Heat Pump versus Natural Gas Heater in North Alabama

[jfmorris]

I've spent a couple of days searching through many old discussions of pool heaters, and understand a lot of the ins and outs of heat pump efficiency versus quicker responsive heat when using a natural gas heater, but feel I could use a little more guidance before making a decision on the way to go here.

I live in Huntsville, Alabama, and while all of MY large trees were cut down many years ago, my pool suffers from the shade of my neighbors trees. Sun doesn't start hitting the pool from the east until 9:30am or so in summer, hits the entire pool by mid day, but by 3pm, large trees to the west are casting their shade, and by 4pm at the latest, there is no longer any sun on the pool. The pool is an 18x36 in-ground pool, about 27,000 gallons (8 feet at deep end + 8 foot wide steps at shallow end), with a diving board. I run salt water.

I bought a solar cover last summer, but have no reel at the moment. It was my job to put it on and off the pool last summer if I knew the kids or grandkids were coming over to swim. And invariably, it would have collected rain water or pollen pods or leaves that dumped into the water, requiring me to then spend time cleaning the pool. My first priority this summer is a solar cover reel of some sort, but it is complicated by the 8 foot diving board at the deep end. The "low" solar reels that will fit under a diving board are insanely priced. And to be honest, last summer, even though we were in a drought, we had a lot of cool nights, and even with the cover, the pool very rarely reached what I consider a swimmable temperature in the mid 80's. Most of the time the pool was in the 78-80 range.

My wife has terminal cancer, and I want this summer and hopefully next summer to be a great time of family get togethers, and in light of that, have told my wife that I am putting some form of pool heater in, so that we can enjoy more time with our adult children and grandkids while we (she) can. Having water at around 85F would go a long way to making folks want to hang out in the pool in the evening or afternoon.

So here is where I am. I have natural gas at the end of the house that the pool equipment is located at, but unfortunately, after talking to my utility company yesterday, my meter and the pipes cap me to pool heaters under 300K BTU's. Looking at what is out there and compatible with a salt water pool, the best I can do would be a 250K BTU Hayward pool heater. Unless I pay $400-500 to the utility company for a new meter. Plus all the other cost to replace the pipe from the meter to the rest of the house with larger pipe than the 1 1/4" that is currently leaving the meter to run to the house. It runs about 20 feet, then decreases to 3/4" iron pipe, with one branch diving into the crawlspace towards the kitchen and fireplace, while the other goes directly to an outside "gas pack" on the HVAC unit.

So, I started looking at heat pumps, and the issue there is a 140K heat pump of course costs almost $2000 more than a 250K BTU gas heater, AND right now, I have a 100A run to that end of the house with a sub panel on the end of the house for the HVAC, which has a 50A breaker, and then there is a 30A breaker to run the pool pump and other items. There is not 50-60A to spare for a heat pump unless I run another complete circuit, which involves going UP a garage wall into the attic, then DOWN an interior wall into the crawlspace, and then through the brick at the end of the house. A lot more work than the gas change probably, but doable.

No matter what I do, I will be digging trenches and relocating my pump and filter to be against the end of the house where the HVAC, gas and electrical are located. Right now they are kinda out in the yard, and are an eye sore. I've wanted to move them for years, but didn't have anything driving it before now.

But back to the heater. Without doing anything about the gas meter, I can support a 250K BTU gas heater, with just getting my HVAC guy or a plumber a couple hundred to run about 10 to 15 feet of gas pipe to it from the existing pipes that run across that end of the house from the meter in the front yard.

The question really comes down to COST of running gas versus a heat pump, if I want to have a pool be 85F rather than 78F for random afternoons that grandkids drop by, or for Saturday/Sunday afternoon get togethers with the entire family. My utility rates are:

Natural gas @ $11.07 per 1000 cubic feet, which equates to pretty much $1.107 per therm.
Electricity @ $0.11735 per kWh.

I would get a solar reel, and do my best to keep it covered at night and when not in use, but looking at heating times, we are talking 6 hours with the 250K BTU unit for an increase of 5F (80->85 degrees). With 140K BTU, you are talking about around 8 hours to make that same 5F increase.

Best I can tell, if I am doing my math right, if the pool is at "natural" temperatures, which last summer ran 78-80 with the solar cover a lot, it would cost me $5.98 and 8 hours with a heat pump go get it to the temp I want. With the gas heater (250K unit), it would take 4 hours, but cost me $14.34 in gas. If I understand the math right.

