Shop Temp

Probably around the edges of and thru the overhead door. Overhead doors are hard to seal and only have about an inch of styrofoam insulation.

-- Bruce, Boise, ID

If you have 10 inches of blown insulation I doubt it is the ceiling, unless you have huge gaps and cracks and while loosing some heat to the concrete slab shouldn’t be a very quick process. Now 10 foot ceilings would concern me however from a different perspective. Do you have a ceiling fan? Grab a step ladder and see what happens as you go up. Made night and day difference in the temperature in my shop and how I heat now. I secured a box fan to a beam blowing down in my shop and went from wearing long sleeve shirt and light jacket with the kerosene heater on high to t shirts and shorts no problem with it on the lowest wick setting. With out the fan the shop would “cool” quickly on my working level and the top 3 feet be toasty warm.

I don’t think it’s the slab. my last shop and the current one (freestanding buildings) both had uninsulated slabs but were still fairly easy to heat, and held the heat well. The mini split should serve you well, but check to see just how low a temp it can provide heat. But before doing that, I would start trying to track down the heat loss. Circulating the air will also help, but I’m thinking you never get it really warm enough for it to stay warm for a short while. The minimum temp in my shops is usually about 50º since that’s as low as my thermostat would go, but that gets everything warm enough to stay warm when I crank it up to 65.

-- Our village hasn't lost it's idiot, he was elected to congress.

Do you leave the heat on or let it drop when not in use? My shop is 24” by 24” with 10” ceilings and a 8’ by 16’ Overhead door (2” thick). About the same 10” blown in insulation and a 4’ by 4’ window. I use in floor glycol heating and put 2” Styrofoam under the slab and 1.5 ” thick Styrofoam 2 ’ vertical around perimeter(heat sink).
With everything in the shop and a 5” slab of concrete there is a lot of radiant heat to keep thing warm for awhile.
That said when its 20 below thing tend to cool off pretty fast.

-- Lifting one end of the plank.

Since you are not maintaining the heat, you are only heating the air in the shop during the short time you are in it. When you turn off the heat, the heat from the air continues to transfer into the building and everything you have in the building, which is a substantial amount of mass compared to the air. If you are going to continue to shut off the heat and only turn it on for short periods, you will not be happy with a heat pump mini split. It will take longer to heat the air up than your current 50k btu oil heater (you would need about a 4 ton heat pump to get that, not a mini split – additionally, the strip heat would come on because of the demand profile you are using, which defeats the purpose of the heat pump).

The recommendation of a circulating fan is spot on. I use a small portable squirrel cag blower from Lowes to circulate the air – anything that moved it top to bottom or bottom to top – doesn’t matter. 10” insulation in the attic is pretty good, more will help – calculate the R factor and see what’s recommended for where you live.

My shop is an attached 2 car garage, with ~10” attic insulation over it, in SW Missouri. I keep the temp constant at ~63° with a small 1500w electric heater, even when it’s 0° out. 1500w is enough because everything is up to temp. If I turn the heat off and let the temp drop, it takes forever to heat things up. Since I typically spend a little time in there everyday, I keep everything heated up. It’s actually cheaper vs letting everything cool down and then heating it back up every day. Now, if you only go to the shop on weekends, it’s a different story – a different demand cycle.

Many believe programmable thermostats save money. With oil and gas heaters, yes. With heat pumps – no. I’ve studied the typical home demand cycle for heating and cooling (I’ve worked for the largest US refrigerant compressor mfr in engineering for the past 25 yrs). Without going into all the details, for heat pumps and AC, it’s best to set it and forget it.

