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

500,000 btu commercial boiler

MaineTemp Member Posts: 2
edited September 2018 in Gas Heating
Hi. I have a coworker that has a very nice, but large 500K btu commercial boiler available for a hard to ignore price. It's a fully modulating gas condensing boiler which goes down to 20% (100,000btu) of full fire. My house is fairly well insulated, about 3500sqf. The existing oil burner is junk and hobbling along for now. Current boiler is about 150,000btu, oil. Clearly this setup is too much boiler for any plumber or person to purchase for my home, but is it workable without short cycling and eventually killing it? It's like a 10K boiler new, and I can get it for about 1K. It's roughly 6 years old at this point, but still in excellent shape (LAARS NTH500). It's currently setup for NG, but I'll need to convert to LP. Pretty sure it's just a valve swap, like most, but need to research that more.

I couldn't find an efficiency curve to see how efficient condensing boilers are at various levels of firing. If anybody has a guess on that I'd like to know their thoughts. Does the nearly 95% efficiency level only kick-in at say 50% of capacity, or is it across the entire burn range? So if I run it regularly at only 25% capacity, will I be doing myself a disservice and be only achieving 80% or so.


Mid-Maine location


    EBEBRATT-Ed Member Posts: 15,346
    I wouldn't. Do a load calculation. Your existing 150K boiler is likely way oversized. The 500k boiler will short cycle like crazy especially in the spring and fall. No energy savings. Plus your piping and pumps would have to be sized for 500k. Not gonna work very well
    PhilJaydelta T
  • Fred
    Fred Member Posts: 8,542
    Did you ask him why he's taking it out?
  • MaineTemp
    MaineTemp Member Posts: 2
    edited September 2018
    EB, Yeah figured. Was just hoping it would be workable on the lowest possible setting. Thanks.

    Fred, They reconfigured the new design with mini-splits, and modified a bunch of walls in this old place and it wasn't worth redoing all the interior plumping. I'm just hoping the mini-splits work during the subzero weeks. I gave my input which is all I can do.

    I used to have an account here, but my computer died and I lost the username a couple years ago. Not a problem starting over.
  • bob eck
    bob eck Member Posts: 930
    Trying to save money upfront and doing it wrong will cost you more money when correcting your mistakes then spending good money and doing the job right the first time.
    delta T