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Poolservice123, CPO, CPI, CBP
Category: Pool and Spa
Satisfied Customers: 489
Experience:  40+ yrs, NSPF Instructor, NC Licensed SwimPool Contractor
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I have a Pentair Minimax NT Heater. We just replaced

Customer Question

Hello, I have a Pentair Minimax NT Heater. We just replaced the Thermostat today. Everything comes on with no error messages. We tried to heat up the spa today for about 6 hours & the water got luke warm but not hot. We turned the valve off to the pool so the pool water would not transfer into the spa.
Submitted: 2 years ago.
Category: Pool and Spa
Expert:  Poolservice123 replied 2 years ago.
Hello, I am here to help you today. YOu should start to see some heating in the spa by closing off the cooler pool water from entering and leaving the spa. Gas heaters are only at best 85% efficient. That means for every $10 in gas only $8 heats the water. So it's a slow heat up. The gas heats in BTU's (british thermal units) and 1 BTU will heat 1 gallon of water by 1 degree. How quick this happens is dependent on many things such as size of heater (200,00o BTU's? etc) ambient air temperature, wind, evaporative heat loss and radiant heat loss. The water coming into the spa always feels luke warm when starting to heat as it is recovering. The older the heater the less efficient it becomes. Heater's that are 5 years old are only 50% efficient.
The use of a evaporative retardant such as a solar cover, any cover or liquid evaporation retardant can help with heating and retaining heat.
How old is the heater? Are you using a cover or something to stop evaporation as you heat? What size heater? What is the air temp. and what area of the country do you live (humidity)? I need this to see if there is a problem.