needing information on pressurized wood boilers

[ditchdigger]

Tell us how your slab heat is constructed.

Edit: and how dry your original hoard of wood was.

My hoard was log length for years, stacked out back and two years ago we bucked it up and split it, it was either piled outside or in a small wood shed, we also bring in greener wood occasionally and mix it in as we go along. We typically have plenty of logs on hand at all times, its just been such a hectic year we never got any more rounded up and brought home, figuring we had all summer to do so..........but I was wrong and we ran out, probably will never happen again though in my lifetime.

 

[ditchdigger]

The shop is set up with an isolated system right now, we installed a hot water heater to use as storage, and pressurized the shop side of things, and has antifreeze in it as well, we use a plate heat exchanger to transfer the heat from the owb to the shop side of things, not sure that matters, but its what we did to help equalize the lines in the shop, the entire floor was set up on a slope towards the door and the pit floor is seven feet lower than the office. I've had people tell me this is completely the wrong thing to do, others say its ideal and how to do it. We set up a pump between the plate heat exchanger and the water heater, we set the thermostat on the water heater to start and stop the pump, the thermostat is set at 120 degree's or what the temp going into the floor is set for, there is no mixing valves anywhere, we took them out of the equation for the in floor heat, again this is a subject of discussion among some plumbers as to if this is the way to do it or not.

 

[711mhw]

Like someone else mentioned, have you thought dividing up your load with several (smaller) units? I know my Wood Gun throws off a good bit of heat, they all must, and to put all that heat in an out building seems like it would make much more sense in a bsmt. & the shop. It might make sense dollar wise also, the price of a 500,000 btu = how many 100k units? This also spreads out your wood loading to several locations which may or may not be a good thing. If you have guy's in the shop, they can take care of that one, etc. I think a real good heat load figure is the best place to start. Good luck & welcome to Hearth.com

 

[NE WOOD BURNER]

if anyone can balance the load for me, so when its frigid out, I'm not working or sleeping in the cold, or blowing off hot water in the milder temps in order to keep the boiler fired.

ditchdigger: This is the benefit of Batch burning to thermal storage.
some burn to storage and heat from storage and others hook in series so the storage is charged after or during the heat load of the structure. if you go to youtube and look up munchkin gas boilers they have a great explanation of thermal storage using a high efficiency boiler. they use the video to explain the need for their Boiler buddy tanks.
Sounds like your Underground piping is performing well so that rules that out.
one thing to keep in mind is that your OWB most likely has a tremendous amount of standby heat loss. This winter was cold so your heat load and standby losses where increased.
the advantage to thermal storage in the heated structure is that your standby loss will be lost to what you want to heat.

 

[ditchdigger]

Like someone else mentioned, have you thought dividing up your load with several (smaller) units? I know my Wood Gun throws off a good bit of heat, they all must, and to put all that heat in an out building seems like it would make much more sense in a bsmt. & the sh

Yes we've thought about dividing up the load into smaller units, but this gets complicated if I can attempt to explain it right. I grew up with a wood furnace in the house basement, this house in fact I now own, and I don't want the wood or furnace in the basement again, I'd rather have it in a separate building of its own outside somewhere, to eliminate the smoke and debris from the house, along with the wood based critters.

Now comes the strange portion, with my insurance company, any wood furnace, once outside the basement of the house, any structure that its in, won't have any insurance coverage at all, nor can I even go about getting insurance coverage on, even if its inspected and installed via codes and such with a new chimney, which seems to be the hangup with them for some reason, they equate anything wood based with chimney fires. And its a waste of time to attempt to go about it with them with the discussion of efficiency and things like exhaust gas temps and stack temps or anything like that, I've tried. It won't matter what furnace we'd buy and install, unless its in the basement they won't cover any other building at all. Toss into the equation, things like waste oil burners, which some have exhaust temps of over 700 degree's due to being a cheap blast tube design, and so far from efficient in terms of heat transfer its not funny, those are not considered a solid fuel furnace and won't even raise my rates over having no heating source in the shop, and those don't need to be inspected nor installed to any code period. Now if your confused on this, I too sat there scratching my head in total wonder, so I called another insurance company I deal with on my business side, same answer, same reasons, so onto the third company I'd consider, again nearly the same answer on some units other than wood based but basically an identical answer on anything wood based.