The question really is whether someone in the same vicinity of the south-eastern US can comment on their experience with a gas heater versus heat pump. I am hesitant to go with gas if it is going to add hundreds of dollars a month to our utility bill. I don't want to spend $14+ every day we want to swim. If that was just 3 times per week, it would be adding up to a lot per month. But I don't know what it would look like to use a heat pump and let it get to 85F and then just STAY AT THAT TEMP all the time, keeping the solar cover on at night and all non-use days. Would that be cheaper in the long run, even with the expense of the wiring?

Does anyone have any thoughts or guidance for me here? My wife is leaving this entire decision to heat the pool in my hands, as she knows I want to do it so we have some good family times together this year.

Thanks so much!

Jim

 

[SJPoe]

Your pool is essentially identical to mine. I have a 250K NG Hayward heater. Yes, in April/May when I heat the pool from 45 to 85F, the bill can be a bit eye watering, but from then, it's just replacing the losses, not the whole thing.

Your pool already runs 75-80 with no heating, so in reality, once you get it to 85, you're just maintaining the heat. A solar cover is your friend.
My Jun/July/August/September/October gas usage is shown below



Hot water is running on the gas, and the central boiler, so its a little skewed, but for sure Jul/Aug and most of September are probably just the pool.

July - 11.8 @ $11= $130 - $4.30/day
August - 7.4 MCF @ $11 =$80 $2.60/day
September - 9.7 @ $11 = $110 - $3.60/day

We keep the pool at about 88 during the summer. June was super chilly (bare 70s, dropping to 45 overnight) so some of that will be the house heat, October starts to ramp back up as the weather cools too, but still not excessive. I generally figure about $5 a day across the season - barely two cups of coffee.

 

[RHanna]

I went with a heat pump in the Nashville area for a few reasons.
I felt the cost of NG would have been more expensive to run. I've never owned a NG heater but for my heat pump I have to run the pump at a higher speed so factor that in for the cost calculation if NG can run at lower temps. Now that I think about it, I would be surprised if you could run lower speeds with NG since the water is much hotter.
The heat pump I bought also has a chiller which is nice on super hot weeks.

The biggest downside are the weekends in the spring where the temps are super low during the week. It's difficult to pull enough heat out of the air to heat the pool enough for a nice hot weekend pool day.

I like to add liquid solar cover, especially in the spring and fall. I think it mainly helps with evaporation more than anything.

 

[jfmorris]

Thanks @SJPoe - so you just set it to 88F and leave the pool at that temp for the entire summer, with the solar cover on when not in use? If so, those temps are not bad. And you may be adding more heat to the water than I would have to. I guess it depends on what the weather is like this summer.

I guess I can pony up $100 or so a month to have a comfortable pool. As you point out, if I maintain the temp, I am not heating it over from scratch each day either, so I guess it doesn't run the gas as much maintaining the temp (with the cover on) as it does to get there in the first place.

I just need to find a better way to finagle that solar cover, currently rolled up and stored in the shed.

 

[jfmorris]

I went with a heat pump in the Nashville area for a few reasons.
I felt the cost of NG would have been more expensive to run. I've never owned a NG heater but for my heat pump I have to run the pump at a higher speed so factor that in for the cost calculation if NG can run at lower temps. Now that I think about it, I would be surprised if you could run lower speeds with NG since the water is much hotter.
The heat pump I bought also has a chiller which is nice on super hot weeks.

The biggest downside are the weekends in the spring where the temps are super low during the week. It's difficult to pull enough heat out of the air to heat the pool enough for a nice hot weekend pool day.

I like to add liquid solar cover, especially in the spring and fall. I think it mainly helps with evaporation more than anything.

I've done the math, and am confident the heat pump costs less than running natural gas heat all things being equal. It's just the extra $2000 for the unit itself, THEN hundreds or more in wiring and new circuits. It will probably cost more a lot more to put in electrical service to support a new 60A circuit (BIG WIRE) than it would to run the gas pipe I need run.

If the heat pump costs $50 a month in electricity versus $100 in gas for the other option, considering we are just talking at most 5 months (May-Sep), its a lot of years to make back that savings in the unit cost.

So are you saying you use no physical solar cover - just the liquid stuff? Do you have any idea how much the heat pump added to your power bill versus running the pool without it?

