needing information on pressurized wood boilers

My wood doctor is the second to the largest one they make, supposed to be at or near 490,000 btu's, now that said, I'm not thinking it'll do anywhere near that much on its best day, with ideal wood and conditions, factor in lousy, wet, snow covered, and the worst conditions possible, maybe on its best day, half of that, when we run the numbers of the buildings and house, compare that to lp gas of before, factor in a frigid winter and the heat rise we needed this winter, I"m not thinking myself, we had even 250,000 btu's being produced, far more used and needed and no time to gain back any heat lost, add in heat loss of various sorts, and now I'm wonder just how big is big enough for the future?

The more I look at it, I don't think there's any way I'll ever get by with one boiler, as for the furnace in house number two, its two years newer than the one in mine, we figured it would have died a couple years ago, and the whole idea of heating outside the house in the first place, was so I didn't have to replace that furnace with a new one, not sure it's going to be considered a backup even on a good day.

I've been on the phone today with several chip boiler makers, some are interesting to me, others maybe not, I'll have to give it some serious thought on going that route, we've had some discussion on my end and maybe its not ideal, but a chip boiler running almost 24/7 fall till spring, heating storage, and a second larger firewood boiler to kick in with colder temps, have it plumbed to kick it online as needed and shut it off when not. I'm not liking the cost end of things, but after doing some math on the possible what if scenario of costs at lp gas, in a few years of heating costs, maybe its not so bad.

As for the discussion, keep it coming, the more we discuss the more I learn, and learning is never a bad thing, and its sure cheaper than learning by doing, so again thanks people.

First off, what's HDD?? Next the shop is 80 feet long with a 20 foot ceiling, the walls in it are irregular in shape, as compared to the outside walls and range from 10 inches at the least of blow in fiberglass to over two feet in places, we looked at spray foaming it, but while doing the remodel, we gave up trying to figure out to make it work, its a long complicated story as to how we had to go about the process, so in the end we blew fiberglass into the cavity once the whole job was done.

Your right about air movement through fiberglass though, we salvaged used tin for the inside liner of the shop and later found out that even though it looked pretty good, there were excess holes in the tin from the last building it was nailed to, that when the wind blew over 50mph, if you held tissue paper up next to some of the holes, you could see slight movement some of the time, never gave that a thought when we decided to use the tin. I can't argue at all with the insulation in the cement block, I might even add some more to that and say it plain sucks and totally worthless, but I didn't do any of that, it was done decades before my time and now we're deciding the best way to go about to solve that problem, which looks like it'll new studs and tin on the outside of the office.

I'll never argue with spray foam being better at insulating on an inch by inch comparison to fiberglass, but the downside of spray foaming is, if you ever want to change or remodel the structure, you now have a mess to contend with and its almost impossible to scrap or peel it off, yes it can be done, but not near as easy as stripping fiberglass bat's out of walls and around electric wires and having studs and things still usable.

So what's the figure then if its 40-60 below outside and the spouse likes it 75-78 inside months on end then with little if any let up in the weather, much like this winter, keeping in mind, the warmest room in the house has the thermostat in it?? Then calculate that same outside temp for the shop, and we're trying to warm it to 60 inside the shop, near 70 in the office, again months on end and next do you consider wind chill factors, or basic air temps into your equation? I've been told its just air temps, and if that's the case, you'd better lower that to your 20 below outside temp.

Boil and Toil, I've got to reread this several times, and get some help to "think" through this some more, but thanks for putting it plainly so I can understand it. Some variables in the equation, the door on the shop is insulated, we put five and half inches of fiberglass bats to fill the four inch gap, mainly so it filled the ridges in the tin, and even though we had it separated in five foot tall increments, we wanted them to hold in place, and hopefully not settle over time. There are two double pained windows in the door, small basement windows so we could look out to see if anything was in front of the door before someone opened it, not my idea, but I kept the better half happy with two windows. Only one other window in the whole shop, haven't insulated over it yet because we might install a waste oil burner and use the window for a chimney pipe to go through, its about 2 foot square and single pain, as for the new gas filled one's, I laughed when I read your comment, I agree totally, also seen the double pain windows on a new house leak and get moisture in them and on a frigid night, freeze and break the glass, on all the windows on one side of the house, I'm also told the warranty didn't cover it, imagine that.

The lp gas estimate was done long before my wife moved into the house, back then 68 was considered a great temp and sometimes cooler at night, I'd have no idea what it would take to heat with lp gas this winter to the upper 70's, a total guess on my part, but somewhere over 2000 gallons at a minimum I'd think.

No vapor barrier in the shop anywhere, wouldn't have done any good anyhow, between nails off the old roof, and all the construction we did to get the remodel done, there were nails and screws everywhere and other than make one feel good to do the vapor barrier, it would be as hole-y as the tin or worse. The old concrete block wall runs up about 10 feet up on the side walls, and no matter what anyone would do concrete is porous and cement blocks are worse in my opinion, looking back I should have had someone spray foam a portion of the walls on the inside before we were done but then thinking, there's no way to have sealed all the cement block up anyhow, we might have eliminated a portion of the blocks, but never them all. I'll have to ask again if anyone here wants to do the caulk gun idea, it didn't go over big when I asked the last time though, the reply I probably can't print here if that tells you anything.

Two walk doors to the building, with only two inches of insulation in them, the rest we put 10 inches of fiberglass bats over for the winter and osb'd them up on the inside.

Something most don't even think of, and I totally forgot to mention, we have fans in the shop, and when we're welding or running diesel engines, we turn the air over and vent the smoke, how often, depends on what we're doing, maybe run the fans a total of a couple hours a week, and no I can't tell you the cfm's of the fans, standard old barn fans, we only run one, also do this if we're changing machines and going in and out with equipment, guess you could call it a hazard of the trade.