So about comes the idea and concept of building a heated, partially insulated building with wood some wood storage in it, nobody will insurance that building, but they'll still insure my other ones just fine, it would put most of the heating in one location, bring them out of the cold and snow banks in the winter, I could refill the building with a skid steer and with volume [and no I don't stack anything by hand] for the amount we go through.

We've looked at and considered several smaller units in one building, not saying its not the answer, it has plenty of merit, one being, if I tied all the heating together, with valving, I could start up and shut down units as needed to meet the demand as the temps got warmer and colder, and have a backup if needed.

Right now, I've got a late 80's gas furnace in the basement of the house, which hasn't been even fired in at least four years, we just use the fan off the unit to circulate air through a heat exchanger, there's no heat source in the shop at all but a portable diesel powered space heater, and the furnace in the other house is undersized for the addition we just put on it, but works fine for now, it too is at least 25 years old.

My original hope was to install a chip furnace, with a smaller stick wood to use in the milder weather, but when I priced it last, for everything needed by the time it was all said and done, we were in or near that 50k mark and if it ever went down, the smaller wood furnace wouldn't even get the water to stay warm, let alone hot, so I'm not sure we gained anything. To have several units capable of heating what I need done, if one were to go down or cause problems, like my current one has/is doing, I'd end with an identical one sitting waiting to be used, not that I had any trouble with that, but nothing ever breaks down, or causes problems when its nice out and you could live without it, its always the coldest windy day of the year, with frigid temps expected for weeks.

We've looked at and considered hard, two units, a higher efficient stick wood model, smaller in size, and a larger, much larger in fact non efficient wood boiler, much like what I currently have, use the smaller one all the time, and only fire the big one for a few months in the dead of winter, the only problem with that is, if the big one went down in the dead of winter, I'd be screwed to say the least. My other thought is to have a waste oil boiler in the same building as these two wood burners, if one went down, I could fire that up, it would eliminate the hassles of dealing with the waste oil in my shop, I could switch the valves and bring it on line in the most frigid temps if needed, and that would save my buying such a large unit, I'd have three smaller ones, bring them online as needed, and shut them off as needed, and if I didn't need the waste oil, just keep storing it till it is needed, a major plus for me, because I don't think I generate enough to have that as a sole heat source for my shop. If I did this, it would almost have to be in one location to make it all work to bring online or as a backup system.

Another option is to have a waste oil burner, force air style in the shop, to kick on and blow when we open the doors or bring something in, to warm up the shop faster, which might not run often, depending on the winter temps and what we're doing in the shop.

As you can tell, I'm not sure what to do, costs are always a concern, but to answer the question of multiple heat sources in multiple buildings, if they are wood or solid fuel based as the insurance company states it, they're not going to be multiple buildings or multiple locations unless I can figure out how to do it, and still keep the buildings insured.

Now onto the discussion of efficiency, supposedly the higher the efficiency, the higher the cost for the furnace, keeping in mind my equation I use, I don't buy any of the wood, my cost comes in handling the wood, mainly in the form of time, how much higher priced of a furnace can one afford or justify to gain an unknown, non uniform based efficiency factor? The reason I ask is this, I can buy a supposedly 500,000 btu pressurized boiler setup, from manufacturer x that's no too efficient in my eye's, verses one that looks much better from manufacturer y for 3 times more money. None are trouble free, despite the claims, they all have maintenance issues of some sort and in the long run I save an unknown or unproven amount of wood, which is what, 25%, 40%, more or less ?? Is there anywhere I can get a better idea of how much each furnace would require for wood each year besides an uneducated guess from someone like me who's buying the furnace?

