Need advice on gas vs. heat pump in Orlando

[flguy]

We just bought a new house in Orlando that has a pretty good size pool, I would say at least 15k gallons if not more with attached spa (pool is 15x30x6). The current owners had a large propane tank sunk for other reasons so they went with a gas heater.

In any case, I am trying to decide what kind of pool heater to get for the new house. I have a pool at my current house (in Orlando) with a 120k btu heat pump and it's nice and efficient, but it's noisy and takes a long time to heat unless it's above 75 degrees outside. I use the pool a lot (I work from home) and I like the temperature to be between 85-88 degrees when I swim.

I've read some of the pros and cons of the two types of heater, but have not zeroed in on a real consensus for my type of situation. The gas heater would be cheaper to install initially, especially because there is already a tank nearby, but I have no idea how much it's going to cost me in the long run. Propane here is currently around $5/gallon. Electric is $0.12/kW.

In summary: I use the pool frequently, but only for short periods at a time. I like it "hot" (i.e. 85 or above) but I don't want a lot of noise or long term expense. It's a northern exposure, and a fairly large pool with attached spa. There is already a sunken gas tank near the pool area. Which heater would be most economical for my situation? We plan to be at this new location long term, like 15 years.

Thanks.

 

[Bama Rambler]

Where did you live before?

Most economical for your area is likely going to be a heat pump, but if you want fast then gas is the winner. Without constraints the answer would be both. Fire up the gas to heat the pool quickly and then switch to the HP to keep it warm.

The HP will be about equally as noisy as your home system. I don't know what a new gas heater sounds like.

Having said all that, I can tell you that in the middle of summer you're not going to want a heater you're gonna be wishing for a cooler! Your pool will easily feel like bath water in the summer.

 

[flguy]

Still in Orlando. I am just moving from one side of the neighborhood to the other. I have never heard a gas heater in operation, nor have I been able to find any noise comparison charts between gas and HP. Logic tells me that gas heaters would be silent, no moving parts, just a flame right? Can anyone tell me what the noise is like? This might actually be the deciding factor for me, because the HP I have now is noisy and does not help in creating a relaxing atmosphere around the pool, and in both our current house and new house, the equipment in only 10-15 feet around the corner from the pool area. Thanks.

 

[jblizzle]

I have had 2 NG heaters ... they are pretty quiet although you can certainly hear them light up ... WHOOSH. There is generally a small amount of hissing from the gas and some flame noise especially if it is a little windy.

 

[hoosierrun]

At least with a gas heater, you will heat fast and then the unit can shut down. A heat pump runs almost continuously. You are lucky if you can get propane that cheap. Here in Pinellas County (West side of Florida, they (Suburban Propane) charges me $4.79 a gallons plus a bunch of surcharges which makes it come out to about $5 a gallon (it tracks closely with gasoline but more). Who is your propane supplier and how big is the tank?

Your decision may be based on whether or not you are heating the entire pool (heat pump is preferred), or just heating the spa (propane prefered for quickness of heat). If you have natural gas, that would be the winner on all counts.

 

[flguy]

How about costs? If I know propane is $2.79/gal and electricity cost $0.11/kW, how do I do the math to figure out how much it's going to cost me? I tend to spot heat my pool 7 months out of the year: this assumes no heat needed for 3 months in the summer, and 2 months during the winter I won't use it at all. So out of the 7 months, I might typically need to bring the pool anywhere from 75-80 degrees up to 85-88 degrees a few times a week. During the day I might take a lunch break and swim for 30 mins. Sometimes another 30 in the evening. On the weekend I like the pool to be warm when I wake up so I can go in first thing on Sat/Sun, and have the temp remain stable all day Sat/Sun. Those are my ideal operating conditions. With the HP I have now (in Orlando) it varies a lot how much time I need to leave it running. It really, really depends on the outside temp. If it's 80+ degrees I get about 1 degree per hour. I keep the pool covered (at night) most of the 7 months it's in use, although sometimes I'm too lazy and leave it off, then my pool drops a good 5-6 degrees overnight.

I just want to make sure if I get a gas heater that I don't get socked with $1,000 in gas bills every few months. That would be insane, but I have no way to predict right now. Need help.

