Need fast education on wood boilers

Brad_bb · May 15, 2016, 08:45:50 AM

I need a fast education on wood boilers. I'm building my new heated shop right now. I've planned for natural gas to be my primary heat. I mill for fun so I often have a bunch of slab wood and log cut offs. I'm thinking maybe I should have a back up heating method for the shop or the house I'll be building in the spring that I can use the wood for when I have wood. I may not want to load a boiler all the time and then the natural gas can kick in. If I am going to run any underground lines to the shop, I need to do it now. If anyone is really up to speed on this stuff that can tell me about the options, the pros and cons....I need quick help. Thanks, Brad

Gearbox · May 15, 2016, 09:55:49 AM

My OWB is hooked up with a water to water heat exchanger on the return of the gas boiler . 1 thermostat for all 3 ball valves to bypass the return when OWB is shut down . If the wood fire goes out the gas return water will keep the OWB from freezing. Buy the best Insulpex you can find . The only thing you need to do is turn the temps on the gas boiler down to 160 to keep it from running when the OWB is on the low side of its cycle . My gas boiler is a Peerless or Munchkin .

Ford_man · May 15, 2016, 03:04:20 PM

If you are going to heat the shop i would put the heat in the floor it is the most effecent way to heat.

hedgerow · May 15, 2016, 06:58:45 PM

No matter which way you go put the tubes in the concrete in the shop you can always hook them up later. Now for the wood boiler their are a big investment so if you have a good supply of wood and don't mind messing with it you may save some money on heating cost.

Brad_bb · May 15, 2016, 10:24:44 PM

Thanks for the inputs so far guys. Been watching Central boiler videos. Haven't yet come across one where they talk about best application to know if your situation is best suited for that solution. Still more to look through though. I have to decide quickly if I'm going to do it in the shop slab or not. I have more time to consider for my house. House and shop are about 100 yards apart, so probably couldn't do one boiler for both.

scleigh · May 15, 2016, 10:39:47 PM

Brad,
I'm no expert on the outdoor wood burners, but have been thinking of doing the same thing later on. My house and building are 330' apart and I've been told that an owb in the middle could heat both. I'm considering a shed half way with a solar kiln and owb under the same roof, with the owb heating the house, shop and kiln when needed.

svart ole · May 15, 2016, 11:46:03 PM

Brad,

Not a expert here ether but here are my thoughts. First thing would be how much wood do you produce that you could use for fuel and how much would it cost to get more if that wont meet your needs. Heating your shop is a good way to use what you have. If you have to buy wood to heat the house to will that cost be less than NG, if not you may want to skip that. I would still think about running the lines to the house on the chance things change in the future. As for the shop I love heat in the slab. You may want to also hang a heat ex-changer with a fan for quick make up when you open a overhead door to run something inside. The heated slab will let you fire intermittently and the hanging unit will bring the temp up fast once you get a fire going when you get to it. Lets you leave for a few days and not come back to a stone cold shop. If you keep the circulation pump (put in two in case one quits when you are gone) and you should not have a issue with freeze up. That is what I do here in Northern Minnesota and it has worked for me. Do some pencil work on fuel cost on heating the house to. I would think about some type of gas heat in the shop for the times you may not have wood or are not in a mood to fire and have to keep it above freezing. It all comes down to money.

thecfarm · May 16, 2016, 06:13:24 AM

Don't forget to look at Heatmor OWB.
No expert here,and I have no idea of the size of your house and shop. But sounds like you would need a bigger one than just one that a house owner would need. Those cost more. I have a big one. I thought I would have a working garage,shop,for me. Has not worked out that way.

WmFritz · May 16, 2016, 08:54:56 AM

No matter the heat source, I recommend hot water radiant heat for both buildings. I absolutely love floor heat. I built a two story cabin with concrete slab and under-floor on the second level. The temps are even throughout and no noise or drafts like forced air. It's nice getting out of bed and walking barefoot on warm floors. I used an on-demand hot water heater for the first four years until I had the money for an OWB. That heater worked fine, but I hated buying LP. Last year I got the boiler set up.

