Calculating btu's for heating a shop

[Randy88]

We got my shop infloor heat hooked up and finally going this winter, I've talked to all the experts on heating demands for it and according to everyone of them my current owb should do it, now that said this winter is extremely cold and windy but we're having problems getting enough heat out of the owb to keep up.    I've run the calculations myself and it depends on who's calculator figures you use, the shop is 32x80, that portion has 20 foot ceilings in it, along with a heated service pit that's 3 foot wide by 7 feet deep by 50 foot long, and another office that's 15 foot square with 8 foot ceilings.    The office is cement block with granular insulation that you pour into the blocks as its built, can't recall the exact name, it comes in sacks you can still buy at menards as a pour in insulation.  I know that's not idea but its how it was built, this is a remodel job on an existing building.    The rest of the shop is also insulated, almost 8 inches of blow in for the walls and over a foot in the ceiling, my large door only has 4 inches of fiberglass in that cavity.     Everything in the shop is in floor heat, the cement is right at 8 inches thick, some the tubes are in the middle of the concrete tied to the rebar, the rest is stapled to the insulation under the concrete. 

Some tell me to use a calculation for the square footage, others tell me I need to figure cubic feet for a more realistic figure.    We're also heating an old farmhouse that's really well insulated and has descent windows in it, that is a two story house with a full basement under it that's not finished, but the two floors we do live on are about 2000 square feet or about a 1000 a level.    We also heat the hot water in the house

Right now we're running a wood doctor the second to the largest model they made, we fill it three or four times in 24 hours and the fan never shuts off, if the wind doesn't blow and its not much below zero, we can keep up, if the wind blows or its really cold, like we've been having this winter of -20 below plus wind chills, the shops slightly above freezing and the house is barely 70 degree's.   On mild days the shop gets back up to about 40 degree's.   I was hoping on 55 for the shop all winter long and about 75 in the house on the main floor, and upper 60's on the second floor.     

I live in northern Iowa and am thinking about going to a larger owb, but with the cost of them, everyone's is the ideal unit and big enough to handle this easily, I'd like opinions on what others think I need not a salespersons opinion, I'd rather not find out again, my next furnace won't keep up either.     The calculations I came up with were in the neighborhood of 750,000 btu's, then add in the efficiency factor of X of the owb and it gets up close to a million btu's.  I've used another btu calculator and came up with under 400,000 btu's if you figure on square footage and not cubic footage.     

Any suggestions or opinions?

[beenthere]

I've often wondered if sizing one large enough OWB is the best way to go, rather than having two and maybe three smaller OWB's to share the load.
Seems your example is a good one for such consideration as all winters likely will not be like this one, and the load is not equal for the full heating season.

In addition, those heating DHW year around would not need the full capacity of one OWB sized for the winter season.

A lot of things to figure in, and not something I need as my indoor unit is sized perfect for my needs.
But in reading about other applications on the forum, I can't help but wonder.

[Randy88]

Beenthere, from my past experience on heating hot water in the summer, we were using from a 1/3 to almost half the wood it took to heat the entire house in the winter months, we did this last summer and I ran out of wood in mid january this year, and have to be cutting wood and directly burning non seasoned wood, also adding to the my problem of keeping up.    From my calculations, with the pumps I have installed in the system, to heat hot water, for only a few people now verses all we had before in the house, the electrical consumption was about what my electric bill would be to heat the hot water, and I save all the wood for the winter.   

We've thought about going to a wood chip furnace in the past but to size one for the load was about impossible, I might have to rethink having more than one furnace in the system and one burning wood chip and the other firewood.     

To have anything more than two in the system, would not save much, I'd need a couple pumps more per furnace to run constantly to keep the systems from freezing and to keep everything up to temp.   But you do bring up a very good point, anyone have experience with two or more owb's per system, would I then need a hot water storage someplace and then just kick in each furnace as its needed to maintain temps?     

At this point I'd entertain any and all ideas, I've been focusing on one large unit but maybe two equally sized one's might be the way to go, anyone have experience with this?

[LittleJohn]

Randy, what kind of temperature drops and GPMs do you see across the loops of the infloor.

OK, few more questions about shop;
  How much insulation under slab?
  What kind of loop length and pipe size? if known
  How many loops and or zones are in shop?
  Also how often to garage doors get opened?

