actual btu output

[muncybob]

I had an installer here yesterday and we both agreed that my oil boiler is not very efficient. We guess it's 60% at best.He stated that it is rated at 130,000 btu at output...if it's 60% then I'm actually getting 78,000 at best...is that math correct? With this in mind a replacement boiler should be in this ball park?

 

[BrownianHeatingTech]

I had an installer here yesterday and we both agreed that my oil boiler is not very efficient. We guess it's 60% at best.He stated that it is rated at 130,000 btu at output...if it's 60% then I'm actually getting 78,000 at best...is that math correct? With this in mind a replacement boiler should be in this ball park?

Don't just guess. How much fuel do you use during the heating season?

Joe

 

[muncybob]

Joe, we average 840 gallons oil/yr....heat and dhw

 

[BrownianHeatingTech]

Joe, we average 840 gallons oil/yr....heat and dhw

Based upon your oil usage, and the heating hours in central PA, you're looking at an actual usage of 60k or less.

Joe

 

[MrEd]

Joe, we average 840 gallons oil/yr....heat and dhw

Based upon your oil usage, and the heating hours in central PA, you're looking at an actual usage of 60k or less.

Joe

Whats the actual math that gives you 840gallons x ??? = 60K BTU


I used 2000 gallons in each of the past 5 years +/- 50 gallons, and went with a 200K boiler.

My guess is that I slightly oversized it, but with storage felt it would not be a problem - also, 90% of my wood is soft maples so BTU capacity will be less than something like oak.

 

[BrownianHeatingTech]

Whats the actual math that gives you 840gallons x ??? = 60K BTU

840 gallons x 140,000 btu/gallon x .65 (estimated system efficiency for a typical oil system) = 76,440,000 btus actually used by the house.

76,440,000 / 2500 (heating hours per season, for central PA) = 30,576 average btu/hr used

Peak is pretty much going to be double the average for nearly any real house. So peak would be 61,152 btu/hr. That includes making domestic hot water, so it's going to be high. This only works "properly" on hot air furnaces without an oil-fired water heater, since then you actually have a heat-only number of gallons.

It's not perfect, but it will be darn close in most cases. It certainly works as a "reality check" against your other numbers, just like figuring the btuh per square foot number, to see if it is realistic.

Joe

 

[muncybob]

Makes sense...just did the heat loss calculation with the Slant Fin software and it came to 68k. So...since I plan to use water storage(lp tank) it would make sense to "oversize" the wood boiler to say 100k?

 

[BrownianHeatingTech]

Makes sense...just did the heat loss calculation with the Slant Fin software and it came to 68k. So...since I plan to use water storage(lp tank) it would make sense to "oversize" the wood boiler to say 100k?

Yeah, the Slant/Fin software has a pretty hefty "safety factor" built in.

The size of the boiler will depend upon the size of tank. You would want to be at least at a 100k, but if you go with a larger tank, jumping to a 150k boiler would be beneficial, in order to reduce the time it takes to heat the tank.

Joe