electric heat in a small shop

tybalt

hey there.  i am planning to put up a small woodshop in northern south dakota, part old, part new. the old is 20x18, 8' sidewalls with avg 10'6 ceiling. the new would be 8x18, 8' sidewalls with avg 9'6 ceilings. the old would be all r-13 except for a 20x8 attic section that would be around r-30 or more. the new would be r-13 walls and r-19 ceiling.  i am also planning to insulate the floor with probably 1 1/2 hd foam before i pour. putting in 3 small windows, one entry door, and an insulated 9x7 overhead door(r-6 i believe).

i am planning on using a small wood stove for quick warmups and most general heating, at least on the colder days.  i also have a propane heater i can do the same with.  

i was thinking of using electric wall mount radiators or electric wall/ceiling mount heaters w/fans. (although with all the dust i would rather not have the fan type. box fans are cheaper). these heaters would be more for keeping the temp constant and maybe keeping the temp at a decent level overnight.  

i've done some figuring on the output i need for the electric part, but that has included raising the temp.  what i would like to know is what i would need just to keep the temp constant once everything is already warmed up. example: i run a fire all morning and early afternoon until it dies out. then i keep it at 65-70 until 9 at night. then turn it down to 50-55 for overnight and maybe for another day if i don't make it out to work that day.

another option would be electric radiant floor.  i could also use some comparison info on this, too.  operating costs, efficiency, initial costs, things like that.   i haven't looked into this as much yet. but beings i am doing the floor, i will possibly put in tubing even if i don't go that route right away.

but any info, advice on these matters would be greatly appreciated. thank you much

Paul Fredricks_3

I'm no expert on this

but let's say, for example, you did a load calc on this structure and came up with 25,000 BTU's of heat needed at design conditions. I don't know what deign is where you are, say it's 0°, and you want to maintain 70° inside. Then when it's 0° outside you can keep it 70° inside if you have 25,000BTU's worth of heat. If it's warmer outside, you can keep it warmer inside, and vise-versa.

tybalt

reply

thanks for the reply

so once i get my shop up to 70, and all the tools, materials, floor, walls are all warmed up, and i kick in the electric, i'm still gonna need 25000 btu's to keep the temp at 70 at 0 outside? how about 30 outside?

25000 does seems high to me. i've been heating a garage with my propane heater. it's rated at, i believe, 15000 to 23000 btu's.  the garage is 14x22 with 9' sidewalls and 14' peak, open walls and no insulation.  on a 30 degree day, once its warmed up, i can keep it over 70 running at 15000.  and there i normally end up turning it off for awhile. 

that's why i'm thinking 25000 might be high (for maintaining the temp), but i want to be sure with all this. i can't afford to be experimenting right now.  so that's why i'm here asking and learning.

LarryC

Air infiltration concerns

DISCLAIMER:  I AM NOT A HEATING PROFFESSIONAL !!!

 

Where does the combustion air for the wood stove and propane heater come from?  Making the building envelope tighter will reduce the heat requirements but increase the chances of CO poisoning.  Do you have a dust collection system?  Where does the make up air come from?

Seperately, electric heat is very efficient however it is usually very expensive.  Perhaps you might be interested in an outside wood burning boiler.  Heat up a suitable storage tank inside the insulated shop via a small pump.  A second small pump could then feed wall or ceiling mounted radiators or a radiant floor.  A concern would be freezing which could be addressed via a suitable antifreeze solution.  Inside tank could even be a large electric water heater which could provide an alternate heat source.

Brad White

Warming the space -or you?

If the electric heat is to form the baseline, say to keep things from freezing, that is one approach- when you are there, you have the wood stove as you said. But if there is no water piping to freeze and electric heat is your choice, why not electric radiant heaters at or near the ceiling and in corners? With good coverage it will warm you even if the space is not up to temperature and make things tolerable while you are waiting for the stove to fire up.



LarryC brings up some excellent points regarding other options, radiant floor, wood fire hydronics, but above all- combustion air. Take heed of what Larry says.



Paul is spot on in that if your heating input is less than the design heat loss, you will find a balance point and when it gets colder outside, generally speaking, you will drop degree for degree. The variables in play are the stored heat in the structure and objects as you said, but also infiltration. If windier outside when colder, your losses will be greater in proportion than just temperature differences. I hope that makes sense.



But give radiant a try, in any of its forms!



Brad