Pool Heater Propane Tank Size

[JavaBrewer]

Researching online and having local propane company out for a consult I still don't fully get tank sizing. My pool heater, Ruud, is a 400K BTU model so that works out to 4 gallons per hour.

It was connected to a propane company owned tank, a huge (300 lb) tank at the end of my property. I need access and the space for a travel trailer so I had that tank removed and we have been without a heated spa for a few years now. Time to get heated pool back online.

So my confusion lies here. The propane company said I need 250 lb or more for this application. Not just for reduced refill intervals but also about surface area needed to convert liquid to gas for my 400K BTU heater. Install galvanized 1" pipe run is 30'. We only plan to heat the spa probably on an occasional Sat or Sun evening.

Due to space and aesthetics I want the smallest tank possible, 120 lb works out to ~ 30 gallons of propane. Am I just overthinking this or do I have to submit to a 250 horizontal tank?

Thanks Folks!

[cabmandone]

The propane company is saying if the tank isn't large enough, you can pull off vapor faster than the liquid propane can turn to vapor in the tank. What happens is the tank starts to frost as the vapor is drawn off too quickly. Ask them if they'll bury one.

https://www.propanetankstore.com/blog/why-does-ice-form-on-the-outside-of-a-propane-tank/

"If your vapor withdrawal rate for your appliance is greater than the liquid conversion rate, the tank walls will begin to freeze.
Why? Because the liquid propane is demanding more and more warmth and it attempts to draw that heat from the tank walls. Propane's ability to draw heat is in direct relationship to the ambient temperature out side of the tank and the amount of wet surface (surface in contact with liquid propane) inside of the tank"

[masraum]

Originally Posted by cabmando

The propane company is saying if the tank isn't large enough, you can pull off vapor faster than the liquid propane can turn to vapor in the tank. What happens is the tank starts to frost as the vapor is drawn off too quickly. Ask them if they'll bury one.

https://www.propanetankstore.com/blog/why-does-ice-form-on-the-outside-of-a-propane-tank/

"If your vapor withdrawal rate for your appliance is greater than the liquid conversion rate, the tank walls will begin to freeze.
Why? Because the liquid propane is demanding more and more warmth and it attempts to draw that heat from the tank walls. Propane's ability to draw heat is in direct relationship to the ambient temperature out side of the tank and the amount of wet surface (surface in contact with liquid propane) inside of the tank"

that's interesting, thanks. Learn something new...

Sounds like a cool collar would solve a lot of those problems!

[greglepore]

Yeah, its worth burying the tank. Not sure if they'll do it with a rental tank, but keep in mind that if you "rent" the tank you're paying a higher per gal price for the fuel.
I have an inground 500, but I heat spa, backup heat for heat pump, hot water and dryer and cook.

[Rtrorkt]

what is the capacity of the pool. Mine is 18k gallons or so. Takes most of my 250gal propane tank to raise the temp 10 degrees,

[mgatepi]

Damn guys this seems crazy expensive to me. Have you considered changing to a Heat Pump instead of propane?
I have a heat pump on my 14K gal pool and maintain it from end of may to early Sept. I keep it set at 86 degrees which is comfortable here in Ohio....according to my wife too warm but I like it and she doesn't know how to adjust the thermostat!!! Runs me about 60 to $80 per month.

[cabmandone]

^^^
Heat pump is definitely not a bad way to go.... but he already has the heater. So a 500 gallon tank dropped in the dirt and plumbed in would seem to be the less expensive route.