 

[Homebrewale]

I had a heat pump at my old house and a natural gas heater at the current house. As for the cost added to run the heat pump, I have no idea and it would be difficult to determine that cost. That's because it is also the time of year when we start using the AC and I had two units on the house. What part of the electric bill was AC and what part was the heat pump? If you think about it, the hotter it was outside, the more I use AC and the less I use the heat pump. It's the exact opposite on cool days.

I never really looked at the gas bill during the summer for the current house. I could make an estimate for the gas usage if I compared the early and late season gas bills to the August bill where I likely never use the gas heater. All my gas usage would be the gas appliances in the house (water heater, stove, grill). It would be a little hard to compare to my old house since I have more direct sunshine on the current pool.

At both houses, a solar cover was important during April, May, first half of June and late September through October. If left off overnight, I could lose 5-10 degrees overnight. If left on overnight, the loss was less than 5 degrees except on the coldest nights. If left on during the day when the pool was in in use, the temperature would actually rise a few degrees. A solar reel was important in the use of the solar cover. I have no place to pile up the cover on the concrete deck and I can't put it on the grass because it would kill it. The reel made it easy to put on and take off. It helped both pools were a rectangular shape.

 

[Newdude]

So are you saying you use no physical solar cover - just the liquid stuff?

Liquid solar cover works surpirisingly well, but the slightest breeze pushes it all to one side and it's effectively not on the pool more often than not.

Let's see a wide angle picture of the pool area for better thinking about reel ideas.

My cover cut my heating bill in half.

 

[RHanna]

I've done the math, and am confident the heat pump costs less than running natural gas heat all things being equal. It's just the extra $2000 for the unit itself, THEN hundreds or more in wiring and new circuits. It will probably cost more a lot more to put in electrical service to support a new 60A circuit (BIG WIRE) than it would to run the gas pipe I need run.

If the heat pump costs $50 a month in electricity versus $100 in gas for the other option, considering we are just talking at most 5 months (May-Sep), its a lot of years to make back that savings in the unit cost.

So are you saying you use no physical solar cover - just the liquid stuff? Do you have any idea how much the heat pump added to your power bill versus running the pool without it?

I don't really know the impact of the heater on my electric bill. We only use it in the spring and fall to heat and sometimes we use the cooler if it's really hot.

I add the liquid cover after I've started to heat the pool in the spring and then in the fall when temps drop and I'm trying to extend the season. I wouldn't mind a solar cover but for a few reasons I don't want it. I'm worried if one of my dogs or my kid fell in they would drown. I think I would be ok as long as I stayed calm but the animals and kid would flip out. I also don't want to worry about storage.

Even saying all of that, I would probably go NG if I was in your situation.

 

[SJPoe]

Thanks @SJPoe - so you just set it to 88F and leave the pool at that temp for the entire summer, with the solar cover on when not in use?

Yep. My wife is of the opinion that anything below 88F is 'ice cold'. If we aren't going to use the pool for a couple hours, or we want the skimmers to work for a bit etc, then we won't cover it up, but normally, the cover goes back on. Takes the two of us literally 30 seconds to pull the cover over. On my own, maybe a minute.

If so, those temps are not bad. And you may be adding more heat to the water than I would have to. I guess it depends on what the weather is like this summer.

Pretty sure the climate in Mid-Michigan is a fair bit cooler than northern Georgia, especially in the June and September months.

As you point out, if I maintain the temp, I am not heating it over from scratch each day either, so I guess it doesn't run the gas as much maintaining the temp (with the cover on) as it does to get there in the first place.

Raising 27,000 gallons by 1F takes - 8.33 BTU/Gal/F = 225k BTU
Maintaining 88F in 80F weather = 18x36x5x8 (sqft * 5btu * difference) = 26k BTU - throw a cover on that cuts that in half, and it's 13k BTU

More interestingly, you can run it backwards - assuming no wind etc etc (and take this with a grain of salt) but at 13K BTU loss per hour, it would take 20 hours to drop a whole degree.

You can kind of see that in this chart from my pool :



You can see the pool temp (top line) drops down to about 86.7 and triggers the heater - which runs for about 3 hours to bring it back up to 89F. Then the pool cools for a bit to 88, back to 89 etc,
You then see the long decline during the daylight hours (sun + warmer day etc). The period between midnight and 4am is a good place to look at calculations, as the outside temp barely moved.

