Pentair Heat Pump Calculated Savings vs. Propane - South West Michigan

[Vogt5059]

We are getting quotes for an inground pool and we are certain that we would like a heater but are trying to decide between a propane heater and a heat pump. So I ran the calculator on Pentair's website using my zipcode and utility costs for a 20x40 36,000gal pool heated to 82F May through September. The yearly cost savings that is calculated is ~$2600 I am questioning how realistic this number is? If this number is anywhere close to accurate then it would seem to make sense to me to go with the heatpump as the savings would offset the additional ~$3000 upfront cost of the heatpump after just 1-2 years. I would love to hear opinions on what heater would be best for us and the accuracy of Pentair's calculator. I did verify that our current propane cost is $1.63/gal which I multiplied by 1.1gal/therm to get $1.79/therm and that our current price for electricity is $0.11/kwh. Here is a screenshot from the calculator:

 

[mas985]

You are probably right to question the accuracy of their model. Without any detailed explanation of the assumptions behind the model that are not shown, I wouldn't trust either.

Having said that and even though NG heaters are now closer to 96% efficiency, with those rates, the HP will still be cheaper to run (3:1). However, it will take longer to heat the pool each day. And if you want to do on demand heating, NG is the only way to go.

 

[Dtkokay]

I have a huge heat pump / chiller for my 25K gallon pool. I think it's going to be hard to come up with an accurate cost savings between the heat pump or a gas heater. I would follow the advice directly above: do you want to keep the pool warm ALL the time, or only as needed for the weekend or special events? Heat pumps are viewed as better for maintaining a constant temperature all the time; gas heaters are better for on demand heating.

If you're getting a spa, then it's a no brainer to get the gas heater.

I went the heat pump route because my wife and I swim laps 3-4 times a week, so I want to keep the pool at a comfortable temperature all winter (hopefully).

 

[Vogt5059]

You are probably right to question the accuracy of their model. Without any detailed explanation of the assumptions behind the model that are not shown, I wouldn't trust either.

Having said that and even though NG heaters are now closer to 96% efficiency, with those rates, the HP will still be cheaper to run (3:1). However, it will take longer to heat the pool each day. And if you want to do on demand heating, NG is the only way to go.

I ran the calculation again changing the gas heater efficiency to 96% and the savings went down to $2000/yr.

 

[Vogt5059]

I have a huge heat pump / chiller for my 25K gallon pool. I think it's going to be hard to come up with an accurate cost savings between the heat pump or a gas heater. I would follow the advice directly above: do you want to keep the pool warm ALL the time, or only as needed for the weekend or special events? Heat pumps are viewed as better for maintaining a constant temperature all the time; gas heaters are better for on demand heating.

If you're getting a spa, then it's a no brainer to get the gas heater.

I went the heat pump route because my wife and I swim laps 3-4 times a week, so I want to keep the pool at a comfortable temperature all winter (hopefully).

We are not getting a spa just the pool.

We are thinking that it would be nice to get the pool up to around 80 a little earlier in the season and then maintain it through out the season. Not looking to through a party when its still snowing here in April or anthing crazy like that. Will a heat pump be able to extend our season at all or will it only be able to slightly raise temp during the season?

 

[SDor]

I think that model is suspect.

I live in north of Chicago, have a 35,000 gal pool with a 96% efficient NG heater. We generally use our pool from mid-May to late-Sept. My wife and kids complain if the temp is less than 85 (in the summer). May and Sept (and unusual cold snaps) I can get away with 83. I checked my summer gas bills, and they run about ~120-140 therms/mo. In addition to my pool, this includes my home hot water, stove and oven. Late July - August is usually somewhat lower since it's usually warm enough to not really need the heater. After school starts, I usually keep the temp around 78 and warm it up if the weekend weather looks like it will be nice (but still burn ~140 therms). I don't have a solar cover, but I am careful not to heat the pool to 85 unless there's a good chance of it being used.

Anyway, at 140 therms/mo and 1.79/therm, that's ~$250/mo. X 5 mos = 2250. Which means the heat pump will cost $250 over 5 month? I guess I know nothing about heat pumps, but that sounds crazy cheap.

One more factor... my pool is in the sun most of the day so I do get a lot of nature solar heating.

 

[Newdude]

Don’t forget the taxes, fees and ‘power delivery surcharges’ on the electric bill that double the $0.11 per KW rate for most areas.

i have your pool and a heat pump. It takes BTUs to heat gallons and you will have 35k of them to heat. It will need double the runtime for you than it will for someone with an 18k gallon pool. When your pump is struggling to keep up in the northern climate it will need longer again. (3X or 4X). The calculators dont necessarily show the whole picture.

