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Outdoor boiler heating a pool

I bought a econoburn ebw-200 in hopes I would be able to heat my pool very efficiently with it, however the issue im having when heating the pool with the wood boiler is that the temperature of water returning to my boiler is so low that my boiler can’t keep up. How can I raise the water temperature returning to my boiler. I have a 200,000 btu boiler, im using 1-1/4” pex line for the loop, I have the heat exchanger hooked up that they said I would need for my size pool 18x36 Inground pool. What can I do to raise the return water temperature. Thanks in advance if someone can help me.

Comments

  • What is the temperature of the pool water as you started this heating, and what is the desired pool temperature when cooked enough?
    It takes a lot of heat to raise up the number of gallons you have from chilly to warm, so maybe you have to wait a little longer for the desired result.
    You certainly will never be chilly when hauling that amount of wood to the boiler!—NBC
    HVACNUT
  • Robert_25
    Robert_25 Member Posts: 401
    Just pipe in a bypass, so you can throttle the load to the boiler.
    Ironman
  • Ajsmaldon13
    Ajsmaldon13 Member Posts: 8
    Right now the pool is in the 50’s I would like to keep it around 80-82. I just wonder if there is a way to warm the water returning to the boiler after it’s gone through the heat exchanger for the pool?
  • HVACNUT
    HVACNUT Member Posts: 4,546
    Increasing the pool supply temp is the only way to increase the return temp.
    Raising the pool temp by 32° is gonna take a long long time. And you want it to stay at 82°?
    Is there a conveyer belt constantly feeding wood to the boiler or have a 3 shift labor force to keep the fire going 24/7?
    Bad idea IMO.
    Kiddie pool maybe.
    The ones with the built in slide are pretty cool.
  • Jamie Hall
    Jamie Hall Member Posts: 18,699
    At the risk of pointing out the obvious, if you could warm the temperature of the water returning from the pool to the boiler, why would you need the boiler? Isn't that what the boiler is for?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Gordy
    Gordy Member Posts: 9,514
    Typically a closely matched pool heater will heat at a rate of 1/2 a degree per hour. So in your case it will take over 2.5 days to bring the pool up to temp.

    To heat a 24’ round 52” deep with a 150k gas pool heater the above was spot on. In your case the boiler is 200k with a larger pool, and a heat exchanger that loses some of that output if it’s properly sized.

    The only way to raise the return temps is as mentioned above with a boiler protection valve so you can get the return temps up if it’s boiler protection you are worried about.
    GBart
  • Ironman
    Ironman Member Posts: 6,860
    Are you keeping the pool covered while trying to heat it? If not, it will never catch up.

    As mentioned, a bypass around the heat exchanger should be done and the valve should be throttled so that the wood boiler return temp stays above 150*.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rod
    hot_rod Member Posts: 16,118
    You would need a stainless heat exchanger between the pool and steel boiler.

    Use a valve like this designed specifically for protecting bio or wood boilers. It doesn't matter what the load is pool, radiant, tank, etc.

    There is a company up in Canada that builds a stainless wood fired pool boiler. I've seen them at some trade shows. But you already have the boiler. Be realistic on your expectations as to what 200K boiler can do for that load.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Ajsmaldon13
    Ajsmaldon13 Member Posts: 8
    I already have a heat exchanger with everything hooked up. How much temp change should I expect with this size boiler?
  • Ajsmaldon13
    Ajsmaldon13 Member Posts: 8
    edited February 2019
    Yes pool is covered with solar cover and it is an indoor pool. My problem is once the water from the boiler goes through the heat exchanger at the pool pump it is coming out too cold going back to the boiler and the boiler can’t keep up the constant temp of 180 I have it set at.
  • pecmsg
    pecmsg Member Posts: 2,813
    Whats the GPM

    How Hots the heat exchanger

    Just too many variables with wood!
    Gordy
  • Gordy
    Gordy Member Posts: 9,514
    edited February 2019
    My example above was with a gas fired pool heater. Their performance when sized correctly are pretty predictable.



    I would concentrate on protecting the boiler from the cold return temps as a priority. The temp rise on the pool side is what it is. Hopefully the HX is sized close.

  • TAG
    TAG Member Posts: 605
    I have a 20x40 pool w/diving board .. so it's deep on one end. my NG heater is 400k BTU. They typically run in the low 80 % efficiencies. I can get 1 degree per hour.

    You need to figure your total gallons.

