Anyone knowledgeable on garage heaters?

I'm looking to have a garage heater installed and I think the size recommended might be too much. Anyone in the industry?
Garage is all dry walled and insulated (1989 insulation codes when built) with one average size window. It has a double and a single 8ft door and the foot print is 30 deep by 40 wide with 10ft ceilings. The gas and electrical outlet is in the rear right corner at ceiling height. This is where the work area is.

I know you have to figure the actual output and for 5300ft elevation. Any reccomendation on BTU's needed to keep it at 65 while working on projects in the winter? Also a 2 stage would be nice so it's not full blast when on to regulate the temp. I was quoted a 125,000 Hot Dawg HD 2 stage.

Any help would be great before I pull the trigger and order.
Thanks.

I have a gas unit heater in the garage. 95k or 98k BTU (I forget which) and single stage. Currently it is jetted for propane but re-jetting for natural gas isn't a problem. Heats a 24'x30' space pretty well.

I'm going to wood heat, so this heater is for sale. PM me if you are interested.

I have a 75K BTU in an uninsulated 35'x35' shop with thermostat control. It does a pretty good job down to about freezing, below 15-20 degrees it runs continuously to keep it around 70 degrees. I actually have it up for sale since I bought a 250K BTU construction heater that does the job with less gas. No thermostat on that one but I only run it when I'm out there anyway.

There are several online BTU calculators though they seem to vary greatly and I'm not in that industry but you want to calculate the delta; how much do you want to raise the temperature from ambient? E.g. if it's 30 outside and you want it 65 you need a big enough heater to raise the temp 35 degrees in that space, if it's 10 below outside you're going to need a bigger heater to raise it 75 degrees to the desired temp.

edit: Ha! guess I should have said "PM me if you're interested" as well.

I bought the smallest Hot Dawg they make, because I was told it was "plenty big enough for my 2-car garage". I wish I'd gone with a bigger one. But someone here mentioned that you DON'T want to go too big, but I don't remember why. He made a lot of sense though. But my Hot Dawg is a good product, I like it...I just think it's too small, takes forever to get the garage comfy. And if it's really cold out, forget it.

Might be a tad over sized. If the thermostat and heater are both set up for two stage heat it should be okay.

The first thing to do before installing a heater would be insulating the shop. I have a 24x30 (10' sides, 14' peak) pole barn (metal) with spray foam insulation. R value is R7 per 1" i have 2" sprayed in. Using a ready heater 28K propane unit the shop is t-shirt comfortable within 30 minutes. There are 2, 52" ceiling fans at each end running for 5 minutes to distribute the heat. If i run the heater for more than 30 min, average indoor temp is 60-70 when outside is 30 or colder.
Good insulation, air circulation and even :) carpet helps keep the work area warm without running a heater 24/7

This

i am using this to heat my shop 24x36 insulated pole barn, 12 foot sides, 16 foot peak, r-10 celings, r-19 walls insulated doors open soffits though so a lot of air flow

will heat the shop to 70 if i let it run on a cold night, adjusted to a 3200 watt setting
http://www.northerntool.com/shop/too...D-_-707-_-CONF