 

[ditchdigger]

Sorry about the format, I haven't quite figured out how to work this system yet and do the replies and get just the quote in the blue box each and every time

 

[NE WOOD BURNER]

house 1: 2500 S.F. /FHA and side arm DHW /annual LP usage was 1500 gallons
garage 1: TBD

house 2: ?
garage 2: ?

Shop: in floor radiant with a plate exchanger

So break it down into pieces. heat loss calculation/analysis of individual structures. this will determine your total heat load.
The main problem I see is the shop with 32x20 full open door. you wont recover fast enough with in floor for immediate comfort.
Growing up in the garage environment the emphasis on timing of repairs in the winter was critical to save heat. Bring in equipment early as possible and heat when you are not in the garage. can the door be partial opened or just all or nothing? We had FHA waste oil burner and a wood stove. Over head doors only opened to height we absolutely needed. Tough to police with employees.

 

[ditchdigger]

House two, has in floor heat in the new portion of basement, never hooked up yet, insulated and cemented the same it is about 700 square feet with the in floor and the old portion was just concrete, roughly another 700 feet, the whole house is forced air with a gas furnace. Garage two is also done new with in floor heat, fully insulated and never hooked up the in floor heat yet, insulated garage doors and it by itself keeps pretty warm, even with the frigid weather this winter, it only ever dipped a few times below freezing in the garage, square footage is roughly 700 feet, the whole house has new windows, all new insulation in the walls, under the siding and over a foot in the attic, the basement walls are also insulated on the outside with insulation board.

I forgot to mention, all the concrete floors with tubes in them, have a vapor barrier under the concrete, and before anything was done, more drain tile installed than anywhere on the planet per square foot to eliminate water issues ever under or around the floors.

As for the shop, the door hinges at the top, one piece opens up, we only open it far enough to get what we need out and back in, but as the door opens, it swings open so the crack is fully to the top and gets wider as it opens. Its not the amount we open it, its the amount of time its open for and how often we have to open it is what gets us, we try to do it at the end of the day so it has all night to heat back up again. Now for the subject of in floor radiant heat, I've been told it yields roughly 25 btu's per square foot of floor space, no matter how you go about it, or roughly 60,000 btu's in the main shop from the floor heat alone, has anyone else used this same figure per square foot, and if not, what is the amount to use?

Anyone have an opinion on a Royal pressurized boiler, are they somewhat better as far as efficiency goes, or just about like all the rest the owb's out there? Anyone with experience with them, had one at one time or still do?

 

[NE WOOD BURNER]

so in house1 and house2 is there room to install a water storage tank inside the structures?
house1 I assume is your dwelling. is there away to install an indoor boiler in there?

Garage door: that a tough one. only thing that comes to mind for that is a bellow for the top portion that will open with the door and seal out the wind. and possibly a hanging plastic curtain similar to what you would find in a walk in cooler. That size door makes a big hole.

FHA works best with higher temps. so the theory is to utilize low temp emitters(radiant) allowing you to maximize time between burn times.

Thinking out loud here:
thermal storage in house 1 and 2 heat from storage. possibly install an indoor unit in house 1 convenient for first batch in morning giving you a jump on your next batch in a Garn type boiler in or near the shop.

now if your convinced that you want pressurized from your experience with your OWB I would reconsider for sake of looking at a Garn and the proven track record I read about here.

if you insist on pressurized than I would install a gasser in an outbuilding near your existing setup and have divorced storage in the structures.

just thinking out loud-many ways to skin the cat here. the difference here is the concept of batch burning to storage rather than a one fire keep it going method.

 

[Vizsla]

I like this guys attitude, not afraid to get dirty and get in it to get it done.

I'm gonna go out on a limb here and guess that this large load being fed thru just 1" green pex( which is usually .876" ID) and only seeing a degree difference. Means that water is a Flyin' in that pex. A job this size should have a minimum of 1.25"ID to deliver this large of a load. So the current measurements aren't much use. Just out of curiosity what is the depth of the pipe and does it hold snow or frost like the rest of the yard? I seen pictures of some pex that looked like it was sand blasted or melted from the inside out. Giant pump , small pex, lots of bad stuff.

