Outdoor Wood Boiler- sizing question

[Looking4ewes]

Greetings,

We just put a deposit on an OWB and we are now reconsidering which size would be most appropriate. We will be heating a 1300sq ft house with w/o basement, hot water, and a 500 gallon hot tub. Eventually, we will add on a 3 car garage. The unit we are buying is sized for 5000 sq ft. The next size up is rated for 10,000 sq ft. There is a $2M price difference between the two sizes.

Any advice would be appreciated.

[just_sawing]

I over sized mine since wood is better than free I have to get rid of it. I now believe that the reason people complain about the lack of efficiency is that fact. I would not over size unless I was SURE that I was going to expand.
People complain about the smoke issue and they are correct but I feel the over sizing is the culprit more than anything else.
Question for the forum has anyone undersized and couldn't heat there home?

[Ross]

Ours is an Empyre 450 it will heat the 5000 sq feet it is supposed to (3 zones or buildings) When we installed it and got it heatign the first building @1100 sq ft (I can't remember the exact amount of wood) but say it burned X amount of wood. Adding the second didn't change the amount of wood we burned. Adding the third building did probably by 50% max. The other Empyre 250 we use to heat 1500 sqft is a bit taxed at times to do so but it does. It burns less than half the wood the other does. I suspect its the house's antique duct work rather than the boiler's fault for any deficiencies. Don't over size unless you plan to expand close to the boiler's design or have free wood. Measuring heating capacity by square feet is nonsense anyhow but so is once a day loading, so be reasonable. If you have a leaky old farm house you need more capacity than a well insulated and sealed modern house. None of our buildings are perfect by any means.

[Looking4ewes]

Thanks, Ross, I was hoping you would respond. The house is a sieve now but we are installing new insulation, doors, windows, and siding. We like to heat the house to 65 deg F and the outbuilding isn't built yet. Since the new building will be for storage only, the heating requirements will be less. We have 45 acres of woods and could burn downed trees for years. We are buying a Heatmor 200, though the DH likes the larger firebox of the 400 model.

[salmonslayer]

Originally Posted by Looking4ewes

Thanks, Ross, I was hoping you would respond. The house is a sieve now but we are installing new insulation, doors, windows, and siding. We like to heat the house to 65 deg F and the outbuilding isn't built yet. Since the new building will be for storage only, the heating requirements will be less. We have 45 acres of woods and could burn downed trees for years. We are buying a Heatmor 200, though the DH likes the larger firebox of the 400 model.

We have the Heatmor 200 that came with our house and it kept us nice and warm this past winter. We use it to heat our71 year old 1500 sq foot stone farmhouse and a greenhouse and the thrid zone is currently not used.

We went through about 6.5 cords of wood but we like to keep our house at about 72º and much of our wood wasnt well seasoned. I do wish the fire box opening was a little bigger as I have a bad back and cut my wood just a little too big so it was physically challenging to load the stove at times but that was my own fault.

We put new Argon gas filled double paned thermal-E windows and insullated steel doors on the house along with new siding on the back half that wasnt stone and it made a huge difference in keeping out drafts and keeping warm even though our attic insullation looks like someone just threw a couple of handfulls of laundry lint up there and called it good. I can also confirm that sealing up your duct work with mastic and then insullating them will have a significant impact. Our stove doesnt smoke much but I can see where that would be a problem if you had close neighbors (thankfully we cant see pr hear any neighbors).

One other thing to consider, our wood shed protects the stove from the north wind but I will be expanding it to cover more of the stove and particularly over the fire box opening. Overall we were very pleased with how it functioned. Our neighbors have a smaller place and heat with propane and their heating bill ran about $400.00 per month not including electricity while our wood is free and our electricity bill averaged about $60 - $70 a month. We shut it down about 2 weeks ago and switched to propane..we are still staying warm but the heat coming out of the register and the hot water isnt nearly as hot or warm as that provided by the OWB, you do get spoiled.

[agmantoo]

Looking4ewes
Have you read the reviews and comparisons on the internet of the Heatmor 200? Seems there is a lot of complaints, particularly about the inefficiency and parts failure.