So, assuming 60F ambient, and 88 average pool, we have at least 100k BTU/hour in losses. That leaves about 110-120k BTU from the heater (80% efficiency etc) to heat the pool from 87 to 89. My pool is 24500 gallons, so needs 205k BTU to raise it 1F - so at 100-120, we should see a rate of about 0.5F/hour. We actually see about 2 degrees in 3 hours, so about 30% is unaccounted for...so must be the cover helping avoid losses.

As it turns out it was actually windy and raining that night too - so that 30% savings is probably significantly higher...as the wind and rain would have increased the losses, leaving less 'excess' heating the pool.

 

[jfmorris]

Liquid solar cover works surpirisingly well, but the slightest breeze pushes it all to one side and it's effectively not on the pool more often than not.

Let's see a wide angle picture of the pool area for better thinking about reel ideas.

My cover cut my heating bill in half.

Thanks @Newdude - any ideas about a solar reel are appreciated!

Here is a shot I just ran out and took, looking over the pool area. Safety cover won't come off until all the pollen pods from my neighbors oak trees quit dropping in huge clumps. This one is looking from the shallow end of the pool. Again - 18x36, with 8 foot wide steps that are 3 steps deep on the shallow end, with a hand rail that I install when I uncover things.



Looking closer at the diving board end:



The constraint for a solar reel is really the diving board. Then what to do about it, as you have about 8 feet of concrete on the house side of the pool, but just a 3 foot walkway around the other corner of the deep end.

I was digging around in the forums after reading something about a DIY solar reel, and what I came across appeared to be the use of some kind of floating pipe that my Lowe's and HD do not seem to stock, that you connect to the solar cover and then I guess spin to roll the cover up on to it, then drag off the water. The issue is the cover is slightly larger than the 18x36 + steps of the pool, so that it laps up the sides slightly. I would have to cut the cover into several sections, in order to do these floating reels, as the pipes were only 10 feet long...

Thoughts?

Thanks!

Jim

 

[jfmorris]

Yep. My wife is of the opinion that anything below 88F is 'ice cold'. If we aren't going to use the pool for a couple hours, or we want the skimmers to work for a bit etc, then we won't cover it up, but normally, the cover goes back on. Takes the two of us literally 30 seconds to pull the cover over. On my own, maybe a minute.

Pretty sure the climate in Mid-Michigan is a fair bit cooler than northern Georgia, especially in the June and September months.

Raising 27,000 gallons by 1F takes - 8.33 BTU/Gal/F = 225k BTU
Maintaining 88F in 80F weather = 18x36x5x8 (sqft * 5btu * difference) = 26k BTU - throw a cover on that cuts that in half, and it's 13k BTU

More interestingly, you can run it backwards - assuming no wind etc etc (and take this with a grain of salt) but at 13K BTU loss per hour, it would take 20 hours to drop a whole degree.

You can kind of see that in this chart from my pool :

View attachment 637034

You can see the pool temp (top line) drops down to about 86.7 and triggers the heater - which runs for about 3 hours to bring it back up to 89F. Then the pool cools for a bit to 88, back to 89 etc,
You then see the long decline during the daylight hours (sun + warmer day etc). The period between midnight and 4am is a good place to look at calculations, as the outside temp barely moved.

So, assuming 60F ambient, and 88 average pool, we have at least 100k BTU/hour in losses. That leaves about 110-120k BTU from the heater (80% efficiency etc) to heat the pool from 87 to 89. My pool is 24500 gallons, so needs 205k BTU to raise it 1F - so at 100-120, we should see a rate of about 0.5F/hour. We actually see about 2 degrees in 3 hours, so about 30% is unaccounted for...so must be the cover helping avoid losses.

As it turns out it was actually windy and raining that night too - so that 30% savings is probably significantly higher...as the wind and rain would have increased the losses, leaving less 'excess' heating the pool.

View attachment 637044

Thanks! That is a LOT of data! I think you have helped lean me towards just rolling with the 250K gas unit. While a 400K BTU heater would heat faster, I don't want the extra expense of having the utility company out to upgrade my meter, and the expense to "replumb" the pipes from the meter to the rest of the house to 2 inches, which is what the utility company told me over the phone.

 

[jfmorris]

I don't really know the impact of the heater on my electric bill. We only use it in the spring and fall to heat and sometimes we use the cooler if it's really hot.