I will second the chip boiler just for ease of feeding and ease of fuel source. I mean what tree arborist doesn't dump free loads of chips.

 

[Boil&Toil]

I'd definitely think about radiant ceiling/upper walls AS WELL AS the radiant floor and fan-coil-units for the shop with the huge door. You can (guessing) probably run through the fan-coils and then into the radiant. Lower walls only get nominated if nobody's going to drill anything into them. Upper walls and ceiling get a stencil along the lines of "radiant heat loops - do not drill, dummy!" every 4 feet or so d;^) I know in my case that's just me reminding myself not to be a dummy, not calling anybody else names...

 

[ditchdigger]

Depth of the pipe in the ground, my trencher we used digs six feet deep, so I'd guess its slightly over five and half feet deep, buried with the water lines we put in new at the same time, the only place its shallow is by the boiler where it comes to the surface and hooks to the boiler, nothing ever melts anywhere near it, and this winter, I'm guessing its encased in frost by the water temps I'm seeing coming out of my water lines in the same trench.

As for the houses, any storage that can go through a 28 inch wide door can go into the basement of my house, or house number one, and house number two has three foot door ways in it. As for storage, anything can be done, as for the boiler, meaning wood in the basement, not going to happen, if I want to remain married, not sure I can afford a divorce, that would pretty much kill my budget for a new furnace for decades As for house number two, storage isn't a problem, but a boiler in the basement won't happen either, I don't want to be disowned by my mother any time soon.

Radiant tubes in the walls and ceiling, that's a new one for me, how do you go about that, now that the ceiling and walls are insulated and tinned, have all my electric lines run and all my lights in place? Are you talking stringing up water pex lines on the walls to allow them to radiate heat off as is?

As for chip boilers, anyone know anything about them, have one or been around one? Any idea's how to size one, there's only one I know of anywhere near me, I'm thinking its a million btu's and he has major storage, and far more heating needs than I do.

 

[Boil&Toil]

Given that it's finished and that it's a shop, probably just put it on the surface with heat transfer plates and leave it exposed.

In new construction or remodelling, you normally put it on top of/behind the drywall. You can run it a bit hotter than floors without making anyone uncomfortable, and it puts out roughly the same BTUs/hr per square foot - so added square feet ups your BTUs/hr.

For chip boilers, Lopper-Drummer is one brand that I've seen mentioned; I have not met one in person. 42-460 KW (142,000 - 1.5million BTUs/hr)

http://www.loppernorthamerica.com/turner-chippellet-boiler.html

Someone on here in Canada has one of their stickwood units (without the auto-loader option).

I passed on the option to buy a chip-boiler of unknown make or efficiency a while back, primarily because it was a "hurry up and get the heavy thing out of here" sale after a death - had been used for greenhouse heat - and I wasn't really ready for it.

 

[711mhw]

Look around here, I think that there is a guy in VA that heats a farm operation with wood chips.Can't remember his name. I'll go look, but he might be able to help some.

edit; fuelfarmer

 

[NE WOOD BURNER]

I've been told it yields roughly 25 btu's per square foot of floor space, no matter how you go about it

do you know the design temperature that was used for this output determination?

 

[ditchdigger]

Boil and Toil, what are heat transfer plates? I've never heard of anyone ever doing this before so I'm sorry I'm asking stupid questions, also how do you fasten the tubes to the wall, without damaging them, do they make an insulated holder of some sort that you can clamp the line in, and screw that to the wall. I know they make things to hold the lines so you can install them on basement ceilings to direct the heat up through the floor above.

711 mhw I'll check that out and see if I can get a personal message off to him, thanks for the information.

I'm sure progress has been made in the development of a smaller chip boiler in the last few years, and I've not talked to anyone who has a newer version, but all the older chip boilers were a challenge to size for heating demands, because every set number of minutes they'd have to fire in order to keep the flame going so they would start back up again.

