My heater just got delivered. I'm anxious to get it fired up. If things go well, it should be running by the weekend, or early next week.
I bought a Detroit Radiant Re-Verber-Ray. It is a low intensity, two stage, with a pusher motor and is 20 feet long. My shop is 29 feet square with a 9 feet ceiling. A had to get a low intensity because I have a low ceiling. Two stage because it uses less fuel and again low ceilings. I would have preferred a puller instead of a pusher, but I don't think it matters much
One of the reasons I went with detroit radiant is because they have been in business for a long time, and that it is the preferred brand with my local propane supplier. That way if I ever need parts I should be able to get them locally, and the guys are familiar with it.
I looked at a lot of brands, and was surprised at how similar they are in price and features. Some brands start cheaper, but by the time you add hangers, chains, thermostat, and intake/exhaust the most end up about the same price. Of course that sale at farmtec looks pretty good.
From the looks of your shop, I would put a single tube down the center from one end to the other. If you can do that and avoid lights doors and such. With my heater pointed straight down it only needs 30 inches of clearance total side to side, and 50 inches below it for combustibles. It looks like that would fit between your lift and ceiling fan. My 20 foot heater needs 23 feet to install it. The tube is 20 feet long, 2 feet for the burner, and a minimum 1 foot exhaust before any cap or elbow. So for your 40 foot shop, a 30 foot tube, or a 25 foot if your big door gets in the way. Or you could get a longer tube and put a 90 degree in it to make it L shaped. Maybe start it between your little door and ceiling fan and end it where your current heater is.
Remember your intake and exhaust can only be about 20 feet long.
I'll end this long and rambling post with what I learned talking to people and reading, it may help you pick out a heater.
Shop layout heater placement: The higher you mount the heater, the better coverage it will have. My heater says it should have direct heat 15 feet away on either side of the heater. Beyond that 30 feet of coverage I've heard it gets colder, but not much colder.
Intake-exhaust: I think this is the most important thing. I ended up having to put my exhaust through the roof, but would have preferred going out the wall. If you do go out a wall, don't have the exhaust going into the wind. I guess a strong head wind can cause major problems for these heaters.
Tube layout
Straight tube: hotter at the burner, cooler at the end.
U tube: balanced heat all the way across. Plus intake and exhaust can go out the same wall. But you have to keep the intake and exhaust seperated.
Push or pull blower
Push: with this style blower is in front of the tube. hotter at the burner, cooler at the exhaust. It is supposed to be the most reliable since the motor only sees clean intake air.
Pull: The blower pulls air through the tube. This provides even heat in tube, but the blower may not last as long.
stages:
single stage: cheaper to buy than two stage
two stage: uses 10% less fuel than single stage
Keep us posted on what you decide.
good luck