[Looking4ewes]

Agman, I've read so much I've made my head spin. I choose the Heatmor because of the 409 SS and it's simplicity over other models. Also local dealer support that his been in business over 17 yrs. The Empire dealer, which is over 150 miles away, is on his 3rd brand. I do not like the Central B for several reasons. And the DH, who does all the wood work, has no patience for the cutting, splitting, stacking, and aging required for the gasification units. We've used indoor fireplace inserts for the past three years, and the dirt, smoke, and fire worries are hard to overcome. Lastly, I know of two neighbors who have been operating the Heatmors for 15 + years w/o issues.

Btw, our quote for geothermal was 20 grand, which, after rebates, is on par with the Heatmor plus an AC unit. But the complexity of the unit paired with the limitations of not being able to heat an outbuilding and hottub turned us away from that option. Plus we have all this wood lying around. Feeding the stove is no biggie as we have dogs and dairy animals and have daily obligations on the farm.

[suitcase_sally]

Many places are starting to regulate these due to the smoke issues. I have three neighbors across the road that are all using wood burners and it looks like the woods are on fire most of the time. The only reason I haven't complained is that I am on the west side of the road and the wind keeps the smoke away. I feel sorry for the people that live on the east side of them, especially if they have respiratory issues.

[Ross]

I gotta say unless some green wood or wet wood gets into the boilers smoke is only a rare issue. But it was when I had an indoor wood furnace too. Heck my oil fired water heater occasionally dumps exhaust down where we can smell it.

[MNBobcat]

There is virtually no difference in efficiency between the smaller and larger boiler. You will go through the same amount of wood.

The difference between the two sizes is how long you can go between refilling the boiler with wood. A small boiler means you have to refill it more often. Whereas with a larger boiler, since it holds more wood, you can go longer between refills. Ideally, you want the option of refilling no more often than every 12 hours.

Its a misnomer for a boiler company to say this size boiler heats this size house. We have a 7,000 square foot house. Our forced air furnace is about the same size as what we had in our 2,400 square foot house. This house is better insulated and pretty easy to heat -- all things considered.

With a boiler, the more BTUs you draw off of it, the more often the damper on the boiler opens and the more wood you go through.

One foolish thing I've often heard...is skimping on the pex tubing that runs between the house and the boiler. A fair number of people seem to skimp and then complain about how much wood they burn...at the same time saying the snow melts on the ground where their pex tubing runs. If the snow is melting, that means your heat from the boiler is going into the ground. That's not good.

I ran thermopex (central boiler product) and I lose about 3 degrees between the boiler and the house (250 foot run). I also installed Grundfos pumps rather than Taco pumps. Grundfos pumps are adjustable with 3 speeds. Allowed me to tune the rate of flow for best efficiency.

I can understand your being concerned about the size of the boiler. The whole thing (pumps, tubing, etc) function as a complete system. Its important to think about every component when you go to install it.

It might ease your mind to find out from other people with the same boiler how frequently they fill it. If everyone is saying 12 hours...you're probably good to go with the size you ordered.

[Ross]

The idea boiler size is the only consideration is very wrong too. The instalation details supplied are often overly simplified and scant to say the least.

The instructions directed us to bury the insulated pipe 2 feet under ground. Thats crazy. Our frost line will sink 3-3.5 feet bedded in sand a foot under and 2 above, excavated to a dry/well sump 8 feet deep. The idea being water will wick away heat from the lines so get rid of the water! We used ecoflex lines to get the heat from the boiler to the house. Very pricey but sealed. I think it's only has an R factor of 5-7 so it's important to make the effort to keep it dry. I measure a delta T from boiler outlet to house inlet of 2 degrees. I'm happy with that. I know of some where the snow literally melts the snow above. When using an airhandler type system to set up the rad and air speed. You will find with measuring and adjusting water flow and air speed you can get a reliable delta T of 20 and return water to the boiler that won't apply any thermal shock to the unit. I want a temp rise of 70 degrees when the water is at 160f. 3 speed pumps are fine but you can throttle them with ball valves or globe valves too. Lots of ways to cheat that too. I have one zone set to pull 30 degrees off the water and about 18 off the other but before returning to the boiler it mixes. With the different GPM I'm fairly sure we're in that delta T of 20 on the return loop. Of course it depends on the use, so if one zone is off (not circulating air ) the delta T is much higher. I've screwed that up a bit by adding a side arm for hot water but so far it seems reasonably stable temp wise. I'm off to fix a poor instal where the in floor zones run constantly over heating the rooms they supply and chilling others by interfereing with the furnace /rad comb thermostat. Slapped together systems have ruined the reputation outdoor boilers could have had.