Only reasons I ask these questions is I live in EC Minnesota, and run about 7000sf total between two building (48'x80' garge with 12' ceiling and a 3000sf house), with a CB eClassic 2400 (gasser) and its rated at a MAX of 250k btu/hr and I am able to keep up except that week it was -20s and -30s.  I do have to feed the OWB several times a day, but my choosing; if I where to jam firebox full on a -20 day guessing that I would see a burn time of 10-14 hours

[Randy88]

Heat lines are half inch, each run is 300 feet or less, some had to be roughly 265 to come out, there are 8 loops in the main shop, two more in the office, we hooked them to different zones for priority in shop, two zones and pumps in the shop and one for the office, there is the two inch thick insulation board under the entire floor everywhere, but we put pylasters on the pit walls, and those are hooked directly into the floor slab, but those pylasters and pit walls have insulation board all around them before we backfilled, not an ideal setup but was the best we could do to get strength we needed to support the pit walls.   

We've used a temp gun to get direct readings off the floor, the incoming floor lines are about ten degree's warmer than the outgoing lines on each loop, unless it really cold, then we're having trouble keeping the temps high enough on the incoming loop lines to even maintain temps, which takes forever to gain back once the winds and bitter cold weather subsides.   If we could get the water to maintain a constant temp out of the furnace we could keep the floors warm, this winter, its taking so much to maintain the temps, the floors cool off and its a losing battle, in the office we added electric heaters, due to freezing temps on the water system, the waterline, toilet and sink froze one night, with -60 wind chills.   

As for opening the door, its full width of the shop, or 32 by 20 foot tall one piece hydraulic door, we open it several times a week, more if I'd ever get the shop warmed up enough to use it much, then maybe every day in the evening, but seldom open it all the way, just enough to get equipment in and out usually skid steers and trucks, is open less than a couple minutes at one time ever.     

Right now, we're filling the furnace in the morning, mid morning, mid afternoon, late evening and again about 4 am, the blower never shuts off and the water temps never get high enough to allow it to kick off, in the really bitterly cold windy days where it got down to -60 below wind chills, we were filling it or adding to it, every four hours around the clock.    All the lines are below ground to and from the furnace, in the insulated pex lines, two per four inch tile foamed in, not much water temp drop to and from the buildings on those lines.   Its the wind this year that sucks the heat out of everything, not the frigid temps as much.   

When it warms up outside, and wind does die down, everything gets back to normal again and keeps up, but it takes days if not more to warm the shop floor back up, and before then we are down in the deep freeze or the wind kicks up again and we start all over again.    In the fall we had the shop warmed up to about 65 degree's and everything was working like clock work, then the cold kicked in big time and its been a losing battle ever since.   We keep the temps in the house up by slowing the circulation pump in the shop somewhat, otherwise we'd have to kick in the lp furnace in the house instead to keep that warm.   I'd eventually like to add an attached garage onto the house and put infloor heat in that as well, there's no way this furnace can handle anything more, can't even handle what we have on it now, unless the bitter cold and wind never come back.   

[doctorb]

Do you have temp gauges on the outflow and inflow lines?  Many radiant heat systems require a re-entry loop (sorry, I don't know what the correct plumbing term is) to lower the temp of the hot water down to about 125 degrees before entering the flooring system.  My understanding is that really hot temps can crack the concrete.  Do you have such a system design?

While others have been very successful with radiant heat supplied from an OWB, it is the use of the return loop through a mixing valve to purposely lower the water temp in the flooring that makes me question its effectiveness in large systems like yours.

I'll try to explain my thinking and then those with more knowledge and experience can correct me.

It's takes a TON of energy to bring a large, concrete slab up to temperature.  When that slab is in contact with a large, cool air mass, it loses heat faster than in a more controlled environment like a home, with lower ceilings, rugs, etc.  Yet most radiant heat systems purposefully decrease the temp of the return water to the OWB, making it work it's tail off.  Most domestic OWB's with a heat exchanger have a return water temp in the (guessing) 160-170 degree range.  So the OWB only has to raise it 20-30 degrees.  In the standard home, the volume of returned water to the stove compared to the volume capacity of the OWB, expressed as a percentage of the OWB water capacity, is usually pretty small.  In a large system like yours, the percentage of water that's cooling in your radiant loops (compared to the volume of your OWB) is much greater than in the standard home use,  further demanding the OWB to work harder.  The return temp from radiant flooring is 110-120 degrees (again, guessing), so the amount of energy needed is significantly more than in normal home heat exchanger use, and the volume of water needed to have that increase in temperature is much greater, so I can see how an OWB would have difficulty keeping up.

