Heating a small detached garage office without dying.

So I've been heating my 12x12x12 garage office with a mixed system the last few years. First I fire up propane heater to knock off the chill (one of those 100k BTU garbage can looking deals), then I switch to a small electric heater aimed under my desk. When the little electric heater can't keep up, I fire up the propane monster again for a few minutes. Rinse, repeat, air our the office a few times a day to help with exhaust. This was effective, but very stupid to be doing five days a week.

This year I got a heated floor mat to keep my feet warm, works great. But I wanted to ditch the devil's trashcan heater for something that vents outside. I like propane because it is cheap, and I have a refill station 500 feet from my house (handy!). Last time I tried heating my office with just electric my power bill went nuts, so I don't want to do that again. Now I'm looking at what I'm guessing would be a small furnace that I can mount on the wall (or outside the garage) that blows only heated air into the space.

This seems like the solution: https://www.usstove.com/gas-appliances/gas-stoves-fireplaces/11000-btu-direct-vent-propane-heater/

I'd need to rearrange a few things on my external wall and cut a hole for the vent, but the idea seems solid.

What I think I'd really like is a tent heater like this: https://www.homedepot.com/p/VEVOR-17000-BTU-5000-Watt-Diesel-Air-Heater-All-in-One-Diesel-Heater-with-Remote-Control-and-LCD-Switch-12-Volt-ZCJRQYTJ5KWDFKYJ1V0/318766139

I like the idea of just plumbing an intake vent through a window pane, and mounting the heater itself on the outside wall of the garage (I have really wide 36" eaves all the way around). I'd need to fuel it up more often than propane, but not having to give up interior wall space is tempting. And for less than $200 I can chalk it up as an test if it doesn't really work.

Any other options I'm missing?

I heat my 25 x 25 x 10 shop with that same Vevor diesel heater. They're a copy of the Webasto units but way cheaper. Buy it on Amazon instead of Home Depot. It needs a 12V power source and a battery charger won't quite cut it on startup. Mine is wired with a used motorcycle battery and battery maintainer. Works great.

Mine runs a 50/50 mix of diesel and waste oil with a splash of stale gasoline thrown in (I have all three fluids in abundance).

It pulls clean combustion air from outside and exhausts outside. It heats room air and returns it to the room. I have a 5000 Watt electric monster that I use in addition if the temperature gets below -20.

In reply to ShawnG :

How is the noise and fumes compared to a kerosene torpedo heater?

In reply to gearheadmb :

Much quieter and no fumes. Combustion air gets exhausted outside.

How's the insulation?  Improving that will certainly reduce heating requirements and probably will save money in the long run.  I'd think a 12x12 space in Georgia shouldn't take much.

In reply to stuart in mn :

Insulation is decent. I have fiberglass in three walls and 2" foam board in another wall (due to reasons). Ceiling is insulated, but not great due to access limitations. Floor is concrete with a big rug. It gets in the 40s during the day during winter and sometimes below freezing at night. The rest of the garage is not insulated, so by Monday morning it is an ice box again.

The diesel heater idea is growing on me. There seems to be a LOT of people using them for sheds, shops, and of course camping. Looks like I could mount it outside in a little enclosure: https://www.instructables.com/Chinese-Diesel-Heater-Workshop-Install/

I'd probably use metal box to house it, maybe scrounge  and old utility box.

https://grassrootsmotorsports.com/forum/off-topic-discussion/help-me-build-a-thermosiphon-solar-heater-for-my-g/144999/page4/

First hand experience with the diesel heaters here.  I have one in my big dumb (diesel) van.

It is a truthism that they are pretty awesome.  

They have a heat exchanger just like any other high efficiency furnace so you have separte heating circuits and combustion circuits so thats nice.

They like to be run wide effing open to not soot up so don't think "bigger is better".  A smaller one running more frequently and hotter will be happier than a big one running less frequently with intermittant cycling.

The 8K and 5K BTU are the same units, this is just Chinese bologna, the 8K BTU unit cant move enough gas to actually make 8K BTUs due to the fuel pump size

The air that comes out of them is nice and warm.

The exhaust that comes out of them is hotter than hot.  They are not very efficient.

The accessories that come with the heaters are hot garbage.  I used genuine webasto intake and exhaust piping and fuel lines and its way nicer stuff.

The heater in the box is probably not the best option for you.  Best option would be to mount the unit outside in a metal container, and then run both the heat and cold air return into your office space.  You want to draw the cold air return from the same space you are heating.  

The "12V battery and a maintainer" is a great option.  They draw 8ish amps on startup and then drop back to about half an amp when just the fan and fuel pump is running.

The exhaust is a bit loud when they are warming up or running wide open.

Me personally?  I wouldn't want to mess with one for every day heating my office would get one of those direct vent propane heaters or a pellet stove and be done with it

If you do decide you want to go for the Chinesium heater, you 100% want an Afterburner controller.  Read the tutorials and FAQs first of course.

https://www.mrjones.id.au/afterburner/

In reply to mtn :

I thought about doing that with black pipes and plexiglass years ago, maybe for the main garage someday. For now the gables are vented to keep down the moisture inside.

Are you still in Atlanta? 

I would go with a mini-split heat pump. 

I use a 24k BTU heat pump in my shop but you could probably get by with a 9k btu. Heat in the winter, AC in the summer. One unit. 

You can pick up a cheap one for about $500 and they take a couple of hours to install. 

That was my first thought as well, Toyman. Mini split. A lot more efficient than a resistive electric heater.

I kept the natural gas infrared heater and added a window AC unit to my shop when I moved in. I had to run a gas line to the shop to do this. I've regretted not going with some mini splits ever since.

In reply to Toyman! :

A mini-split is my plan for when my window shaker dies and business picks up a little more. I'll throw it on the research pile again.

In reply to slefain :

In that case, the little diesel heaters work fairly well.

I would be hesitant to leave it running unsupervised for extended periods of time but they put out a surprising amount of heat and are reasonably inexpensive to operate.  

As far as powering it goes, I use one of these. 12v 30 amps. No battery needed. $20. 

I keep my thermostat low in the winter because my electric HVAC system uses more power in heat mode than A/C mode. 

I bought a heated seat pad and it keeps me warm locally.  Its one of the kind with the heat and a massage feature that use occasionally for back pain.