 

[flguy]

At least with a gas heater, you will heat fast and then the unit can shut down. A heat pump runs almost continuously. You are lucky if you can get propane that cheap. Here in Pinellas County (West side of Florida, they (Suburban Propane) charges me $4.79 a gallons plus a bunch of surcharges which makes it come out to about $5 a gallon (it tracks closely with gasoline but more). Who is your propane supplier and how big is the tank?

Your decision may be based on whether or not you are heating the entire pool (heat pump is preferred), or just heating the spa (propane prefered for quickness of heat). If you have natural gas, that would be the winner on all counts.

I contacted AmeriGas for the $2.79 quote. I'm sure there are other monthly fees but that's what they told me per gallon.

I prefer to heat and use the pool vs. the spa. The rest of my family (wife, kid, mother) prefer the spa. I'm definitely not worried about the spa.

 

[jblizzle]

Even with a gas heater, you are not going to be able to come home at lunch, flip on the heater and get a 10 degree rise quickly. It is going to take a LOT of gas to heat the pool.

Ever consider solar? I would think that would allow you to maintain the 85+ water most of your 7 months if you are using a cover with only the initial cost of installation.

Then maybe also have a gas heater to be used for a quick heat of the spa when needed.

I know there are threads here that step through how to calculate the gas usage required to heat a pool ... may have to do some searching.

 

[flguy]

Ever consider solar? I would think that would allow you to maintain the 85+ water most of your 7 months if you are using a cover with only the initial cost of installation.

Unfortunately, the back of the house has a northern exposure. There isn't a good place to mount solar, but I sorta like the idea of a hybrid system. I'm sure a hybrid system would cost a lot up front though. Again, need to find a way to do cost calcs. If you can point me to any other threads or web sites with calculators for evaluating all of this that would be wonderful. I didn't find much when I initially Googled it. I just get standard boilerplate Web pages that talk about pros/cons.

 

[jblizzle]

Well, here is some info to start with cost estimates:

It takes 1 BTU to raise the temperature of 1 lb of water by 1 degree F.

Your pool is ~17,000 gallons x 8.33 lbs/gal = 141,610 lbs of water
Assuming you need to add 10 degrees you need:
141,610 lbs * 10 degF = 1,416,100 BTUs to heat the water (this ignores maintaining the temp and heat loss due to evaporation)

Lets also assume a gas heater is 85% efficient.
A 400k BTU heater will put out ~340kBTU/hour
It will take 1416100/340000 = 4.2 hours to heat your pool by 10 degrees (ignoring losses)

A 250k BTU heater will put out ~212kBTU/hour
It will take 1416100/212000 = 6.7 hours to heat your pool by 10 degrees (ignoring losses)

Now we enter an area I am not 100% clear on.

A gallon of propane has ~91500 BTUs ... lets again assume 85% efficiency of the heater giving 77800 BTUs/gal propane.
To heat your pool 10 degrees will require:
1416100/77800 = 18.2 gallons of propane

Assuming $3/gallon this is $55 every time you heat your pool 10 degrees (ignoring evaporation cooling losses in the process).

Not sure about electric ... I will keep looking.

Although I just found {EDIT ... I removed the PDF as I think it may be infected} with some interesting information ... although the piece missing in the calculations is the way to determine how long you have to run each of the various systems for the same heat rise.

 

[jblizzle]

Found the info on electric (not sure I am using it correctly though) which has ~3400 BTUs / kW.

So if you need 1,416,100 BTUs to heat your water by 10 degrees that is
1416100/3400 = 416 kW
@ $0.11/kW (does this include all the fees?)
416*.11 = $46 every time you heat your pool 10 degrees (ignoring losses ... and I am not sure this it right)

Looks like electric heaters range from 10kW to 60kW, so to get 416kW out to heat your pool would take 41 hours with the smallest heater and 7 hours with the largest.

**** Disclaimer: I will not stand by these calculations as I feel like I missed something

 

[flguy]

Found the info on electric (not sure I am using it correctly though) which has ~3400 BTUs / kW.

So if you need 1,416,100 BTUs to heat your water by 10 degrees that is
1416100/3400 = 416 kW
@ $0.11/kW (does this include all the fees?)
416*.11 = $46 every time you heat your pool 10 degrees (ignoring losses ... and I am not sure this it right)

Looks like electric heaters range from 10kW to 60kW, so to get 416kW out to heat your pool would take 41 hours with the smallest heater and 7 hours with the largest.