I understand that, once the radiant floor is up to temp, it holds heat very well, like the stones of a fireplace with a wood stove burning all night.  But if the air above that flooring is cold, and the volume of air is large enough that it requires a lot of energy to have the air temp increased, then the flooring will be asking for energy all the time, and you will not see your OWB cycle off, as is expected.

Long ago, when I was a nicky-new-guy to the Forum and to OWB's, I made a comment that, in certain situations, OWB's may not be a great source of heat for radiant heat systems.  I received some differences of opinion then, and I'm sure I get some more now.  But, if the energy demands of the radiant heat system are extremely large, and the system cools the return water to the OWB to protect the flooring construct, then I think that there's a tipping point at which radiant heat may not be the best solution for heat in that space.  From the sounds of it, the only solutions are, 1) Put the shop in a warmer climate  ;), 2) Enjoy working in the cold  ;) , 3) Increase the temp in the flooring (adjust the return loop flow) so that more energy enters the system.  This should increase the temp of the return water to the OWB and ease its burden.  Or 4) Get a larger heat source.  How much wood are you using now?  I can only imagine.

OK, friends, tell me where I'm off kilter.  Best of luck, Randy.

[Holmes]

I have been playing with your numbers.  80 x 32 = 2560 sq. ft  If you are getting 30 btu's of heat per sq. ft {and that's a lot} = 76,800 btus per hour delivered into the building.  That is enough to heat the building in cold weather but not frigid conditions.   I have come up with # around 300,000 btus and up for the garage.  The garage needs supplemental heat but you can not get it from the boiler you have.
  You could look into 2000 gallons of storage to help get thru the cold spells [ around 1,750,000 btus] 12 hours of storage.
  You may be a good candidate for a Garn boiler in your shop.  I believe the commercial unit holds 3200 gallons 700,000 btu's
Ps my math could be wrong.  Your situation is challenging

 

[reride82]

I could be wrong, but if the wind is taking such a large toll, I'd say you have a pretty large air leak somewhere in that building. I'd look at temporarily adding weatherstripping to that big door and see if that helps. A draft in that large of a space would be impossible to battle. Just my two cents.

[red oaks lumber]

your water temp going into the floor should be around 170 deg. it wont hurt the concrete at all. been doing that temp in crete for 20 yrs no problems.if your pumps are going to slow to much water temp is removed, thus return temp to low for the stove to re heat .

[LittleJohn]

your water temp going into the floor should be around 170 deg.

COMPLETELY DISAGREE, water going into a slab should never exceed 150f - that is WICKED hot for a slab and you run the chance of concrete wanting to crack and fall apart. 

With the 8" slab you are talk about 100+ tons of concrete so reaction time will be increase on initial start-up (4000sf garage takes a full day to get up to temp in fall).   That being said openig and closing a door even a HUGE one like yours, if the slab was up to temp recovery woudl be instant once door is shut.

I have been playing with your numbers.  80 x 32 = 2560 sq. ft  If you are getting 30 btu's of heat per sq. ft {and that's a lot} = 76,800 btus per hour delivered into the building.  That is enough to heat the building in cold weather but not frigid conditions.   I have come up with # around 300,000 btus and up for the garage.  The garage needs supplemental heat but you can not get it from the boiler you have. 

Assuming SNOWMELT conditions (150btu/sf), for garge 32'x80' = 2560sf +15'x15' = 2785sf x 150btu/sf = about 400k BTU/hr

[Holmes]

 Little John   Minnesota , are you in John Barba's territory?

[Randy88]

In my shop we totally isolated those systems with in floor heat, we put in a heat exchanger on a hot water heater, and have a circulation pump installed in that to kick in when the temp inside the water heater gets below 120 degree's and reheats the water inside the heater, the floor loops are taken off the water heater and that entire system is pressurized which is really nice, we used anti-freeze in the shop loops and system in case we'd have issues with enough heat, which I'm glad we did this year.     

With this system in order to feed the house first and foremost, we just lowered the temp in the water heater and cooled that system down some, to allow more heat to go to the house and keep that warm, works like I wanted, at least the house isn't cold, but we are robbing from the shop to feed the house, a double whammy when it comes to a warm spell, then my floors are cold and it takes all the heat the furnace will produce to get things back up and warm, and this winter, we never have enough warm days to allow that to happen.     

