Hot water baseboard questions

Well, bought a house that has a finished, three-season room, about 20x26, two exterior doors, seven windows, western exposure here in sw Ohio...floor will be laminate or wood. The wife says, "Make it usable for winter-time", I know this means it has to make 70F min for her to use the space.

I am wondering if hot water baseboard around the perimeter is the way to go, but don't know too much about it. Rest of the house is heatpump/furnace, so am thinking this room has to stand-alone for its heating needs. My biggest question is, what do these baseboard water heat systems use to heat water, an actual boiler or jsut a hot water heater? If this unit only has to heat this room, do they sell systems for that small an area? The amount of water in the system couldn't be that much, 8 or 9 gallons maybe? Could I use on of those instant hot water heaters mounted in the corner or will I need the higher temps of an actual boiler?

Thanks for any advice you can give to get me going down the right road. The wife is in Iraq right now (Army nurse) so I have this summer and fall to make it happen.

The first thing you need to do is calculate a heat loss value at your local outdoor heating design temp. Download a heat-loss program like Slantfin's Hydronic Explorer, or Crown Boiler's spreadsheet heat loss calculator and measure up the room, doors & windows, enter it all in, see what it comes up with. You'll have to look up your heating design temp and enter that too, but I'm guesstimating that it would be about 5-8F ofr a 97.5% number- it's +6F for Cincinatti. The Slantfin tool always seems to overshoot reality by 30% or more, so using the 97.5% ASHRAE binned hourly number would still have PLENTY of margin, and you could even undercut it 15% from their in the design and never actually be cold (except maybe at 6AM on the coldest hour of the coldest day of the century.)

Then figure out if you have enough perimeter area to get there with baseboard at anything like domestic hot water temps. At 120F fin-tube puts out ~200BTU/linear foot, at 140F it puts out ~300BTU/ft. There are low temp panel radiator options as well (eg Runtal) if you need more BTU per linear foot to hit your design-day heat load numbers.

Do you have natural gas? Do you have a natural gas fired hot water tank? If yes, it's highly likely that you could run a heating loop off of it (through a plate-type heat exchanger.) No matter how much glazed area you have, if it's double-pane and the rest of the room is reasonably air tight the room would need well under half the output of a gas-fired HW heater's burner even on the coldest hours of the year.

If you want to make it extra-cushy and have the budget, putting radiant floor in there using a low temp system such as WarmBoard (tm) would make it more comfortable at 66F than fin-tube baseboards would be at 70F room temps. Going with low temp panel radiators or radiant-baseboard (either cast-iron like Burhnam BaseRay for the "classic" look, or something Runtal UF-2 for a more contemporary look) is more comfortable than fin-tube type baseboard too, which would be intermediate in cost.

I hope your wife comes back safe & healthy in body & spirit- just the background stress has to take a toll, and then there are suretly some acute incidents to mentally process. She deserves to come back to some home-comforts after a sacrafice like that, and I commend the both of you for your respective efforts.