**** Disclaimer: I will not stand by these calculations as I feel like I missed something

I just spent a good 30 mins going over the calcs myself. The gas calc looks right. I think what you've missed above regarding electric is that a 125k BTU heat pump, for example, only requires 7 kWh to run. I saw the same calc that electricity is 3400 BTUs/kW but that is just standard resistance "electricity", not a heat pump.

Thus, if I need 1,416,100 BTUs to heat my water by 10 degrees that is:
1416100/125000 = 11.3 hours @ 7 kW/hour
@ $0.11/kW, 11.3 * 0.11 * 7 = $8.70 every time I heat my pool 10 degrees vs. $55 for gas, or 6 times less than the cost of gas. Wow.

Of course, this assumes IDEAL conditions when running the HP. The numbers above for the 125k BTU heater are for a Rheem M8350ti and are based on AHRI 1160 Standard which is 80/63/80 (air temp F/% relative humidity/water temp F entering the unit). I just picked this one out of the sky because it had good data.

http://www.rheem.com/documents/rheem-cl ... nical-data

If the outside temp drops to, say, 50 degrees you're looking at only 82,000 BTU output, and the pool might be losing as much BTU per hour that a heat pump can put into it, so you could be running the thing forever and not gain a degree of heat (this has happened to me) and wasting money regardless how "efficient" it is.

So the big difference seems to be: a 400k BTU gas heater will heat the pool in 4.2 hours vs. 11 hours running a heat pump. So heat pump takes almost 3 times as long to heat, and that's with ideal conditions at 80 degrees air temp those whole 11 hours (not too likely).

So @ $8.70/11 hours = $0.79/hr for heat pump vs. $55/4 hours = $13.75/hr for propane.

Does that sound right? It costs 17 times as much per hour to run propane vs. HP but only figured 6 times as much for a 10 degree increase. Why do I feel like I'm comparing apples to oranges here? The logic escapes me at the moment. Which calc do I want? The hourly or the full 10 degree heat-up?

Anyway, it certainly looks like propane is wicked expensive compared to a heat pump, with the only advantages being very quick heat up time, lower initial product cost, consistent temperatures regardless of air temp, and less equipment noise. I definitely want quick heat up and less noise and less up front cost, but I'm not sure I'm willing to pay the long term fuel costs.

Please chime in if I've missed something or you have any other observations. Oh yeah, the 400k BTU gas heater costs about 1/2 the 125k BTU heat pump. Maybe I need to throw some ROI calcs in there as well. :? My brain hurts.

 

[Melt In The Sun]

For the HP, the 125k BTUs are at peak efficiency. That means hot air and cold water. When the air is cooler (which is when you want to heat), it won't produce that much heat.

 

[jblizzle]

My electric calculations were not for an electric heat pump ... they were for an electric resistance heater.

I will try to look at your numbers, but I too an struggling to see if we are comparing the same fruit

The pdf I linked (and then un-linked) actually stated the propane efficiency at 70% instead of 85%. I do not think it is infected, but I got a weird BOT notice at work about the same time I looked at the PDF ... so waiting to see if I can determine if it is the PDF before I post a link again.

 

[jblizzle]

So @ $8.70/11 hours = $0.79/hr for heat pump vs. $55/4 hours = $13.75/hr for propane.

Does that sound right? It costs 17 times as much per hour to run propane vs. HP but only figured 6 times as much for a 10 degree increase. Why do I feel like I'm comparing apples to oranges here? The logic escapes me at the moment. Which calc do I want? The hourly or the full 10 degree heat-up?

Looking over your numbers seem reasonable (I think) I am not sure how useful an hourly cost is because that does not tell you how long it actually takes to get the water heater, thus it misses the total cost. That is why I think the metric to look at is the time and cost for a specific heat rise.

Heat pumps should be one of the most efficient (cheapest) methods, but the drawback is the time to heat.

Do you have room behind your house to put a South facing rack to hold solar heaters? Or you can put them on the South facing side of your house roof if there is one. I really think they would work well at maintaining your pool at the higher temperatures you want without the wait and cost for each time you want to warm the pool. Although the initial investment will be higher, you would not no more noise than your pool pump.