The downside to an undersized furnace is it never catches up, and never gets up to operating temps, compounding the problem even more, as they say, a bad situation worse, by not getting things up to operating temps we're having issues with creosote buildup and I'm sure a lot more things I'd never thought of but I'm sure someone will point out.   

As for the amount of wood, I don't think anyone could imagine how much we're pushing through the system, and I'm not sure I want to dwell on that for the moment either, it would be very depressing to say the least, but far cheaper than buying lp gas is my only positive thought on the subject.   

As they say I know we have problems, when bad situations come along, problems compound as they are in my situation, with low boiler temps, come lower temps to keep the in floor heat hot, and as the floor cools off, the more temperature the floor requires to heat drawing off far more heat difference between the incoming lines and out going lines on each manifold, making things far worse than I'd imagined or could have, if the floors are good operating temps, there is about 10-15 degrees between the two, when the floors cool off, that increases even more to up to and over 30 degree's, so when my water heater temp is backed off from 120 to 80 or less, the lines coming out of the returns are far below 60 and before long, the water in the water heater is at 60 and things stall out very fast if that makes sense to anyone.   

If this had been a mild winter, things would keep up and do fine, my current furnace is supposed to be near 500,000 btu's output but is non pressurized, others make a similar in size furnace that's pressurized and they claim it would play with my system even in adverse cold spells, so the big question is, would you gamble on a 15k furnace to find out just how accurate they might be?, or even higher priced to get another just like mine by the time all the prices are figured into the equation and keep two running?

The next issue we're having is something I'd addressed before on the forum, in floor heat having not enough surface are to shown to heat the building its in, or insulating the heat source from the heated area, right now we've had the shop full of equipment taking up far too much room in the shop and covering the floor space far too much, it won't allow the heat to rise and warm the shop.   My plan to combat this was to eventually put forced air heaters hooked to the hot water too, to warm it up quicker when we're in there, but right now I don't have enough water temps to do much good.   

As for air leaks and a draft, its an old barn, we insulated it the best we could but its not new or draft free by any means, I won't every claim it were, we tinned the inside with old used tin, and there are holes in the tin from before, so there's no real way to make it air tight in stiff winds, if it were new tin, it probably wouldn't have been so bad, this I never took into account when we used it, in fact it never crossed my mind it would be an issue, add in some area's that are concrete connected to cement block and also tinned and we have some air movement, not much but some, nothing like the curtains in the house blowing in the breeze but enough to add up over time on a large cavity called a shop.   Nobody I talk to with furnaces have any real idea how take this into account, which was my original question of using square footage or cubic footage for figuring heating needs in the first place, its not new construction by any means and how does this increase heating needs for a boiler anyone want to venture a guess?   Sorry this is so long winded but to get all the variables taken into account I didn't want to leave things out. 

[LittleJohn]

DING DING DING

I see a potential issue, if drop across loops is greater than 30 degrees and water is exiting floor at or near room temps you may need to increase pump speed.
   Also, what kind mix (anti-freeze to water are you running) are you running?   Anti-freeze can GREATLY affect pump speed/GPM cause its hardder to pump.

What kind of water temps are you see out at the OWB?
Also I know its been said 100x maybe more, but are you burning decent wood?
   In regards to wood comsumption (7000sf - has comsumed 16 cords and counting); luckily know a logger who likes to drop of wood by the semi load for $$ of gas and maybe a beer or six

[thecfarm]

I used one of those infare red guns?? The ones that you point at a door to see the heat loss. That will tell you a lot too.
I heat my hot water with my OWB. I have a 54 inch one. I burn a lot of branches when I heat my hot water. May have to so called fill it,2-3 times a day,but I don't use much "wood".

[beenthere]

COMPLETELY DISAGREE, water going into a slab should never exceed 150f

littlejohn
I've had hot water at boiler temps running through concrete for just over 45 years and have seen no deterioration in the concrete. Temps set at 180°
So am curious where you are getting the 150° max info.
Does it have to do with expansion/contraction of the concrete or something else?

I suspect the water may be 180° but the concrete doesn't reach near that temp.