    Most online pool supplies companies have calculators for total gallons and heater size.
  • Ajsmaldon13
    Ajsmaldon13 Member Posts: 8
    Pool is about 36000 gallons I used their calculation to size my heat exchanger. I had a propane heater hooked to it when I bought the house but I was costing me an arm and a leg. I have 38 acres so wood for me is plentiful. I’m not worried how fast it heats the pool my main concern is how do I raise the temp of water returning to the boiler from the heat exchanger
  • nibs
    nibs Member Posts: 470
    As mentioned in other posts I heat a 350 gal hot tub with a self built and designed wood boiler, it works very well. It takes a large amount of wood to raise the temp of the tub from 50 to 80 degrees.
    You will have to chuck a lot of wood into the hole to warm that pool.
    Dry wood will give you about 1000 btu's per cubic foot.
    Lots of folk on this site can tell you how many cu/ft you will need.
  • GBart
    GBart Member Posts: 746

    Pool is about 36000 gallons I used their calculation to size my heat exchanger. I had a propane heater hooked to it when I bought the house but I was costing me an arm and a leg. I have 38 acres so wood for me is plentiful. I’m not worried how fast it heats the pool my main concern is how do I raise the temp of water returning to the boiler from the heat exchanger

    you have to put in a bypass from your supply to return and throttle it so that some supply is going right into the return, the old boiler must have been piped this way, no boiler takes 36,000 gallons straight on
  • TAG
    TAG Member Posts: 605
    Think I do 44k gallons. Are you concerned about cold water returning to the boiler and damage?

    A pool heater keeps the heat exchanger above condensation level by restricting flow though the exchanger-- using a bypass. What's the minimum flow required through the boiler ? I think you have to make sure your boiler pump is providing enough flow and that the loop to the pool is not too fast and pulling too much heat from the boiler loop.
  • Brewbeer
    Brewbeer Member Posts: 616
    edited February 2019
    300,000 BTUs/hr to raise 36,000 gallons 1 degree F.
    200,000 BTU/hr boiler. So, about 0.5 F temp rise per hour at full throttle, accounting for efficiency.

    To go from 50F to 80F requires 9 million BTUs, assuming none of the heat added to the pool is lost.
    A cubic foot of eastern dry hardwood (oak, maple) has about 190,000 BTUs.
    Assuming 100% efficienty, about 47 cubic feet of eastern dry hardwood needs to be burned to raise 36,000 gallons by 30 degrees F.

    Call it 1/2 cord (64 cubic feet) of wood to go from 50 to 80F in 60 hours.
    Hydronics inspired homeowner with self-designed high efficiency low temperature baseboard system and professionally installed mod-con boiler with indirect DHW. My system design thread: http://forum.heatinghelp.com/discussion/154385
    System Photo: https://us.v-cdn.net/5021738/uploads/FileUpload/79/451e1f19a1e5b345e0951fbe1ff6ca.jpg
  • Leonard
    Leonard Member Posts: 903
    edited February 2019
    I assume you have a separate heat exchanger between boiler and pool water.

    As I see it you have 2 slightly separate subjects.

    1) return water to boiler is too cold .... Typically want boiler temp to be at least 135 deg F so don;t get condensation in exhaust side of boiler, It rusts the boiler.

    2) If water going to pool is too cold , say if you want to float a blow up mini-pool in it so make a "floating hot tub" ( cousin did that, ~ 105+ deg). Install a valve (bypass) that bleeds some of hot returning pool water into cool water drawn from pool. Result will be hotter water, but BTU/hr delivered to pool may go down a bit.

    This can also solve 1-st problem of "return water to boiler is too cold".

    Cousin had large insulated in ground pool, 30 years ago cost him $1000 to heat it over summer, propane, NH.
  • Gordy
    Gordy Member Posts: 9,514
    The valve @hot_rod posted is what you need. All your troubles will be gone. Except cutting wood, and feeding the boiler :)
  • hot_rod
    hot_rod Member Posts: 16,118
    It is what it is are far as temperature rise with the BTUs you have. With wood, the input really depends on the fire you can maintain, especially with a consistent load like that.

    Rarely do you see anything below 180K, gas or LP on a pool that size.

    Boiler , thermostatic valve, HX, a super simple piping to give you all the protection you need. Could even be all electric free, unless the boiler has a gasification fan?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • TAG
    TAG Member Posts: 605
    FYI -- My bypass works off temp.

    Early in the season with cold water in the pool -- the bypass will be on max -- and the water is still too cold to stop condensation. Eventually -- the pool water gets warm enough that this stops and the bypass eventually fully closes and almost all of the return water flows through the exchanger and back to the pool.

