Garage Heat Loss?? 50k hr sound right?

[JP11]

I did a heat loss calc.

the suppositions:

-10F coldest temp
36x72 barn 13 foot walls.
Concrete slab
12' walls
3 garage doors insulated 10x10s
1 garage door 12x12
1 man door.

I did R20 walls R50 ceilings.

Came out about 50k BTUs per hour.

My plan is to only heat sporadically. I have the heated radiant garage in the house if I really want to warm or thaw something. I can't imagine myself heating more than a few days a year.

My thoughts were this. I'm not home all the time. The idea of putting in a GARN or something similar to heat the slab and keep it hot seems like a waste of wood. I thought of MAYBE eventually walling off a bay to keep hot all the time. I think I'd HAVE to spend 5k or so in radiant insulation and plumbing NOW on the front end of project if I go heated slab. That's unavoidable. It would eventually be 20k in heating costs for the barn.

OR.. my thought was to skip the radiant floor. Not be forced to spend ANYTHING on it now. If at the end of the project I have the money to insulate.. Great. If I still have money left over.. a few thousand dollars would buy a SERIOUSLY oversized modine heater that would run off propane. It's clean, no MTX and if I size it big it would work good for the occasional.... "ok I want heat NOW"

Like I said.. I don't PLAN to heat it at all. I was thinking loss in efficiency heating occasional. But I just want the ABILITY to heat. I can buy a lot of propane for what the boiler would cost me. Not crazy about space heaters.. but task heating would be ok. I hate the idea of the noise of the modine or space heater.. but I think I can live with it for the few times I'll use it.

Comments, Thoughts?

JP

 

[Bob Rohr]

I did a heat loss calc.

the suppositions:

-10F coldest temp
36x72 barn 13 foot walls.
Concrete slab
12' walls
3 garage doors insulated 10x10s
1 garage door 12x12
1 man door.

I did R20 walls R50 ceilings.

Came out about 50k BTUs per hour.

My plan is to only heat sporadically. I have the heated radiant garage in the house if I really want to warm or thaw something. I can't imagine myself heating more than a few days a year.

My thoughts were this. I'm not home all the time. The idea of putting in a GARN or something similar to heat the slab and keep it hot seems like a waste of wood. I thought of MAYBE eventually walling off a bay to keep hot all the time. I think I'd HAVE to spend 5k or so in radiant insulation and plumbing NOW on the front end of project if I go heated slab. That's unavoidable. It would eventually be 20k in heating costs for the barn.

OR.. my thought was to skip the radiant floor. Not be forced to spend ANYTHING on it now. If at the end of the project I have the money to insulate.. Great. If I still have money left over.. a few thousand dollars would buy a SERIOUSLY oversized modine heater that would run off propane. It's clean, no MTX and if I size it big it would work good for the occasional.... "ok I want heat NOW"

Like I said.. I don't PLAN to heat it at all. I was thinking loss in efficiency heating occasional. But I just want the ABILITY to heat. I can buy a lot of propane for what the boiler would cost me. Not crazy about space heaters.. but task heating would be ok. I hate the idea of the noise of the modine or space heater.. but I think I can live with it for the few times I'll use it.

Comments, Thoughts?

JP

Sure for that kind of useage a forced air may be a better choice. Infrared heaters are nice also for fast wrm up with radiant effect. Working on a cold concrete slab is not the best option, even if the air is warm, keep in mind. The tube ceiling heaters will warm whatever they "see"

I've done some shops where I used a horizontal air handler instead of a unit heater. They have much quieter fans, ECM variable speed motor options, and you can install them with a filter rack to keep the fin coil clean.

Also you can slip an A coil into them for cooling or de-humidifing. Remember hot air rises, so duct them to blow down against the floor or all the heat is stratified at the ceiling.

 

[mikefrommaine]

My last workshop I picked up a free oil forced hot air furnace with a small crack in the heat exchanger. Couple of passes with a mig and it was good enough for me... I only fired it up when I was working to take the chill off. Could be in short sleeves within the hour on 0* days.

 

[ewdudley]

Just some thoughts:

Sounds like your heat loss might be figured for room temperature. If all you're doing is keeping the floor at 45 degF or so during the dead of winter your heat loss would be dramatically less. For as much heat as it would take to keep a radiant floor from freezing I don't see how you would ever regret insulating the slab and installing the PEX. You would probably need some other air heat for the days you're actually using the space, but keeping enough heat in the floor to keep it perfectly dry is definitely worth it in my book.

