Right size natural gas heater?

[Sar138]

I keep getting conflicting information from various pool companies around me regarding BTUs I need in a new natural gas heater. Hoping this group can help.

I have an 18k gallon inground pool (saline and liner). It’s in full sun in the northeast. I have a new Pentair VSP. I’m looking at gas instead of a heat pump because I really want to extend the use of my pool in the colder months, and the air is too cold for the heat pump to work. I do use a solar cover in the early/late season.

One company recommended a minimum of 333 BTU and a max of 400 BTU. Another company I met with today said 400 BTU was oversized, and wouldn’t heat the pool up that much faster at the end of the day, so save the money and go with 250 BTU. He said you can only oversize so much and it is diminishing returns.

I don’t want to spend an extra $1,500 just to heat my pool up an hour faster, so trying to get a sense from folks here what you think makes sense. If we’re talking 4-5 hours faster maybe.

Thanks in advance for all your advice!

 

[PoolStored]

Buy the biggest you can afford. Going from 250k to 400k will just heat your pool faster. It won't cost more or use more gas. It always takes the same amount of energy to heat a pool from point A to point B. A bigger heater just does it faster. If you don't care about speed, go with the 250.

I have a 336K on a 30K pool. I start it May 15 and run it until October 15. I do not cycle it on/off. I leave it at 83. Cost me $1200 in gas and delivery last year. (Northern Ohio...fairly similar latitude).

If we’re talking 4-5 hours faster maybe.

This is the real question. Let's run some "rough" numbers....

Determine Time Required to Increase Water Temp 1 Degree F:

1. Multiply the total gallons of water in the pool by 8.3
This will give you the total weight of the water
(18,000 gal x 8.3 = 149,400 lb)

2. Divide the weight of the water by your heater's BTU * .8 (80% efficiency is close enough).
This will give you the hours it takes to raise the water temp 1 degree F
(149,400 lb / (250,000*.8) BTU = .747hrs)
(149,400 lb / (400,000*.8) BTU = .466hrs)

Determine Total Time Required to Increase Water Temp the Desired Amount:

1. If the current water temp is 65 degrees and you want to raise it to 80 degrees (15 degree increase) ..
Multiply 15 degrees by the time it takes to raise the temperature 1 degree F
(15 degrees x .747hrs = 11.2hrs)
(15 degrees x .466hrs = 6.99hrs)

This is a rough calculation. There are lots of inefficiencies not accounted for, but if you have a solar cover, puts you in the ballpark.

 

[ajw22]

There is no substitute for BTUs.

There is only the one time greater acquisition cost to getting the largest heater your gas service can support.

Check your gas meter and pipe sizes to the heater location and confirm you can supply adequate gas for the heater.

If you use your heater to heat on demand before you plan to use the pool then the faster time to get to temperature can be a benefit. When we get a cold or rainy spell for a few days and there is going to be no pool activity I turn off the heater.

 

[Sar138]

Thanks all! I do actually have a new meter being put int that can accomodate 400BTU, so it sounds like that’s what I’m going to what to go with.

One last question (and I think I now know the answer based on this forum). Hayward or Raypack? My instinct was Hayward because I’m more familiar with that brand it it cost more, so ignorantly I thought “better heater”. Sounds like this forum agrees that Raypack is the better manufacturer though? I got an initial quote of $6,400 for a 400 BTU Raypack and it seemed pretty high (but did include the non-plumbing labor), so I’m shopping around a bit.

 

[ajw22]

The Hayward 400K gas heater is a forced draft heater with an air blower and complex controls.

The Raypak heater is a larger natural draft heater that has simple operation but since it’s burners are open at the bottom it tends to develop corrosion around the burners.

Two very different designs. Each with its strength and weakness.

Otherwise heaters are a commodity. Hayward, Pentair, Jandy and now Raypak all have forced draft heaters with blowers. They have a smaller footprint, sealed combustion chamber, and are less prone to burner corrosion and clogging. They also have more complex controls and are noisier when running.

Older heater models all used to be natural draft. The natural draft Raypak heaters eventually corrode from the bottom up…

If you want a Raypak heater I would look at their new Avia model. People have been saying good things about it.

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