 

[ditchdigger]

NE WOOD BURNER, no I don't know the design temps used, all I was told by two of the local plumbers, when it was 50 below out for weeks on end that part of my heating problem was in floor heat puts out only 25 btu's per square foot, and I needed additional heat added to the shop if I ever expected to keep it warm enough to work in [they were trying to sell me lp ceiling radiant heat tubes at the time]. We started the shop over five years ago now, finally got it done, and I can't remember what I was told to expect out of the in floor heat back when it was discussed that long ago, nobody in the family could either. I was wondering what everyone else used for btu's per square foot, I've looked on the internet and couldn't find anything practical I could apply to a shop setting.

 

[Karl_northwind]

Depth of the pipe in the ground, my trencher we used digs six feet deep, so I'd guess its slightly over five and half feet deep, buried with the water lines we put in new at the same time, the only place its shallow is by the boiler where it comes to the surface and hooks to the boiler, nothing ever melts anywhere near it, and this winter, I'm guessing its encased in frost by the water temps I'm seeing coming out of my water lines in the same trench.

As for the houses, any storage that can go through a 28 inch wide door can go into the basement of my house, or house number one, and house number two has three foot door ways in it. As for storage, anything can be done, as for the boiler, meaning wood in the basement, not going to happen, if I want to remain married, not sure I can afford a divorce, that would pretty much kill my budget for a new furnace for decades As for house number two, storage isn't a problem, but a boiler in the basement won't happen either, I don't want to be disowned by my mother any time soon.

Radiant tubes in the walls and ceiling, that's a new one for me, how do you go about that, now that the ceiling and walls are insulated and tinned, have all my electric lines run and all my lights in place? Are you talking stringing up water pex lines on the walls to allow them to radiate heat off as is?

As for chip boilers, anyone know anything about them, have one or been around one? Any idea's how to size one, there's only one I know of anywhere near me, I'm thinking its a million btu's and he has major storage, and far more heating needs than I do.

Heizomat will be bringing in boilers this year; down to 200,000 btu. the RHK series will burn nearly anything you can feed in. only no cordwood. chips, sawdust, straw, corn stover, etc.

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not cheap, but no screwing around either. they've been building them for 30 years. Kinda like the Garn Philosophy: big solid steel heavy, etc.
Karl

 

[NE WOOD BURNER]

no I don't know the design temps used

The reason for the question is that most BTU outputs are based on a certain water temperature. You would make a reduction based on your design temp available.

so if design temp is 180 and you have 140 it effects the amount of BTUs out. obviously if you add more tubes you increase your btu output, wall and ceiling idea is a good one.

We have lp radiant panels in ceiling in a very large shop ~9000 s.f. and FHA waste oil burners. The waste oil does the Lion's share and the ceiling panels make it comfortable they are hung at 22' ceiling is 25'. you wear at hat so you don't get sun burn on the dome. It does warm the equipment nicely.

I would think you could estimate the length of tubing and use a standard btu rating for the brand of pex(adjusting for water design temp.) to determine the output.

I am currently sizing cast iron radiators for my residential install in the same fashion.

 

[Boil&Toil]

Boil and Toil, what are heat transfer plates? I've never heard of anyone ever doing this before so I'm sorry I'm asking stupid questions, also how do you fasten the tubes to the wall, without damaging them, do they make an insulated holder of some sort that you can clamp the line in, and screw that to the wall. I know they make things to hold the lines so you can install them on basement ceilings to direct the heat up through the floor above.

Most PEX design guides come out closer to 45 btu/sq ft - might depend on your tubing spacing/size. Linear foot-wise, ~25 btu/ft for 1/2" diameter tubing, which is normally spaced closer than a foot apart. What's your floor surface temperature when running? I see you are running 120F water into it, but what 's the surface at - if it's not uncomfortable, turn up what you are sending it until it is, then turn it down a touch. The other question would be the return water temperature - if there's a huge drop (like it's below 100F), more pump might help. Floors are somewhat limited since they get uncomfortable if too hot - walls and ceilings can be run hotter if you have the water temperature available. The ability to work with low temperature water is one thing that makes radiant good for use with storage, but non-floor radiant can use hotter water if you need to and have it (and still does work at lower output with low temperature water.)

