I would like some help on the best way to heat a 30x36 shop. I pex in the floor and it will be well insulated with 10 ceilings. I will use the shop for play. I would love to heat it all winter but I think it will cost a lot. Or should I just put in a overhead heater that I can try on when I go out there. Let me know what you think. I have LP. If I did up a do a boiler for in floor what would be the best LP or elect. Some with an overhead heater what would be better LP or elect. I live in Michigan. Please let me know what you think would be the best.

Use an efficient water heater rather than a boiler. Boilers for that application are pointless. A good water heater can be purchased for under $1K. There is a great company up in VT you could research. I bought my equipment there years ago and they heat a 5000 sqft. commercial space with ONE Polaris water heater, I saw the setup myself and it was very simple yet effecient

Open loop,
I think you have that backwards,
A polaris unit runs about $3,000.00++ parts, freight assembly time, lost square footage, stand by heat loss.
Might as well put in a quality wall hung modulating condensing boiler (check Larrs Mascot among others). same basic price, no stand by loss, built in grundfoss pump will handle 2,000 feet of pipe easy. This 30x36 shop, 1/2 pex on 12 inch pattern = 1,200 feet of pipe.
Or the electric boiler assume 30 BTU per square foot (I can not provide a accurate heat loss here) 30x1,200=36,000 BTU.
Look at a modulating electric boiler, again only on when there is a demand. A thermolec 34,000 BTU Boiler will run around $1,000.00
Add pump, flange, expansion tank, back flow prevention, air scrubber, low water cut off, perhaps some glycol, your maybe in to it for $1,600.00 to $2,000.00 tops.
There are 2 good system examples that are proper and will out last any water heater, and have maximum fuel efficiency.
Dan

a mod/con almost always makes more sense than a very expensive water heater like the Polaris. not always, but nearly always. You can exceed the efficiency rating significantly on very low temperature systems as well.

that said if the area is only going to be intermittently heated, slab radiant is not a very good choice and something for "spot heat" would make more sense.

Am I wrong in thinking boilers are specifically designed to boil water? I also may be wrong in thinking most radiant systems need only warm or heated water.  I bought a used AO FOR $500 and it heats my house beautifully I usually always end up having to turn it down, the pex was the most expensive part of my system, funny.
My heat, and all domestic runs me $350-400 a month in the coldest months using propane. Installation was a retrofit and I have travertine floors with a mud job.

yes, you are wrong in thinking that boilers are specifically designed to boil water. there is some "microboiling" on the heat exchanger surface, perhaps, but the name simply harkens back to the days of steam, when they actually were boilers. These days I would consider a boiler running hot enough to equal your water heater "medium temp" as opposed to "low temp", actually. Incidentally, I don't know why it's impressive that "the VT company" heated a 5k sq ft facilitate with a heat source with around 100k in output, like the Polaris. 20 BTUs/sq ft is a pretty typical load and it's actually kind of high for a large building like that. Now if they heated it with your AO unit, that might be impressive (depending on what your unit is).

the fact is, a mod/con could easily drop 20% off of your water heater bill, and probably more. with your bill, your payback would have been in very reasonable timeframes and your ROI very respectable, significantly higher than any interest on a loan so borrowing to make it happen would have made very good sense. So you made a mistake choosing a cheap tank heater, assuming you weren't trying to cheap out in order to flip the house on someone less savvy about mechanical systems and that you are actually interested in your own medium to long term interest in this house. Lucky for you, it's probably not too late to rectify the situation, but you added close to a year to your payback by buying the tank, and if your system is now filled with non-barrier pipe, then you might need to be careful with the unit you buy to avoid corrosion. I'd recommend a prestige solo and an appropriate pump, or maybe a munchkin VWH.

Hope you can get to saving money this year! Supposed to be a cold one, might get you a jump on that payback period.