[red oaks lumber]

concrete can easily handle 180 deg. the myth and sales pitch is run cooler water temp and run you lines a foot apart, hum that comes from the guys selling the tubing. if you run hotter water and have a tubing spacing at 2 feet you'll have real good results.
my 20 yrs and beenthere's 45 yrs running 180 deg water with zero problems should put to rest any negative thoughts. 

[Randy88]

I know we have less heat transfer from anti- freeze mix but I didn't want it freezing this winter either, its mixed how the boiler people recommended for me, as for the pumps, those are grundfos pumps that are three speed and we run them on high, my plumber told me we could do the whole main shop on one pump it had enough capacity, but we run two for the main shop and another for the office.     When we got things up and going this past fall, we had it ideal for incoming temps, outgoing temps, the floor was right at 78 degrees and the shop was toasty warm, there was about 15 degrees difference between the two, and was told it was great, but as it got colder, really colder, like in the below 25 temps and more, the water temps at the furnace are harder and harder to keep up, and when the temps at the circulation water heater dropped below about 100 things went down hill fast, the lower the temps at the water heater, the larger difference between the ingoing temps in the floor and outgoing, today we have the temps at the water heater about 70 degrees and the floor temps are right at 55 and the shop is right at upper forty's at head high levels, my furnace blower hasn't shut off in weeks and today the air temps are back up warm, and the wind picked back up to over 40 mph and its like trying to start the shop heat up from scratch, the entire cement is cold and not warming much at all and won't till the boiler temps come back up.    Two days ago we had wind chills over 40 below and things haven't caught back up again yet, but I'm hoping this weekend sometime they will and my shop floor is back warm again.    Another bottleneck is the plate heat exchanger in the office for the water heater, it will only transfer heat so fast, I was told it was plenty big enough, but I don't know for sure now if it is, it seems to transfer about 20 degrees off the furnace side to the water heater side, not sure if that's enough or not but its what we have to work with.   When we robbed the heat from the shop to feed the house, we just switched the pump speed from high to medium and that slowed the heat transfer to the shop water heater and cooled off the shop.   

I crawled up and looked down the chimney again today, tomorrow we're going to clean it out again, I'm starting to get concerned we'll have to cool the whole furnace down and get inside to clean everything out the way its looking, we usually just do it when we service it for the year but due to the really cold temps and not being able to get it hot enough long enough, we're getting far too much buildup and its affecting the draft of the furnace now.   

As for the wood, yes I'm aware of that, I don't know if I mentioned it, but we ran out about a month ago, and have been cutting anything we can find, and mixing them as we go, its the best we can do for now, again compounding the problem, had it not been for the absolute bitter cold this winter, we had figured we had enough to last till early summer when we shut down, as they say its gone downhill from there, we had logs piled up in the timber to bring home this summer, but those I can't get to at all.   So we're using what we can get to, both dead and alive and mixing them as we go.   
   

[Holmes]

  Radiant heating schools teach you to not exceed certain temperatures because it can create problems. Things COOK.    Beenthere and Redoaks your  systems have been running at those temps for a long time and you are satisfied with them.  I could not run a system at those temps for fear of tile breaking, cement failure, burning feet, and the huge amount of expansion and contraction it creates. I have seen cooked floors and they are a lot of work to fix, nothing like walking across a tile floor and hearing the sound of broken glass under your feet on every step.

[Holmes]

 Randy I have done heat losses on your building from your description and come up with 210,000 btus, but. If you have any cracks and openings to the outside that # is not valid. A 30' door sitting above the floor by 1/8" is almost a 4" hole to the outside.  My version was for an 80 degree differential.  An infrared temperature ,thermometer may well be worth investing in, and they are fun to investigate with. 8)

[OntarioAl]

Randy 88
You have an insulation problem. The cold and the wind are wicking away your heat.
Rent,  beg,or borrow but get your hands on an infra red camera similar to the one Holmes uses  on (Holmes on Homes).  It will show you where the heat is "leaking" out.
You can buy a lot of insulation for the price of a larger stove.
Hope this helps
Al

[Don_Papenburg]

If you have equipment that needs oil changes (grease pit) you could supplement your shop heat with a used oil burner.   Plug any air  leaks you find .  This has to be done or you will never keep up with the wood burner.   
I never put 1/2 inch pex farther apart than 6"on center .  Pex is one of the cheaper parts of the heating system.  If you have heat tubes more than a 8" apart you will have heat striping in your floor . [ hot over the tube cool in between.]