Heat transfer plates, or spreaders are the same things used on wood floors - aluminum channels, ranging from expensive extrusions down to aluminum flashing with a "u" pressed into it. Aside from holding the tube, they conduct the heat out across a larger area of ceiling/wall/floor. I'm making the assumption that in the shop, you won't have an issue with being able to see these. In the house, nobody expects to get away with that and remain married, so they go inside the walls/ceiling/floor, as they would if put in when the shop was being built. Rather than "directing" the heat, they spread it over a larger area.

(broken image removed)

Contemplating really out there ideas, you could possibly toss a greenhouse-type structure beyond your big door to serve as a machine-sized airlock, but you still have (as you originally noted) the large mass of cold metal to heat when bringing one in, so it might not make enough difference to be worth the bother.

As for design help (just beware the our-brand-is-best-ism they all have, especially considering you already have whatever you have in the floor, and can't change that much):
http://0323c7c.netsolhost.com/docs/PEXDesApplGuide.pdf

(broken link removed to http://www.radiantcompany.com/manual/manual.pdf)

(broken link removed to http://www.roth-usa.com/PDF_Download_Files/Install_radiant_heating_system.pdf)

 

[ditchdigger]

As for the floor temps, earlier this past fall when things were actually working like they should, we had floor temps in the upper 70's and low 80's, and it was hot in the shop, water temps were good too in the water heater and we could keep that 120is degree heat in there as well, then the return line temps were about a 15-20 degree's less than ingoing temps, then it got cold, really cold in a short amount of time, and things went bad in a hurry. In the most frigid temps, we had an impossible time to even get to or stay at that 120 mark in the water heater, and they went downhill from there, we even slowed the transfer rate more still by slowing the pump on the furnace and also the at the plate heat exchanger to keep from freezing in the house on the most brutal days, and we added the knipco heater in the shop to help that out, and as the temps lowered in the water heater, the temp spread increased in the floor, from the ingoing to outgoing temps, and then it never warmed up at all outside, and it was a losing battle from then on all winter long. Couple owb water leaks, snowy covered wood, wet wood, and some undesirable wood and things just kept getting worse, the only bright spot is, spring's got to be near soon, so I can end the misery of this winter, and bide time to decide what to do for next winter.

I'm told a cold start up for a floor is nearly impossible to get up to temp in the middle of winter, it will take all the heat an owb will put out, I've been doing that all winter long, and losing the battle, the time between cold snaps this winter were hours, not days or weeks, and once we cooled down the floor to rob heat off that to keep the house good, we never gained back what we took away from the shop, even today, my temps in the shop are not hot enough still to get back to 120 in the water heater, and by now, I'll be honest and tell you all, I've got a severe attitude problem and just gave up for this winter, and we're using a knipco in the shop.

Thanks for the information on the wood chip boilers, most of the makes posted here I'd never heard of, same goes for wood gaser units either.

 

[NE WOOD BURNER]

Thanks for the information on the wood chip boilers, most of the makes posted here I'd never heard of, same goes for wood gaser units either

This site has been a real eye opener for me as well. What is interesting for me is that even if a person hasn't purchased a top of line unit the add ons and practical experience here usually will get the person heating as efficient as possible.

from your last post sounds like your return water temp was very low to the OWB. The manuals and advise here is to have a valve that controls the temp of the return water to the gasser boiler to avoid premature failure. FYI

I visited a shop that routinely brought in track vehicles they would run them in on rubber mats on top of foam board insulation to isolate the heat draw from the cold iron. they had in floor tubes as well. not sure if it helped. I will have to visit again to see if they had good results.

