A pool heater can be undersized: if it cannot replace the heat lost through evaporative cooling, the pool's temperature will fall below the ideal. However, there is no such thing as oversizing a pool heater. The larger the heater's output, the faster it heats the water in the pool, and it will not begin short-cycling.
Generally speaking, you should oversize the heat pump as much as possible. You'll never regret going too big, as doing so means warming the pool at a faster rate without running the heater as much.
When your heat pump is too big, the heat pump will heat the room for a shorter time, and the furnishings in your home have less time to absorb heat. Your heat pump will have to heat the room more often because it cools down quicker.
It is true that larger heaters heat your pool faster than smaller ones. A 400k BTU heater will heat a pool twice as fast as a 200k BTU heater and burn gas twice as fast. Heating up a pool versus a pool/spa combination requires less BTU power.
We would recommend at least an 85,000 BTU heat pump for a 20,000 gallon pool. If you would like to extend your swimming season into the late Fall or early Spring or you live in a colder area we would recommend a larger unit like the AquaPro 112,000 BTU or AquaPro 137,000 BTU models.
Heat Siphon Z700HP Pool Heat Pump, 145,000 BTU
The Heat Siphon Z700HP is one of the most powerful pool heat pump models available with 145,200 BTUs, perfect for the biggest pools' warming needs.
Find the volume of your pool, and pick a heat pump model with heating increase of 0.25 and above. The higher the number, the faster your pool heats up. For example, if you have an 50,000L pool then the minimum recommended size would be the 18KW model (0.27c per hour).
15000 X 8.3 X 30 = 3,735,000 BTU
To get the hourly BTU produced you need to divide by 24 - which is equal to 155,625 BTU. So, for a 15000-gallon pool you need a pool heater capable of producing 155,625 BTU.
If your heat pump is too large for your home, it will short (or rapid) cycle, which isn't healthy for the motor. If too small, it will constantly try to run to meet your temperature needs. Not only are both issues annoying, but it can cost you.
If a heat pump is undersized for a room, the negative effects can become quite obvious, fast. It's simply not going to adequately heat or cool the room it's in, and it will certainly work harder than it should in order to do so. Naturally, this can lead to a host of mechanical problems over time.
If a Heat Pump is Undersized or Oversized
If a unit is too small, it will struggle to produce enough energy to heat and cool your home. To compensate, it will work harder to meet temperature demands, wasting energy and money or breaking down altogether.
Pool heaters measure their power in BTU (British thermal units). One BTU raises the temperature of one pound of water by one degree Fahrenheit. There are 8.33 pounds of water per gallon. That means that if you have a swimming pool that holds 20,000 gallons, it requires 166,000 BTUs to increase by one degree.
By adding a solar blanket to your pool during heating you will greatly increase the efficiency of the heating process and keep evaporative heat loss to a minimum. Heat pumps will use around 5,000 watts or 5 kilowatts per hour per 100,000 BTU's. For a typical size 100,000 BTU heat pump, that's 5 kilowatts per hour.
Too large of a pump can cause poor filter performance and even damage it, if the filter is not also oversized accordingly. Another possible consequence is pump cavitation in which bubbles form in the water inside the pump and then burst with great force, resulting in damage to the impeller and other internal parts.
For pools up to 24 Ft Round, use a 1 HP pool pump. For pools over 24 Ft Round, we recommend using a 1.5 HP pool pump.
Pool gallonage x 2 (the recommended number of cycles in a day) ÷ daily hourly run time ÷ 60 (minutes in an hour). So, for a 30,000-gallon pool that runs continuously (24-hours), the formula is: 30,000 x 2 ÷ 24 ÷ 60 = 41.6 or rounded up it's a 42 GPM minimum flow rate.
A heat Pump, when properly sized, can maintain any desired pool temperature between 80 and 90 degrees, regardless of outside weather conditions. A Heat Pump will work when the outside air temperature is above 45 degrees.
Sizing a gas heater for inground pools is done by first matching pool heater BTU output to pool size in gallons. Or approximately 100K BTU's for every 10,000 gallons of pool water. For inground pools less than 20,000 gallons, small gas heaters like the Raypak 206K BTU output are suitable.
On average you'll need between $200 to $500 to run it monthly with a pool cover. Electric heat pumps from trusted brands can last between 10 and 20 years. They're energy-efficient, and their use of surrounding air qualifies them as one of the most energy-efficient heating systems.
They are the same exact unit, just a different name badge. Raypak is the parent company. They are the best heater on the market today.
The fastest way to heat your pool is to use a gas pool heater and a solar cover. It's like heating up your coffee in the microwave and putting a lid on it. No matter how you plan to heat your pool, you should at least have a solar cover (or liquid solar cover) to help you retain the heat.
General rules for a rough calculation
For a heat pump or wall-mounted air conditioner, it's about 1,000 BTU per 100 square feet. So for a 1,000 to 1,200 square foot area, your heat pump would be about 12,000 BTU. For the same area, if space is limited, the power can be reduced to 9,000 BTU.