Explain gas heat for a pool to me, like I'm a 4 year old

[joseywales]

Here's the deal. The Mrs wants to weigh our options. I'm thinking solar, but it would be "ugly" and I'm not sure we get enough sun to make it worthwhile. Our solar cover helps, but we need more heat to get almost daily use form May-September.

We have natural gas and I have been wanting a natural gas grill anyway, so perhaps we kill two birds.

From the meter to the heater: straight run of @ 27', then left for another 10'. My fahter-in-law can run the line, since he worked in HVAC for years. I've read about larger meters, but I can't see running more than the pool heater and perhaps the gas grill at one time, so the demand shouldn't be huge.

Questions:

1 - with 235 sqf of surface, how many BTUs are minimum? 400BTU? I don't need a spa, just like to add 8-10 degrees of heat. Water temp of 75-78 should be fine.

2 - what's the most accurate way to figure the monthly cost of operation?

3 - If there's a site that I can calculate these figures, just point me in that direction!

Any other comments you have would be welcome. Just based on conversations with friends, etc., it's almost certain that gas will cost less to run than heat. I'm headed to the township to check on possible permit costs, etc.

Thanks for any suggestions, etc. you can provide.

 

[jblizzle]

I think you are underestimating the "demand" of the pool heater. A 400k BTU gas heater probably need more gas than your house heater and needs a pretty significant sized pipe and meter (gas company should replace the meter for free).

Typically gas heaters seem to be used for "quickly" heating water and not necessarily maintaining a temperature.

Most calculators I have seen just estimate the cost of heating the water by a delta T and not really about how much it would cost to maintain a temperature.

Also regardless of the size heater, you will generally use the same amount of gas to do the same job, but a 100k BTU will take 4 times longer than a 400k BTU heater.

I think solar and electric heat pumps seem like better options for adding a small delta T and then maintaining it.

 

[bk406]

I've read about larger meters, but I can't see running more than the pool heater and perhaps the gas grill at one time, so the demand shouldn't be huge.

The meter size has to do with how much gas and at what pressure it can deliver enugh gas to the heater to fire it properly. some residential gas meters are big enough, some are not. It is worth a call to the gas company. As far as the line goes, there are codes that dictate gas line size as well. The installer needs to get a permit to run the line (in most jurisdictions that I know of) and needs a gas fitters license.

Questions:

1 - with 235 sqf of surface, how many BTUs are minimum? 400BTU? I don't need a spa, just like to add 8-10 degrees of heat. Water temp of 75-78 should be fine.

There's not a hard and fast number for this. You can heat a pool with a 100k BTU heater, it just takes longer. Gas useage is generally linear. A 400k BTU heater burns more gas per hour, but it doesnt run as long. Generally, we would recommend getting the biggest heater you can afford. Given a 400k heater doesnt cost that much more than a 250, i'd get the 400.

2 - what's the most accurate way to figure the monthly cost of operation?

Thats more difficult. A lot of it deopends on how you use the pool, gas rates, solar cover use, etc. I can tell you how much it costs to raise the water by a certain number of degrees, but to hld it there is a little more dificult to calculate. More info from you here would be helpful.

 

[bk406]

JB and i posted at the same time :-D

 

[joseywales]

Ok. I was hoping for a formula to punch my numbers in.

Are you saying that electric would be the best route?

 

[JasonLion]

It all depends on how you are going to use the heater, maintain temperature or heat for the occasional weekend, extend the season a lot, or insure very comfortable on cooler summer days, and so on. Other factors that enter in include what the relative price of gas and electricity are in your area, available electric on your main electrical panel, available gas flow from your meter, and so on.

 

[jblizzle]

I did not mean electric resistance heater (those are the worst to run), but the heat pumps are the most efficient. They are relatively cheap to run, but they add heat slowly so they are good at slowly warming the water and maintaining it as long as your air temp is > 50 degrees or so.

Gas heats fast, but that does not really sound like what you are after.

 

[joseywales]

Re: Explain electric heat to me, like I'm a 4 year old

I knew you meant heat pump. According to my wife, you are correct :-D

She claims she and kids will use the pool almost every night. If that is true, then the heat pump is the way to go. I only have one 40AMP breaker and that's for the A/C unit. So I need to have a 50AMP installed?? I believe the electrician told me we had plenty of service for that, so it shouldn't be an issue.

I knew that about the pool pump, which I'm not crazy about. Mostly because of extra wear/tear on the pool pump. Will it be less stress on the pump, if I recirculate "most" of the time and only filter when necessary? I figure maybe there's less resistance, since the filter isn't involved.

Last year, using only a solar cover, I was able to maintain 70-73ish temps.