[Randy88]

I'll try to locate a infra red heat gun, anyone know where to buy one and what they cost?    We can try that but I'm not sure we're going to ever get it as air tight as house or wood working shop, just by what we are working with and its basic design and nature of it being used as a shop.     

So in order to deal with what I have, a large equipment working shop, what can I do to help the situation out beside  looking for air and heat loss, would it do any good to add water storage to the existing system for heat reserves to be built up for the cold spells and hopefully when it warms back up [like we usually get most winters] it can catch back up again and replenish the system.   

Would it be economical as far as wood burned to buy an industrial outdoor boiler to replace my existing owb but a lot larger both in water storage capability and also btu's or will that just burn excess wood in the warmer milder weather in the fall and spring, would it be any different than two or three smaller units or do you gain in efficiency when I'd go larger in one unit, any thoughts or ideas on that question?

I know I have a lot of concrete to warm up, if I recall right its in the neighborhood of 150 yards, my lines were between 6-10 inches apart depending on where the lines ran and how it came out for the footage on each line and also what part of the shop we wanted warmer.   

I'm not thinking we're ever going to get anything down to the efficiency factors to do the heating in x number of btu's like the charts claim.     

I know when we priced to have lp gas convection heaters hung on the ceiling they used cubic foot calculations to do the math, and were putting in a lot more total btu's of heating in the shop only than any of the outdoor wood boiler people recommended, they told me when I asked, your not dealing with a house, its a shop and the doors opening and closing and size of the room required far more heat and that's all I got for an answer, then they wanted to install a lp boiler to run the in floor heat on top of that.     

I understand that my heating needs are much higher than most, I'm also prepared to handle the wood and fill the furnace to match my heating needs I knew this when we set it up, my only concern is not going overkill, and not under sizing the system either.     

Anyone have now, in the past or know of anyone with experience dealing with large industrial sized outdoor boilers, I know a few company's make up to 3 million btu outdoor boilers, that million btu that I had calculated isn't out of the question, or I could go with another similar sized outdoor wood boiler to add to my existing system.     

Anyone know anything about wood chips and outdoor wood chip boilers, I've considered in the past going with an average sized wood chip boiler and hooking it up along with my firewood boiler for the extreme cold temps, anyone with experience with those units, good, bad??

[red oaks lumber]

randy
i added up my sq.footage at the shop, my footage is alittle more than what your doing. i looked at the type of stove you have ,best i can tell mine is about the same size. all my heaters are modine style(forced air) my big door is 18x11 which is opened several times each day.running a large dust collection which sucks alot of warm air out. my kiln which runs 130 deg.(1050 sf) is also supplied by the one stove. even with all the extreme cold this winter my stove runs less than half the time.
is your stove being fired the proper way? i'm not asking what your fueling it with but, there are right and wrong ways of feeding the stove. don't take it personal i'm just wondering.
your stove isnt a gasser is it?

[doctorb]

Real good thread here.

Randy, would you mind supplying us with the actual temps of the water entering and leaving the radiant system instead of just stating the temperature drop (15 degrees)?  thanks.

What are the temp settings on your OWB and how close does the effluent water temp get to that top setting?

[Hilltop366]

From what I have experienced all factors have to be included for a proper estimate of required BTUs, the calculators that I have found on the web are mostly rough estimates and rule of thumb compared to getting a real quote.

I priced out a few heating system for a buildings over the years, I do remember being asked for things like insulation value, kind of windows, area of windows and doors, ceiling height, weather stripping, shading and exposure to wind. there may have been more that I forgot.

My experience with in floor heating is limited to my house but have much the same problem except on a much smaller scale, my living room is about 1/4 of the sq footage of my house but I send most of my heat to it. The ceilings in most of the house are 8' but the living room has a cathedral ceiling and much more glass area.

I don't use zone valves but instead I balance out the system with the ball valves on the manifold, with the living room getting most of the heat and it still takes way longer to get it up to temperature than the rest of the house, I'm pretty sure the living room is getting more than enough BTUs if the heat was delivered a different way but the floor can not radiate the heat to the room fast enough to fill the demand, I get by but one of these days I would like to add some rads to the living room to deliver the heat faster.

If you do find that you need more output I wonder if it would make sense to split the system and use the current OWB for the shop and get a smaller one (cost less) to do the house, If the house was taken off line for a few days you could see if the OWB would be large enough for the shop.