I add the liquid cover after I've started to heat the pool in the spring and then in the fall when temps drop and I'm trying to extend the season. I wouldn't mind a solar cover but for a few reasons I don't want it. I'm worried if one of my dogs or my kid fell in they would drown. I think I would be ok as long as I stayed calm but the animals and kid would flip out. I also don't want to worry about storage.

Even saying all of that, I would probably go NG if I was in your situation.

Thanks @RHanna - I think after reading all the advice, I am leaning towards the NG unit. I was doing math assuming I had to heat from 78 or 80 EVERY DAY to get it back to a swimmable 85, which make me think I would spend $15 in gas each day we swam. But it seems if I keep the cover on, and retain heat, and maintain the temperature, it may not be nearly so bad.

I may also use the liquid cover as well as the regular solar cover, as my wife and the daughter who brings kids over the most to swim won't be able to manage a cover even with a reel.

 

[Newdude]

Put the real in the shallow end, with a rectangle cover and a seperate small piece for the stairs. I had 5 ft between the pool and fence at my old place and plenty of room to walk by.

Even if it's really tight and you have to side step by it, the ability to run laps on the patio is overriden by the necessity of removing the cover.

Or if it's so tight you can't get by it, the inconvenience of walking around the deep end is less than that of wrestling with the solar cover

Or cut the 36 ft into thirds to make the 12x18 pieces more manageable.

 

[SJPoe]

Thanks @Newdude - any ideas about a solar reel are appreciated!

Here is a shot I just ran out and took, looking over the pool area. Safety cover won't come off until all the pollen pods from my neighbors oak trees quit dropping in huge clumps. This one is looking from the shallow end of the pool. Again - 18x36, with 8 foot wide steps that are 3 steps deep on the shallow end, with a hand rail that I install when I uncover things.

View attachment 637065

Looking closer at the diving board end:

View attachment 637066

The constraint for a solar reel is really the diving board. Then what to do about it, as you have about 8 feet of concrete on the house side of the pool, but just a 3 foot walkway around the other corner of the deep end.

I was digging around in the forums after reading something about a DIY solar reel, and what I came across appeared to be the use of some kind of floating pipe that my Lowe's and HD do not seem to stock, that you connect to the solar cover and then I guess spin to roll the cover up on to it, then drag off the water. The issue is the cover is slightly larger than the 18x36 + steps of the pool, so that it laps up the sides slightly. I would have to cut the cover into several sections, in order to do these floating reels, as the pipes were only 10 feet long...

Thoughts?

Thanks!

Jim

18x36 is fairly standard. I bought a new solar cover two seasons ago for about $200 - I don't think they really last much beyond 2 or 3 seasons regardless of the warranties. I had a manual reel that came with the house - its about 20 feet long, has straps that tied onto the cover and you just wind it up. You can pick up cheap ones for $100-150.

Wife can happily roll up the cover onto the reel herself, and putting the cover back on is super easy with two people (grab a corner each and walk down the pool), and easy enough with one (takes a little fussing at the end to get it 'square'). Most of the time, I pull the cover while I'm in the pool - grab it in the middle, swim/walk to the shallow end, and pull it behind me.

The step area you have, I'd be tempted to just have a spare little bit if you can get one - a 7 x 7 square is about $30, and just cut it around the handles - otherwise trying to find a 39 or 40 x 18 might be harder. TBH, your losses from that 8 x 3 bit are going to be super minimal anyway, (8x3*5 = 120 BTU...if it were freezing outside, you'd lose 10k BTU/hour from your 85F pool...)

 

[jfmorris]

Put the real in the shallow end, with a rectangle cover and a seperate small piece for the stairs. I had 5 ft between the pool and fence at my old place and plenty of room to walk by.

Even if it's really tight and you have to side step by it, the ability to run laps on the patio is overriden by the necessity of removing the cover.

Or if it's so tight you can't get by it, the inconvenience of walking around the deep end is less than that of wrestling with the solar cover

Or cut the 36 ft into thirds to make the 12x18 pieces more manageable.

Unfortunately, the shallow end for a traditional solar reel is a no-go for several reasons. There is a step railing I just installed last year, that drops into some holes like my pool ladder does in the deep end. You can see it in this pic I found from last summer:



Then, there is an angle behind the pool, and two sets of stairs coming down from the house and two small decks, to get to the pool, that would be blocked. The angle part is actually a drop down to what WAS the original patio behind the house, with the pool UP a step due to a little retaining wall on the corner towards the house. Accesss to the pavilion would be blocked too.



