Water Heater in North Carolina

[meatyor]

Hey all, I’m just looking for some opinions on the value of, and usage of a heater for a 23k gallon pool in central North Carolina.

Imo, some fluctuation in summer isn’t a big deal, so not really looking to maintain a perfect temperature. More wondering about within our climate is the heater going to extend the season a month, or can we swim deep into the fall, and nice and early in the spring with a heater. Are there cost efficient heaters, or are they all energy hogs?

 

[PoolStored]

Get the biggest one you can afford. Gas will be more efficient late and early.

Assuming a 30K gallon pool. 140K heat pump., 400K gas heater. Further assume 5dF (degrees F) demand daily (may be off, but just an assumption). You can change any assumptions and recalculate.

Heat Pump.
30,000 x 8.3 = 249,000lbs of water.
249,000 / 140,000 = 1.77 hours to raise temp 1dFF ( this will be optimistic for a heat pump, heat pump efficiency varies dramatically with the air temperature, only reaching the listed BTU number when the air is quite warm)...but let's roll with it.
1.77 * 5dF = 8.85hours of heating. Because of the optimism above, let's say 10hours
Heat pump Consumes about 5,000W/hour per 100,000 BTU. So 7,000W per hour for 140K unit.
10 hours, 7,000W, $.38/kWh = ~$27/5dF. (You can change $ to your rate)

Gas heater
400,000 BTU * .8 efficiency =320K BTU
249,000 / 320,000 = .78 hours to raise 1dF
Gas heater consume 1g/h/100K BTU
Hourly consumption = 4g/h total
.78 *5dF = 3.9 hours
3.9 hours * 4g/H = 16g/day
16g/day = 19 Therms
Assume Gas is $1.63/therm (assumption without delivery $, change to your rate).
19 x 1.63 = 30.97/Day

You can change to your rates and re-calculate.

If you want to heat something quickly, get a gas heater (like the spa when you want to use it). If you want to maintain a constant temperature, get the heat pump.

 

[meatyor]

Get the biggest one you can afford. Gas will be more efficient late and early.

Assuming a 30K gallon pool. 140K heat pump., 400K gas heater. Further assume 5dF (degrees F) demand daily (may be off, but just an assumption). You can change any assumptions and recalculate.

Heat Pump.
30,000 x 8.3 = 249,000lbs of water.
249,000 / 140,000 = 1.77 hours to raise temp 1dFF ( this will be optimistic for a heat pump, heat pump efficiency varies dramatically with the air temperature, only reaching the listed BTU number when the air is quite warm)...but let's roll with it.
1.77 * 5dF = 8.85hours of heating. Because of the optimism above, let's say 10hours
Heat pump Consumes about 5,000W/hour per 100,000 BTU. So 7,000W per hour for 140K unit.
10 hours, 7,000W, $.38/kWh = ~$27/5dF. (You can change $ to your rate)

Gas heater
400,000 BTU * .8 efficiency =320K BTU
249,000 / 320,000 = .78 hours to raise 1dF
Gas heater consume 1g/h/100K BTU
Hourly consumption = 4g/h total
.78 *5dF = 3.9 hours
3.9 hours * 4g/H = 16g/day
16g/day = 19 Therms
Assume Gas is $1.63/therm (assumption without delivery $, change to your rate).
19 x 1.63 = 30.97/Day

You can change to your rates and re-calculate.

If you want to heat something quickly, get a gas heater (like the spa when you want to use it). If you want to maintain a constant temperature, get the heat pump.

WOW, thanks for such a great and detailed response, appreciate it!

 

[JoyfulNoise]

While the above calculations are fine and within reason, the biggest issue with heating a pool is heat loss from evaporation of the water. In the early spring and late fall, the air above the pool has a dew point temperature many tens of degrees lower than the water temperature. I live in an area where the dew point temperature can be as much as 40°F lower than the water temperature. In short, this means that warm water from the pool’s surface will evaporate like crazy because the air is highly undersaturated and the process of evaporation removes a lot of heat energy from the water.

SO … unless you are willing to cover the pool constantly in the spring and fall with a bubble cover and then deploy and remove that cover as-needed to swim, all of the heat you add to the pool will easily “evaporate” over night. Think of it like burning your hard earned money in the gas heater …

A lot of people are totally ok with covering their pool … until they actually get a cover and wrestle with a soaking wet cover when the air temps are cold … then they realize they are not ok with covering their pool …

 

[PoolStored]

While the above calculations are fine and within reason, the biggest issue with heating a pool is heat loss from evaporation of the water.

+100…I should have included an assumption/caveat about a solar cover. I’ll do that in the future.

 

[meatyor]

While the above calculations are fine and within reason, the biggest issue with heating a pool is heat loss from evaporation of the water. In the early spring and late fall, the air above the pool has a dew point temperature many tens of degrees lower than the water temperature. I live in an area where the dew point temperature can be as much as 40°F lower than the water temperature. In short, this means that warm water from the pool’s surface will evaporate like crazy because the air is highly undersaturated and the process of evaporation removes a lot of heat energy from the water.

SO … unless you are willing to cover the pool constantly in the spring and fall with a bubble cover and then deploy and remove that cover as-needed to swim, all of the heat you add to the pool will easily “evaporate” over night. Think of it like burning your hard earned money in the gas heater …

A lot of people are totally ok with covering their pool … until they actually get a cover and wrestle with a soaking wet cover when the air temps are cold … then they realize they are not ok with covering their pool …

That’s great context, thanks JoyfulNoise!