The 120 degree supply temp is very low directly from your boiler. FHA in house must have been cool.

I would still keep in mind possibly installing some low temp heat emitters in house1 and have divorced thermal storage inside there. House 2 sounds like you should be good with your in floor system but certainly thermal storage there wouldn't hurt either. my thinking on this is that once the tanks are to temp your boiler would serve the garage and house would maintain on the storage going from say 180-120 before recharge. in the garage you could stand up 1000 gallon lp tanks for thermal storage. so four tanks from the scrap yard would be $2000. so now most of your stand by loss will be lost to the structures. how you heat the storage: I like the idea of two units since you have the houses. one unit could be chip and the other cordwood even.

I was chatting with an engineer at work today regarding the garage heat situation. he thought an easy solution would be to use concrete curing blankets on your slab when you need to open the doors. I think that is a good idea especially if you could also use them in your business.

 

[Boil&Toil]

As for the floor temps, earlier this past fall when things were actually working like they should, we had floor temps in the upper 70's and low 80's, and it was hot in the shop, water temps were good too in the water heater and we could keep that 120is degree heat in there as well, then the return line temps were about a 15-20 degree's less than ingoing temps, then it got cold, really cold in a short amount of time, and things went bad in a hurry. In the most frigid temps, we had an impossible time to even get to or stay at that 120 mark in the water heater, and they went downhill from there, we even slowed the transfer rate more still by slowing the pump on the furnace and also the at the plate heat exchanger to keep from freezing in the house on the most brutal days, and we added the knipco heater in the shop to help that out, and as the temps lowered in the water heater, the temp spread increased in the floor, from the ingoing to outgoing temps, and then it never warmed up at all outside, and it was a losing battle from then on all winter

You can heat up a cold slab in the winter, but you can't heat a slab if you don't have adequate heat - and this tale basically says you lack adequate BTUs for cold weather (yes, I think you are aware of that.) NE WoodBurner, I'm pretty sure the 120F is what's feeding his floor, but he couldn't maintain that without freezing his house, so he turned it down. He's generating that from a heat exchanger off the OWB, it's not the OWB output temp directly. Two issues - insufficient heat exchange capacity if not able to maintain 120F with more temp in the boiler, and then turning it down to maintain heat in the house - which basically says insufficient BTUs input. It's a pretty typical temperature to heat a floor with, but going down from there was not going to have good results - could have tied in an oil-fired (waitaminnit! house 2 has GAS heat - you have GAS! Use GAS! (unless you mean propane)) waterheater when the system couldn't maintain that, or do what was done with a different type of heater.

As for stressing about the door openings, this jarred loose a tid-bit a guy who used to do practical solar thermal worked out.
(broken link removed) skip down to heat storage discussion if you don't want to read the rest, and to explanation if you're really in hurry (or don't go at all). He basically worked out that for a 10 ft high shop, less than a tenth of an inch of concrete stored enough energy to re-heat all the air in the shop when the door was opened. It's the 10 tons of -20F steel you need to worry about.

 

[NE WOOD BURNER]

Boil and toil: That is a good read I read the thermal storage portion. I do not disagree with his logic. But I think that is derived from a warm slab heating the air in the shop. If the floor is heated at 120 water in. assuming the floor has lost the thermal storage with the extended door open times and cold machinery. the response time to heat floor and then the air to recover a working heat range of 50 or above would require a large BTU heat source. the blanket idea would keep much of the slab heat in storage thus helping the recovery time(in theory). there is no replacement for displacement! more btus certainly!

I do agree that with his current system a supplemental boiler would be needed.

kinda the reason I was thinking two boilers one could feed the structure load and excess to storage and the other could just run to heat the storage.
I did forget about the heat exchanger and was thinking he had only 120 from the source.
He will need big btus for garage heat load and that will aid in the recharge of the house thermal storage as well in the evening or when he is not in the shop.

 

[Boil&Toil]

Yes, Morris does point out that average BTUs in must meet or exceed average BTUs out to make it work; and that's the main issue here.