I have a 240v 350 gallon LA spa, it had a 5.5Kw heater and that would heat up the water 8-10deg/hr. I just put in a new heater element but it is only a 4.5Kw and I am only getting 2-4Deg/Hr. This does not make sense to me I expected it to heat at 5-8 deg/hr. I have checked the voltage supply during the heat cycle and I am seeing 120v at both inputs, after installation I checked the heater element and It had the correct resistance per the manual, I believe it was 14 ohms. Any one have any input or suggestions.

Thanks,

Fran

A 350 gallon tub has 1325 liters of water weighing 1,325,000 grams. A 14 Ohm resistor at 240V is a 4.1 KW heater. Supplying 14,810,400 Joules per hour which is 3,537,234 calories per hour ( 4.187 J/C). Your 350 gallons will take 736,111 calories to heat one degree Farenheit. Thus you should expect no more than 4.8 degrees F per hour heating. If you were a little off on the resistance measurement and the element really is 4.5KW, then the best you could expect is 5.2 degrees per hour. Your old heater would have done about 6.4 degrees per hour. It would take a 7 KW heater to heat at 8 degrees per hour. The calculations assume no loss (losses will slow heating) and no gains from motor power.

check voltage at the element. Forgetting all that calorie/joules stuff... a 1.4KW heater will heat a 350 gallon tub with 110 power at about half the rate you are getting. A 220V 5K heater will do nearly 14 per hour. Those are real world figures from personal experiance with several tubs. I would check to see if you are getting full voltage AT THE HEATER ELEMENT. If you are, ensure you have the correct element (even if the seller told you it was a 4.5KW). Ensure you are well insulated, and the cover is on the tub during this time. Also make sure the blower isn't on and the air induction valves are closed.