Some years ago I built myself a ground blind "hunting shack" in which I could wait out coyotes that were raiding the sheep herd on the farm of a friend. Usually arrive at least an hour before dawn and if there is to be any activity it is usually just as the sky lightens but before the sun is actually out. Twilight, is probably the correct description... The blind was 4x8ft floor plan and the peak of the roof 8ft high so that it was efficient at using plywood sheets. The 4 foot dimension was really too narrow in hindsight, I wont do that again...
Initially it had 3 sliding windows, single pane. The walls were built using 2x4 studs laid on their side so the "core" of the walls was 1.5" thick. It had 1/2" plywood outside, rigid foam insulation 1.5" thick and 1/4" plywood on the inside. The roof was also insulated with 1.5" of rigid foam. Initially I had a "Mr Buddy" catalytic heater running off a 20lb cylinder, later I went up to a 30lb cylinder for longer times between filling. The door was hand made without insulation, 2 layers of 1/2" plywood.
Suffice to say that the water vapor produced by the ventless heater had the windows covered with a layer of frost on the inside, long before the space was comfortable, and then I had to wait until the frost thawed, before I could use a towel to wipe the condensation off the window to peer outside. This obviously was completely useless at its intended purpose. Also, after a bit of snow and the first thaw, all the window channels were full of ice which meant that the windows could not slide to open. Also pretty useless when you needed to poke the rifle barrel outside to shoot the insurgent coyotes as they launched an attack.
So then came version 2 of the shack, out came the sliding windows, to be replaced by double pane tilting windows (casement windows I believe). They were a bit of a hassle because the tilt mechanism wouldnt hold them in position so I had to add some paracord ties to hook onto the latch arms to hold them in position if I needed the window open. The Mr Buddy heater was replaced with a Marine Dickinson propane heater which was vented (or so I thought)....
The way the product picture is taken as well as the fact that this is intended as a heater on a boat, would make you think that it has a sealed combustion system. As it turns out, it is basically built like a single burner heater like used for camping, with a cone positioned above the burner to capture the combustion products and a woefully inadequate 1" flue pipe... Anyway, I digress...
The combination of double pane glass and somewhat vented heater did mean that the windows were no longer frosted up and only minimal condensation ocurred on the inside of the glass. So the changes did resolve the issues I set out to cure. This was in a space that had a volume of less than 256 cu ft and it was sealed up pretty tight excluding the B vent style flashing poking through the roof into which I ran the 1" flue pipe.
Now this is a rambling kind of post which doesnt seem to be making any point, so here it is: Neither the Buddy heater, nor the inadequately vented Dickinson heater produced any sort of safety problem, headaches or otherwise. I will say that the vented heater was a much more functional solution.
Now if I need to work on my truck in the barn, I am usually working with a diesel powered torpedo heater about 6 feet away and I would just be one of millions of northeners who have to do this in order to get work done when it is sub freezing outside. I dont think anyone has invented a portable, relocatable vented heater yet. so we just do what we need to do and as Mike Rowe says, perhaps its safety second and not safety first....
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