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.
Thanks
Mid-Maine location
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