    It's obviously not as efficient when in bypass -- you can feel the temp of the flame is higher
  • hot_rod
    hot_rod Member Posts: 16,118
    Some pool boilers have a thermostatic disc built into the header on the boiler between the S&R ports. I'm not sure the accuracy of if they are 100% shutoff.

    The valve I show above is 100% shut off as it has a 3 rd port to allow full flow to the boiler when the return port closes off.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Zman
    Zman Member Posts: 7,295

    I bought a econoburn ebw-200 in hopes I would be able to heat my pool very efficiently with it, however the issue im having when heating the pool with the wood boiler is that the temperature of water returning to my boiler is so low that my boiler can’t keep up. How can I raise the water temperature returning to my boiler. I have a 200,000 btu boiler, im using 1-1/4” pex line for the loop, I have the heat exchanger hooked up that they said I would need for my size pool 18x36 Inground pool. What can I do to raise the return water temperature. Thanks in advance if someone can help me.

    Back to your original question. If your problem is that the boiler is not keeping up, that has nothing to do with your return water temp. Raising the return water temp to the boiler is a good idea as it will make the boiler and vent last longer and run safer.The ideas mentioned above will take care of that.

    Is the boiler able to run at high fire constantly? If you post the other details of your system, we can help you sort this out. In general, wood boiler companies are not very good at design. It is probably a good idea to back check their plans.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hot_rod
    hot_rod Member Posts: 16,118
    you can't really raise the temperature coming out of the pool itself. What you can do is blend some of the boiler output with some of the return to keep the boiler operating at a safe temperature, That is what a thermostatic 3 way valve can do. Manual valves can to some degree but they cannot react to big temperature swings. If you set it when the pool is cold, it would require a different adjustment when the pool approaches set point temperature to be effective.

    Slow the flow thru the pool side of the HX will work also. If the pool pump is being used to circulate that side you would need to pipe a bypass to avoid reducing the pool pump flow requirement.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Ajsmaldon13
    Ajsmaldon13 Member Posts: 8
    I guess after reading everything everyone wrote my main issue is the return to my boiler being to cold? I don’t want to harm my boiler with the cold temp.
  • hot_rod
    hot_rod Member Posts: 16,118

    I guess after reading everything everyone wrote my main issue is the return to my boiler being to cold? I don’t want to harm my boiler with the cold temp.

    Correct, most all boilers start from a cold condition at some point. The goal is to get them above condensing temperatures within the first 10 minutes of running.

    With wood fired devices this is particularly important mainly because of creosote formation. Most all wood and bio mass boilers sold in Europe include a return protection valve. I think the US manufacturers highly recommend a valve or other method of protection.

    Pinning down the adequate return temperature to a wood fired boiler is a bit more complicated due to the moisture content of the fuel and how the air mixture is dialed in. I'd suggest 135- 140 minimum return within 10 minutes of operation, or less.


    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • hot_rod
    hot_rod Member Posts: 16,118
    If that 3 way thermostatic is sized, installed and working properly it should provide the protection you need. Got a spec sheet showing installation orientation and temperature spec?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Ajsmaldon13
    Ajsmaldon13 Member Posts: 8
    That valve is hooked to my thermostat on the wall. I set the temp to my desired temp and when the pool calls for heat it opens and sends the boiler water through to the heat exchanger and when it doesn’t call for heat it closes and circulates the boiler water back to the boiler. I think what I need is a mixing valve to mix the hot water coming from the boiler with the cool water going back to the boiler so that the temp of the water going back to the boiler isn’t too low.
  • hot_rod
    hot_rod Member Posts: 16,118

    That valve is hooked to my thermostat on the wall. I set the temp to my desired temp and when the pool calls for heat it opens and sends the boiler water through to the heat exchanger and when it doesn’t call for heat it closes and circulates the boiler water back to the boiler. I think what I need is a mixing valve to mix the hot water coming from the boiler with the cool water going back to the boiler so that the temp of the water going back to the boiler isn’t too low.


    Yep, you need a valve that can sense and respond to temperature at the return port.

    It could be a motor operated valve, if that is what you have, the control needs to read boiler water not a wall control.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • nibs
    nibs Member Posts: 470
    Without considering condensing, by warming the return water, you will be able to make your fire burn hotter & more efficiently.
    Tho' BTU's is BTU's & you will need a firewood processor to create enough firewood.