 

[flguy]

Do you have room behind your house to put a South facing rack to hold solar heaters? Or you can put them on the South facing side of your house roof if there is one. I really think they would work well at maintaining your pool at the higher temperatures you want without the wait and cost for each time you want to warm the pool. Although the initial investment will be higher, you would not no more noise than your pool pump.

No, the back where the pool is faces due north, so the south side is the very front of the house. HOA would not allow that. I could possibly get away with a WEST facing installation. Still, I have to decide how much all this convenience is worth to me. I really like the idea of a solar/gas hybrid the more I think about it. Solar to maintain heat, gas to back it up when I really need heat in a hurry and for the attached spa of course. I have no idea how much solar installs cost. But I am willing to spend up to $5k total for a solution either way.

Thanks for everybody's input here. I am really surprised how much response I got in a 6 hour period; it has definitely helped!

 

[jblizzle]

No, the back where the pool is faces due north, so the south side is the very front of the house. HOA would not allow that. I could possibly get away with a WEST facing installation.

FYI, the HOA can NOT deny you putting up solar panels by federal law (just like they can not deny antennas or satellite dishes). So you can certainly put them on the south side if you are OK with the aesthetics. Depending on the area, you may need to have panels on the S and W side.

Ball park, I think a solar setup is in the $3k-$5k range if you pay to have it done, but greatly depends on your sun exposure. I bought some used panels and doing the install myself for less than $1500 ... really should have been less had a done a little more research.

 

[Brentr]

We have solar and a heat pump. You should get quotes from the top three manufacturers. Solar by far for us the the most efficient way to go. It should be noted that we have a small pool and that we have 1:1 ratio sq footage of panels to pool surface area. It also should be noted that we have a very large Heat Pump with a high COP. The Heat Pump is located about 20 ft from the pool, side corner of the house and we cannot hear it when it is running. We also use a bubble solar cover which retains the heat at nite and reduces evaporation and chemical use. We will have the solar cover on till May when the nite time temps drop to mid to high 60's, at which time I will take it off and store in the garage. We have been swimming since the middle of February and we keep the pool at 92 degrees. The girls like to swim at nite so I use the heat pump to maintain the temp. Look at our solar install in the Sig. Hope this helps

 

[Poolsean]

http://aquacal.com/oce.html
Use this calculator to see which size heat pump would be best for your pool. The default temperature will take you to either 80 or 82 degrees. Override it to match your desired temperature increase.
There are differences in sound levels between gas and heat pumps... and even between heat pump manufacturers.

 

[flguy]

At least with a gas heater, you will heat fast and then the unit can shut down. A heat pump runs almost continuously. You are lucky if you can get propane that cheap. Here in Pinellas County (West side of Florida, they (Suburban Propane) charges me $4.79 a gallons plus a bunch of surcharges which makes it come out to about $5 a gallon (it tracks closely with gasoline but more). Who is your propane supplier and how big is the tank?

Your decision may be based on whether or not you are heating the entire pool (heat pump is preferred), or just heating the spa (propane prefered for quickness of heat). If you have natural gas, that would be the winner on all counts.

I contacted AmeriGas for the $2.79 quote. I'm sure there are other monthly fees but that's what they told me per gallon.

I prefer to heat and use the pool vs. the spa. The rest of my family (wife, kid, mother) prefer the spa. I'm definitely not worried about the spa.

Okay, I made a mistake. $2.79 was their "intro" rate for my first tank of gas. Thereafter it's around $5/gal as you quoted above. That makes heating with gas even less attractive, however, I just found out it will cost me over $1,000 to run the necessary 50amp wire for a HP, so gas is looking good again.

I can get a 400k BTU propane heater right now for $2,300 installed (Leslie's is running a 20% promo). A 125k BTU heat pump would cost me $3,300 (also promo price), plus the extra $1,000+ to run the wire. So for an extra $2k right now I can convert to a HP, or else suck it up and pay the propane costs long term. I hate this idea because the weather is always pretty warm in FL so a HP works efficiently most of the year. I'll have to do the math again to see what the long term costs are based on how I like my pool/spa heated.

Anyway, it is getting towards the end of summer and my pool is no longer staying in the high 80s by itself, so need a solution soon. The pool is one of the main reasons I bought this new house so I want to use it, plus my son loves it (but he gets cold fast).