Next question asked a while back and I forgot to answer, firewood is free, but not to cut it down, work it up, and bring it home and prepare it to go into the furnace. How much we burned, or usually burn, a total guess on my part, but we figured in the area of 20-30 cords of firewood per year, but that's a guess at best, we pile it up as we cut and split it, shove it up with skid steers and have piles all over the place and in one shed, can't even begin to guess how many semi loads of logs we've used this year, we're always adding and using off the piles as winter goes along. When we used to live on another place, we did all the processing here and loaded it up and hauled it with a semi to the house we lived in, back then we burned 8-10 24 foot semi end dumps a year and I'd have to remeasure the trailer again to figure cords, its been too many years since I had that figure and I've lost it to CRS over time.

The sidewalls in the shop are not straight up, there is a knee brace towards the top, for two reasons, one to have a straight wall to tin and second, to use for strength for the roof and false rafter we installed, so the whole shop wall is 23 feet on both sides, for a 20 foot ceiling height, and the floor is sloped in the shop, so its a foot taller on one end than the other, not sure how to figure that in, other than 23.5 feet of sidewalls.

Boil and Toil, I'm not getting how you came up with your numbers, I looked on the web, and took some of the nearest airports to me for the HDD and came up with 12850 for the heating season, I added up the HDD for each month for the desired temp I wanted for the house, and added all the months we'd heat the house and came up with 12850, did the same thing for the shop and came up with 9083 for the heating season, haven't done the office yet, but is that right first off, and if so, how did you convert that into a number for btu's per hour, could my numbers be correct, I'm a lot further north than ames, but twice as many HDD days in a heating season??

Questions, I looked up on the web www.degreeday.net and they had this years data for airports that were current, and closer to me, now I scanned through this data and they had a base temp on there at 65 degree's, I took the month's I'd heat and added them up, then switched the 65 to a number of 77 for the house, which raised my HDD's up to the number I got before, might be different than how Boil and Toil did it, but I also assumed I'd used more than 2000 gallons of lp gas year too. The data that's been posted was from very mild winters, of 2006 or last winter, this had data from this winter and I took march, april and may from 2013 and came up with the larger number. If this is wrong, help to explain how it's wrong, this winter kicked my butt and I wanted something much more accurate than averages.

Next question is that's converted into btu's per hour considering the furnace runs nonstop, correct? So if it cycles on and off and you have people coming and going, etc, etc, and lets say for example wind does affect my house and shop, how many more btu's does it take to actually make the system work, a furnace 25%, 50% or twice as large as the btu's per hour, so its not struggling or running nonstop and never shuts off?

Last question for the morning, anyone want to venture a guess as the efficiency for the wood doctor owb I currently have now, seeing how I'm pretty sure its not 100% efficient and if it were 50% efficient or even less, I'd have to have that much larger of a boiler, correct? Isn't the figure in btu's per hour, actual output needed after efficiency is factored into the equation.

If the building would call for lets say for discussion sake, 100,000 btu's per hour and my furnace was 50% efficient, I'd actually need a boiler capable of putting out 200,000btu's per hour, not even considering the loss of efficiency in windows, insulation and etc. Or am I wrong on this?

I used the math formula provided and will try to show some figures and you tell me where I went wrong.

House number one, we took the figures of 7788 HDD days, and assuming it would have used far more than the average lp gas this year, we took 2000 gallons to use so 2000 gallons x's 91500 is 183,000,000 btu's of heat, then took 7788 x's 24 to get 186,912 and then 183,000,000 / 18,912 equals 979 btu's per hour, times temp differential of 120 [-40-80 for simple figures] equals 117,480 btu's per hour for the house alone. If I did it wrong let me know where.

Next is the shop and office, it got complicated due to some walls thicker than others, some odd shapes and given some estimates on sizes of shapes of the ceiling and walls. so bear with me.

The office is 17 foot square x 8 feet tall and cement block and in floor heat, or 17x8x100 degree heat rise x's 4 cement block walls of virtually no insulation or 54400 btu's per hour. The ceiling is 17x17 times 100 degree heat rise divided by R23 equals 1256 btu's and then the floor is heated and 17x17 x 60 degree's heat rise divided by 10 for the under floor insulation equals 1734 btu's of heat or a total of 57, 400 roughly for the office.

Next is the shop, which is complex for the odd shaped walls and such but I'll attempt to narrow it down somewhat, two partial walls are only insulated block, total square footage is 376 square feet times 100 degree's, [-40- plus 60] and no insulation virtually or 37600 btu's per hour, the walls remaining are 3560 x's 100 and then have an R30 equals 11867 btu's per hour,

The ceiling is 23x80 feet long, x's 100 degree heat rise, divided by R38 equals 6737 btu's

The door is roughly 32x20 x's 100 degree's divided by R19 equals 3369 btu's per hour.

The floor is 32x80x's 70 degree's heat rise divided by R10 for the foam board is 17920 btu's.

The remaining end wall is going to be roughly 12 x 28 times 100 divided by R23 equals 1461 btu's

The windows should be roughly 2'x 3' times three of them x's 100 and virtually no insulation is 1800 btu's

If I didn't forget something, did my math wrong, it should be about 80760 btu's for the shop alone, or the whole barn is 138160 btu's of heat per hour.

Someone can tell me where I screwed up on my figures, but to me it doesn't come out right, we have the infloor heat going in the shop, and we added the knipco diesel heater when it was that cold out, and it was rated at 170,000 btu's and we never shut it off the whole time we were in the shop, plus the in floor heat, and in the office we had just a simple electric ceramic heater and was toasty warm in the office at all times,along with the infloor heat, that heater couldn't be much its rated at 1250 watt however that translates into for btu's.