 

[jblizzle]

Re: Explain electric heat to me, like I'm a 4 year old

I knew that about the pool pump, which I'm not crazy about. Mostly because of extra wear/tear on the pool pump. Will it be less stress on the pump, if I recirculate "most" of the time and only filter when necessary? I figure maybe there's less resistance, since the filter isn't involved.

Not sure what this is referring too. There is no problem running your pool pump 24/7 ... not sure why you would not have the filter going too though as the added head of the filter will not really affect the pump (they are designed to run continuously).

 

[thadius65]

Re: Explain electric heat to me, like I'm a 4 year old

I knew you meant heat pump. According to my wife, you are correct :-D

She claims she and kids will use the pool almost every night. If that is true, then the heat pump is the way to go. I only have one 40AMP breaker and that's for the A/C unit. So I need to have a 50AMP installed?? I believe the electrician told me we had plenty of service for that, so it shouldn't be an issue.

I knew that about the pool pump, which I'm not crazy about. Mostly because of extra wear/tear on the pool pump. Will it be less stress on the pump, if I recirculate "most" of the time and only filter when necessary? I figure maybe there's less resistance, since the filter isn't involved.

Last year, using only a solar cover, I was able to maintain 70-73ish temps.

Be very careful about how a wife describes use. I went down this road and mine commented one way during selection and build (heat pump), then heard others input after it was to late to change (in-laws know better than me most times) and changed her mind and wanted on-demand type from natural gas. Thank God that I was able to obtain a good deal on another heater, which gave me dual options, but at a price. Cost me $1000 to run the gas line!

I live in central PA. I have been in the pool twice over long weekends (F-Mon). I have taken my pool from 53F - 83F in 17 hours to prep for the first, covered for the next week (65 outside) and ran it another 4-5 hours to get it back to 83F. Total gas investment to do so - approx $70. Now, when hotter weather gets, here, I will shut down the NG heater and go to heatpump to maintain temp.

Good luck!

 

[MattM]

Over the last few months reading this and other forums, I see that there are generally two times of pool users:
- Dedicated Swimmers, Those that have long swimming seasons and can see themselves or someone else in their family swimming every day: These seem to be best served by having an oversized solar heater (which provides the real oomph for heating) and then a heat pump that runs rarely but is capable of maintaining the existing pool temperature even if it is cloudy and solar can not run at all for a week. This means pump run times are long and during daylight hours and a good 2 speed or variable speed pump is very helpful.
- Convenience Swimmers, Those that want to swim once or twice a week and may view it as a social event and plan their usage and can manually toggle heating on at least an hour or two before they get in the pool. Pool builders generally design for this type of owner, and put in a 400K btu gas heater (at least in southern california) and either a single or dual speed pump. The gas heater is especially useful if you have a spa. It is not uncommon for these owners to run their pumps for short periods whenever the electric rate is cheapest.

 

[Ohm_Boy]

I seem to recall some gas/heat pump/btu/energy cost calculations done in this thread. Perhaps a read through it may help?

 

[JasonLion]

Generally on the east coast a heat pump works out better if you want to keep the water up to temperature all of the time, while a gas heater works out better if you only want to heat the pool every once in a while. The heat pump is more energy efficient (given common east coast US prices) when maintaining a constant temperature, while the gas heater is far far faster at getting a cold pool warmed up for the weekend. Heat pumps don't do so well at the far edges of the swim season. As the air temperature goes down, especially below 50 degrees, they get less and less efficient and heat more and more slowly. For extending the season into the early spring and late fall you tend to need a gas heater (or extra large solar system).

Another thing to keep in mind is that heating the pool can get fantastically expensive, with either kind of heater, especially for significant extensions of the pool season. It is fairly common to plan lots of swimming, until the energy bill comes in and then change your mind. For my pool, heating for a sudden warm weekend in October can run $20 or $30 dollars, but heating for the entire month of October can run into many hundreds of dollars.

One thing I have found is that my family doesn't enjoy swimming when the air temperature is below 70 degrees, regardless of water temperature. That puts some significant limits on how much we extend the swim season. Of course, not everyone is like us.

 

[CraigMW]

With regard to the gas line, you can look up requirements for this in the online manuals of gas pool heaters. Our 400K unit calls for a 1 or 1 1/4" line. This is quite a bit larger than the line that enters our home and handles all of our gas appliances. We ended up going with a 1 1/2 line to the pool heater, with a T and 1" line going to the BBQ island. BTW, if your FIL does this, make sure he uses the appropriate material for code. It used to be galvanized, but now most use yellow polyethylene (PE) piping. This may require a special welding plate tool, though I believe there are now compression fittings that will hook up segments of PE.

 

[joseywales]

Thanks a of good advice for sure.

I do agree about the outside air temp, with regard to the comfort of swimming. We are a May - early Sept family for sure. I don't see us in the pool before/after that.