Here is another view from the shallow end last summer where you can see the problem of the hand rail my wife asked for with the steps.



The deep end the real issue is just that stupid diving board. If we didn't use it so much, I'd just remove it.



Do you think I could get a conventional solar reel, and just put REALLY LONG straps or ropes on it somehow, so that the cover could be manually manipulated over the diving board, then just wind it in, with the straps across the ground to the area behind the diving board?

I am not sure when you say cut it to 12x18 sections what you mean?

Thanks for your advice!

 

[jfmorris]

18x36 is fairly standard. I bought a new solar cover two seasons ago for about $200 - I don't think they really last much beyond 2 or 3 seasons regardless of the warranties. I had a manual reel that came with the house - its about 20 feet long, has straps that tied onto the cover and you just wind it up. You can pick up cheap ones for $100-150.

Wife can happily roll up the cover onto the reel herself, and putting the cover back on is super easy with two people (grab a corner each and walk down the pool), and easy enough with one (takes a little fussing at the end to get it 'square'). Most of the time, I pull the cover while I'm in the pool - grab it in the middle, swim/walk to the shallow end, and pull it behind me.

The step area you have, I'd be tempted to just have a spare little bit if you can get one - a 7 x 7 square is about $30, and just cut it around the handles - otherwise trying to find a 39 or 40 x 18 might be harder. TBH, your losses from that 8 x 3 bit are going to be super minimal anyway, (8x3*5 = 120 BTU...if it were freezing outside, you'd lose 10k BTU/hour from your 85F pool...)

Yeah - the issue, which wasn't shown until I posted a few pics above just now, is that I install a railing in the middle of the steps, which blocks rolling up anything at the shallow end.

To be honest, if it wasn't crazy, a 36 foot long reel off to the side up against the house would be ideal!

 

[Newdude]

There is a step railing I just installed last year,

Ok that kills the idea, as does the lack of clearance from the deck by the house.

The access to the Pavillion would have been a minor inconvenience having to go the long way there.

I am not sure when you say cut it to 12x18 sections what you mean?

Three 12 foot pieces (18 wide)and the end one has the stairs flap too. Small pieces would be much more manageable. Roll them on the house side patio up by hand, carry them like rolled up carpet and toss them wherever to swim.

 

[SJPoe]

I just put a split in my cover, and it rolls right over the handle/railing of the steps I'll see if I can find a picture

 

[JamesW]

Gemini:

Let's break down the pros and cons of each option and try to estimate running costs to help you make an informed decision.

Analyzing Your Situation​

• Pool Size: 18x36 in-ground, approximately 27,000 gallons.
• Shade: Significant shade from neighbors' trees, limiting direct sunlight hours.
• Solar Cover: You own one but need a reel, complicated by the diving board. You've noted issues with rainwater and debris.
• Desired Temperature: 85°F for comfortable swimming.
• Current Pool Temperature: 78-80°F with the solar cover last summer.
• Natural Gas: Available, but current meter limits heater size to under 300K BTU. A 250K BTU Hayward is a likely option without upgrades. Upgrading the meter and pipes would cost $400-500 plus plumbing work.
• Electricity: 100A service to the end of the house, with a subpanel for HVAC (50A) and pool pump/other (30A). Likely need a new circuit for a heat pump.
• Utility Rates:
  • Natural gas: $11.07 per 1000 cubic feet ($1.107 per therm).
  • Electricity: $0.11735 per kWh.

• Heat required to raise 27,000 gallons by 5°F:27,000 gallons×8.34gallonlbs×1lb⋅∘FBTU×5∘F=1,125,900 BTU

Now, let's recalculate the costs based on this correct BTU requirement:
1. Natural Gas Heater (250K BTU, 80% efficiency)

• Usable BTU output per hour: 250,000 BTU/hour×0.80=200,000 BTU/hour
• Time to heat by 5°F: 1,125,900 BTU/200,000 BTU/hour≈5.63 hours (This aligns more closely with your initial estimate of 4-6 hours, considering some heat loss).
• Total BTU of gas needed: 1,125,900 BTU/0.80≈1,407,375 BTU
• Therms of gas needed: 1,407,375 BTU/100,000 BTU/therm≈14.07 therms
• Cost per heating cycle: 14.07 therms×$1.107/therm≈$15.57

2. Heat Pump (Assuming COP of 4)

• BTU of electricity needed: 1,125,900 BTU/4=281,475 BTU
• kWh of electricity needed: 281,475 BTU/3412 BTU/kWh≈82.49 kWh
• Cost per heating cycle: 82.49 kWh×$0.11735/kWh≈$9.68

Revised Analysis:
With the corrected BTU calculation, the cost difference between the two heating methods for a 5°F increase is still significant, but the absolute costs are higher than my initial rough estimates.

