Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

Replacing a1958 270,000 BTU boiler

RandolphoRandolpho Member Posts: 6
Need some advise from others. I've had 3 HVAC estimates and all have different ideas. I have a monoflow system throughout my tri-level home from 1958. Still has original boiler. There is only one zone/ pump (variable speed/manual only). The system has 1.25" supply that goes all the way around the house. The house is right about 2100 sq ft, well built, all new quality windows. One of the company's based their sizing estimate solely on the size of the existing 1.25" pipe. They estimated about 104,000 BTUs. I read a little about how pipe size works with GPM/BTUs/Delta-T, yada yada, but I'm a total layman about heating systems and am not sure about making a call based solely on pipe size? I do have an addition that was added to the system some time in the past and those 2 rooms do not heat well. The gentleman who based all on the 1.25" saw that the T-diverter that is feeding the addition was just a , normal T. So that was a plus for him, the other two missed that. The other 2 estimates both suggested 122,000'ish for the new boiler. These 2 both took size of the house into consideration, one measured base board fin footage and the other, based on his 4 + decades of experience came up with the same number base on approximate house size. Originally I also was looking at adding a zone for the addition mentioned early, it's a master suite, but perhaps just putting a diverter-T there instead of the normal T would fix that issue? Please give me any feedback you can on this. I will provide more numbers if someone needs them. Thanks


  • JUGHNEJUGHNE Member Posts: 7,203
    Did anyone look at your chimney? What worked before may not pass the code today. Might need a liner$$$
    How do you heat your domestic water now?
    Is it practical to run a separate set of pipes for the added zone/addition?
  • HVACNUTHVACNUT Member Posts: 3,516
    None of the above. I'd be surprised if you needed more than 70K. Someone has to do an actual heat loss calculation. You can certainly cut and cap the Tee's to the master bedroom (as long as they're definitely not monoflo Tee's) and make it it's own zone piped back to the boiler. If you can't get a thermostat wire where you need it, there are wireless thermostats.
    Those are the same contractors who, bidding A/C jobs, stand in the road and hold their hand up to the house to determine what size system is needed. 3 fingers = 3 ton. 4, 4 ton etc.
    Find new contractors or click "find a contractor in your area" at the top of the page.
  • RandolphoRandolpho Member Posts: 6
    edited March 2018
    JUGHNE, they did not look to closely at the chimney beside seeing that it was an outside chimney, to existing old fireplace now with gas insert. I heat domestic water with a NG heater, exhaust goes to furnace flu then all together into chimney. It would be easy enough to run a set of pipes to the addition the way they tie in come off the main mono-flow line is right in the basement room with the boiler.
  • RandolphoRandolpho Member Posts: 6
    Thanks HVACNUT, got a chuckle with the finger method. The wiring for a thermostat won't be a problem the addition has a crawlspace and there is an opening into the boiler room. I actually have another contractor coming over Tuesday. I will ask them to do a heat loss calculation.
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 7,316

    The ONLY way to size the boiler correctly is to do a heat loss of the house. None of your contractors have done that.

    Don't give the job to anyone until you find the right contractor

    Have you tride "find a contractor" on this site. Where are you located??
    RandolphoErin Holohan Haskell
  • RandolphoRandolpho Member Posts: 6
    I found a Heat Loss Calculator on line. It seems pretty straight forward. Would there be a reason I could not do one myself? Something I wouldn't know about determining the sq/cu footage of door/windows/walls/ceilings etc?
  • BrewbeerBrewbeer Member Posts: 611
    You can do your own heat loss calc. You can use one of the on-line calculators, or you can do it yourself using a spreadsheet.

    Sometimes it is also possible to use a method where you look at gas consumption over a given period of time and compare that to heating conditions recorded at a near-by location.
    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:
    System Photo:
  • Peter_26Peter_26 Member Posts: 63
    I don't think you should suggest or ask the contractor for a heatloss to be performed. Any contractor that does not perform a heatloss in the time he is at your home should not be considered for the job. Take the suggestion of the experts here and click on the "find a contractor" if you want it done right the first time!
  • RandolphoRandolpho Member Posts: 6
    I just tried 'FIND A CONTRACTOR' no one listed within 100 miles of my zip code.
  • RandolphoRandolpho Member Posts: 6
    @ Peter. That is good advise and I will follow it. I've led contractors by the hand before thinking I would get the result I wanted and sure'nuf, that did not work out so well.
  • BrewbeerBrewbeer Member Posts: 611
    A good heat loss estimate will take several hours to perform properly, it's not reasonable to expect a respectable contractor to do the heat loss calculation for free. It should either be priced into the job (and performed once under contract), or be paid for and performed independently.
    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:
    System Photo:
  • try2hardtry2hard Member Posts: 26
    It's so shocking how many contractors are stillnot explaining the importance of heat loss calcs. I agree I wouldn't offer them free unless under contract but it's one of the first topics I would discuss with a customer.
Sign In or Register to comment.


It looks like you're new here. If you want to get involved, click one of these buttons!