Sounds like electric, along with my solar cover, is a good way to get started. I might consider some solar assitance, maybe via a ground unit that I've seen, instead of building a rack or hanging panels on my roof (neither of those seems desireable to our situation).

 

[BoDarville]

1 - with 235 sqf of surface, how many BTUs are minimum? 400BTU? I don't need a spa, just like to add 8-10 degrees of heat. Water temp of 75-78 should be fine.

2 - what's the most accurate way to figure the monthly cost of operation?

3 - If there's a site that I can calculate these figures, just point me in that direction!

I realize that this is an older thread, but in case anyone is watching, I have recently posted an Excel spreadsheet that calculates the cost of running a natural gas heater to heat your pool by X °F here: Natural Gas Heating Time & Cost Calculator Spreadsheet

 

[joseywales]

Old, but timely. The wife is pushing hard for a heater, and I'm thinking electric at this point, so you chart could be interesting to view. We get no afternoon sun and the sun we get earlier is blocked by our neighbor's ever growing trees. Solar would require panels hung on front of the house roof, or possibly the back, but they'd be over 20 feet above the pool. Wife aint going for it and there's just nowhere else these panels make sense.

 

[Soupy]

Generally on the east coast a heat pump works out better if you want to keep the water up to temperature all of the time, while a gas heater works out better if you only want to heat the pool every once in a while. The heat pump is more energy efficient (given common east coast US prices) when maintaining a constant temperature, while the gas heater is far far faster at getting a cold pool warmed up for the weekend. Heat pumps don't do so well at the far edges of the swim season. As the air temperature goes down, especially below 50 degrees, they get less and less efficient and heat more and more slowly. For extending the season into the early spring and late fall you tend to need a gas heater (or extra large solar system).

Can you explain how the math works out on this? I live in your neck of the woods (Derwood, MD), and here's how the math seems to work out for me:

Washington Gas charges $.23 per them over 180 therms total. Assume 80% efficiency on the heater.
Adding 1 therm of energy into the pool via gas costs $.23 / .8 = 28.8 cents.

1 therm equals 29.3 KWh. Pepco charges about $.12 per KWh. Looking up specs for a Hayward HeatPro heat pump, they have a Coefficient of Performance (COP) of 4 to 6 depending on temperature/humidity, so for this exercise, assume a COP of 5.
So to add 1 therm of energy into the pool via heat pump costs $.12 * 29.3 / 5 = 70.3 cents.

So it seems like natural gas is always a clear winner, at least in my neck of the woods. Keep in mind that there has been a huge boom in domestic natural gas production in the US, so prices have gone down. In Wikipedia's article on Heat Pump COP, it mentions that the average US price for natural gas in 2009 was $1.16 per therm. That's five times the price, and certainly flips the comparison around; at $1.16 per them, that's 145 cents ($1.45) per therm of energy in the pool, over twice as expensive as the heat pump at 70.3 cents.

Can anyone correct my assumptions? It seems like JasonLion's recommendation to use a heat pump for maintaining steady temperature, and natural gas for heating a pool a large amount quickly, goes completely out the window. I don't know how much natural gas prices vary across the country, or what propane prices might be in areas that don't have natural gas, but here in Maryland, gas seems to be the winner. And that's even with us having pretty cheap electricity.

 

[drow]

So it seems like natural gas is always a clear winner, at least in my neck of the woods. Keep in mind that there has been a huge boom in domestic natural gas production in the US, so prices have gone down. In Wikipedia's article on Heat Pump COP, it mentions that the average US price for natural gas in 2009 was $1.16 per therm. That's five times the price, and certainly flips the comparison around; at $1.16 per them, that's 145 cents ($1.45) per therm of energy in the pool, over twice as expensive as the heat pump at 70.3 cents.

Can anyone correct my assumptions? It seems like JasonLion's recommendation to use a heat pump for maintaining steady temperature, and natural gas for heating a pool a large amount quickly, goes completely out the window. I don't know how much natural gas prices vary across the country, or what propane prices might be in areas that don't have natural gas, but here in Maryland, gas seems to be the winner. And that's even with us having pretty cheap electricity.

You're misreading your natural gas prices, I'm pretty sure. From http://www.washgas.com/FileUpload/File/Tariffs/MD/md0305.pdf that $0.23/therm is the distribution charge - it doesn't include the actual cost of the gas! Try looking at your last gas bill, and see what additional line items it has.

For comparison, I paid about $1.02/therm in Pittsburgh, PA in May. I'd expect MD commodity prices to be reasonably close but I'm not prepared to guess that

 

[mas985]

If you want to compare the cost of a NG heater with a Heat Pump you can use this spreadsheet:

Heater Comparison Spreadsheet

But usually NG wins in most areas.