Please Help - Hydronic Heating Using the Ceiling as a Radiant Heating Panel

I am painfully doing up a late 1950‘s house. The construction is fairly standard New Zealand practice for the time, timber frame, weatherboard, concrete tile roof, 18mm tongue and groove flooring over a vented crawl-space and 10mm fibrous plaster walls and ceilings. The original construction of such houses was totally uninsulated and very drafty. (Although we have a temperate marine climate, New Zealand is no tropical South Seas paradise. We do get a few degrees of frost in winter and the whole place is horrendously windy all year around.)

The ceiling and under the floor has subsequently been insulated, but unfortunately so poorly that I will have to redo them. I also have to come up with some way to heat the place economically, preferably using wood. Hydronic heating, with its ability to zone heat and use storage, seems ideal. I am not too happy with the whole idea of radiators or baseboards, which leaves radiant heat.

The usual preference is to use under-floor heating but I have a few problems with that. Under-floor radiant heat requires that the floor be insulated. I discovered a disaster after I first bought the house, there had been a flood in the en-suite and the underfloor insulation, which was a sort of bubble-wrap aluminium foil stapled to the underside of the joists, had trapped quite a few gallons of water between the joints. No wonder the place felt a bit damp. As a result, I would prefer to insulate and condition the crawl space, rather than insulate under the floor. This is not so good for under-floor hydronics.

Searching hearth.com, I came to this excellent connection of links compiled by Colin Morris.
http://www.hearth.com/talk/threads/gasification-links-and-tom-reeds-research.11640/
One of Colin’s links was to a pdf on the www.heatinghelp.com site. The pdf contains a 160-page “Manual of Modern Hydronics”. It seems very good stuff. I had not ever considered the ceiling as a radiant panel but the manual points out that, since the heat mechanism it radiant, it doesn’t matter where you put the panels. Since wall panels are not very practical in my case, ceiling heating starts to look very appealing.

The manual only shows one layout for ceiling heating. This is for pex-Al-pex in aluminium heat-transfer plates, that is only possible with a totally new ceiling. This would be very expensive and inconvenient. I wonder if it would be practical and effective to use the joist-space heating concept that the manual describes for under-floor use in the ceiling? This would have the pipes nail-clipped to the sides of the ceiling joists. A reflective layer would be stapled across the joints and normal ceiling insulation placed on top. If this can work, what water temperature is required? (The manual states that the temperature needs to be higher that if heat-transfer plates were used, but doesn’t say by how much.)

Any Ideas?

I would say that the temps would be comparable to what mine run. Buried in the concrete mine runs (sorry, F) 100 to 110 degrees. I have underfloor staple up radiant.. that is insulated beneath by 2" hard foam foil faced insulation. Those pipes run at 140 degrees.

In my case, my floor.. which is I guess structurally the same as your ceiling.. I have pipes running each 8 inches. My home is built with 2 foot on center trusses. Each "bay" has 3 pipes running in it. 2 pipes are within 4 inches of each truss, with 1 pipe running down the middle.

In my case.. the radiant has to heat thru a sub floor, decoupling membrane, mud and tile. In your case the pipes could be placed just above your wallboard in the ceiling. Would work good I think. Properly sized, and proper length loops are critical.

JP

Why not use wall radiators?

The biggest advantage of radiant walls or ceiling is that the surface temperature can be driven much higher than a floor which can become too warm to be comfortable on your feet. Certain floor coverings can also be damaged. Not so with walls/ceilings of plaster or sheetrock/drywall.
Plates or other transfer medium are nearly mandatory in a wall or ceiling regardless of the type of pex used. P/A/P is used often because of its more limited expansion characteristics compared to regular pex.

Just adding. I did not use any transfer plates. I used the wirsbo staples that hold it tight to floor, but allow a bit of sideways movement. Stapled under subfloor. Left an inch of air space.. then 2" foam beneath. Of course.. my space beneath is heated..so no real "losses" anywhere.