• Gas: Approximately $15.57 per 5°F increase, taking around 5.6 hours with a 250K BTU heater.
• Heat Pump: Approximately $9.68 per 5°F increase, taking significantly longer depending on the heat pump's BTU output (a 140K BTU heat pump has a lower heating rate).

Key Takeaways from the Corrected Calculations:

• Gas is still more expensive per heating cycle. The cost is considerably higher than the heat pump for the same temperature increase.
• Heating time is still a significant factor. The gas heater will heat much faster.
• The importance of the solar cover is amplified. Reducing the need for such large temperature increases will directly translate to substantial cost savings for either system.

• Heating Frequency and Duration: If you only want to heat the pool for occasional weekend gatherings, the faster heating of gas might be appealing, but the per-use cost is higher. If you aim to maintain a more consistent, warmer temperature throughout a longer period, the heat pump's efficiency could lead to lower overall costs.
• Shoulder Seasons: In Huntsville, you might experience cooler evenings and mornings even in the summer, and the shoulder seasons (spring and fall) can be quite cool. A heat pump's efficiency will decrease in these cooler temperatures, potentially making gas more cost-effective for quick heating during these times. However, gas will still be more expensive for maintaining temperature.
• Solar Cover: A solar cover is crucial regardless of your heater choice. It significantly reduces heat loss (by 50% or more) and evaporation, lowering your heating costs and chemical usage. Addressing the reel situation is important. Perhaps exploring options that work with the diving board, even if pricier initially, will pay off in ease of use. Consistent use of the cover will dramatically impact the economics of both heater types.
• Maintaining Temperature: Once the pool is at 85°F, maintaining that temperature will be less energy-intensive than the initial heating. A heat pump is generally more efficient at maintaining a set temperature in moderate climates. However, heat loss at night (even with a cover) will require reheating.
• Electrical Upgrade Cost: Factor in the cost of running the new electrical circuit for the heat pump. This could negate some of the potential long-term savings.
• Gas Meter Upgrade Cost: Similarly, factor in the cost of the gas meter and pipe upgrades if you want a larger gas heater for faster heating.

Recommendations and Next Steps​

Given your desire for more consistent swimmable temperatures for family gatherings and your wife's enjoyment, here's a possible path forward:

1. Prioritize the Solar Cover Reel: Find a solution that works with your diving board. The consistent use of a solar cover is the most cost-effective way to retain heat and reduce the load on any heater. Explore online forums and pool supply stores for creative reel solutions for pools with diving boards. Even a more manual but easier-to-manage system than last year would be beneficial.
2. Get Quotes for Electrical and Plumbing Work: Obtain firm quotes for running a new 50-60A circuit for a heat pump and for upgrading your gas meter and piping. This will give you a clearer picture of the total upfront investment for each option.
3. Consider Your Heating Needs: How often and for how long do you realistically envision needing the pool heated to 85°F? If it's primarily for weekend afternoons during the warmer months, a heat pump might be more economical in the long run for maintaining that temperature once reached. If you anticipate needing quick heating for more frequent, shorter uses or during cooler periods, gas might be more practical despite the higher per-use cost.
4. Factor in Climate: Huntsville has warm summers, which favors heat pump efficiency during the main swimming season. However, spring and fall evenings can get cool, where a gas heater would perform better for quick warm-ups.
5. Estimate Seasonal Costs: Based on your anticipated usage and the per-cycle costs calculated above, try to estimate the total seasonal cost for both a gas heater and a heat pump. Consider scenarios with consistent solar cover use and occasional heating.

