I've got a 600 sf shop that is insulated with spray foam. I have an 18,000 BTU mini split that does an awesome job of cooling the shop off in the summer, but the heat function is marginal at best. I am looking for an option to heat the shop in the winter.

Shop is all electric, no gas. All I really have to work with is one dedicated 20 amp circuit that I use to run 4 fans in the summer. I don't want to run another 30 amp circuit. In theory, I could tie into my air compressor circuit if needed, but I would much rather just use the 20 amp if I can find an option that will work.


Anyone have any ideas? Trying to keep cost to a minimum.

I'm assuming that the 20 amp is at 110v? I don't think you will find much to heat that much space that isn't 220v.

Can you get a propane heater and pipe it inside with bottle outside.

It'd try to get 45 btuh/sqft unless you are in the North.

I am in DFW. In theory, I could get a propane heater and mount it in the wall and pipe it outside. I would like to avoid cutting any holes through the wall if at all possible.

Yeah its 120v. I know that isn't ideal. I do get heat from the mini split, this would be to supplement. Also, I don't need it to be toasty and hot in there, just knock the edge off the cold and make it where I can work in there in the winter without freezing.

I have seen some infrared heaters that operate on 120 that claim to heat 1000sf, but I have no experience with them.

One of these probably wouldn't heat up an entire shop that size, but I walked by one at Costco and was impressed with the amount of heat it put out and how far away you could feel it. If you're generally in one area of the shop for a while, it might do well enough to make it comfortable nearby (or buy a couple if and put them at opposite ends of the shop if you move around a lot).

https://www.amazon.com/Presto-Heat-Parabolic-Electric-Heater/dp/B005T5UH4A

we have an old school propane heater and this is how we heat our deer camp. Punched a hole in the wall and have the bottle setting out back. It does the trick good enough where we dont need to be bundled up to eat dinner or sleep.

edit to say 1/2 the camp house is a screened in porch with just 1/2" Styrofoam insulation we put up.

Get a couple of the ceramic $50 heaters from a retailer. Should do the trick

Any idea how long a 20 lb bottle would last for a 30,000 btu propane heater? I've got a spot in mind where this might be feasible.

I have an 18k mini split and it does a fine job heating up my 3 car garage. Are you sure you don't have a leak somewhere? All your doors are insulated and weather sealed? I am also in DFW.

I don't think i have a leak. It cools outstandingly. What would be leaking?

I have an oil filled electric radiator heating that does a good job with what you describe, even has a thermostat on it.

Use it to supplement a large area in the house thats far from the thermostat. (downstairs)

With (1) 20Amp 120V circuit the max you can heat is 1920W. The closest sized heater is a 1.5-1.8KW unit heater, which you can get as a normal plug in type heater. This is the same power as a blow dryer so don't expect much.

To be honest with you this is not enough power to heat the area. You would need a 5KW heater to get somewhere. If you a 208V 30 Amp circuit you could get that done. If you have another 120V circuit available, combine the two and it gives you 208V. At this point get an electrician involved because you will have to up size the wire and the breakers.

Otherwise you need gas out there. You will have to vent the gas though.

My shop is 1200 sq ft and I have a patio heater (propane) that works great. Got it at Lowe's

Home improvement board might could help

Most you're gonna get from a 110V circuit is a 1,500W heater.

How tall is the ceiling?
What temperature are you trying to maintain?

1,500W is about 5,100 Btu/hr.

Required Btu/hr = (insulation quality x volume of garage in CF x temperature differential in F) / 1.6

Insulation quality is:
Good - 0.5
Average - 1
Bad/None - 1.5

So if you have 8' ceilings, you've got 4,800 CF. If your insulation is good and you're trying to overcome a 20F temperature differential, you'll need 30,000 Btu/hr.

Take whatever your mini split does and make up the difference.

rlb28 said:

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Home improvement board might could help

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BS!! This is the Outdoors Board. We know stuff!

As Todd 02 just pointed out.

I just meant an air leak. My garage is mostly uninsulated and is 600 square feet and my unit does fine. My garage doors are insulated though and I put weatherstripping around them. I figured with spray foam your unit should be able to keep up easy unless you had air leaking in from outside.

Thanks Todd02! From your math, I will most likely have to go propane.

