What does it cost to run a pool heater anyway

[Pogo]

We have been considering putting in an LP gas pool heater with hopes of getting a couple or three more months of use out of it especially since I require water exercise for my arthritic joints.
But,
A friend of ours who doesn't have a pool himself but knows a number of others who do and reports nobody he knows who got one still uses it due to the cost which he reports to run anywhere from $500- $1000 a month.

Anybody else find such expense to run these things.

 

[PoolGuyNJ]

Lots of variables here

1) Cost per gallon for LP
2) Size of heater
3) Size of pool, in gallons and surface area
4) Temp desired
5) Use of a Solar Cover or Rings
6) Plumbing and equipment

My 300K enjoys its diet of about 3 gallons per hour when it's firing.

Scott

 

[polyvue]

We have been considering putting in an LP gas pool heater with hopes of getting a couple or three more months of use out of it especially since I require water exercise for my arthritic joints. But, A friend of ours who doesn't have a pool himself but knows a number of others who do and reports nobody he knows who got one still uses it due to the cost which he reports to run anywhere from $500- $1000 a month. Anybody else find such expense to run these things.

Are you determined to get a gas heater? If extending the season where you live means average temperatures in the 50s or higher you may want to consider a heat pump. They're less expensive to operate but they're not really capable at much cooler temperatures (below mid-40s). Also, depending on temperatures and sun angle you may be happy with solar panels -- very little extra cost to run (just the pool pump) and their use with a solar/pool cover could warm the water enough for an extra month of swimming.

PoolGuyNJ has enumerated the needed variables to construct an estimated cost of operation for an LP heater. But anyone north of the Caribbean who heats their pool in cold months and doesn't use a solar or automatic cover will receive a monthly energy bill that is a mulitple of the actual cost to heat the water.... Evaporative cooling will siphon both the pool's heat and the pocketbook.

Here are a couple of threads I found that might give you more information. Alas, nothing much in terms of a spreadsheet or procedure to estimate heating costs.

The best way to heat my pool?

Pool Heaters any recommendations!

 

[gkruske]

The experts have good info. I'll supply my opinion, from the owners perspective. I know this is in regards to an LP, which I don't have, but this is to address the swim season extension via heating.

I have a Raypak natural gas unit, no idea what the BTU's are. We are weekend warriors in the pool, and during the work week, it's usually empty. I'll flip the switch on a Friday, and let it go all the way until Sunday night or so. I like to keep it about 88 (I hate a cold pool).

I didn't notice a huge jump in the gas bill, probably due to not running it all the time to maintain temp 7 days a week. We also use it in conjunction with a stand-alone hot tub. It will get it to 100 degrees in about 15 minutes. We'll use the hot tub maybe 3 times a week, about 20 minutes at at time. No big usage there.

As for extending the swim season, don't expect that. I found that even though an 88 degree pool felt nice in September, a breeze with a 65-70 ambient temperature is enough to make you want to get out.

In my opinion, a heater doesn't extend the swim season, just makes it a lot more comfy.

 

[PoolGuyNJ]

If it's just a pool as opposed to pool/spa combo, a heat pump, while more expensive up front, typically costs about 1/2 to 1/3 to use in terms of energy dollars. They are slower but more efficient.

Scott

 

[JasonLion]

We usually extend the swimming season by about one month on each end of the season with a natural gas heater. That ends up costing $200 to $300 per month. Costs to continue heating as it gets colder go up rapidly from there.

If you have the space, a solar heater and solar cover are far more cost effective, though the system will need to be rather large to work in the winter.

 

[frustratedpoolmom]

Ditto as Jason said, we extend our seaon with the heater, but I also use it during the season as I prefer a warmer water temp. I'd say ours runs an avg of $100 a month but this varies with the air temp, if we have a cold spell obviously it will be more. I'm an avid user of a solar blanket as well, especially when at night but also whenever the pool is not in use, this helps retain heat. So if you can't use a solar blanket in combo with a heater you will certainly spend more on the gas costs.

 

[bk406]

I have a heat pump. I typically keep the water at a constant 82-83 degrees mid May thru late september. Run times vary obviously with ambient temp. In May it runs quite a bit, not so much mid June thru mid August. Heat pumps wont heat up the pool as fast as gas, but it's MUCH cheaper to maintain the pool at that temp 24/7 than with gas. My electric bill due to the heat pump averages about $100 a month higher than baseline (thats avg, may it runs $175, July maybe $40).
LP cost quite a bit more than NG. You can figure about 1 gallon per hour per 100,000 BTU for LP, and 1 therm per 100,000 BTU for NG. For a typical 400,000 BTU heater, thats 4 therms or 4 gallons per hour, roughly. Now, LP runs ~ $2.50 per gallon (at least up here) and NG runs ~$1.00 per therm. So in this example, 1 hour on propane will cost $10.00. 1 hour on NG will cost $4.00.