In any event be sure to insulate the floor even if you don't heat it so you don't have a cold sweaty floor that is miserable to work on and will cause rust and condensation.

Also a little solar can go a long ways in a shop.

 

[JP11]

I've been in many airplane hangars that have the propane burners with the black tubes that are radiant. Some places even use that method to de ice airplanes. What kind of cost are they? I like that.. it would FEEL warm fast. The STUFF would get warm too. It also eliminates my number one dislike of the forced air... the dang NOISE!

I don't plan to be rolling around on the floor working in winter. I can always bring what I need into the main house with radiant in that garage. This is more of a "get all my crap under a roof" storage. But not so rough as to mess with pole barn and dirt floor. Doing full frost wall, poured, pitched floor with a center drain channel.

 

[jebatty]

I lean in favor of ewd's comment. My shop, 32 x 48 x 14, about the same insulation, etc., had a calculated heat loss of 35k btuH at -30F. The highest heat loss in a 24 hr period, as determined by lbs of wood burned, has been a little under 20,000 btuh, and the great majority of winter heating is at 12-15,000 btuH. I heat the floor at a constant 61F. I agree the heat loss would drop a lot if I heated to a lower temp. And the bldg stays dry, comfortable. Do insulate the floor and do put the pex in the floor. You never can do that later.

 

[rkusek]

How taxed is your Vigas 60 during those -10F days heating your home? I can't imagine needing a second boiler to maintain a constant decent temp in the shop. My 30x60x14 Morton building has an insulated 12x18 O/H and 2 steel walk-in doors. One door has a window but that is the only window in the building. R19 walls & R38 ceiling all fiberglass. I believe the slant fin heat calc came up with about 35kbtu at 10F but my slab is uninsulated unlike Jim's. I couldn't do the slab insulation and pex at the time due mostly to time (late Nov, wife and 2 kids living outside in a rv) and money to a certain extent. I'm not doubting the radiant floor and insulation is the way to go but an uninsulated floor has it's benefits also. My floor pulls quite a bit of heat from the ground keeping it very comfortable inside from late fall until the end of the year. In the summer it feels like I have a/c even before I added a small dehumidifier. EW is right about the the humidity in the summer but the little dehumidifier took care of that. My air temperature stays above 65F in the dead of winter without running the fan on my homemade water/air heater. It's a recycled outdoor residential heat pump (a/c type) condenser that I replaced the 240v fan motor with a 120v from grainger. If I run the fan the EKO 40 will never idle and I can bring the barn up to 80 pretty quickly. There was really no need to change that fan motor and I wish I had rigged something up to turn it very slowly instead. Even with just the water circulating through the coils you can feel the heat coming off it like a cast iron radiator. I agree with Jim's numbers that the 35kbtu heat calc is more like 10-20 for most of the winter. My design numbers for my home were also 35kbtu for the main floor and about the same for the walkout basement which has an uninsulated slab with framed walls on 2 sides with quite a bit of glass. My heat loss calcs seem a little off to me because the EKO 40 can keep everything (about 6200 sq ft) at 70F in below zero temps and still idling. I envy Jim's wood calculations and will try to weigh my wood this winter on those cold days to see what my actual BTU load is. My gut feeling is that it's about 60-70 kbtu/hr on those days based on the 6-7 hr burn times.

I don't think you can go wrong with the pex and insulation in the floor if you can afford it. Spray foaming my buiding was about $10k so I went with the fiberglass R19 & R38 instead for a fraction of the cost. Insulation and insulated doors is the key. If the U/G to your Vigas would not be too expensive you may be able to keep it warm enough 90-95% of the time and later add the overhead propane radiant for comfort working if that wasn't sufficient or took away too much from the Vigas's main job. I would not immediately discount heating the shop year round if it's with wood. I find it easy to go down and work on something for an hour or two whereas if I had to wait for it to warm up or spend money on propane to heat it up I would not do it. It all depends on how you plan to use it.

 

[JP11]

It's just flat too far from the vigas to where the barn is going. probably 4 to 500 ft.

It's not so much that heating with wood has me concerned about wood consumption.. but I go away for a week at a time. Getting my wife to run ONE boiler was tough enough. Heating the unoccupied barn would be a bridge too far.

JP