Thank you for your replies. There appears to be an almost religious schism between those who believe staple-up is acceptable and those who swear that transfer plates are absolutely vital. It is a pity that there doesn't appear to be any independent research to look at.

JP, my situation would not be a simple inversion of yours, because I would not be able to mount the pipes directly on the fibrous plaster. I would not be confident that the plaster could take the weight and in any case the back (top) side of fibrous plaster is extremely rough and uneven. Heat transfer would principally be by radiation between pipe and top of ceiling. In your case, I suspect that significant radiation also occurs but you also get a measure of direct conduction as well.

Would I be correct in assuming that even spacing of the pipes is not so important for ceilings, since hot stripes will not be perceptible, unlike the case with floors?

The reason that I don't like the idea of wall plates is , firstly, what with windows, doors, wardrobes, bookshelves, pictures and other furniture, I don't have a lot of clear wall. Secondly, the amount of work and disruption would be a lot worse than ceiling work, provided a simple clip-to-the-joist system can work.

I have just remembered that the master bedroom, which is a later addition to the house, has a different ceiling from the rest of the house. It's a very low density wood fibre tile, which I suspect is quite a good insulator. (I knew that! I must have got over-excited when I discovered the concept of ceilings as radiators . ) So for that room I'll have to do something different. Has anyone seen any reference to a suspended panel design that could simply be clipped up below the ceiling proper?

Peter

Snail..

absolutely different now that you say that. Mine is stapled every 18 inches or so along the pipe.. so lots of surface contact.

I think you may be counting out some of the more high tech, wall mount radiators too soon. Sounds way simpler. I sympathize with your wall issues. My house has very few interior walls. I went with high velocity central air, only because I didn't have a lot of walls to bury duct work in.

You kind of have the opposite issue with ceiling radiant. Radiant works great on the floor. It lets you keep the majority of the air cool.. I have high cathedrals and heating the air top down would STINK! I'm sure radiant would be better than forced air from ceiling down.

Do you have ducts now for central cooling?

I have P-A-P in the ceiling with the alum plates and it is very nice. How is it going to be so expensive to rip down your ceiling and install it with the plates "normally"? You might pose your question over at: http://www.greenbuildingtalk.com/Forums/tabid/53/afv/topicsview/aff/12/Default.aspx or do some reading there.
Good luck.

Thanks mhw,

The folk at greenbuilding are pretty scornful about staple-up it would appear. It may be that since we don't have such a high delta-T I may still be able to get away with the less efficient system but clearly I will have to do the calculations in detail.

Since we have a mild climate, we don't heat our bedrooms in our current house. Mind you, it would be too cold for most American or Europeans, we Kiwis are notorious for our cold houses. A Swedish friend, whose hometown is just below the Arctic Circle and can have snow up to the house eaves, told me that she had never been so cold in her life as the Winter she spent in Wellington! On the other hand the 3 months I spent in an apartment in Warsaw were uncomfortably hot (for me). Even with the heating off and the windows ajar, so much heat came from the apartments above, below and around that i could not sleep with even just a sheet on the bed.

However the old house I am doing up to move into has a much less favourable alignment for solar gain so some heating would be nice even for Kiwis.

JP, whilst I agree that toasty feet seems very acceptable, I don't think that ceiling heat would be quite as stink as you feel it would be. Radiant heat doesn't heat the air much at all, as it is transparent to infra-red. it is heated mostly by contact with surfaces. In a hot floor setup, the air is heated at floor level, but then immediately rises due to convection. So the hot air ends up at the ceiling fairly quickly anyway. In a hot ceiling, the air will heat at the ceiling and stratify. This reduces the cooling of the radiant surface increasing the amount of heat that can be radiated.

In all types of radiant heat, it is my understanding that the real advantage is that as you are heated by radiation, you don't need the air to be as warm anyway. So the fact that the air is warmer the higher up in all cases isn't such a problem.

The worst thing about ceiling radiation is that it is a bit more intense on the top of the head than for floor heat, More of a problem for the balding amongst us I imagine!