Ok, how long do you run the heater. That all depends on how you use the pool and how many degrees you need to heat it up to.

Ok, some assumptions we can use. If you want tto fire it up on friday and run it thru the weekend, lets figure it's early May, your pool temp is 72 degrees and you want to rasie the temp to 86 degrees. Thats a 14 degree rise. You have a 25,000 gallon pool. To figure all this out, you need to know that 1 BTU will raise 1 pound of water 1 degree. So, for 25,000 gallons of water, that 208,250 pounds of water (8.33 pounds of water per gallon). Doing the math, thats 2,915,500 BTUs that need to go in the pool. For a 400,000 BTU heater, that means it will have to run ~7 hours to bump the temp 14 degrees. For an LP cost of $2.50, that $70 to jack the temp on a friday. Do this 4 weekends in a month, that $280 a month. This does not take into account what the drop is overnight thru the weekend.

Lots of assumptions in terms of pool use, the temperature delta, use of a solar blanket, etc. But you get the idea. The same scenario with NG would cost ~$120 a month. I dont have NG where I live, only LP, so the heat pump looked mighty good.

 

[mas985]

Heat pumps aren't always cheaper to run, especially in California. Many people with pools, including myself, are in the third tier and are paying $0.40 per kwh for any incremental electricity use. With COP of 5.0, the cost per 100,000 BTUs is about $2.34 ($0.40 per kwh tier 3). The same 100,000 BTU for gas and 80% effiiciency costs $1.56 ($1.25 per therm teir 1).

The break even is about $0.26 per kwh which is below tier 2 pricing so you really need to be in tier 1 pricing for the heat pump to look more cost effective which is nearly impossible with a pool and AC. So it is highly dependent on where you live as to the cost effectiveness of a heat pump.

 

[bk406]

I should have said California excepted

You guys have some of the highest price stuff in the nation. Last time I was in that awful place (joking, kinda) it was 2001 and even the cost of groceries were outragious. Yea, electric rates at .40 per KWhr is terrible. I think the national average is around 0.12?

And, i would agree that if you have NG, the cost may be similar to a heat pump in a lot of areas. f i had the option of NG, i might have gone that route too. The OP said he was going to use LP, so I figured a HP was going to be more economical, and he is in Texas, where the electric charges are not all that bad.

 

[geekgranny]

Not intending to hijack here. For the cost of heating a pool a good sized free standing spa would be pretty quickly paid for. We are all electric (Texas), keep the water temp at 100 constantly, 24 hour low flo circulation for filtering, and two 5 hp jets for amazing massage and the electric cost is very manageable. During the few times I've had the spa off I haven't noticed much reduction in electric bill. The spa is large enough to move around in for exercise and the spot massage from jets is incredible for soft tissue problems and arthritis. 6'2" DH even puts a float in to sunbathe. That's what we chose 23 years ago and have been very happy with our decision (especially after acquiring our third and best spa, locally produced, Dallas area, in '02).

gg=alice

 

[mitch08]

The experts have good info. I'll supply my opinion, from the owners perspective. I know this is in regards to an LP, which I don't have, but this is to address the swim season extension via heating.

I have a Raypak natural gas unit, no idea what the BTU's are. We are weekend warriors in the pool, and during the work week, it's usually empty. I'll flip the switch on a Friday, and let it go all the way until Sunday night or so. I like to keep it about 88 (I hate a cold pool).

I didn't notice a huge jump in the gas bill, probably due to not running it all the time to maintain temp 7 days a week. We also use it in conjunction with a stand-alone hot tub. It will get it to 100 degrees in about 15 minutes. We'll use the hot tub maybe 3 times a week, about 20 minutes at at time. No big usage there.

As for extending the swim season, don't expect that. I found that even though an 88 degree pool felt nice in September, a breeze with a 65-70 ambient temperature is enough to make you want to get out.

In my opinion, a heater doesn't extend the swim season, just makes it a lot more comfy.

I am in 100% agreement with you. We do the exact same thing. Around 88 (Or sometimes higher ) during the weekend, and not much use during the week.

Our spa is attached and that we use about 3 times a week.

I also have no significant change on my gas bill during the summer months.

 

[chem geek]

As for extending the swim season, don't expect that. I found that even though an 88 degree pool felt nice in September, a breeze with a 65-70 ambient temperature is enough to make you want to get out.

In my opinion, a heater doesn't extend the swim season, just makes it a lot more comfy.

