Tankless Water Heater to Heat My Pool

[stewbets]

Moved from here.

I’m going to hook up tankless water heater to my “smaller” 11000 gallon pool, I’ll update how it goes in a couple months.

I'm doing the same thing with my 8,000 gallon pool I'm putting up. I ran my natural gas line outside and bought an $80 3.2 gal/min tankless water heater. Should be a fun experiment regardless of whether or not it works. This heater has given me a 38 degree rise at 3 gal/min in my tests, so it can theoretically raise the water 15 degrees in a day. This project also caused me to run a line to my propane grill. I've wanted to convert it to natural gas for a while now and can happily report that it works better than ever!

 

[mknauss]

Welcome to the forum!
How many btu/hr is the tankless heater?
To heat 8000 gallons of water by 15deg in one day will take ~9,000,000 BTU's. Or the heater would need to be 375K BTU/hr.
I suggest you read ABC's of Pool Water Chemistry and consider reviewing the entire Pool School eBook.

 

[CJadamec]

3 gallons a minute x 60 minutes x 24 hours = 4320 gallons per day only half the volume of the pool.

I'm not sure it will even survive running for 24 hours continuously. You will want to keep a close eye on that safety hazard. You also want to make sure that you are there to shut the pump off when the heat exchanger breaks.

 

[setsailsoon]

Moved from here.



I'm doing the same thing with my 8,000 gallon pool I'm putting up. I ran my natural gas line outside and bought an $80 3.2 gal/min tankless water heater. Should be a fun experiment regardless of whether or not it works. This heater has given me a 38 degree rise at 3 gal/min in my tests, so it can theoretically raise the water 15 degrees in a day. This project also caused me to run a line to my propane grill. I've wanted to convert it to natural gas for a while now and can happily report that it works better than ever!

Welcome to TFP!

Interesting experiment. Two areas you should look at are flow capacity of the heater and metallurgy. Pool pumps can put out much more than normal house flow. This could cause pressure levels higher than the heater rating. I'd check the shut in pressure on your pump (from it's pump curve) and make sure this is lower than the pressure safety valve on the heater. On the metallurgy, you could have an issue with chloride stress cracking if the house heater doesn't have metallurgy that's rated for this. Not trying to poke holes just give you some watch-outs. I hope it works and can't wait to see your test results.

Best regards,

Chris

 

[cfherrman]

A 4 gpm water heater is 80k BTUs
It will work but slow

 

[CJadamec]

It's not the heat output that's the issue, my heat pump is only 75k it still warms my pool.

The issue is the style of heat exchanger and the flow of water it is designed for. Tankless heaters are not designed to operate for long periods of time at full fire. The heat exchanger will be damaged quickly by the excessive amount of flow the pool pump will push through it.

The unit as a whole is not designed to be used outdoors. The exhaust from the unit will be a problem if it is not ducted correctly.

It's an engineering problem not a problem so much with the heat output of the unit. If you could design a pool heater that will heat a pool for 80 dollars they would be flying off the shelves and a major company would already be doing it.

 

[stewbets]

Welcome to the forum!
How many btu/hr is the tankless heater?
To heat 8000 gallons of water by 15deg in one day will take ~9,000,000 BTU's. Or the heater would need to be 375K BTU/hr.
I suggest you read ABC's of Pool Water Chemistry and consider reviewing the entire Pool School eBook.

Thanks for the welcome! I've done a lot of reading over the past couple years. We started with a 10 ft Easy Set 2 years ago and moved up to a 15 ft one last year. I just got our new 20 ft Ultra Frame set up and it's almost filled with water. I've learned a good bit about pool maintenance along this journey and really appreciate this site. Anyhow, l really enjoy doing things unconventionally (sometimes also known as cheaply) and that is what led me to consider a tankless water heater. It will take a lot of BTU's to raise 8,000 gallons by 15 degrees, but I don't think your math is correct (unless you're factoring in some insane thermal losses). 1 BTU = 1 lb of water raised by 1 degree. 8.33lbs in 1 gallon, so 66,640 lbs in my pool equals 999,6000 BTU's to raise it 15 degrees with perfect efficiency or around 1.2 million BTU's at 80% efficiency, not factoring in thermal losses of course. My water heater is from China. I don't believe any of the specs on it, but figuring from results I've obtained from my tests, it should consume about 68,000 BTU/hr, assuming 80% efficiency. This is all a fun experiment for me.

 

[stewbets]

3 gallons a minute x 60 minutes x 24 hours = 4320 gallons per day only half the volume of the pool.

I'm not sure it will even survive running for 24 hours continuously. You will want to keep a close eye on that safety hazard. You also want to make sure that you are there to shut the pump off when the heat exchanger breaks.