The electric bills are sky high early and late in the season but drop to $100 ish in the hot months.

The gas bill is a constant regardless of time of year, and with 3X the BTUs it can run around 1/3 of the time for similar gains. But if you are using it in the warm parts, you will still be paying a few hundred a month just like when it was cold out and ‘worth it’.

this is not an easy choice for most people. As a general rule of thumb take the middle of the country as the break even point. The further south you go, the better a heat pump is for most and the further north you go, the better a gas heater is for most.

Of course there are extenuating circumstances that can alter this for some folks, like rooftop solar to help the electric bills, or no access to gas, or one of them is particularly expensive in a certain area.

 

[Vogt5059]

I think that model is suspect.

I live in north of Chicago, have a 35,000 gal pool with a 96% efficient NG heater. We generally use our pool from mid-May to late-Sept. My wife and kids complain if the temp is less than 85 (in the summer). May and Sept (and unusual cold snaps) I can get away with 83. I checked my summer gas bills, and they run about ~120-140 therms/mo. In addition to my pool, this includes my home hot water, stove and oven. Late July - August is usually somewhat lower since it's usually warm enough to not really need the heater. After school starts, I usually keep the temp around 78 and warm it up if the weekend weather looks like it will be nice (but still burn ~140 therms). I don't have a solar cover, but I am careful not to heat the pool to 85 unless there's a good chance of it being used.

Anyway, at 140 therms/mo and 1.79/therm, that's ~$250/mo. X 5 mos = 2250. Which means the heat pump will cost $250 over 5 month? I guess I know nothing about heat pumps, but that sounds crazy cheap.

One more factor... my pool is in the sun most of the day so I do get a lot of nature solar heating.

Thanks for the info! Being that you are north of Chicago I feel like that is a going to be a pretty close comparison for us. You heat mid May through September which is what I feel like we will probably be doing as well. Our pool will be in the sun most of the day as well but we are planning on using a cover so that should require a little bit less heating.

That being said if you are using around 140therms/mo that would be ~$250/mo for us using propane like you said but that would only be $1250 for the 5 month season. That really makes me not believe the Pentair calculators number at all.

 

[Vogt5059]

Don’t forget the taxes, fees and ‘power delivery surcharges’ on the electric bill that double the $0.11 per KW rate for most areas.

i have your pool and a heat pump. It takes BTUs to heat gallons and you will have 35k of them to heat. It will need double the runtime for you than it will for someone with an 18k gallon pool. When your pump is struggling to keep up in the northern climate it will need longer again. (3X or 4X). The calculators dont necessarily show the whole picture.

The electric bills are sky high early and late in the season but drop to $100 ish in the hot months.

The gas bill is a constant regardless of time of year, and with 3X the BTUs it can run around 1/3 of the time for similar gains. But if you are using it in the warm parts, you will still be paying a few hundred a month just like when it was cold out and ‘worth it’.

this is not an easy choice for most people. As a general rule of thumb take the middle of the country as the break even point. The further south you go, the better a heat pump is for most and the further north you go, the better a gas heater is for most.

Of course there are extenuating circumstances that can alter this for some folks, like rooftop solar to help the electric bills, or no access to gas, or one of them is particularly expensive in a certain area.

Thanks for the input newdude. I just checked the taxes, fees, and surcharges and this is what I found:
Energy usage @ 0.108/kwh
Energy optimization surcharge @ 0.00198
State sales tax @ 4%

Combining them all togetherI get around $0.114/kwh

I get what you are saying about the heat pump struggling at times in the northern climate. I have seen how at lower ambient temperatures the heat pumps are rated lower. I guess I thought that when I put in my zipcode for the calculator that the model would take that in account for the calculations.

I just ran the calculator again will all the same imputs expcept I changed the zip code to a Phoenix zipcode and it now says $350 savings per year so it does look like they take into account your location in some way.

 

[Newdude]

Notice how they didn’t include October and April ? May and September are generally warm anyway. If you went 2 weeks into October and April to extend the regular season, you would wipe out any savings and then some. I’m not saying that either way is better for you, just that the calculator is clearly only showing the times when it favors the heat pump.

Also, @SDor appears to have a typo. They have a 16x32 compared to your 20x40 which would roughly be 20k gallons to your 35k. That’s a substantial difference and you will be heating 43% more water either way. Doing it with less BTUs will also be a substantial difference.

