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[muncybob]

Looking at various sites I see quotes for certain size boilers based on square footage. Does the measured square footage take into account ceiling height? Exaclty how do I determine how many btu I need for my living areas? Is there info perhaps on my oil boiler that will be useful?

[RX7145]

It's hard to say. The BTU of a unit does not have anything to do with how large a house/shop it could heat. My CB 4436 is rated at 250K BTU but it could not heat a 5K sqft house. Well it might but woould need wood added every four hours. How many sqfeet are you wanting to heat? What units are you looking at?

[muncybob]

Have not really started looking "seriously" at any one unit, but it sems I need to know what my btu needs are to match up against the proper unit? We have apprx. 1700 sq ft of living area and around 30% of it is newly constructed that is very well insulated. The only mention on my present oil boiler of anything btu shows Water MBTU 125.2/hr.  Not sure what that means but this boiler provides plenty of heat and hot water for our needs.

[mtfallsmikey]

Do a complete heat loss for your house. Slant Fin (www.slantfin.com) and other sites have software to do this with...check also on heatinghelp.com.... a word to the wise: NEVER let an OWB dealer sell you a boiler based on how many S.F. you have. Too many variables. And keep in mind also that a OWB does not have a constant BTU output, nor does any other woodburning appliance.

[ugenetoo]

Have not really started looking "seriously" at any one unit, but it sems I need to know what my btu needs are to match up against the proper unit? We have apprx. 1700 sq ft of living area and around 30% of it is newly constructed that is very well insulated. The only mention on my present oil boiler of anything btu shows Water MBTU 125.2/hr.  Not sure what that means but this boiler provides plenty of heat and hot water for our needs.

not sure but i think your boiler is 125200 btu. if it runs at 92% efficency, that would be 125200 X.92 = 115184btu output.
OUTPUT efficiancy for owbs vary widely depending upon wood moisture content, heat loss from the shell and piping, how well the boiler transfers heat from the fire to the water and how long the fire idles (smokes) without calling for heat.
some say as low as 30% for a poorly designed and poorly operated boiler.
add to that the many different opinions of the people youre going to talk to and as far as i can see, its a crap shoot!
check out these guys; http://www.hearth.com/econtent/index.php/forums/
they tend to lean toward the new gasifiers with storage but there are some really good boiler people there that will help you

steve

[userdk]

Looking at various sites I see quotes for certain size boilers based on square footage. Does the measured square footage take into account ceiling height? Exaclty how do I determine how many btu I need for my living areas? Is there info perhaps on my oil boiler that will be useful?

As far as I know, It is simply averages. Average winter. Average house insulation. etc

[slimjim]

As far as Hearth.com, I find they are quite anti outdoor wood boiler and I don't waste my time with them.
 The best and most accurate way I know of to determine load on an old building is to look at your history for your building, How much do you consume with your current setup, don't go by the size of your oil boiler as they may have sized it improperly to begin with.  Do you know what size nozzle is in your oil boiler and what the oil pressure is when it is running?

[userdk]

 

[Steinacher Sales]

Muncybob,

What part of the country are you from. I use a rule of thumb of 50 btu's per sq. ft. here in Illinois. You could use 55 for colder areas and 45 for not so cold areas. Of course there are a lot of variables and this gives you a place to start. Need to know how well your home is insulated, where you live, and is your wood dry or not etc.

Greg Steinacher
618-401-0726
www.midwestoutdoorfurnace.com 

[mlappin]

Um, isn't that backwards? 55 Btu per square foot for cold area's and 45 per square foot for not so cold?

[Steinacher Sales]

mlappin,

Yes my mistake, Thanks! Old age I guess!

Greg Steinacher

[mlappin]

Rule of thumb here in Northern Indiana, if it's zero out your source of heat should run near constantly. Doesn't matter if its wood, nat gas, oil or Lp.

Too small and your going to freeze your but off if it runs constantly at 10 degrees.
'
Too large and it cycles constantly at the lower temps and it will rot itself out from never running long enough to get hot and burn any condensation out.

[userdk]

There's a formula for figuring the exact BTU's you need. It figures in the difference between the desired inside temperature and the minimum outside temperature.

Q=A x DeltaT x U

Q represents BTU loss per hour.
A represents the complete area on which you are figuring heat loss.
DeltaT is the difference between the desired inside temperature and the minimum outside temperature.
U represents 1 divided by the R-Value on the insulation job of the area you want to figure.

You have to figure each area of the wall separately. For example, the windows have a different R-Value than the Door, which has a different R-Value than the Wall, and etc. Remember to figure for the floor too. Almost all outdoor wood furnaces have a BTU rating.

[LittleJohn]

....I use a rule of thumb of 50 btu's per sq. ft. here in Illinois. You could use 55 for colder areas and 45 for not so cold areas. Of course there are a lot of variables and this gives you a place to start...

Please tell me you are running a fan coil or something like that!!! 
...because when my in-slab layout was designed, it was designed at 20 BTU/ft2, and I live in Minnesota

[Steinacher Sales]

Littlejohn,

What is a fan coil?

Greg Steinacher