The shop has 9 ft walls and it's about 12' in the center, with two roll up doors, one 10x8 and one 6x8, neither are insulated.

Gigemags05 said:

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Any idea how long a 20 lb bottle would last for a 30,000 btu propane heater? I've got a spot in mind where this might be feasible.

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Well, a pound of propane contains 20,000 btu. Since the max fill on a 20 lb bottle is 80%, you've got 16 lbs of propane, or 320,000 btu in the bottle.

At 30,000 btu/hour on your heater, you'd have about a 10 hour run, if you ran the heater on max.

You also have to worry about the maximum vaporization rate of propane at colder temps, but since you're only talking about a 30,000 btu/hour heater, I'd say you're good.

The vaporization rate issue only comes up when you're trying to pull large amounts of propane out in a short period of time. You may have 320,000 btu in a full bottle, but in cold temps, it won't flow out at high amounts without freezing up a 20 lb bottle, as there is not enough surface area in that size bottle to absorb the amount of heat need to turn the liquid propane into vapor propane. That's why you usually see the 'salamander' style heaters married to a 40 lb or 100 lb bottle.

Wwmfbd?

You might have your mini split checked out. I have a 300 square foot shop and a 19 SEER 9000 btu Mitsubishi mini split and it is comfortable all the time. I can never really hear it running.This is a stick frame building with 4in insulation in the walls and ceilings. It also has radiant barrier in the ceiling.

The mini split puts out warm air. If it isn't terribly cold, it does just fine. But last year around Christmas when it got really cold, it couldn't keep up. There is no ceiling in the shop, which means there's a lot more for it to heat.

Not to hijack, but why do some refer to a standard plug as 110V and others 120v?

It's a range. Sometimes referred to as 115 also. It all depends on your transformer and your distance from it. My house voltage is about 117 volts. I have a workshop about 150 feet away that is 115 volts.

Might try adding a ceiling fan to blend the air and push the warm air down

nonameag99 said:

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Might try adding a ceiling fan to blend the air and push the warm air down

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This. I have a huge open space in our living room. 20' ceilings. We have to run the fan to keep the hot air circulating. It's a ***** but the wife loved it when we saw the house. I saw AC and Heat bills.

How about a wood burning stove. They're very common in shops here in Oregon. You get to feed it all your wood working mistakes and heat lunch/coffee at the same time. A cord of wood will get you through a few winters down there.

I've got four fans in there that I'll try to use next time I have the heat on.

When I originally dreamed up the shop a wood burning stove was in the plans. Had to scrap it when I realized how tight space was going to be in there. I would love to have one though. Would be awesome.

Was just on Ask This Old House this weekend:

I agree with the propane tank heater. Could you use that to take it up to your desired temperature then shut it off and just use your split unit to hold the temperature where you want it?

Yeah that is what I'm thinking now too. It isn't like this thing is going to be used non stop. Just for the few times it's really cold when I want to work, or act like Im working but really just sitting in the shop and watching a game or something.

The shop at my old house was about this size, insulated, but not sealed particularly tight.

I used an old school kerosene heater. Did just what you said, knocked the edge off, where I could strip off my Carhart and work in a sweatshirt. MI is colder than DFW, fwiw.

An IR electric radiant heater is what I would suggest.

Doesn't create issue with fumes that propane does and doesn't move the air.

http://www.leevalley.com/us/wood/page.aspx?p=44590&cat=1,43456,43465,44590

Volume of air doesn't really matter. It's surface area of your walls. I'm not suggesting you do a full blown Manual J calculation, but there's better ways to estimate heating loads.

(Area*TempDiff)/SurfaceArea

Assuming you want to maintain a 40 F temp difference and you have 1" of spray foam with R=5, then each square foot of wall or ceiling surface area would require 8 Btu/h to heat the space.

That doesn't account for man doors, windows, and air leaks, so put in 15-20% overage just in case.

In the event that you have different insulation in walls vs ceiling, you can calculate each separately and sum the results.

ETA: insulate your doors first. That's 128 sq ft of R=1 (and that's being very generous). You're losing nearly 5000 btu/hr at a 40 F differential. That's over half of your mini-split capacity right there. Get some blueboard at Lowes and glue in place. It'll help in the summer too.

The doors are roll up doors. Is there a good way to insulate them?