This is definitely a personal preference. My wife uses the pool as a therapy pool so has it be around 88F (not lower than 86F when in use). We use solar most of the time, but with gas assist she is able to use the pool into an extended season from April through November. Outside that range, the colder outdoor temps make using the pool very unpleasant (and the gas heating costs get extremely expensive) so she switches to an indoor community center pool at that point. Average monthly data where I live are the following for my 16,000 gallon pool with a mostly opaque safety cover and FAFCO solar panels and (unfortunately) 80% efficient gas heater:

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
.56..62..64...68..74..78...81..81..80...75..64..56 ... Avg. High Temp
.40..44..44...45..48..52...54..54..54...50..46..41 ... Avg. Low Temp
.49..54..55...58..62..66...69..69..68...64..56..50 ... Average Temp (slightly more weight to daytime temp)
7.9 5.8 4.9 2.0 . 0.3 0.2 0.1 0.1 . 0.4 2.1 5.6 6.3 ... Average monthly rainfall in inches
3.1 3.9 5.0 6.2 . 6.8 7.0 7.3 6.9 . 6.2 5.0 3.5 2.9 ... kWh/m²/day from the sun (30-year average for month; panels facing south tilted at 38-15=23 degrees)
. - .. - .. - ... 6 ... 2 .. 1 .. 0 .. 0 ... 3 .. 8 . 11 .. - ... Gas Avg. Therms/day used for pool heating (1.67 Therms input per ºF increase)
. - .. - .. - . 300 100 . 50 . 0 . 0 . 150 400 550 . - ... $ Cost @ $1.68/Therm

Without any pool heating, including sun exposure, the water temp would roughly be the average day/night temp. Even with sun, however, an uncovered pool heats up some from sun during the day, but generally loses most of that heat at night from evaporation (depending on humidity) so the water is not much warmer than average air temp (< 5F higher). Use of a pool cover that still lets light through typically gives a 10-15F temp increase. Using a black plastic flat mat type of solar system in conjunction with a cover typically gives 20-25F temp increase (depending on solar panel area and time of year) or even higher depending on the insulation of the solar cover.

Our use of gas is mostly for days that are cloudy and when the air temps get lower, so usually April, May, October and November require the most gas assist with very little during the June to August period (June and September are iffy depending on the amount of cloudiness). I would guess that trying to heat the pool with gas in December and January would cost between $750 and $1000 per month, February and March probably around $500 per month. If we were to do that, we would probably get a more thermally insulating secondary cover, but the air temps are too cold, it rains too much, so is a moot point unless we were to get an enclosure (and that's also expensive -- we've looked into it).

[EDIT] I think I have 11 4' x 10' SunSaver (39.5 sq. ft. effective area) and 1 4' x 8' Revolution (31.6 sq. ft. effective area) panels and my pool is 15.5' x 32' (496 sq. ft. area) for solar area that is 94% of pool area. [END-EDIT]

Everyone's situation is different, but this can give you some idea of how it works for us, which admittedly is unusual due to the higher desired swimming pool temperature and the requirement for nearly daily swim exercise.

Richard

 

[Pogo]

Thanks for all the input. We are going to look into the spa angle. We have had others tell us that might be the way to go too and least costly when all is said and done and still take care of our medical needs.

 

[macdenewf]

I'm still lost on how to calculate the cost of heating. There are some great answers here to start from so maybe i'm just missing a simple conversion.
I live in Houston. I have installed a 400,000 BTU heater and have a 30 thousand gallon pool. One of the posts above gives a good example on how to determine how many BTUs it will take to heat a pool to a certain temp. for mine that is the temp difference ( assume 85 - 70 for a delta T of 15 degrees ) * that by 30 thousand gallons * 8.3 lbs per gallon. That equates to to about 9 hours to get from 70 degrees to 85.
Where I am lost is I can not figure how to convert BTUs to SCF per min ( which is how my gas supplier charges me ). There are references to gallons but that doesn't fit the way my supplier bills.

Does anyone know that conversion? ( btus per hour to SCF hr? )
Best regards. Mac

 

[chem geek]

Does anyone know that conversion? ( btus per hour to SCF hr? )

Welcome to TFP!

SCF stands for "standard cubic feet" and is a volume measurement that is standardized to specific conditions of temperature and pressure. 1 BTU is the amount of heat needed to raise one pound of water 1ºF (technically from 39ºF to 40ºF). 1 SCF is approximately 1030 BTU. So 1 SCFM (SCF per minute) is 1030 * 60 = 61,800 BTU/hr.

Is the 400,000 BTU/hr rating for your heater the input or the output? If it's input, then 400,000/61,800 = 6.47 SCFM (SCF per minute). So in 9 hours that's 9*60*6.5 so around 3500 SCF to heat your pool by 15ºF assuming no heat or efficiency losses (so in reality it will be more). Gas prices from CenterPoint Energy in Houston are around $0.68 per CCF (hundred cubic feet) so 3500 SCF would be 3500/100 * $0.68 = $23.80.