Base your decision on how you plan to use your shop. If you spray solvent finishes, getting rid of oil or gas heat is a great idea. Do you want AC in the summer? How does a heat pump compare to oil for heating cost in your area? Calculators are available online to help. Do you need to stop using oil for some reason? Do you use the shop daily or a day or 2 per week? Thinking through the plan and costing information will help you make the best decision.

first off… define “not maintaining heat with a reasonable amount of time”. temperature heat loss per hour, for example? I have a 65k BTU natural gas blower, R-19 insulated ceilings, attached 2 car garage, 1 out of 4 walls insulated due to the house and roll up door not insulated (yet). I have not counted how often it kicks on and off, but I do not expect my workshop to be super sealed up, as a house would be. So there are expectations of heat loss here and there. I know I could go all out and seal with diligence and make things more efficient… but eh, i’m happy as is :)

-- The Carpenter Bee is derived from the Ancient Greek word wood-cutter "xylokopos/ξυλοκὀπος"

I probably have unrealistic expectations as to how long my shop should stay warm when I bring it up to 70 degrees, it stays comfy for about 15 minutes if it is really cold outside. At its coldest here it has never gotten below 32 degrees in the building with no heat.

OSU55, I would like to be able to warm it up like your shop and maintain a constant temp when not in use, right now it is getting used at least 8 hours a day. I fully get the fact that until it’s all warmed up and kept that way then I am never going to be satisfied. Can you give me some more details RE: your 1500w heater.

Thanks to all who have responded, your input is greatly appreciated.

-- Brad

going to time my on/off/duration this weekend and report back :)

-- The Carpenter Bee is derived from the Ancient Greek word wood-cutter "xylokopos/ξυλοκὀπος"

I agree with OSU. It’s because you are not leaving warm for long enough to warm up that concrete and other very dense things. When those are warmed up, then it will stay warmer in there. I would say keep it warm out there for a couple days so those things warm up. Then you can turn it up and down with less loss of heat.

-- Bill M. "People change, walnut doesn't" by Gene.

I use this heater, but about any will do:

and plug it into this. The tstat on the heater won’t keep temp very well. Yeah, it’s programmable, but it’s what I found. I just use the “hold” function and keep it at one temp.

What type of oil heater do you have? It’s not tstat controlled? Is it a kerosene wick type heater?

“What type of oil heater do you have? It’s not tstat controlled? Is it a kerosene wick type heater?”

Heater is not on a thermostat, it is a Mr. Heater 50,000 BTU Contractor Series . Burns #1, #2 or Kerosene.
I do not think an electric heater would be very economical for me. I have LP avail. and am now considering the following.

http://www.totalhomesupply.com/30000-BTU-unit-heater-p/reznor-udap30.htm

-- Brad

OSU, I have been considering that same thermostat. I take it it works good. I’d like to use it to set at the lowest setting while I’m gone and turn it up when I’m in there.

-- Bill M. "People change, walnut doesn't" by Gene.

brad.. you will LOVE that reznor. I have the 60k BTU version. wow. night and day when comparing to the torpedo heater i was using for a winter. I installed it myself, but did have a HVAC contractor come out and tap into my gas line, ran 5’ of gas pipe, and pressure test it (to make it official for city inspection). 4” duct thru the wall with a thimble, right above the garage door (clears it by 3”) with a 1”+ gap above where I still have to sheetrock. Just do not ask me what I paid for mine :)

-- The Carpenter Bee is derived from the Ancient Greek word wood-cutter "xylokopos/ξυλοκὀπος"

My shop is 20’ X 30’ with 10’ ceilings on an Alaskan slab. I use 2 of the little heaters like OSU and they keep it in the low 50’s and the cost isn’t too bad to run them. I think I paid around $20 each for them at the BORG a couple years ago. Once I start working and running machines in the shop, it gets warm real quick.

-- Dave, Colonie, NY

I bought a 50k bigmaxx gas heater and keep my garage at 55 when not in use and 68 when working. Once the heater gets the garage up to temp it only cycles for short periods. This is the first winter with heat and it is great. I should have worked on it harder and put it in 5 yrs. ago. Total cost was about $650.00 for the heat and a few gas line parts. My son in law installed the gas line so the pipe was free and I had to buy what he did not have on hand. It cost me another thirty dollars for labor for the flue to go out the roof.