Wood Stove Operation

[KBCraig]

Just a reminder, pellet/corn stoves do require electricity. If you want heat when the power is out, you best have a backup source. They don't require much, so a UPS and a generator will keep you going for weeks, but if your only source is the grid, you're SOL.

Kevin

[Dreepa]

It actually sound's pretty cool, to sit and read by a wood burning stove.

Yup
That is what we liked our first winter... Haven't had to fire the stove up yet this year.

[MaineShark]

How much wood?

Okay, for starters, it depends on the wood.  Each species has a different energy content.  Greenwood Furnace has a nice list on their website.  If you look at the different species, you'll note that they each contain a different number of BTU's per cord. (and, of course, no method of heat extraction is 100% efficient, so you won't get all those BTU's into your house)

BTU's are the common unit of energy in the US.  On BTU is the energy needed to raise one pound of water by one degree (Fahrenheit).  We measure power in BTU's per hour (ie, the amount of energy needed to raise one pound of water by one degree in one hour.  Of course, the actual value of a BTU is different at different temperatures, because the density of water changes relative to temperature (but they are all within a percent of each other).  In heating, we typically will use "MBh," which is "Mean BTU's per hour," and uses the average density of water.

Okay, so to figure out your needs, you would need to know how much heat you lose to the outdoors, and that would let you know how much you need to replace by burning some fuel.  Unfortunately, the best you can do is guess, because the amount of heat you lose varies depending on the weather (outdoor temperature, solar gain).

However, if you know how much oil you currently use, you can get a pretty good estimate.  Let's say that you typically use 500 gallons of oil per year for heating (just for a round number).  If you use oil for heat and hot water, subtract your oil usage for the six warm months from the oil usage in the six colder months to account for the amount used in making hot water, but not heat.  And let's say that you have a typical boiler which is around 55-65% fuel efficient (fuel efficiency is different from combustion efficiency, which is the number they give you when you have your boiler cleaned).  So let's call it 60% efficient.  Okay, so we've actually used the heat from 300 gallons of oil, and sent 200 gallons of oil up the chimney.

Well, oil has about 140,000 BTU's per gallon, so we've used 42 million BTU's of heat.  Now, our woodstove is not 100% efficient, either, so we need more than 42 million BTU's of wood.  Let's call our woodstove 50% efficient.  So we actually need 84 million BTU's of wood.

So let's compare it to that fancy table from the beginning.  If you were burning hickory, that's about 3 cords.  If you were burning pine, you might be using almost 6 cords.

Make sense?

Joe