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With my 12 x 22 ft. shop's newly-installed R-13ceiling insulation, I stand
a chance of being able to work in all but the very coldest weather the
Inland Northwest can muster, probably -4 deg F on the coldest of
mornings.

I've found that with the propane Heater Buddy that I use to bring up the
heat with the two oil-circulating electric heaters to maintain the
temperature, I can easily maintain the inside temp a about 45 degrees or
more above the outside temp. So, when it was 20 deg out the other day,
it was 65 inside. Not so great for gluing or finishing, but a start. My
question is, if it's 20 deg F outside and 65 inside, can I expect the same
difference if it's 0 deg F outside?

Thanks for any input.

_________________
now known around here as Pat Foster
_________________
http://www.patfosterguitars.com

I don't know Pat but I can tell you what happens here.

The colder it gets outside even though my furnace will maintain any temp I want my humidifiers become taxed and have to run much more.

So I suspect that as you require more heat the drying action of the additional heat will require you to increase your levels of humidification.  Knowing your climate a bit as I do you may find that what ever you currently use to humidify is no longer enough for the coldest days.

There seems to be a tremendous difference in the levels of humidification that my place needs between 30F and 20F.

Yes, the differential should stay the same regardless of the outside temperature.

That is, assuming that the heaters are running full time to maintain the stated 45 degrees difference, and wind and humidity conditions remain the same.

Mark

It has to do more with the type and quality of insulation that you have through out the entire shop versus the level of outside temperature drop. To say that the inside shop temperature will drop in a linear relation to the outside temperature would be IMO inaccurate.

If you have fiber type insulation with some "R" rating which really doesn't mean much when you compare it to a solid insulation board like foam there are a few things that effect it's efficiency. Pat you live in an area which gets pretty windy I bet and in the winter times, that wind can drop the outside temperature substantially. Also that same wind can seep into the shop easier than "the cold" and lower your shop temperature if the insulation and vapor barrier isn't up to snuff.

Have a read through here for a lot of reading on insulation.

I would think that a R-13 fiber insulation is not even close to adequate for your climate. I would have thought R-40 would be really what you want at minimum in the ceiling, that's what I have and R-30 in the walls. Your really going to be spending a lot more $$ over the next couple years on electricity and fuel than you would by upping the insulation in your shop.

I don't have the extremes that you do Pat, but my shop can hold a steady 70*F regardless of the external temperature. last year when it dropped down to -20*C (-4*F) it was a toasty 70*F in the shop, I was wearing shorts and tee-shirt.

It's all about having effective insulation otherwise the heat just escapes and the money keeps going out your pockets. There goes another fine set of Zoot.

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I should mention that a small turn of my thermostat will easily raise the inside temperature as high as 85*F if I wanted to sweat the entire time I'm in there or was doing some glue ups. I have two electric baseboard heaters (1-1100W and 1-750W) which heat my shop as much as I want.

Effective insulation is really the key though.

_________________
My Facebook Guitar Page

"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

Hi Pat,

Rod is right on the numbers, and giving you excellent advise!

I can add one thing. The rule of thumb for insulation, is to “complete the envelope”. This means,
you need to not only, insulate your ceiling, but, also walls and floor. (Unless it’s a concrete floor)
Code requires in my area, a minimum of, R-38 in ceilings, R-13 in walls, R-19 in floors.

Can you tell us about the construction of your shop?

One more thing. If it is possible for you. You can save a lot of money, if you go with a propane
heater of the type that hangs on the wall. I believe a 10,000 to 15,000 BTU unit would be quite
adequate for the size of your shop. Don’t get the “radiant” type, (The ones with the ceramic tiles)
their OK, but the “Blue Flame” (flame behind glass) type is much more efficient.

There is another option, but, it involves burning wood. You have probably already thought of this.
There are pro and cons of course, but if you have access to a lot of wood, its not a bad way to go!
A small buck stove would be more than enough.

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Everything has beauty, But, not everyone see's it!

Insulation is the key.

My shop is 26 X 32 on a concrete slab. The slab has R-10 perimeter insulation. The walls are R-20 and the ceiling is R-30. I run two portable  electric, oil radiator, type heaters set on medium. That's 1600 watts total. I have no problem maintaining 65 degrees inside even when it's 0 F. outside.

Gas is not always less expensive than electric. Here in Montana, propane is over $2.20 per gallon, electricity is 4.8 cents per KWH. It is much less expensive to heat with electricity.

Mark

Great feedback, gentlemen.

A little more on my situation. I don't intend to keep the temperature up all the time. Mainly I want to keep it above freezing when I'm not out there, and be able to bring it up to a decent temp during the 4 to 8 hours per week I'm able to squeeze out of my schedule.

The building is a 1 1/2 car garage, minimal but decent construction, wood frame, shingle siding, hip roof. It had no insulation but now has 1 1/2" foam on the steel door and the R-13 in the ceiling, which have made a huge difference in both winter and summer. I expect we'll be moving in a few years, so I don't want to put much into it. There's also a budget issued. But if we don't move we'll raze this building and have something larger and more substantial built, with insulation like Mark's. We're about 4 hours apart and have similar climates. Right now it's just barely adequate, workable if I don't buy any more stationary tools.

I was mostly wondering if what I currently use for heat is going to enable me to keep it above freezing at the lowest expected outside temps. Looks like I can, using propane and the electrics to bring up the temp, then maintain it with the electrics. The humidity is another matter, but I'll be keeping the wood in the house and taking it out to the shop for gluing when the RH isn't too far out of line. Right now it's been holding at 39 to 45% RH, so that may not be an issue.

Thanks for the enlightenment!

_________________
now known around here as Pat Foster
_________________
http://www.patfosterguitars.com

Pat, when I did my shop, I knew I had one shot and wanted to do it right the first time.
It on a concrete slap which I have no idea what the R value is. But I went wall to wall with horse stall mats. (Those very hard 3/4" thick rubber liners that weigh almost 100lbs for a 2x4 sheet) Walls are R 19 insulation and R 38 in the ceiling. 6 mil vapor barrier around the whole thing (walls and ceiling) and then drywalled. The space is tight as a drum. I have one external combustion/external exhaust propane heater which never gets above its "low" setting. And it's always 65 degrees in there (unless I let my tanks run out on a Friday like I did last winter) Even after 2 days of no heat it was 45 degrees when in was about 10 outside.
If you can keep your humidity in check, it doesn't really matter what type of heat you use. Just remember that open flames will dry things out much more quickly than other sources of heat.

The vapor barrier Paul mentioned is really a great thing. I did the same in my shop. I covered the walls and ceiling, taped all the seams, and then hung the drywall over it. My concrete slab got two coats of concrete sealer and 2 coats of semi gloss varnish to seal it up (made it look nice too). It is REALLY easy for me to control the humidity now!!

Mark

Hey Pat....I am one of the least experienced builders here and don't feel comfortable with giving some advice.....I would like to give you my experience with my workshop....I live in a cold climate. The temp outside now is -23 C,,,,I had problems with controlled heat and humidity...I asked a lot of questions in here and got a lot of good advice....I was using a 2000 watt electric fan heater....The heat and the humidity could not be controlled....I installed  electric baseboard heaters..I set the thermostat to a very comfortable 20 C. The humidity fluctuates a little bit but is easily controlled for building purposes....Maybe some will disagree on this point....I feel that the type of heating used in your work shop has an effect on your humidity...In my case the fan heater was drying the air as fast as I was putting moisture into it....Larry