Propane Heater Size?

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Nate4429

Nate4429

Well-known member
Mar 8, 2019
88
Marysville, Wa
I had a pool guy come by the house and give the run down for a few things I needed to get done and he told me how to do them all my self pretty easily ? so I also told him I was looking at getting a 400btu heater but he said to go with a much smaller one to save $2-3k on the front side and that a small heater would cost less, use the same amount of propane and just take longer to heat. I like the idea of saving money up front and I kind of trust him since he didn’t try to sell me anything and spent over an hour with me at no charge. What do you all think? 36,000 gallon pool in the PNW.
 
1 BTU will raise 1 lb of water 1 degree. Your 36,000 gallon pool is about 300,000 lbs. A gas heater runs ar 80% efficiency so a 400K BTU heater with output about 320K BTU. That will raise your pool 1 degree an hour. To me that is already slow heating.

A smaller heater will use more propane, which is expensive, since it needs to run longer at 80% efficiency.

What size heater were you thinking of and what temperature rise do you want? What model heater?

Will you have a pool cover? A pool can lose 5 degrees or more on a cold night.
 
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Nate,

It's nice that the pool guy spent time with you but I have to say that what he's telling you doesn't make a lot of sense to me. Consider your operating cost. Operating cost (very rough estimate) of a 400K BTU heater is about $10/hr which works out to around $1500 per month at 5 hr per day. Clearly operating cost is way bigger than up front cost so it wouldn't make a lot of sense to give up operability for up front costs. The devil's in the details for pool heat in your area. Here are some things to consider:
  • There are 3 non-solar choices for pool heat in order of lowest cost per deg F raised. Electric (heat pump), natural gas, propane.
  • Heat pumps don't work very well below 50 deg F
  • Hourly operating costs for 400k Btu are about $2.40 for heat pump, $4.00 for natural gas, and $10 for propane.
  • Assuming 5 hr per day, monthly fuel costs are $360, $600, $1500 respectively for heat pump, nat gas, propane
  • Up front cost of 400K BTU are
    • $10,000 for heat pump (4 at 100K BTU each)
    • $2,500 for natural gas heater
    • $2500 for propane heater
  • A pool cover will dramatically reduce operating costs. They cost about $2000 for a manual one and $5000+ for an automatic.
As you can see you really need to work out the details for your specific case with a design optimized for you and your location. Costs and temperatures vary widely. For example electric power varies by a factor 3-4 across the country. Average temps, propane, natural gas also vary widely. This may sound a little daunting but it's not really that hard to do and should be done before you commit big $.

I hope this helps.

Chris
 
setsailsoon said:
There are 3 non-solar choices for pool heat in order of lowest cost per deg F raised. Electric (heat pump), natural gas, propane
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I think it's safe to say propane is more expensive for most use cases, but heat pump and natural gas not so much. That's highly dependent on utility costs and temps. For example, even with my relatively low electric costs of $0.12/kWh, a natural gas heater would win out for me, since it's so much cheaper than electric that even in the summer at peak of COP the heat pump would cost about the same as natural gas would, and more outside the peak of summer when the COP drops off.
 
ajw22 said:
1 BTU will raise 1 lb of water 1 degree. Your 36,000 gallon pool is about 300,000 lbs. A gas heater runs ar 80% efficiency so a 400K BTU heater with output about 320K BTU. That will raise your pool 1 degree an hour. To me that is already slow heating.

A smaller heater will use more propane, which is expensive, since it needs to run longer at 80% efficiency.

What size heater were you thinking of and what temperature rise do you want? What model heater?

Will you have a pool cover? A pool can lose 5 degrees or more on a cold night.
Click to expand...
We have a Solar pool cover. I’m not sure on the size. We were looking at a 400btu propane heater. That pool guy said that it will take the same amount of propane to heat the pool no matter what size the heater it will just take longer for a smaller one. We would like to get the pool to 78-80 starting in mid April. Then we most likely wouldn’t use it during the summer when it holds about 76-78 on its own for June-August. And then run it again for Sept. Price is the deciding factor here but I’m realizing that’s hard to even get a ballpark on ?
 
Nate4429 said:
We would like to get the pool to 78-80 starting in mid April.
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What will the pool water temperature start at?

How much pool temperature will you lose at night and how long will your heater need to run to get back to the desired temperature?

Will you run your heater during rainy or cold weather or let the pool cool down and then need to heat it up?

You need to decide if the waiting for the pool to heat up is worth the savings in the smaller heater.
 
Nate4429 said:
Start temp would be right around 55ish. Previous owner would open pool around Mid May when the pool temp hits the 60ish mark.
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Raising the pool from 55 to 75-80 would take a 400K heater around 24 hours and a 250K heater about twice that.
 
ajw22 said:
Raising the pool from 55 to 75-80 would take a 400K heater around 24 hours and a 250K heater about twice that.
Click to expand...
Also, evaporation heat load can be significant if there is any wind. For example at 68 deg F and 50% humidity:
  • if the surface area is 970 sq ft and wind speed is 1 mph the heat loss is about 34,000 btu/hr.
  • If wind speed is increased to 10 mph heat loss from evaporation is 112,000 btu/hr
So a cover is pretty important especially when it's windy.

Chris
 
setsailsoon said:
Also, evaporation heat load can be significant if there is any wind. For example at 68 deg F and 50% humidity:
  • if the surface area is 970 sq ft and wind speed is 1 mph the heat loss is about 34,000 btu/hr.
  • If wind speed is increased to 10 mph heat loss from evaporation is 112,000 btu/hr
So a cover is pretty important especially when it's windy.

Chris
Click to expand...

In post #5 Nate said he had a solar cover.
 

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@Nate4429 - decide on anything? We are looking to add a heater as well, and the Propane numbers as scary (we don't have NG service here). I'm worried that an electric heat pump won't work well for what we want (extended swimming season, not so much to heat the pool a few degrees over summer).
 
Nate4429 said:
This info is overwhelming ? I think I’ve been talked out of ever trying to heat the pool. Thanks for all the info though guys. I would have hated to spend the money and then not be able to heat for a reasonable cost.
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Yeah, heating a pool isn't cheap. I doubt we'll ever pay to heat our pool (NG or heat pump), though I'm considering solar panels. They are expensive and need a lot of space, but after install the heat is free, need only pay for running the pump.
 
Solar is great but it isnt point of use like a gas heater. Having both is the ideal setup but pricey. Propane is expensive period no matter what the size. Hes kinda right but a pool that size needs a 400k heater. Too long to heat with smaller. Also the upfront isnt true. It's a small difference in cost of heater from 250k to 400k btus. Not thousands difference maybe a few hundred
 
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