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150 kBTU pool heater question

dandhb Member Posts: 9
I am planning on installing a 150 kBTU pool heater and the gas line installation would be so much easier if I can replace the gas line to my gas fireplace with a 1” pipe vs the current 1/2” pipe. However to do that I would have to go from 1/2” to 1” at the main supply tee. I could use a 1” to 1/2” reducer coupling through a short 2” nipple off the main gas tee. My main gas line is 1” and I plan to run a 1” gas line off the reducer couple to my pool heater which is less than 30 ft from the nipple. So I would have about 2” at the 1/2” pipe size then go immediately to 1” pipe. I looked in some gas pipe sizing charts and it says a 1/2” pipe with a 0.62” diameter can support a 170 kBTU for 10 feet. Based on this I think I’m ok but looking for advice from some of you experts. Thanks!


    EBEBRATT-Ed Member Posts: 15,350
    It's not just the branch piping you have to be concerned with. You need to make a sketch of all your gas piping and the btu rating of every appliance. 1" is probably not large enough for a pool heater plus any appliances you have now. 170,000 is a small pool heater as pool heaters go is that the rated input of the pool heater?
  • dandhb
    dandhb Member Posts: 9
    Hayward says 3/4” pipe up to 100 ft is fine for a 150 kBTU heater. My furnace is 100 kBTU and is tee off the 1” main with 10 ft of 1/2” pipe to furnace. Furnace works perfect and is the original 26 yr old furnace.

    Regarding my pool heater question the California low pressure gas attachment below states 1/2” pipe for runs under 10 ft can support 172kBTU. My 1/2” run would be 2” and more like a orifice. See sizing chart below. My pool heater orifice size is 5/32” inch. Just wondering if anybody ever did this before with success.

  • dandhb
    dandhb Member Posts: 9
    3/4” pipe is safe up to 50 ft not 100 ft as I incorrectly said above for a 150 kBTU pool heater. My plan is to run 1” (With the exception of 2” run at a 1” x 1” x 1/2” tee of 1/2” pipe in middle of run) and my total distance is 50 ft max so I’m positive that 1” pipe for that run is totally adequate. My only question is the 2” section of 1/2” pipe.
  • pecmsg
    pecmsg Member Posts: 4,704
    edited April 2020
    dandhb said:

    3/4” pipe is safe up to 50 ft not 100 ft as I incorrectly said above for a 150 kBTU pool heater. My plan is to run 1” (With the exception of 2” run at a 1” x 1” x 1/2” tee of 1/2” pipe in middle of run) and my total distance is 50 ft max so I’m positive that 1” pipe for that run is totally adequate. My only question is the 2” section of 1/2” pipe.

    Please...………………... call a contractor that knows, your guessing!

    How big is this pool? 150K is good for MAYBE 15,000 Gallons, That's a small pool!
    HVACNUT Member Posts: 5,761
    How many BTU per square foot does the sun provide?

