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Pool heater as backup for wood boiler

<chuckle> Thanks HR. Yep - I am fond of finding "alternative applications" for all sorts of things. ;~)

BTW - this unit is not going to be used for primary heating, and will only need to provide safe backup temps to prevent damage to piping, buildings and contents. Efficiency is not a major concern due to the highly infrequent need for it's service. My rationale for the use of the propane heater is to eliminate the oil furnace in my house altogether. The long term reliability, fuel stability, and reduced maintenance factor are in the propane fueled appliance's favor.

The HX on this particular Hayward has a SS bypass valve, but as far as I have been able to determine it is pressure actuated, not temp. I spoke to the techs at Hayward, and of course they would not give me a straight answer on what the max allowed temps through the HX were. All the over-temp "controls" are thermodiscs, so I will check to see what they are rated at. I have to believe I can run this thing up to 165 without much issue. At 150k Btuh (input), and a delta T of 20, I can run 15gpm through it no problem with a Grundfos 26-99. The HX is rated up to 22 GPM, IIRC. The unit and it's piping will be filled with glycol mix, and seperated from the GARN water by a FP HX.

The liability on this one is all on me, as it is my house/unit. Of course I am going to approach this carefully, and testing will be thorough before I relegate it to sentry duty.

I was just wondering if anyone knew what the "typical" outlet side temps were on a propane fired pool heater like this Hayward.


  • Jim K in PA
    Jim K in PA Member Posts: 13
    Pool heater as backup for wood boiler

    I have a GARN WHS2000 that I installed last year and brought online 5 December 2008. The unit is a burn/store wood gassification unit with a max input of 425k Btuh (www.garn.com). I am currently operating it in a range of 150-200 deg F. I burn twice daily in cold weather, 2-3 hour burns.

    I have it piped P/S, with Grundfos 3 speed pumps. There is currently only the house load (70k Btuh max heat load) pulling heat from the storage tank. I am sending hot water to the house via 120' (each way) of 1.25" PEX, and through a 50 plate GEA FP HX integrated in the return leg of an EFM 142k Btuh input oil fired furnace. Only about 60' is buried, the rest runs through my 24x36 garage, (only partially insulated at the moment). I will be adding heat to the shop above the garage and a yet to be built small greenhouse. The garage/shop will add about 30k Btuh load, and the greenhouse will add about 35k Btuh.

    I would like to use a propane fired pool heater as a backup heat source on a secondary loop for times if/when the GARN storage temps drop below 140 and no one is around to re-fire it. I already have a Hayward 150k Btuh pool heater. Is there going to be a problem using it to raise the GARN water from 140 to say around 160+? I have never owned or used a pool heater, and do not know what the output water temps are for them. I have enough excess capacity in the BB rads in the house to be able to live with 150 deg water down to single digit outdoor temps. The GH and the shop will be using a combo of radiant and fan coil supplement.

    Let me know if I left out any important facts that would be relevant.


    I will likely convert the controls on the Hayward to low voltage from millivolt, mostly because I do not know how reliable the existing controls are any more. The unit was infrquently used for about 10-12 years.
  • hot_rod
    hot_rod Member Posts: 22,479

    it wasn't designed to be used that way :) They generally need some large gpm flows to keep the HX happy.

    I don't think it would be very efficient.

    Some have thermostatic bypass valves built into the S&R header. I don't know what temperatures those can handle. Some I have seen have plastic disc components.

    Will it even run up to those temperatures without changing the operating controls?

    It all seems like a lot of work and liability to modify that to be a heating boiler?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
This discussion has been closed.