Thanks for your input but you forgot the most important part, the 38 degree rise. Raising 54% of my water (4,320 of 8,000 gallons) by 38 degrees is the same thing as raising all of it by 20.5 degrees (.54 x 38 degrees). You are correct that I need to keep a close eye on it. I'm not going to be running it for 24 hours straight. I'm going to be using a W1209 thermostat connected to a timer that cycles it at whatever rate I decide is reasonable. I won't really know what that is until I test it. That's the fun of it!

 

[stewbets]

Welcome to TFP!

Interesting experiment. Two areas you should look at are flow capacity of the heater and metallurgy. Pool pumps can put out much more than normal house flow. This could cause pressure levels higher than the heater rating. I'd check the shut in pressure on your pump (from it's pump curve) and make sure this is lower than the pressure safety valve on the heater. On the metallurgy, you could have an issue with chloride stress cracking if the house heater doesn't have metallurgy that's rated for this. Not trying to poke holes just give you some watch-outs. I hope it works and can't wait to see your test results.

Best regards,

Chris

I appreciate the advice! I'm not going to be using my main pump/filter for the heater, but a smaller pump designed for Easy Set pools. My Ultra Frame conveniently came with 2 outlets that I will be using for the inlet and outlet for my heater circuit. I didn't need these as I installed a skimmer instead. Now, on your metallurgy point, I fully agree that this is an issue. It isn't a question of if the heat exchanger will break, but when. I'm hoping to get at least a season out of it. I've come across a few posts online where people have tried this, but nothing too detailed and no long-term results, so I wanted to seriously approach this and share how it goes for others who are wired like me.

 

[Donldson]

So you have this thing running off of a 60 amp 240 volt breaker?

 

[Poolzzz]

My main concern would be safety under the many possible failure modes. You are using it completely differently than designed.

Even if it lasts through your first 24 hrs of continuous operation I wonder how long it will last exposed to pool chemicals in the water, being operated on a radically different usage rate than it was designed for, or being operated in a significantly different environment than expected. A lot could go wrong and safety should always be the priority, not just for the experiment but in use.

Edit: how long would it have to last to be cheaper than buying a proper pool heater? $80 every year probably adds to more than a real pool heater. Two seasons for $80 might be cheaper but I wouldn't want to deal with random failures and replacement every year or two. If it lasted reliably for 10 years then you might be on to something.

 

[stewbets]

It's not the heat output that's the issue, my heat pump is only 75k it still warms my pool.

The issue is the style of heat exchanger and the flow of water it is designed for. Tankless heaters are not designed to operate for long periods of time at full fire. The heat exchanger will be damaged quickly by the excessive amount of flow the pool pump will push through it.

The unit as a whole is not designed to be used outdoors. The exhaust from the unit will be a problem if it is not ducted correctly.

It's an engineering problem not a problem so much with the heat output of the unit. If you could design a pool heater that will heat a pool for 80 dollars they would be flying off the shelves and a major company would already be doing it.

My aim is to not be offensive or condescending, but you can make incorrect assumptions about anything you hear and go on and on about how it will not work because of those assumptions. However, I hope we can agree that this is a fruitless exercise. I attached a chainsaw engine to my daughter's old 16" bike frame (for me to ride, not her). I just used old bike parts to fabricate the gear reduction necessary for this. Now there is a lengthy list of disclaimers that you could share and dozens of reasons you could come up with for why this wouldn't work. But it did. And it still does a couple years later. And while some people bite off more than they can chew in an effort to save money or simply out of ignorance, I don't have a habit of doing that. Please don't assume otherwise. I am sharing what I'm doing for the benefit of others, and I certainly don't mind helpful comments and warnings. But your comment really just seems aimed at destroying my project. And I have said many times to my wife and kids that this plan could be a flop and I'd be fine with it, but that's not my expectation. I think we all benefit from a little outside-the-box thinking every now and then.

 

[stewbets]

So you have this thing running off of a 60 amp 240 volt breaker?

It's a natural gas heater.

 

[stewbets]

My main concern would be safety under the many possible failure modes. You are using it completely differently than designed.

Even if it lasts through your first 24 hrs of continuous operation I wonder how long it will last exposed to pool chemicals in the water, being operated on a radically different usage rate than it was designed for, or being operated in a significantly different environment than expected. A lot could go wrong and safety should always be the priority, not just for the experiment but in use.

It's not that I don't value safety, but I think there is a good bit of irrational fear surrounding this topic. I'm not just going to turn this heater on and go on vacation for a week. I'm going to test it and see how it holds up to various periods of usage. I'm going to closely monitor it. The heat exchanger is what I anticipate to be the weak link in using a heater like this for a pool. What happens when a heat exchanger goes out in a water heater that's installed in your house? The pool water will more agressively eat away at the exchanger. The burner will see more usage than normal. Eventually, it will fail just like any other pool heater or propane grill for that matter. It will just likely fail more quickly.