Since your shop build is happening sooner, I would start my planning with the slab first. Insulation is key. You'll need to decide where to set up your mechanical area so you'll know where the boiler lines will come in.

doctorb · May 16, 2016, 12:08:37 PM

My thoughts. How often do you think you'd be firing up the OWB? While the wood could be a fine heat backup, it's not the kind of thing that you want to fire up weekly. It takes time and a handful of "revisits" to the OWB to get it up to heat. Not just a flick of the switch. Further, an OWB is not the kind of expense I would do for "back-up" heat. Big investment. Used part time, it will take you many, many years to recoup your $, even if the wood is free,

So, as an OWB guy, I would not envision that, once you have accumulated enough "slabs" to provide you with heat for a while, that you would be turning off the natural gas and using the wood burner. While you could do that, and it is nice to make use of that discarded wood, you will then be doing what you said you didn't want to do....loading the wood boiler all the time. I might envision that an indoor wood stove might be a better option, but that won't heat your shop. I just don't see a seamless transition back and forth between the two methods.

WmFritz · May 16, 2016, 01:12:24 PM

Quote from: doctorb on May 16, 2016, 12:08:37 PM
My thoughts. How often do you think you'd be firing up the OWB? While the wood could be a fine heat backup, it's not the kind of thing that you want to fire up weekly. It takes time and a handful of "revisits" to the OWB to get it up to heat. Not just a flick of the switch. Further, an OWB is not the kind of expense I would do for "back-up" heat. Big investment. Used part time, it will take you many, many years to recoup your $, even if the wood is free,

Excellent points Doc.

Brad, what size is your planned shop?

LittleJohn · May 16, 2016, 01:23:30 PM

Quote from: Ford_man on May 15, 2016, 03:04:20 PM
If you are going to heat the shop i would put the heat in the floor it is the most effecent way to heat.

By far easier to put in now!!!!

...plus the nice thing in lower water temperatures are required

John Mc · May 17, 2016, 07:06:11 AM

Have you considered just putting a wood stove in the shop? No worries about it freezing up when the shop is not heated, and might be more suited than an OWB to just running an occasional fire.

Brad_bb · May 17, 2016, 10:12:21 PM

John Mc, that's probably a better thought for the shop. It's kind of late in the game and there are too many things going against doing it there. It's quite a distance from the house. I am only planning for an on demand water heater for the bathroom and sinks. The slab areas that I would potentially heat are 1560 sq ft., less than half of the total shop space- 2 specific rooms.

I'm probably better off taking a better look at the house alone. Also, when I am talking about back up, I don't mean the wood would be occasional as a back up. If using an OWB, I understand I would have to keep it going every day as long as I have wood. If I ever had a problem with it, the natural gas heat would kick in. So Maybe you'd call that the back up. I figure I'd run the OWB when cold weather really starts in December and end about March 15. I'd use gas heat in Oct/Nov and Mar/April/May as needed. Does that make sense, running it for 4 months of the year?

John Mc · May 18, 2016, 07:27:33 AM

I just mentioned the wood stove as an option. If you are keeping the shop heated more-or-less continuously (even if it's kept at 45 or 50˚F till you are ready to use it) that might be a better match for a wood boiler & radiant heat in the slab. If the shop will be cold until you are ready to use it, it can take a good while to heat up a large slab with radiant heat. You generally don't run "boiler temperature" water through the slab. You use a mixing valve and run a lower temperature. A thick slab is a LOT of mass to heat up, so there is some time lag from turning it on until you get it comfortable.

Regardless of how you go, I would consider laying the tubes in the slab for possible use in the future. No one says you have to use them, but it would be a bummer to not have them if you end up with a system that could drive them. I wish I had done that for my shop, but didn't.

