Help with right size heater please

Sep 21, 2018
8
Wausau WI
#1
We need to install a heater for a 30' AG and could use some input as to how many BTU's will we need or what you consider normal for a pool this size. Would also like to hear any yea's and nea's on particular brands. Fairly hefty investment so we hope to do it right the first time.
We have propane if that matters. House is new to us and 1st time pool owners. Thanks for any input!!
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,682
Tucson, AZ
#2
Is electricity cheaper than propane? Propane gas heaters are typically the most costly to run.

It’s not a matter of absolute BTUs that you’ll need but more about how quickly you want to heat up your pool that determines which heater is the best fit. Pool heaters are rated in BTUs per hour with largest residential gas heaters maxing out at 400,000 BTUs/hr. Electric heat pumps typically max out at around 130,000 BTUs/hr.

So, for example, if your pool had an attached spa on it and you wanted to use the heater to both maintain the pool heat AND allow you to quickly heat up a spa when desired, then a 400kBTU/hr gas heater would be the way to go (fast heating). But, if you just have the above ground pool that you wanted to start using a little early and maintain water heat through out the season, then an electric heat pump is a good choice if electricity isn’t too expensive (slow heating).

Either way, a BTU is a BTU no matter how you add it to your pool (fast or slow), so however much energy you use, it’s going to cost you. A BTU raises 1 lb of water 1 degree Fahrenheit. So 26,000 gallons of water weighs 216,840 lbs and will require 216,840 BTUs to raise the temperature 1 deg F (assuming ideal/perfect efficiency and no heat loss). A gallon of propane has 91,330 BTUs in it. So it takes roughly 2.4 gallons of LPG to heat your pool 1 deg F. Depending on how much propane costs you, you could be looking at a hefty heating bill.

In all situations, if you heat your pool, you must use a bubble cover on it because if you don’t, most of the heat you add will be lost to evaporation in the overnight hours when it’s cooler.
 
OP
OP
N
Sep 21, 2018
8
Wausau WI
#3
Is electricity cheaper than propane? Propane gas heaters are typically the most costly to run.

It’s not a matter of absolute BTUs that you’ll need but more about how quickly you want to heat up your pool that determines which heater is the best fit. Pool heaters are rated in BTUs per hour with largest residential gas heaters maxing out at 400,000 BTUs/hr. Electric heat pumps typically max out at around 130,000 BTUs/hr.

So, for example, if your pool had an attached spa on it and you wanted to use the heater to both maintain the pool heat AND allow you to quickly heat up a spa when desired, then a 400kBTU/hr gas heater would be the way to go (fast heating). But, if you just have the above ground pool that you wanted to start using a little early and maintain water heat through out the season, then an electric heat pump is a good choice if electricity isn’t too expensive (slow heating).

Either way, a BTU is a BTU no matter how you add it to your pool (fast or slow), so however much energy you use, it’s going to cost you. A BTU raises 1 lb of water 1 degree Fahrenheit. So 26,000 gallons of water weighs 216,840 lbs and will require 216,840 BTUs to raise the temperature 1 deg F (assuming ideal/perfect efficiency and no heat loss). A gallon of propane has 91,330 BTUs in it. So it takes roughly 2.4 gallons of LPG to heat your pool 1 deg F. Depending on how much propane costs you, you could be looking at a hefty heating bill.

In all situations, if you heat your pool, you must use a bubble cover on it because if you don’t, most of the heat you add will be lost to evaporation in the overnight hours when it’s cooler.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
3,744
Northern NJ
#4
Get the highest BTU heater you can afford. 110K-140K Heat Pump (HP) or 300K - 400K BTU gas heater. You only use and pay for the BTU energy cost you use with where you set the thermostat. A larger heater will use the same BTU's as a smaller heater to heat to a set temperature, it will just do it quicker.

A gas heater will work efficiently in any air temperatures and water temps above 50 to 60 degrees.

HP BTU output is variable and falls as air temperature drops. A HP shuts down around 50 degrees air temperature. See the chart below.

Gas propane heater will cost more per BTU then a HP. Gas will heat quicker then a HP. HP will require your pump running for close to 24/7 to maintain the water temperature.

If you want gas look at Raypak heaters. If you want a HP look at Pentair.

