Boiler sizing question

[hemlock]

Hello again,
Sorry if this is a dumb question. I am trying to size up a boiler (pellet or electric) to replace my oil boiler. Currently, it is rated for 105,000 BTU minimum (210,000 max). Originally, the boiler also fired an indirect hot water tank, which I have replaced with a Marathon electric. The boiler is now only theoretically used for in floor radiant and hot water base board for a roughly 2000 sq ft house. How many BTU's should I subtract (if any) to account for the removal of the indirect fired hot water? Thanks.

 

[Como]

Was the oil boiler sized correctly?

 

[hemlock]

Was the oil boiler sized correctly?

As far as I know.

 

[btuser]

Gotta do a heat loss calculation. Its really the only way to know within reason, because the old boiler may have been installed when the house was smaller, had different windows, and different insulation. My original boiler was 164k for a 2600sqft home in a 7000 degree day area with a design temp of -9 degrees. Then over 1700 sqft was added to it without a change to the boiler. When I did my heat loss before replacing the boiler my calc came to 91k btu and I was like NO WAY THAT'S TOO SMALL. But I bit my lip and installed the correct size boiler. Even when its -10 outside the boiler doesn't come close to maxing out. With the wood stove going full bore it doesn't fire more than 1/4 of an hour. I'm not even done with my energy improvements either. I'm very confident it could handle my entire heat/hw load.

Build it Solar has a great heat loss calc that will get you within reason. Tougher choice is which fuel. If you've got natural gas I'd go with that.

 

[afblue]

+1 on the Build it solar heat loss calculator.

The average shower uses 10,000 BTUs. You can figure it as a high demand for a few mins, or spread the load out over the day, 5 showers = 50K BTU / 24 hrs = 2100 BTU per hr. It's really not much of a load considering the average heat home heat loss is in the 30-40K BTU/hr