OWB effiency vs rated output

[midcoast]

hello all
I'm new here and would love to hear what others have to say about the more efficient OWB. The new rated boilers are rated at a certain BTU output. If the homeowner can't mete the output load, the fire dampens down.

Most houses use a zone here and there and don't need designed heat loss except for a few days a year.

If the OWB isn't using all the heat that the rating implies, does the efficiency drop down due to the smoldering fire? Do these units need to deliver the rated output to maintain high efficiency?

 

[Hanko]

I think there is a boiler section on this web site. It might be more helpfull than this forum. Good luck

 

[Nofossil]

In general, woodburning appliances are most efficient at full throttle burn. Idling is much less efficient, and the lost energy goes up the chimney as unburned hydrocarbons. You didn't mention a specific model, but I suspect this is true of all OWBs. Some boilers use a more sophisticated approach to combustion called gasification. These boilers will use about 40% less wood to generate the same amount of heat. However, they're essentially no more efficient than anything else when they're idling.

You're right that most installations can't absorb the full output of their boilers. There is a general tendency to oversize, and this seems to be especially true for OWBs. In most cases, I think you want the smallest boiler that's big enough to keep you warm on the coldest day.

If you can see or smell smoke, you're losing efficiency.