Electric radiant floor heat questions

[KLF]

In doing a renovation of a sunroom that will be insulated and upgraded so it can be used in the winter. Currently there is no heat out there, so I have a clean slate. No foundation, this is a boxed insulated floor sitting on piers (open below), ledgered off the back of the house. Footprint is approx 9' x 12' (inside). Originally I was going to just put an 8' strip of electric baseboard heat out on the far wall, controlled on a thermostat on the wall by the door. I don't plan to use the space every day in the winter, so most of the time the heat will be shut off. If I wanted to use it in the winter, plan is to turn the heat and ceiling fan on, let it sit for an hour or so, and it should be up to usable temp.

A friend is trying to convince me to do radiant floor heat instead. Probably the Schluter DITKA system. But at about 15W/sq ft, I would only be able to get about ~1600 Watts of heating (the 8' strip is 2500W). I can do the baseboard for ~$300 total, assuming I do all the wiring (easy). The radiant floor is gonna be close to $1500. I can't really justify that for an occasional use room.

How good is this stuff at heating a room, as the only source? Seems like most of the time it is a supplement for a bathroom or other hard floor location, where the room already has an ambient system. Would it be able to take a room like that up to temp from say... freezing, in a reasonable amount of time?

 

[sogafarm]

Have you considered a propane wall heater? Heats fast and on demand. They are also cheap. It can be plumbed to a 20 Lb propane bottle.

 

[KLF]

There will be no significant exterior walls to mount something like a propane heater. Just doing a short (~22" high) knee wall below the DH windows.

I don't like that it needs combustion air, and the potential for moisture or odors. That bottle sounds like a nuisance, I don't have propane now.

 

[PAToyota]

I've only really specified the electric radiant systems for bathrooms or such where it is basically supplemental heat. I've never done it for a larger room or as a primary heat source. That plus being open underneath (even if insulated) and open (I'm guessing) on three sides plus the roof is not likely to work well for you. The electric radiant will struggle to heat that space adequately.

 

[KLF]

Here's what it looks like from the outside now:

Those panels are just 3'-0 x 6'-8 doors with mostly glass. Interesting method, but now 2 of them are busted, and they are all leaking. Time for them to go. Roof is 2x8's with 1" XPS continuous soffit baffle, then ~5.5" of Roxul, R28 total. Gable and knee walls will be 2x6 with Roxul, R23. Windows are high efficiency Marvins, one external ThermaTru fiberglass door. I might also yank all the fiberglass out of the floor and do some XPS and Roxul. So not a shabby leaky porch, I'm trying to get it as tight and energy efficient as possible, but also lots of glass (it's a sunporch).

I suppose I should do some quick heat loss calcs, see how many BTUs/hr it will need.

 

[PAToyota]

Yep!