Based on the information, here's a general leaning:

• If your primary goal is to extend the swimming season into cooler months or have very rapid heating for infrequent use, and you are willing to pay a higher per-use cost, a 250K BTU gas heater might be the simpler initial route, avoiding the more complex electrical work. However, be mindful of its ability to heat your pool quickly from a lower temperature, especially with shade.
• If you prioritize lower long-term operating costs and plan to maintain a warmer temperature more consistently during the warmer months, and you are willing to invest more upfront in the unit and electrical work, a heat pump could be the better choice. The efficiency in warmer weather would likely offset the higher initial cost over several seasons.

A Hybrid Approach (Potentially):

• If budget allows, you could consider the gas meter upgrade in the future if the 250K BTU heater proves insufficient for your needs.
• Regardless of the heater, maximizing the effectiveness of your solar cover will be key to minimizing heating costs for either system.

In conclusion, without knowing the exact cost of the electrical and gas upgrades, it's difficult to give a definitive answer on which is cheaper in the long run. However, focusing on consistent solar cover use is a no-brainer for cost savings with either type of heater. Get those quotes, think about your usage patterns, and then weigh the upfront costs against the estimated long-term operating expenses. Your desire to create a comfortable space for your family is admirable, and carefully considering these factors will help you make the best choice.

 

[JamesW]

ChatGPT:

Let's break this down in a practical, dollars-and-sense way, but also keep ease-of-use and lifestyle in mind.

Gas Heater (250K BTU)​

• Installation: Easiest and cheapest in terms of infrastructure; you've got gas right there.
• Performance: Great for on-demand heating. If you know a warm weekend is coming up, you can preheat the pool that morning or the night before. Great responsiveness.
• Cost to Heat 5°F (78 → 83): ~$14.34 (Your math is correct. Each therm adds 100,000 BTUs. You’d need about 250,000 BTUs per hour for 4–5 hours to raise it 5°F, which equals roughly 6.5 therms.)
• Usage Pattern: If you’re doing this 2–3 times per week, you’re looking at:
  • ~$43/week
  • ~$180/month (during swim season)
• Pros:
  • Fast warm-up
  • No need to run for days
  • Fits your existing setup well
• Cons:
  • High running costs for frequent use
  • Least efficient (only ~82–85% efficiency typically)

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Heat Pump (~140K BTU)​

• Installation: More complex for you (electrical upgrade and wiring), but it’s a one-time project. Might cost more up front.
• Performance: Not great for same-day heating. More of a keep-it-warm-all-week system. Works well if you're trying to maintain temp (especially with a solar cover).
• Cost to Maintain Temp:
  • Once the pool is at 85°F, maintaining that temp with a good solar cover could be just $2–3 per day, depending on outside temps and nighttime losses.
  • Raising the pool from 78°F to 85°F might cost ~$6 once (your estimate is solid), but that won’t be needed daily.
• Realistic Weekly Cost: If you heat it up early in the week and keep it there, maybe ~$20–30/week. That’s potentially half the cost of gas, or better.
• Pros:
  • MUCH cheaper to run over time
  • More eco-friendly
  • Quiet and low-maintenance
• Cons:
  • Slower heating (6–12 hours for a big rise)
  • Less effective in cold snaps (<50°F)
  • Needs a better electrical setup

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Numbers Summary (Based on Your Pool Size and Rates)​

Heater Type	Heat 5°F (One-Time)	Daily Maintenance	Weekly Cost (Est.)	Installation Ease
Gas (250K BTU)	~$14.34	~$5–10	$40–60	Easy
Heat Pump (140K BTU)	~$5.98	~$2–3	$20–30	Harder

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Recommendations Based on Your Goals​

Since this is about quality time and spontaneity with family (especially grandkids), and the pool won't get full sun, gas is your more responsive option. You won't always be able to plan 24 hours in advance to preheat with a heat pump.


But — if you see yourself heating the pool regularly and want to keep it warm all week, and you're okay with the upfront electrical work, a heat pump + solar cover is probably the smarter long-term option.


You might even consider this hybrid option:

• Install the gas heater now for responsiveness and immediate results.
• Add a heat pump next year (or later) if it makes sense for regular maintenance, and use gas only for quick boosts.

This gives you flexibility, especially if this summer ends up being cooler again.

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Extra Tips:​

• A good solar reel is a must—worth every penny for your back and sanity. Look for offset, deck-mounted reels if you want to clear the diving board.
• Consider a liquid solar cover (like Heatsavr) as a supplement to the reel when the cover isn't practical.
• A small solar temp sensor and Wi-Fi controller could make heating decisions easier to automate or monitor from your phone.

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