I see you're using natural gas. My pool heater uses #2 with only a 40% efficiency. We don't have natural gas to the house. Do you have any thoughts on using a heat pump to get the spa up to temp for us desert dwellers?
Newbie - Pool Heater Question
- Thread starter sleepysdad
- Start date
- May 23, 2015
- 25,709
- Pool Size
- 16000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
You can use a heat pump but it will take a longer time than gas. Depends on the spa volume, the BTU output of the heat pump and you'd want to have the spa covered while heating.
I have about the same volume spa as you and thinking of putting a 140K heat pump in.
CJadamec
TFP Expert
A 140k heat pump is plenty big. Its not going to be as fast as a gas heater but if you don't have gas that's not really an option. That is plenty of power heat pump to get a 650gal spa up to temp and keep it there in a reasonable time. Keeping your spa/pool covered will help tons by keeping everything warm. The dry desert air is murder on evaporative heat loss.
Don't skimp on the power supply to a unit that big, its going to draw around 45 amps continuous while running the compressor you don't want to have issues with undersized wiring on something that size.
Don't skimp on the power supply to a unit that big, its going to draw around 45 amps continuous while running the compressor you don't want to have issues with undersized wiring on something that size.
We probably aren't that far apart in cost per btu. My 100 was conservative and my heater and pool are nearly double the size. Either way, I'm happy to pay it in order to extend my season on either end.
Why is it that water loss occurs mostly at night and not during the day. This is why a solar cover is recommended at night and should be removed as sun is beating down on the pool.
I mostly stayed awake in physics class and based on what I can remember I'd say the opposite. As the night air cools the relative humidity (RH) increases. High humidity lowers evaporation rate. At low enough temperatures the air reaches the dew point (100% RH) and evaporation stops.
The steaming pool is actually a sign of low evaporation since the steam is water condensing rather than evaporating. During the day the air absorbs the moisture coming from the pool (ie it evaporates) so you don't see the steam.
The only thing I can think of that would make water evaporate faster at night would be increased wind. But often that isn't the case and I don't think is being suggested here.
The highest period of evaporation should be occurring during the day.
All this is separate from the question of heat loss. Evaporation is an endothermic process which consumes heat. Lots of it. So keeping the solar cover on saves a lot of heat loss. Very noticeable at night, and would be noticeable during the day except the sun is adding heat and hiding the evaporative heat loss. Personally I keep my cheap bubble wrap solar cover on during the day since preventing the evaporative heat loss more than makes up for the reduction of solar energy due to the solar cover. On calm days with very high humidity the balance could tip in favor of removing the cover but one would have to test it carefully.
It takes 1 btu of heat to raise the temperature of 1 pound of water 1 degree F.
It takes 960 btu of heat to change the state of water to vapour or solid, so
if 10 gallons of water evaporate from my pool in the morning I will loose roughly 96,000 btu of heat.
1 gallon = 10 pounds. 10 x 10 x 960 = 96,000 btu.
I used to think it was cool to walk out in the morning and see the steam rising off of my pool, now my cover is on except when we swim.
My pool looses roughly 2-300 gallons per week
It takes 960 btu of heat to change the state of water to vapour or solid, so
if 10 gallons of water evaporate from my pool in the morning I will loose roughly 96,000 btu of heat.
1 gallon = 10 pounds. 10 x 10 x 960 = 96,000 btu.
I used to think it was cool to walk out in the morning and see the steam rising off of my pool, now my cover is on except when we swim.
My pool looses roughly 2-300 gallons per week
Last edited:
I think what I meant was "heat retention" and not water loss and the question was answered based on what I really was asking. The solar cover at night makes a big difference in retaining heat. I know we a weekly cold spell and water held at 84* for the first 4 days. The next 4 days, the water drop because the spell lasted too long. Have no idea about evaporation. I know the hotter the weather, the faster the water loss.
Originally Posted by Catanzaro
Why is it that water loss occurs mostly at night and not during the day. This is why a solar cover is recommended at night and should be removed as sun is beating down on the pool.
I mostly stayed awake in physics class and based on what I can remember I'd say the opposite. As the night air cools the relative humidity (RH) increases. High humidity lowers evaporation rate. At low enough temperatures the air reaches the dew point (100% RH) and evaporation stops.
The steaming pool is actually a sign of low evaporation since the steam is water condensing rather than evaporating. During the day the air absorbs the moisture coming from the pool (ie it evaporates) so you don't see the steam.
The only thing I can think of that would make water evaporate faster at night would be increased wind. But often that isn't the case and I don't think is being suggested here.
The highest period of evaporation should be occurring during the day.
All this is separate from the question of heat loss. Evaporation is an endothermic process which consumes heat. Lots of it. So keeping the solar cover on saves a lot of heat loss. Very noticeable at night, and would be noticeable during the day except the sun is adding heat and hiding the evaporative heat loss. Personally I keep my cheap bubble wrap solar cover on during the day since preventing the evaporative heat loss more than makes up for the reduction of solar energy due to the solar cover. On calm days with very high humidity the balance could tip in favor of removing the cover but one would have to test it carefully.
Not to not-pick, but A gallon of water is 8.34 lbs. 8.34 X 10 = 83,400, about a 15% difference.
CJadamec
TFP Expert
Originally Posted by Catanzaro
Why is it that water loss occurs mostly at night and not during the day. This is why a solar cover is recommended at night and should be removed as sun is beating down on the pool.
I mostly stayed awake in physics class and based on what I can remember I'd say the opposite. As the night air cools the relative humidity (RH) increases. High humidity lowers evaporation rate. At low enough temperatures the air reaches the dew point (100% RH) and evaporation stops.
The steaming pool is actually a sign of low evaporation since the steam is water condensing rather than evaporating. During the day the air absorbs the moisture coming from the pool (ie it evaporates) so you don't see the steam.
The only thing I can think of that would make water evaporate faster at night would be increased wind. But often that isn't the case and I don't think is being suggested here.
The highest period of evaporation should be occurring during the day.
All this is separate from the question of heat loss. Evaporation is an endothermic process which consumes heat. Lots of it. So keeping the solar cover on saves a lot of heat loss. Very noticeable at night, and would be noticeable during the day except the sun is adding heat and hiding the evaporative heat loss. Personally I keep my cheap bubble wrap solar cover on during the day since preventing the evaporative heat loss more than makes up for the reduction of solar energy due to the solar cover. On calm days with very high humidity the balance could tip in favor of removing the cover but one would have to test it carefully.
I think possibly you aren't acknowledging the micro-scale evironment say in the colmun of air about 1 foot off the surface of the water. The air above to pool will be heated to near the temperature of the water negating the overall rise in humidity levels in the night air so the steam you are seeing above the pool is a direct result of evaporation of the pool water. The steam is the excess humidity condensing out of the water as it interacts with the cold air above the pool heated layer of air. This whole process also drives a large increase in convection as the rising moist air and condensing cold moisture increase air turbulence and don't allow a boundary air layer to develop. Which is why the fog above the pool always is swirling and curling around in the air even on a dead calm night.