 

[Vogt5059]

Notice how they didn’t include October and April ? May and September are generally warm anyway. If you went 2 weeks into October and April to extend the regular season, you would wipe out any savings and then some. I’m not saying that either way is better for you, just that the calculator is clearly only showing the times when it favors the heat pump.

Also, @SDor appears to have a typo. They have a 16x32 compared to your 20x40 which would roughly be 20k gallons to your 35k. That’s a substantial difference and you will be heating 43% more water either way. Doing it with less BTUs will also be a substantial difference.

Appreciate the comments. Nice catch on the size difference on the pools. I picked the months May through September as pool season here is generally memorial day to labor day and I figured stretching it out a couple weeks on either side might be reasonable. Just for fun I ran the calcuator again with April and October included and the calculated savings is almost $3900 for April through October.

 

[Vogt5059]

@SDor can you confirm the size and gallons of your pool. Your sig says 16x32 which I think would be a lot less than 35,000 gallons unless it is really deep?

 

[sktn77a]

Problem with pool heatpumps is their low capacity (usually 100-120BTU). That will take DAYS to heat your pool. Most gas heaters start at twice that capacity and go up from there. Unfortunately, without natural gas, you are in a worst case situation, as both electricity and propane are very expensive.

I have a hard time reconciling those heatpump seller's/manufacturer's "savings" figures.

 

[mas985]

I have a spreadsheet in my signature where you can actually see the calculations and the assumptions.



There is also a much more complicated version that takes into account local weather conditions and all head loss components.

 

[Newdude]

There is also a much more complicated version that takes into account local weather conditions and all head loss components.

I appreciate that everybody's mileage may vary. If any of those heat pump calculations were remotely true we would have tons of threads detailing people gushing over how cheap their heat pump is in a cool climate. There would be a clear winner from a utility standpoint. You can't go 5 threads without reading about a VS pump savings, where are all the heat pump threads ? Think of all the people with solar panels and there is never a thread laughing that the heat pump is basically free. Instead its the same pros/cons and intended usage rehashed 100 times over.

I myself bought into the hype that the heat pump would be a massive savings and was embarrassed to mention it for the first 5 years. I wonder how many other people out there were told similar and feel the same. Its true that a Central AC unit is more efficient than having several window ACs. It does not make the Central AC cheap by any means. Sometimes its cheaper to just cool one room down. The window AC is king in that regard. It was just under $2k to run my heat pump for the season covered and about double that uncovered. It did in fact work on my large pool, but only to its abilities, and it was in no way cheap.

There are still a dozen ways a heat pump may win in the cold climate. Or even as simple as owner preference. I just want them to know the ins/outs to make their best decision

 

[SDor]

About my pool size, you are correct. My 16x32 pool is about 23k gallons, not 35k. Don’t know where 35k came from. Sorry for the confusion and thanks for catching this.

 

[Vogt5059]

I have a spreadsheet in my signature where you can actually see the calculations and the assumptions.

View attachment 152062

There is also a much more complicated version that takes into account local weather conditions and all head loss components.

mas985 I just looked at your spreadsheet quickly and it looks very well thought out and thorough. I am going to have to play around with it a little bit when I have a few minutes. I have a few questions on the screen shot that you posted from it. I see that you changed the gallons, utilties costs, and the gas heater efficiency to match my scenario, thank you for that. I also see that the cover makes a huge difference in the amount of heating needed. The numbers in the column for wo/Cover seem to be close to what the Pentair calculator calculated. Pentair says ~2000/yr for May-Sep and your calculations show ~400/mo which is relatively close. So for the solar cover heat gain you set it to 5 and I noticed when I opened up your spreadsheet it was defaulted to 10. Do you think 5 is more reasonable for my location is that why you changed it to 5? Also would an autocover be about the same as a solar cover in terms of the heat gain?

 

[mas985]

The solar cover heat gain is dependent on the amount of time spent behind clouds. In the summer, we rarely have clouds so a cover can easily have 10F-15F heat gain (actually reduced heat loss). However, in more cloudy areas, the heat gain is less with a cover. In other words, the cover saves more heat when more heat is added to the pool. It is hard to say for sure what your situation might yield. That is what the more complex model is for. I have not run your situation on it yet.

As for an auto cover, the downside is that there is very little solar heat gain with the cover on. But heat retention tends to be higher. Were you planning to open it each day? If so, that particular model will not capture such effects very well.

You really need to use the "Heat Txfr" which captures all of the heat loss effects as well as cover usage. However, it only works for a particular point in time due to the calculation of solar radiation and weather inputs. But you can get a good idea on what some of the losses and gains are going to be.