So what about amortization or payback. The gas boilers seem expensive compared to say wood stoves where the payback time comparing BTU’s of fossils is fairly short--2-3 years for us.
I don't think we can answer payback without knowing install cost. I will run this down with an example in case others want to consider it. Got to be a thread which does it better but anyway here it goes.
The KISS (simple) formula is: Payback= Cost of Install divided by anticipated yearly savings. Yearly savings calculation could be= ( current method's yearly fuel costs + yearly maintenance + amortization + personal value on time spent + bad feeling value) less (proposed method's yearly fuel costs + yearly maintenance + amortization+ personal value on time spent - feel good value). A little humor there in the yearly savings calcs, but you can make it simple and say yearly savings is the difference between the fuel costs and amortization costs.
www.eia.doe.gov/neic/experts/heatcalc.xls
The US DOE site has a nice spreadsheet which you can plug in different fuel costs and efficiencies. One of the columns calculates out the cost per Million BTUs after efficiencies. If you are really trying to do an analysis, you should come up with an estimate of BTUs your house needs to stay warm over a heating season. You said 3 cords so far, so you or your math buddy
can figure that out.
I think I got a handle on it by going to degreedays.net and figuring out the number of Heating Degree days for a 45 day period of time, how much wood I used in that period (in full cords). You know the time you started burning your 3 cords. I estimated 22 million BTUs per cord for me (White Ash, Maple and Birch mix). The math told me how many parts of a cord for a HDD or more importantly in this case, how many BTUs I used per HDD (11,000). Then I downloaded 3 years of daily HDDs from degreeday.net and figured out number of HDD in my "average" heating season. In my case my season has 8,000 HDDs time 11,000 BTUs each which equals 88 million BTUs.
Thus crudely speaking, here costs for a hypothetical Solo40. US DOE says at $200 a cord, my cost of delivered BTUs are $11 per million times 88 or $968. Lets say I amortize this system at $1,000 per year and allow $200 for maintenance/sweeping. I am going to ignore all other costs like electricity to run pumps and the fan. Total yearly is $2168.
In this example I have an existing propane hot water boiler. DOE says that at $2.63 (was 3.23 in May) per gallon with my Burnham unit, my BTU cost is $37 per million or $3256. While cheaper to buy up front, it will not last as long and it will need yearly inspection and replacement of parts over its life. Figure $1000 amortization and a $200 yearly budget for Maintenance. Total yearly cost is $4,456.
The payback= Install/difference in yearly costs. Or $10,000 for a Solo40 install divided by $2,288 ($4456-2168) which is
4.37 years payback Hypothetically speaking of course.
Obviously your numbers will be different. Frankly, if you are happy with your wood stoves, the numbers are going to favor the status quo. Unless of course you want to figure in the resale value of your house, perhaps a change in insurance or some mainie-ack (sic) government regulation that adds costs down the road.
Then, our DHW is a tankless propane Rinnai which can be $$$.
Guess that is 82% effic. So the handy US DOE heat calc says at propane at $2.63 a gal is $35.12 per mil BTUs. So how much hot water do you use, what do you need to heat it up from? Say 100 gals of HW per day, adding 55 degrees of heat per gallon, that is about 17 mil BTUs per year. 17 times $35 is about $600 per year. Figure 2/3 of BTUs will be supplied by the Solo40 above, you will save $272 per year in fuel. I bet the tankless has a much higher yearly maint and amort cost than the Solo40 Hot water.
What maintenance costs are there for the gas boilers and associated tanks, pumps and plumbing ?
First blush, more than a woodstove
But creosote in chimney might even that out.
Are they finicky except for wood moisture
No more finicky than your wood stoves, with all the little tricks you use and don't even think about. But it is true you can't cook on them in a pinch.
Sorry for the long post but you asked a lot of questions. Hope this helps.