If you are going to go with radiant heat in the slab, they make a special thermostat for this type of situation: it has a sensor to measure air temp in the heated space (like a normal wall thermostat); it has another sensor that you bury in the slab. This second sensor keeps the slab from going completely cold. It acts to "If the shop heat is not turned all the way off, keep the slab at least at X˚, regardless of what my air temp is set for". So you could set the slab for a minimum of 45˚, for example, and it would call for heat either if the slab dropped below that or if the air temp sensor said the room was below the set point.

Resist the urge to oversize your wood boiler. Wood combustion does not like to be "turned down". A colder, smoldery fire is what causes creosote, and it burns much less efficiently. In fact, I might size it to heat my house in the cold season, and figure it could heat both the house and the shop when it's not super cold. When it got too cold to keep up with both, you could supplement with the gas heat. (Surprisingly, large commercial systems designed this way - wood boiler sized to handle 2/3 the peak heat load, rather than sized for the peak heat load - end up being able to use wood for a significantly higher portion of their heating needs, Since they can still run the boiler efficiently, and without loading up on creosote in the "shoulder" heating seasons in the spring and fall.)

jdonovan · May 18, 2016, 08:02:31 AM

If you are putting gas in anyway.... spend the OWB money on more/better insulation.

I am ASSuming... the shop that won't be heated to normal temps unless you are out there working, otherwise the heat would be turned back to a much lower setting. So you shouldn't use too much gas to keep they place heated to that level.

So spending 10-20k for a wood boiler and all the ancillary costs to install, plumb and have it ready to run, to save $300-$500 a year in a natural gas bill just seems like a false economy. You would be looking at a 20+ year return on investment, and I'm not sure a wood boiler will even last 20 years with minimal maintenance.

John Mc · May 18, 2016, 08:11:01 AM

Another thought for you:

If you are using an OWB to heat both the house and the shop, and the shop is not heated continuously, I would consider locating the OWB closer to your house, rather than splitting the difference. You want to run your primary heat load as efficiently as possible, and usually, people can put up with a shop being a little on the chilly side better than they'll tolerate that in their home.

Whatever you do, using a good grade of insulated tubing is usually worth it. No point in heating the ground between the boiler and the buildings any more than you have to. I did read somewhere (perhaps here on the Forestry Forum?) about someone who made their own insulated tubing: the dug a trench, then had someone spray in that foam insulation, laid the tubing (I can't recall if they put it inside some black plastic pipe or not), then sprayed more insulation on top of it. Something to consider, especially if you are having someone spray in that stuff in the heated areas of your shop. If you do this, I would check that the stuff they are spraying will not degrade while it's buried underground.

LittleJohn · May 18, 2016, 08:48:52 AM

Quote from: John Mc on May 18, 2016, 07:27:33 AM
Regardless of how you go, I would consider laying the tubes in the slab for possible use in the future. No one says you have to use them, but it would be a bummer to not have them if you end up with a system that could drive them. I wish I had done that for my shop, but didn't.

The more spent on insulation up front, the less you spend on the heating bill ;)

WmFritz · May 18, 2016, 10:21:19 AM

John, that was probably me your thinking about. I discussed my plan for a closed-cell sprayed in foam trench a little over a year ago. I had studied my OWB installation for years while saving up to buy one. I also studied my building heat loss and boiler BTU requirement. Finally, I decided on the boiler. The dealer threw a wrench into my plans when he offered to throw in 90' of a medium grade insulated line, that he had left over as a drop (I only needed 75'). The lower efficiency of the drop didn't bother me as much as the tubing diameter. The drop was 1" and my foamed in lines plan was 1 1/4". My slab is 1350 sq ft with an 8 1/2' ceiling and the second floor is 1000 sq ft with 15' cathedral ceiling.

I have one year on my OWB and the 1" lines have been adequate so far.

LittleJohn · May 24, 2016, 10:58:10 AM

...my old man is running 4000sf of garage off of 1" ThermoTwin Ecoflex, between the OWB and structure . Only issue was the 2 weeks it was -30; but we just cranked the pump up from medium to low, to get more flow out in the garage floor

Also runs a 1.25" line to house, 3500sf and a bit of snowMelt on patios and sidewalk, dad is almost 60 and already has one metal HIP