Underfloor Heating Advice

I'm considering using underfloor heating (wet) in a new conservatory. 3 areas are causing me concern if anybody has the answers:-
1. Some websites seem to claim a heat output of 70W/sq m for a floating floor and 100W/sq m for a screeded floor. Can anybody explain why there should be a difference?
2. Even at 100W/sq m this seems like it is probably not enough to cover the heatloss for a conservatory even when using low E glass (Unless my calculations have gone wrong). Websites don't seem to say that the UFH would need to be supplemneted. Does anybody here use UFH in a conservatory and find it sufficient on its own?
3. Some suppliers indicate that an additional pump is only necessary for floor areas >16sq m. Others seem to indicate that an additional pump is always required. Does anybody have a view on this please?
Many thanks for any help you can give, Jon...
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In the summer I put underfloor heating in our new conservatory, 6m x 2.6 with 1m wall with K glass windows and poly roof. I used 2 x 50m loops of 15mm od poly tube, which was the most I could get in with 150mm spacing. I used equator boards under 50mm of screed. http://www.equator.co.uk/newwebsite/underfloor/home.html and Danfoss valves http://tinyurl.com/lzu4 All connected to existing CH system. Works a treat. Baz
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Thanks for this lead Baz, the equator (Marley) website actually says:-
"It is important to note that the use of the Equator underfloor heating system for conservatory installations will not provide sufficient comfort heat during the mid-winter season."
So, full marks to Marley for being honest about this!

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jon wrote:

I thnk the issue is the temperature you have to raise the air under the floating floor to get that kind of heat output. You can get 3Kw per square meter if you don't mind the floor glowing a dull red colour...:-)
Haet transfer is a function ofteh underfloor insulation, the temperature at the pipes and the conductivity through to the room.
I would say 200W is possible with screed.

No, but I think it would probably be OK. Post your calculations here, for discussion.

Mmm. I would say its always a good idea. You need to reduce the CH water temp somehow, and circulate it separately, and notionally independently of the main CH flow.

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<<<snip>>>

OK, here goes. The conservatory would only have 2 outside walls so I have assumed no heat loss/gain from the other 2. I have also assumed no heat loss through the floor!
Glass, double, Low E U=2.0 dwarf walls, double brick, cavity, insul. U=0.56 Floor area (internal) is 3.92m x 3.52m Outside temp -1 Inside temp 20
Floor -> No losses as such.
Dwarf walls ========== (3.92+3.52) x 0.5 x 0.56 x 21 = 44W.
glass walls ========== (3.92+3.52) x 1.7m x 21 x 2 = 532W
glass roof ========== 2 x 3m x 2m x 21 x 2 = 504W <- 2 "sloping sides" 1 x 3.24sq m x 21 x 2 = 136W <- 1 "sloping end panel" very approx
Air at 1,5 changes/hr. ==================== Volume = 37.26cu m * 0.33 * 21 = 259W.
Total = 1475W
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jon wrote:

Wow. Doesn't all that building reg standard glass lose a lot of heat!
Floor WILL lose some heat too.
A couple of things to note.
(i) The floor. That will lose a bit. Assume U value of about one half. (ii) Do you really want this lot at 20C when its minus one outside and dark? In teh daytimeypu will pick up some watts through light/sunlght, after dark you may find that drawing the curtains - especially if thermal lined - will make a HUGE difference. I stuck in SG windows and the curtains really make a difference. They trap about 6" of air behind then and as long as mo rads are underneath them, it says there and doesn't move. Excellent insulator. (iii) heat input from the rest of the house. I assume uyou have simply ignored the dividing wall - but it may actually be a net contributor.
However, your calcs look of the right sort of magnitude, so you need 150W/m^2 power input. That is on the high side, but doable. Especaily with e.g. tiled floor. Trouble is the floor will be getting HOT.
A final possibility is to heat for 100W/sq meter and then use a convector or gas fire or something on really cold days.
Or is there any way to improve glass insulation? If you can glean an improvement from U=2 to say U=1.5, then already you are nearly on target...or how about not glazing it so completely?
I must say I am a little surprised, but polyplumb do say that UF heating in a totally glass room cannot be expected to completely do the job, so it sounds like you are right after all.
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I think it is to prevent the wood overheating and warping.

If your calculations show it is insufficient, consider fitting something like a Myson Kickspace Floor to supplement the heat requirement. This would take no wall space, although there would be a grille in the floor. You could leave the convector off, except in exceptionally cold weather. Alternatively, the combination of fan convector and underfloor will cause the conservatory to get to temperature much more quickly. Underfloor does take a long time to heat a room from cold.
Christian.
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