 

[mknauss]

It will take a lot of BTU's to raise 8,000 gallons by 15 degrees, but I don't think your math is correct (unless you're factoring in some insane thermal losses). 1 BTU = 1 lb of water raised by 1 degree. 8.33lbs in 1 gallon, so 66,640 lbs in my pool equals 999,6000 BTU's to raise it 15 degrees with perfect efficiency or around 1.2 million BTU's at 80% efficiency, not factoring in thermal losses of course.

You are correct - I slipped a digit somewhere!!!!

Take care.

 

[CJadamec]

My aim is to not be offensive or condescending, but you can make incorrect assumptions about anything you hear and go on and on about how it will not work because of those assumptions. However, I hope we can agree that this is a fruitless exercise. I attached a chainsaw engine to my daughter's old 16" bike frame (for me to ride, not her). I just used old bike parts to fabricate the gear reduction necessary for this. Now there is a lengthy list of disclaimers that you could share and dozens of reasons you could come up with for why this wouldn't work. But it did. And it still does a couple years later. And while some people bite off more than they can chew in an effort to save money or simply out of ignorance, I don't have a habit of doing that. Please don't assume otherwise. I am sharing what I'm doing for the benefit of others, and I certainly don't mind helpful comments and warnings. But your comment really just seems aimed at destroying my project. And I have said many times to my wife and kids that this plan could be a flop and I'd be fine with it, but that's not my expectation. I think we all benefit from a little outside-the-box thinking every now and then.

You are correct my post is meant to discourage any other readers of this post from trying this. What you are doing is not for a novice to try without full understanding of the dangers involved. Any number of people could read this thread and I would like to make sure they think twice about trying what you are doing.

You are using a natural gas device outside of both it's design parameters and its environmental design limits. Both of these things can lead to rapid and unexpected failures of the heater. Plain and simple you are putting yourself and your pool equipment at risk. That's your choice.

I have no idea what your education or your experience is. I don't assume you are dumb because it takes some knowledge to do what you are doing.

I know that my experience and education tells me that what you are doing is not safe and unwise. It should not be tried by anyone who doesn't understand the risks involved.

 

[Txjole]

I think it could be done, been selling tankless for years, they do make an exterior model (now if your is???) Problem I see is calcium building and messing with the flow sensor that controls gas output. It will need cleaned and flushed ALOT.

 

[stewbets]

Edit: how long would it have to last to be cheaper than buying a proper pool heater? $80 every year probably adds to more than a real pool heater. Two seasons for $80 might be cheaper but I wouldn't want to deal with random failures and replacement every year or two. If it lasted reliably for 10 years then you might be on to something.

I'm not trying to twist anyone's arm here into doing the same. I will say that with the advent of Intex pools there are many who will not invest thousands of dollars into their pool experience and it seems I'm catching a lot of criticism from those who already have invested heavily in "proper" pool equipment. So, if you're in the latter group, I'm not sharing this for your benefit. Your system is great! It's very low maintenance. It's optimized. Please don't feel threatened by my posts.

But my request to you would be to respect that this is an alternative means of heating a pool. You wouldn't choose it. I get that. But I would never choose a pool heater. I'm not criticizing pool heaters. However, they are quite expensive upfront. I paid $360 for our 20' pool. I have no idea how long it will last or how long my kids will be interested. For me, the right decision was to try this tankless water heater approach and if it works, we have a heater. If it doesn't, we'll just go without. The other important factor here is that I WANT to do this. I enjoy tinkering. I enjoy pushing the envelope of what is acceptable and possible. I like that people can't understand why I'm doing this. However, at this point, I'd appreciate it if I could have this thread back to share progress on my system.

 

[stewbets]

I think it could be done, been selling tankless for years, they do make an exterior model (now if your is???) Problem I see is calcium building and messing with the flow sensor that controls gas output. It will need cleaned and flushed ALOT.

Do you have any advice on the best ways to clean and flush these heaters? Also, the heater I have is very basic. The only variable gas output is manually controlled with a knob. If the flow is too slow, it will heat up to a certain maximum temperature and shut off.

 

[Txjole]

Do you have any advice on the best ways to clean and flush these heaters? Also, the heater I have is very basic. The only variable gas output is manually controlled with a knob. If the flow is too slow, it will heat up to a certain maximum temperature and shut off.

Buy the descaler kit. Comes in a bucket, with a pump and the chemicals. Haymaker (by Hecules) seems to be the one my customers prefer.