    Kiddie pool?
    Indoor pool?
  • dandhb
    dandhb Member Posts: 9
    Just wanted to let you guys know that I’ve done all the calculations. I’ve got a masters degree in mechanical engineering and have taken numerous courses in fluid mechanics and thermodynamics although it’s been 37 years. I have a PE license (Professional Engineer). My pool is 20,000 gal and calculated that a 150 kBTU heater will produce 125 kBTU with the reported 83.5% efficiency. I always use a solar cover. This heat generation calculation that I made and pipe sizing requirement were calculated by me and verified by the engineers at Hayward products which produces swimming pool products. The heater will raise water temperature from 60 deg to 80 deg in 26.4 hours. The heater is fine for my needs. However my question is has anybody in this group have experience with small pipe lengths and it’s overall affect on gas flow performance. Based on my study, a 2” length of 1/2” pipe should easily be able to support greater than 172 cubic feet per hour of natural gas flow. Not something commonly done but just asking.
  • dandhb
    dandhb Member Posts: 9
    HVACNUT. Actually I use a solar cover religiously and calculated that for a 20,000 gal pool i get a 2.5 deg F temp increase on an 80-83 deg F average/day so it takes 416.6 kBTU input to give me that temperature rise. So if I assume I get 7 hours of sun, the solar cover provides nearly 60 kBTU/hour while it’s sunny out. In the summer with the solar cover on a pool heater is not needed in Detroit, Mi area. My wife just wants pool hotter faster in early season.
  • Brewbeer
    Brewbeer Member Posts: 616
    Most of the crew here would probably replace that 2 inch section that you are wondering about with larger pipe. But others, perhaps you included, would make it so, turn it on, and measure the pressure drop across the restriction to see if it falls within specifications. If that's the case, let us know the results !
    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
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  • Zman
    Zman Member Posts: 7,552
    I would suggest plugging the individual sections into this calculator to verify that the overall pressure drops are less than the 0.5" required by code. My guess is that it will be a non-issue.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • dandhb
    dandhb Member Posts: 9
    Zman, I used the engineering calculator and determined that a 1/2” pipe at 3” flows at 758 CFH. Then I used 758 CFH and calculated the equivalent length for 1” pipe and it was 5.2 feet. I also have to reduce pipe to 3/4” at heater valve so I calculated for a 2 foot length of 3/4” pipe gives me a flow of 666 CFH. I then calculated the equivalent pipe for 1” at 666 CFH is 6.74 feet. I then did the following calculations for equivalent pipe length:

    48 ft of straight pipe. 48’
    9 - .90 deg threaded elbows 2.7 X 9 24.3’
    3” length of 1/2” pipe. 6’
    2 ft of 3/4” pipe 7’
    2 1” threaded tees straight thru 2 x 2. 4’
    2 1” gas ball valves 0.262‘/valve. 0.53’
    Total equivalent feet. 90’

    Getting L/D data on ball valves was tricky. One brochure said it was 3 and then for a gate valve the L/d said 100. If I use the gate valve data I calculate an equivalent foot of 1” pipe is 8.74’/valve. So total would be 17.5 feet. Therefore my equivalent pipe could be 107 feet.

    Next I calculated my CFH for 90 feet and 107 feet and determined I should be fine.

    90 feet of 1” pipe = 182 CFH
    107 feet of 1” pipe = 167 CFH

    Based on these calculations I think I’m good. Ironically Hayward installation manual says you can run 4/4” pipe for runs 0-100 feet. I calculated that it would only give 133 CFH. I definitely think that is insufficient for a 150 kBTU heater.

    Does anybody disagree with my analysis? Thank you so much for your thoughts and support.
  • dandhb
    dandhb Member Posts: 9
    Correction pipe in Hayward installation manual said 3/4” not 4/4” for a 0-100 equivalent foot of pipe. Lol
    JUGHNE Member Posts: 11,021
    Are you retired? ;)

    Please let us know the delivered pressure to the heater and then the amount of drop with all gas appliances turned on.
    I and probably many others here have come across this existing bottleneck that would be a PIA to upsize.

    Your heater sounded undersized to us because we may have only seen muni pools and such.
  • dandhb
    dandhb Member Posts: 9
    JUGHNE yes I’m a retired Automatic transmission engineer that worked for Chrysler. It’s been long time since I studied these type of issues so I was a little rusty but it’s coming back. The pool heater may be undersized for some people that don’t use a solar cover but is adequate for our usage. According to my gas company if I went to a 200 kBTU heater or higher I’d have to install a 400 CFH meter and would have to move my electrical and water service inlets into my house. That’s too much screwing around and costly for what I want. I’m upgrading to a 250 CFH meter and the gas company is ok with it per my gas equipment requirements.
    HVACNUT Member Posts: 5,761
    They can't relocate the gas meter instead?
  • dandhb
    dandhb Member Posts: 9
    They would have to trench along my house and wipe out my electrical service lines, water lines, sprinkler system. It would be a huge mess since I’ve owned the house for 25 yrs and everything is established. All service into house is within 10 feet and the gas meter is at the front of house on the side of house. Pool equipment is 38 ft away In back of house from meter.