[tab]

Have a CB unit. About ten or eleven years of use. Smoke is rarely an issue and it is within ninety feet of the house. Absolutely use insulation around your ground pipes. We used the insulated pex and added rigid foam insulation around that at about 18 inches down. The water table can get pretty high and the manufacturer and dealer made recommendations we decided to follow. The temp in the house has actually been the same as it comes off the boiler. There is some melting of snow but after years of mostly year round use I do not think the depth would matter. I have found the greener the better for wood, less creasote and less smoke with the green wood. We have tried it both ways. I believe that can vary depending on brand and firebox design. We bought oversized with the idea of adding on. It may still happen but at this point wish we had not spent the extra money on the larger unit. Of course we have been making improvements on the drafty old barn, errr house that was not much better than a barn . Living in NNY, heating the house to 68 to 72, depending on whether dh turns temp up or I turn it down, hot water, lots and lots of of water, this past winter we spent about $1300.00 for logs and some cut wood. We still have enough wood to get us through the summer. The one thing I dislike about the CB is the ash removal. It is not pleasant digging ashes out when coals are hot. The rest of the set up is great. Now, because of the age and I believe the life expectancy is about twenty years, we have been looking at changing. May go with an indoor wood furnace as we now have a basement it could go in. Power outages would not be an issue. The EPA is looking at regulating the boilers. Rather than require them to have a certain efficiency to keep particulant matter down, it is going to time of use. We may not be able to use ours this summer as the regs are tightening.
This is some of our experience with ours, sorry to ramble. I remember reading about them until my head spun, too.

[Looking4ewes]

Okay, well, I'll get my husband to try and figure out what you're saying, Ross. ;-) I have no idea what a rad is,; Delta T - does that measure temperature change?

If one burns an over-sized unit, even though it burns the same amount of wood, wouldn't the quality of burn be different? I would think that a smaller unit would burn hotter, meaning less smoke. Please correct me if I am wrong.

The pex we a using is pricey, $11.50/ln ft., and it is being buried 3 ft. I believe that the dealer is using pea gravel or something underneath the pipe, but I will make sure

I have a question regarding the connection to the as yet un-built garage: the dealer suggested, if we could plan well enough, that we use a by-pass connection on the return line at the spot we want to come up into the garage and use an ungraded circ pump. Another dealer said that we should just run a separate line to the garage. We are about 6 months out on the garage build. Any opinions?

[English Oliver]

We ran our Pex 6" off the bottom of a three foot deep trench then had a foam company foam the bottom of the trench. The Pex, insulated and inside of a 4" pipe, is insulated with 6" of foam all around it and I put a foot of vermiculite on top of that before covering it up. If you allow creosote to build up in the firebox it will cut down on the efficiency of the stove and you will use a lot more wood.

"O"

[Ross]

Originally Posted by Looking4ewes

Okay, well, I'll get my husband to try and figure out what you're saying, Ross. ;-) I have no idea what a rad is,; Delta T - does that measure temperature change?

If one burns an over-sized unit, even though it burns the same amount of wood, wouldn't the quality of burn be different? I would think that a smaller unit would burn hotter, meaning less smoke. Please correct me if I am wrong.

The pex we a using is pricey, $11.50/ln ft., and it is being buried 3 ft. I believe that the dealer is using pea gravel or something underneath the pipe, but I will make sure

I have a question regarding the connection to the as yet un-built garage: the dealer suggested, if we could plan well enough, that we use a by-pass connection on the return line at the spot we want to come up into the garage and use an ungraded circ pump. Another dealer said that we should just run a separate line to the garage. We are about 6 months out on the garage build. Any opinions?

