Pool Equipment Troubleshooting

What Size of Pool Heater do I Need. 

Determine what size swimming pool heater you need.

By Allen Hayward

Sizing a heater for a swimming pool is no easy task. Most people try to avoid it altogether because it involves a lot of measurements and calculations. Instead, it is simpler to purchase a large heat pump and heater because it has a better chance of successfully heating the pool.

However, a big heat pump and the heater could mean higher electrical costs than necessary. If you’d rather have power efficiency from these heating sources, then it is better to size your heater so that you consume just the right amount of power for it.

The Sizing Process

When you go shopping for a pool heater, don’t just purchase the first one that you come across. There are a few considerations to make before selecting a pool heater. Some of those considerations include:

The Manufacturer

Propane or natural gas?

The Size

Most people don’t have a problem figuring out the manufacturer and fuel source they need for their desired pool heater. However, their biggest concern is choosing the right size heater. They don’t know which size is the right size for their swimming pool. The lazy way to solve this problem is to choose a large heater. You’ll then know it can heat your pool water no matter if it is a big or small pool. For instance, you could purchase a large 400K BTU Pool Heater and heat your pool water at twice the speed that a 200K BTU Pool Heater could heat it. On the downside, the 400K BTU Pool Heater burns double the amount of gas. But if you have a spa integrated with your pool, then it’ll require the biggest BTU Pool Heater you can afford. Because of this, you’ll end up consuming more electricity because the heater has to heat two different bodies of water. If you only have a swimming pool, then you’re better off calculating the heater size so that you can have better power efficiency.

How to Perform the Sizing Calculations

  1. Calculate the Area of the Pool Surface

What is the surface area of your swimming pool? You must figure this out before moving forward. It is a simple calculation because you only have to multiply the pool’s length by the width of the pool. Then you will have your answer.

Example: Let’s say the dimensions of your pool are 20′ x 30′. The surface area would be 600 square feet.

Contrary to popular belief, you don’t factor in the number of gallons in your swimming pool to calculate the heater size. Even though it is important to know the gallon size, the surface area size is more important. After all, bigger surface areas give heat more of a chance to escape. It also means you have to heat more water because it covers a much larger area, even if the water is not high. Therefore, you must purchase a pool heater that can heat the entire surface area.

  1. Calculate the Minimal BTU Size Needed

Now that you know the surface area of your swimming pool, divide the answer by three. The new answer will give you the “minimal BTU size” to accommodate that particular surface area size.

Going back to the previous example, you have 600 square feet for the surface area of the pool. Divide 600 by three, and you have 200. That means you should purchase a pool heater with at least 200,000 BTUs. Of course, you can go higher than 200,000 BTUs if you want. It is only the smallest recommended size, so don’t go lower than 200,000 BTUs in this case.

Most swimming pools lose heat during the night because there is no sunlight. If you don’t have a solar cover, your only way to retain heat is to have a pool heater with a huge BTU size. Gas heaters work well for this.

  1. Other Considerations

Okay, so you know the minimum BTU size recommended. If you choose to purchase a larger heater for better power efficiency, all related variables should be considered first.

For instance, do you have a solar cover for your pool? Do you swim in your pool often? Are heavy winds frequent in your environment? All these things can affect how much work your heater needs to do.

If you don’t’ have a solar cover, then a 300K BTU Pool Heater model should be acceptable. It will be strong enough to make up for the water evaporation, unforeseen heavy winds, and any additional heat loss incurred. It is excellent for nighttime swimmers too.

But if you were to include a solar cover in addition to the pool heater, then your water will heat much faster. Not only that, but your heater will consume less gas or electricity because it won’t have to work as hard. In this case, a smaller heater that is 200K BTU is fine. It will save you money in the long run.

Sizing the Raypak Residential Gas-Powered Pool Heater

If you choose the Raypak Residential Gas Heater, you can use the convenient gas heater calculator on their website to determine the right size you need. The calculator considers your state and city and the average temperature of the air in that location. Then you can enter your desired temperature for the pool water.

After that, the calculator will give you all the size information you need to know. It will also give you the cost information for the propane and gas required to power it. You can compare these costs to the standard energy costs of electric-powered pool heaters.


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