Hi everyone, We're preparing to install radiant hydronic heat in our remodel. I'm trying to weigh pros and cons of doing radiant walls vs. radiant ceilings. Half of the ceilings in question are cathedral ceilings, and there seems to be some doubt as to whether the angle of a cathedral ceiling presents problems. Anybody have any experience or theory to shed some light on that? With the ceilings "focused" toward the center of the room, would the wall temps tend to suffer? I tend to favor doing it in the ceiling because it will keep the pex safe from nails. I should add that the house has masonry walls with 2x2 firring on the inside and insulated on the exterior side with 8" of EPS (about R40 +) and the ceiling will be insulated to at least R50. The slab is in direct contact with the ground, but is insulated at the perimeter and will have 1" insulation between it and the subfloor. Our design heat load is expected to be less than 15K BTU/h, so we'll probably only be installing about 500 feet of PEX to deliver the heat. Any thoughts would be appreciated.

Anyone?

Do you have a SIPS roof? I don't know much about radiant heat, but wouldn't putting it in the ceiling keep it away from the people down on the ground where you want it?

thanks for the reply--- actually, radiant heat is invisible light, so it radiates out and is absorbed by objects and converted to heat. as far as my understanding goes, in a well insulated, well sealed building, ceilings are as good as floors or walls, and in some instances better, because you have less objects to block the radiation.

If you're curious, I learned a lot by posting the same question on two other threads:

http://www.healthyheating.com/bb2/viewtopic.php?f=25&t=719&sid=74ae50a2b318c2d6f46080b22a9f72fc
http://radnet.groupee.net/eve/forums?a=tpc&s=2411085301&f=4771065301&m=8511014653&r=8511014653#8511014653

Paul

I'll take your word for it - but how are you insulating your ceiling?

And did you say 8 inches of EPS on the exterior of your masonry walls? Now that's insulated! Is your total wall thickness like 1 and a half feet?

Insulating the ceiling probably with blow-in cellulose--- they're scissor trusses on heels to allow for plenty of room for insulation. The walls are 8" masonry + 8" foam, so yeah, about 16" thick plus stucco. Pretty neat.

This is my first time here and if I'm doing this wrong I'll apoligize. Paul, I am very curious about your block walls with the 8" foam. How do I ask more questions about them from you?

feel free to ask. basically, it's a masonry house on slab. We used a synthetic stucco base coat by Senergy to adhere 8" thick pieces of foam to the exterior, then stucco'd over that. Synthetic stucco systems are commonly applied over masonry, but usually in 1 to 2" thicknesses. The only difference is the thickness. This leaves a nice thermal mass inside the thermal envelope to retain heat.

Does that design heat load take into account heat from appliances, people, cooking, etc.? Are you aware just how low that number is? What climate are you in? The reason I ask is because design heat load is for the coldest time of the year, which you are at only a small percentage of the year. Most of the time you won't need the system to put out maybe 10k Btuh max. I'm not questioning the validity of the calculation. It's just that 15k is so low you will have a hard time finding equipment that will run efficiently at that low a demand. Also, your total heating bill for the year may be so low you will have a hard time getting a decent payback on a radiant system. Cooking, etc., may supply your heat a good bit of the time so you won't even be operating the heating system.

I would suggest you seriously look at other options such as in-wall heat pump units, or maybe a small gas fireplace. Even fireplaces are mostly bigger than 15k. You might even be justified in going straight electric heat.

Another option to look at. You surely are planning on having a heat recovery ventilator, right? Since that will be operating much, if not all, of the time you might add electric strip heaters into it's ducting.

The one thing you want to avoid like the plague is an oversized heating or cooling system. With a 15k Btuh heat load that will be a challenge.

Radiant is great, but just like everything in life, one solution is not ideal for all problems. With this low a heat load I'm skeptical. I dropped the idea of using radiant in my house because I'm looking at only about 24k to 30k most of the time and found an alternative heat pump system that will work better for me, I believe.

Radiant heat in the ceiling is feasible. The biggest issue is how to install it economically.

you don't get radiant for "payback", just to clarify. There is *almost* never "payback"... maybe, in structural slab or ceiling applications (very cheap distribution) coupled with real high efficiency equipment, but not in any other case currently that I'm aware of.

Radiant is a question of comfort more than anything, that happens to usually be quite efficient, if designed/installed properly.

Dmaceld, Thanks for the feedback on heat load, etc. I redid the calculations since my first post and it looks like the design heat load is going to be closer to 25KBTU. Still low, but not as low as I stated at first, though like you say, that's only on the very coldest days. I am concerned about oversizing, but we chose this system because we wanted an efficient domestic hot water source (tankless), and at a projected annual heat load of 45MBTU, electric heat is about $800 more annually, so it made sense to use the gas tankless to assist in heating the house. The tankless water heater setup we chose will work with a 10 gallon buffer tank to prevent short cycling. I'm interested in the heat pump option. Can you tell me more about in-wall heat pumps? Any other thoughts would be appreciated. Thanks for the feedback. Paul

a tankless and a buffer tank starts to look a wee bit like a tank water heater, doesn't it? heh.

if you're in a real heating climate, 25kBTUs would normally see payback on a mod/con boiler vs a less efficient water heater/tankless.

yes Rob, but without standby losses associated with a gas tank flue. Mod cons were beyond our price limit, considering the added expenses of hydronic parts and supplies, not to mention the $300 federal and $300 local utility rebate on tankless water heater.

Friedrich is one brand I find. Google on wall mount heat pump will bring up several, I think. I don't have specific knowledge of any of them. I just knew they existed.

Okay, thanks dmaceld... I'd barely even heard of it. We'll have to look into them, at least for the informational aspect. Too overwhelming to think of changing course now, with all the equipment bought and partly installed... I think it'll work out pretty well.

PaulW - did you dry stack and fully grout all the cores of the masonry block walls? And how big are the 8 inch thick pieces of foam - are we talking 4 x 8 foot sheets of EPS - how much did they cost? If one were to put 4 layers of 2 inch thick EPS the cost would be through the roof.

The masonry walls were pre-existing. Not dry-stacked but mortared. We partly filled some of the cells--- every 4 feet or so with rebar reinforcement. Yes, 4 x 8 sheets of EPS at I think it was .15 per board foot = $38 each. It wasn't cheap, or easy.

Paul, I would worry that without floor insulation, any radiant on the floor will soak into the earth before heating the room. My worry about the ceiling is the distance from the people, and the opportunity loss of heating the lower objects that then hold or give off heat. I did a hydronic radiant slab refit recently with 1" of rigid insulation with a 3" over-pour (could have done 2"). Works very well, but you have to watch the temperature of the output with such a low heat load. We stained the concrete floor and used area rugs to very nice effect.

I have also used low-voltage electric, from Step/Warmfloor, which would go onto a thinner floor, even a ply on sleeperw over insulation, and go under whatever your finish is. it is NOT cable and "always on", bu a variable-response material which puts out at differnet levels according the needs. Take a look at their materials. They will also do a take-off and help you design it. (BTW, as an architect, I don't rep it, just use it). http://www.warmfloor.com/.

Otherwise, I would agree with dmaceld about alternate sources.

Have you looked at heat panels from Redwell. They are made to be hung on the walls or ceiling and are very effective and efficient. Visit the website at www.redwell.ca,www.redwell.us or www.redwell.com/eng.