We're doing a massive pool rehab and have a couple questions

#1
I'm new to pools and to spas, First off the pool has an inground spillover spa that had a heater at one time but now none of the related heating items are present. Spa is basically half of an octagon. Approximately 5/7. I'm in southern ms. During the summer the average temp here is 90 at night it's usually in the 70s my question is will a 5.5 letter heater work for this hot tub I have a system from an older above ground spa I was contemplating using but it might not be worth the trouble. Says it's a pinnacle. Anyway any info is appreciated.
 

pooldv

Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
Aug 10, 2012
24,993
DFW, TX
#3
Is that a 5.5 kWh heater? It won't work very well for an inground spa. They are designed to maintain continuous heat for an insulated and covered hot tub. Heating up concrete and the ground around it will take forever and it will have to run a lot to maintain the heat.
 

Esloser

Well-known member
Jun 23, 2016
513
Millville, NJ
#5
I have a 7x7 attached inground spa that is heated with a 400k btu heater that heats the spa from 65-95 degrees within 25-30 minutes. Mine is natural gas, but I don't know how that translates into a kw measure.
 

pooldv

Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
Aug 10, 2012
24,993
DFW, TX
#7
If you want to be able to let it sit at ambient temp and heat on demand then at least a 250k btu gas heater, 400k btu is better. By the way, a 5.5kw heater is a little under 19k btu.

If gas isn't an option you can use a 140k btu heat pump but it will take longer. You might want to cover it and keep it partially heated to speed heat up, say 85 or 90 degrees.
 

Sfpat

Silver Supporter
Jul 29, 2016
113
tulsa
#8
2545 btu/kw so 5.5 kw heater would equal approx. 14,000 btu. Substantially smaller than recommended

My bad, the conversion above is to hp not kw. 3411 btu/kw so about 19 K btu as mentioned above (long time ago when I was a practicing engineer I had all these conversions memorized)
 
#9
Due to the odd shape of the spa some quick figuring shows it to be approximately 301 gallons. The pool seems to be around 19.5k gallons. Would you all still recommend a 400k but gas heater for that size spa?
 

Blap

Member
Jun 1, 2017
15
CA
#10
Big as possible if you want to heat it fast. I'd avoid electric for an inground spa. The bigger one will heat faster and be able to keep up with demand as cold air is pulled in through the jets for your bubbles.