze up in the machine during winter.
In this article, we’ll explain why ensuring you get the right size heat pump for your home is essential to enjoying the maximum savings and the least amount of headaches possible.
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Optimal Operation of Heat Pumps
The optimal operation of a heat pump is to get a room/area to temperature and then maintain that temperature.
A heat pump works kind of like gears on a bicycle.
When you’re first asking your heat pump to bring an area of your home to a specific temperature it works very hard, using a “tougher gear.”
The colder the outdoor temperature and the higher the indoor temperature you’re requesting, the harder the machine works.
Once a heat pump achieves the desired indoor temperature, the machine then switches to an “easier gear”, one that uses less electricity to maintain that temperature. This switch is where the BIG savings come from using a heat pump. The cost to maintain temperature is astronomically less than what it costs to bring a room to temperature.
To achieve this perfect balance, you must ensure that the size of heat pump installed in your home matches the square footage of the space.
What Happens if my Heat Pump is Too Big?
When you install a heat pump that is too large for the area it’s located, two things happen:
- The machine heats the room up VERY quickly and therefore never gets to use it’s easier “gears”. It’s almost always operating in it’s highest electricity consumption zone.
- The heat pump may never run long enough to trigger what is known as a defrost cycle, which keeps the machine from freezing up.
The first issue shouldn’t come as a surprise. If a particular area of your home requires a 9,000 BTU heat pump and you have an 18,000 BTU heat pump installed then the larger machine is going to get the room to temperature very quickly.
Because the larger machine is pushing out so much heat it becomes difficult for the machine to stay on and maintain the temperature. Even at a low setting, the larger machine will still increase the room temperature higher than you wanted. The machine will then shut off and wait for the temperature to drop.
Depending on how cold out it is, the temperature can begin to drop quite quickly, causing the machine to turn back on at full power for a few minutes to heat things up again, only to shut off once more.
The second issue of freezing up can be a big one. Some heat pumps require the machine to run for a set period of time (10-15 minutes) in order to trigger what is called a defrost cycle.
The defrost cycle melts any accumulated ice off the outdoor unit during the colder winter months when the machine is running.
If a larger machine only runs for a very short period of time then ice will begin to accumulate on the outdoor unit. As that ice builds, it will reduce the amount of air the machine can pull in and potentially even cause a failure if the ice was to intrude with the outdoor fan.
Broken fan blades and burnt out fan motors are a big issue when heat pumps are oversized for the area they’re installed.
What size heat pump do I need?
Here’s the “rule of thumb” guide on proper sizing for ductless heat pump units and room square footage.
Use this as a starting point, BUT remember there can be objections to the rule. Having South Shore HVAC into your home to review the square footage, potential heat loss and also potential solar gain your home receives in the winter is the best way to ensure you purchase the right sized machine for your home.
- 9,000 BTU – 250 sq ft – 450 sq ft
- 12,000 BTU – 400 sq ft – 750 sq ft
- 15,000 BTU 700 sq ft – 1000 sq ft
- 18,000 BTU – 800 sq ft – 1200 sq ft
For a residential home, there is very little need for anything larger than an 18,000 BTU ductless heat pump.
To get a professional opinion on the right size and model heat pump for your home, book a 30-Minute In-Home Heat Pump Assessment with South Shore HVAC.
During your assessment we will:
- Determine the best indoor installation location
- Review the possible heat loss of your home
- Inspect your electrical service and panel
- Inspect the exterior of your home for best installation location
- Answer all of your questions about heat pumps, rebates, and financing
To book your in-home assessment call us today at 902-530-5002 or submit the form on this page.