Rad=slang term for radiator it's more properly called a coil but there are other names for it. Essentially I mean a radiator type coil similar to what your vehicle might use. It's simply put into an existing forced air furnace and then the fan is controled by a thermostat. There are much much more involved ways you can do this by running it off a manifold when the hot water is directed to various zones. Say to supply hot water to an in floor area or a DWH side arm or plate exchanger, (for heating water) or a coil as described above.

Delta T is the temp drop int he supplied water. So if you put 160f water in and it comes out at 140f your delta T is 20 degrees. It's probably more important in pressurized boilers but you want the return water to enter the boiler not so cool it cracks the boiler from rapid temp change. 20 degrees is a common return temp considered safe. Lots of ways to cheat, as I did or you can mix some hot water from the supply side into the return to actually heat up the returning water. We're getting complicated now!

I disagree that a larger oversized unit will burn the same amount of wood. Cetainly not our experience. I do think (know) it will last longer and smolder more making more smoke. When the damper (power draft or natural) opens the unit will belch more smoke. We see it in the fall and spring when the heating demands are lower. Green wood makes smoke and creosote just as in a wood stove.

Pea gravel, is a great idea! Pricey here though.

Heating your garage. Both options will work. And there are more. Essentially you either treat it as a continuation of the first loop T'íng off the house's return line or you treat it as a seperate building. Remeber that return line water temperature issue and thermal shocking I mentioned earlier. T'ing off the return and then pulling another 20 degrees off means the water going to the boiler is now 40 degrees cooler. That could be a problem. You can still do it but you have to manage the problem.

One circuit off the boiler here does a similar job. I ran larger PEX to the first house (1.5 inch pex which is too big and why I have a drop of 2 degrees from boiler to house..... but it was cheaper than the 1 inch I wanted I could fix it by increasing the flow and returning some supply in the return loop, and I will some day) When the 1.5 inch enters it goes into a steel manifold where two zone pumps are fed. Each zone pump then feeds an air handler (plus one side arm water heater) I'd like to add a small unit heater to my clothes drier but I think I might rob too much heat when it's cold out so I need to do that carefully. I'll probably add a third zone pump and run more inside pipes.

So to heat your garage I'd run the water into a manifold then run a circuit to the garage and back to the house. That way you have all your return water in one place and if you need to add a bypas from the supply (or hot pump side) to the return to stop thermal shock you're all in one place to do the plumbing. Odds are you won't have to but I'd rather have the option.

[ronbre]

ours is oversized too, would not recommend that

[salmonslayer]

We run separate circulation pumps for each zone (house and greenhouse) and I would recommend you dont skimp on the circulation pump. We replaced the cheap ones we had with Bell and Gosset booster pumps and have been very pleased with their relaibility and durability.

[Ross]

I'm using Wilo Star wet rotar pumps. Same idea as Taco 008 but three speed and seem much more reliable.

[TSYORK]

I have a 500 gallon and it heats my 2700 square feet with NO problem at all!

[solidwoods]

Compare square inches of hot metal to water per units.
The higher btu models will be more efficient because of the increased hot metal to water ratio.
THE best place to put your work with these hot water systems is in the radiation system/s in the home.
The more radiation in the home the lower temp you can run the system.
The problem with hot water systems is the higher temps cause inefficient fuel use.
If you can run your system 150-160deg you will get a whole lot of better fuel usage than 180deg.

I have a Taylor 165k btu (built like a tank and has been the best money maker on the farm I highly recommend that brand).
I heat an 1890 3ksf home, 3ksf wood shop/show room, dog grooming hot water, 2 lumber kilns with my heater.

Use multiple types of heat exchange in the home.
3/4" black steel pipe is fine for radiation or used hot water radiators (not a steam radiator), copper tube in the furnace plentum or behind the couch works .
I put 150' of 3/8" copper tube under the bath tub bingo hot bath tub/towel dryer/room heater
jim