I do not like to use the word cheap. We used to have birds in our store so when people asked what we had that was 'cheap' I could point to the birds :) People often ask what the "cheapest" way to heat their house will be. I know that they do not want a chintzy appliance to heat their home. There is too much risk there. But, we all like to save money where we can, and use the most affordable heat source available. In today's volatile markets that can be a challenge. Especially since there is no one size fits all answer. Fuel costs, and needs in Nevada will be far different from those living in Michigan.
So how do you know what is best for your house? There are a few things to look at. First, is how energy efficient your home is. If it is not well insulated, or has leaky windows and doors any heating system update, or change may produce minimal results. Second, see what fuels are available around you. If you live in the corn fields of Iowa a wood stove may not be for you. Third would be pricing.
Here is an example from Penn States College of Agricultural Sciences that provides a simple graph of differences. (see details at http://energy.cas.psu.edu/energyselector/default.html)
There have been a great many debates as to which calculators or comparisons are most accurate. Some assumptions have to be made to come up with any general formula. The assumptions generally surround the appliance efficiencies. Since very few people have access to a testing lab in their home, an accurate determination is virtually impossible. You can rely on the manufacturer's but keep in mind the regulations, testing labs, variances in fuel, and procedures, for each manufacturer can be vastly different. There are many who will go a step further and argue about the true btu content of one fuel. As a test performed with sample a in Tacoma may produce a different result as sample b in Philadelphia.
I would say a little common sense in using the cost calculator's will help you a great deal. If you are arguing one fuel over another you may use extreme's, but if you are trying to determine what is best for your home be as realistic as you can.
Here are a few calculators I know of. If you have other resources please forward them and I will include them.
Pellet Fuels Institute
Hearth Products Association
Woodpelletinfo.com
Warmair.com