 
OP
OP
N
Sep 21, 2018
8
Wausau WI
#5
I have not really looked into the heat pumps, we are rural so electrical may get pricey.
I'll have to research that. I'm thinking 400k would be great to get the pool to comfortable temps for weekends with the grandkids etc...meanwhile can I just keep the temp reasonable say mid to upper 70's and crank it up when needed. Thoughts>?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
3,744
Northern NJ
#6
I have not really looked into the heat pumps, we are rural so electrical may get pricey.
I'll have to research that. I'm thinking 400k would be great to get the pool to comfortable temps for weekends with the grandkids etc...meanwhile can I just keep the temp reasonable say mid to upper 70's and crank it up when needed. Thoughts>?
As @JoyfulNoise said it takes roughly 2.4 gallons of LPG to heat your pool 1 deg F. How much propane you will use depends on what temp the water is at when you turn on the heater.

You can find heat pump calculators like Heat Pump Calculator | PENTAIR that will give you a cost comparison with gas.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,682
Tucson, AZ
#7
Is there any way to put solar heating in where you are? A nearby roof with a S/SW facing pitch? Solar is expensive in terms of up-front cost but the heat energy is free...given your rural location, it might make sense....
 

swimcmp

In The Industry
Nov 8, 2011
1,043
Moberly,MO
#8
Have a customer with a 200,000 btu heater on a 30' aboveground and they don't even turn it on since they can't get any heat rise. I would recommend a 400,000 btu heater. No doubt in Wisconsin you will need everything you can gain through the daytime
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,682
Tucson, AZ
#9
http://www.fsec.ucf.edu/en/publications/html/fsec-in-23-83/in-23-83-2.pdf

This link has some advanced analysis of heat transfer mechanisms in swimming pools. As @swimcmp alludes to, AGP’s must take into account not only evaporative heat loss from the surface of the pool but also conductive heat loss through the walls. In some instances, if foam insulation is NOT present in between the walls and the liner, the heat loss can be 20 to 40 times larger than a pool that is insulated. In-ground pools don’t typically need to account for heat loss through the walls because soil is a poor conductor of heat.
 
OP
OP
N
Sep 21, 2018
8
Wausau WI
#10
Is there any way to put solar heating in where you are? A nearby roof with a S/SW facing pitch? Solar is expensive in terms of up-front cost but the heat energy is free...given your rural location, it might make sense....
Thanks for the response, I have a south facing garage roof that would be ideal, out of site and steep. Just concerned about the investment vs return. Many in our area have tried solar for homes and abandoned them after poor results. These being older systems, I'm sure the panels have improved. I have pondered the "black panels on a roof " coiled black rubber hose in cased in a panel. My fellow northerner's have any recommendations for solar? We are right at 45 degrees north.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,682
Tucson, AZ
#11
Thanks for the response, I have a south facing garage roof that would be ideal, out of site and steep. Just concerned about the investment vs return. Many in our area have tried solar for homes and abandoned them after poor results. These being older systems, I'm sure the panels have improved. I have pondered the "black panels on a roof " coiled black rubber hose in cased in a panel. My fellow northerner's have any recommendations for solar? We are right at 45 degrees north.
You would optimally want about 1.5X (or greater) your pool’s surface area in panel area. There are different options ranging from glazed/sealed panels to black tubing. What works best depends on a lot of factors but hopefully some successful solar owners in your area can chime in. One critical item is having a proper solar controller that will look at water and air temperature and only run the solar when heating conditions are optimal. One mistake people make is trying to run solar panels when it’s too cool out and that winds up removing heat from the pool and radiating it away.

However, as mentioned above, if your above ground pool isn’t properly insulated, you’ll lose too much heat from the pool. Perhaps that was a factor in why others in your area abandoned their solar setups.
 

jimmythegreek

Bronze Supporter
Aug 10, 2017
515
Morris Cnty NJ
#12
remember above ground pools are harder to heat and retain the heat, so as said if you choose gas go 400k btus and invest in a solar cover and keep it covered. you are not going to want to heat the pool to 70 all the time and just crank it for the swim times, it will cost you a fortune in propane. you just want to keep pool covered at all times and crank it for when you want to swim. look into your electrical rates on your bill, it may be cheaper to just use a heat pump. post your electrical rates and what propane typically costs in your area and we can give you ballparks. also what is your average water temps there through the spring and summer the way it is now