Right now this isn't even drawn out on paper yet. I'm thinking of 4 modine type units, may go with two, who knows. I think i'll get a more balanced/even room temps with 4. Picture 35x75(16ft ceiling) two bay truck garage with at least one, sometimes two 65ft long trucks parked in there, only 12 hours of the day though. Plan on 45f room temp when not occupied by a human. When I'm in there I'll go to maybe 60/65f ? I plan on having the boiler plumbed up similar like my house, which is done per Tarms diagrams. The system will have a T-valve(I think termovar 1) so that when the unit heaters are calling for heat, that will be priority over heating storage.
And yes, i agree jebatty, in the absence of boiler running, storage will loose btu's pretty quickly. Not big deal if it drops below temp in the garage. What i need to learn is location of inlet and outlet into propane tank. Didn't know much about it, other than returning wtaer to tank it should be on the bottom. Would like advice on where to locate inlet and outlet.
I'll be in and out of garage, with truck, basically a 12 hour schedule. I usually leave with truck at 4am and return 3 to 4pm. Usually the garage will stay empty in between those times. If i get home a 3pm and storage is depleted, i will build a fire. If i need to do a few hours of work at that time, I will crank up t-stats and go up to the house for lunch or whatever. I should have 165f+ water rolling thru modines in an hour. 185f+ water shortly after that. With the 4 modines, shouldn't take long to make it toasty in there. In years past I used an oil fired unit heater for heat when I was in garage. It was shut off. most of the time when i wasn't there. Burned 200 to 250 gals a yr. But i want to maintain garage at 45f all the time.
With your guy's input, this should work quite well. I bought that Tarm solo 60kw boiler for $1700, or I should say i kinda stole it. A welder/fabricator, who has done these propane tank conversion before, has given me a price of $950 for tank, all fittings in place. Also he will pressure test it too. I will hire to have everything installed. But that will be with my BIL, he installed the system in my house. Very capable and will treat me fair on price.
What i'm finding out, is with the advancement of pellet boilers, you can find some decent deals on used wood boilers. People lost the interest in handling cord wood, which I feel their pain sometimes. Just be patient and you can find a boiler, maybe.
Maple, I'll look inti variable speed units, but I have a grundofoss 3 speed on my house system, once i found the right setting, i haven't touched it again.