Hot tub help

[Texas Proud]

So, DW loves our hot tub... some of the components are starting to get worn out and broken... our pump just cracked and we will need to have a new one installed... our heater seems to be on its last leg, sometimes working and sometimes not...


So, I am thinking about changing out the heater... DW complains that it takes way too long to heat. We do not keep the heater on when we are not using it. I have tried to find out some info or calculator to help me... but so far no luck...

Here is my question...

How long would it take to heat say 500 gallons of water 30 degrees with a 50,000 BTU heater if working properly


Not sure how much water is in there... but guessing it is between 250 and 500 gallons but closer to the 500....

[RobbieB]

1 BTU will raise 1 lb of water 1 degree F.

1 gallon of water = 8.4 lbs

500 g water = 4200 lbs

50,000 BTU / hr at 80% eff = 40,000 btu /hr

The heater will cause the temp to rise at 9.5 degrees per hour, so about 3 hours.

[irishgal]

Uh oh, a mathematical story problem.

<runs out of thread>


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[Texas Proud]

Quote:

Originally Posted by RobbieB 1 BTU will raise 1 lb of water 1 degree F. 1 gallon of water = 8.4 lbs 500 g water = 4200 lbs 50,000 BTU / hr at 80% eff = 40,000 btu /hr The heater will cause the temp to rise at 9.5 degrees per hour, so about 3 hours.

Thanks for the calc.... one thing it tells me is that we are getting way less than 50,000 BTUs... it takes 5 to 6 hours (or more)...

Which is why I asked!!!

DW is telling me right now that we need to replace it... but that is $1300 installed!!!

[RobbieB]

If your heater is old it's not anywhere near as efficient as newer models and it sounds as if it's having problems too. The bright side is you will use much less gas with the new one.

Maybe consider a solar assist too?

[aja8888]

I had to change out the copper heat exchanger in my 10 year old natural gas spa heater a few years ago. I believe it was a 50,000 BTU unit also. Being a cheap ass, I changed it out myself and found it was heavily corroded (The copper exchanger). So for about $600 in parts, I rejuvenated the heater for a few more years.

Next time it will be a new unit as they are more efficient than my early 90's unit.