Radiant Ceiling

Mpj

I am thinking about doing a radiant ceiling in a small room in my home (14'X16') I call watts radiant (who's software I use) and they said their heat loss software cannot do it, is their another program I could use? Would it work as well as in floor heat (sandwich on frame floor) or am I asking for trouble? I would like to do it my house to see if it would work before I would do it in a customer's home.

NRT_Rob

we usually bank on

about 30 BTUs/ft at 120 degree SWT for a typical flat ceiling. don't know if it's in anyone's software though.



works great as long as you're not doing this over a cold slab. we have some comfort concerns in that situation with cold feet. otherwise the ceiling will slightly elevate your floor temp as well. of course any cold surface should be insulated, and radiant ceiling requires insulation above.

Mpj

Ceiling Radiant

Thanks for the response Rob. Do you think I should do a standard heat loss (Slant/Fin) or a radiant heat loss and divide by 30 BTU'S per square foot of ceiling? Or something else

NRT_Rob

heat loss is heat loss

just don't add duct loss if you don't have cold ducts.



and i'm saying 30 BTUs/sq ft at about a 12" o.c. typical, by the way. you can do wider on centers, we just approximate that by the linear foot of pipe at on centers wider than 12.



best of luck,

Mark Eatherton

I think 30 btu/sq ft/hr is conservative...

I think it is closer to 40 or 45 per square foot per hour. That aside, I think radiant ceilings are THE most overlooked opportunity for delivering high quality comfort.



Who cares where the radiant energy is coming from so long as the occupants are comfortable?



I have every known means of radiant delivery in all of my homes, and the radiant ceiling seems to be more comfy than the house with the radiant floors and radiant walls. And interestingly, the floors ARE warm when the ceiling is active.



Heres a link to industry expert, Tom Tesmar, who is also a major proponent of radiant ceilings.



http://www.tesmar.com/html/radiant_floors_vs_radiant_ceilings.html



Enjoy!



ME

NRT_Rob

I'm conservative

because I have not seen the same incredible numbers as purported in wirsbo/uponor design manuals (I believe penned by Tom).



However, it may be a question of installation as well. we have always used a simple strapping and plate method. I may move to a hybrid strapping and rigid foam method. what do you prefer mark?

Mark Eatherton

Roth Panel...

is what I used up in the mountains, 6" centers to allow me to work with extremely low water temps, i.e. solar or WSHP. It keeps my modcon in the con mode all the time. I value my labor more than most, and am wiling to pay more up front for a "system" as opposed to putting things together in the field. The less time I spend in the field, the better off everyone is.



Here's a pic of my ceiling system prior to covering with sheet rock.



As for output is concerned, I have a flux sensor, and it is currently tied up doing R&D for the Radiant WIndows project, but when it's done doing that duty, I will strap it to the ceiling and give you an accurate picture of the output capacity of the ceilings.



ME

NRT_Rob

well if you're going to use roth panel

you just eliminated 3/4 of the reason to use a radiant ceiling... massive first cost reduction. right?



you can't use any ceiling at temps that would fail to condense... 120, according to uponor at least, is the max recommended water temp.



that is one snazzy looking ceiling for sure though.

Mark Eatherton

Labor is the most expensive commodity...

Roth panel saved buckets load of labor.



I think radiant ceiling are also smart because in most cases, you don't have to cover every square foot of the ceiling. You only need to install enough ceiling to counter your loads, and in a lot of cases, that ends up being the first 4 to 6 foot of exterior perimeter. Hence less first cost.



It also frees up the interior decorator to let them throw bear rugs on the floor if they so desire, without any negative consequences. I made the fatal mistake of telling a male interior decorator that in order for the radiant floor to put out its maximum heat, that he needed to avoid putting carpet down on my radiant floor...



After I picked myself up off the floor, and dusted my self off, he read me the riot act and explained that the reason for him carpeting the floor was to abate echoes.

Whooda thunk. Another excellent reason to consider radiant anything but floors :-)



Technically speaking, in many of todays houses, it is not necessary to put 1 foot of tubing in every square foot of floor space, but if the consumer hits a cool spot on the floor with their bare feet, they immediately assume their system has an issue, like a leak or something. They can't contact the ceiling, and with the right controls, they will not even realize where the comfort is coming from, nor do they care, because they are



c o m f o r t a b l e....



And bottom line, we are ALL in the comfort business, not the heating biz...



Don't get me wrong. Radiant floors have their place, like the bathroom. But I think that we as an industry have over sold radiant floors. We need to focus more on delivering radiant comfort, regardless of the emitting surface.



And as houses get even more efficient (i.e. Passive House), the need for expensive floors and their supporting casts becomes less and less. Radiant ceilings can also provide radiant cooling to base load these spaces, resulting in a significantly smaller physical plant for the balance of the cooling load.



I'm a big fan of radiant anything, but I like the concept of radiant ceilings, which in my neck of the woods, were more prevalent than radiant floors at one point in time.



ME

NRT_Rob

I'm a fan too

out here though, everyone already straps their ceilings for drywall. happens to be 3/4" profile. It's very hard to look at that and see stapling plates up and snapping tubing in as 'extra labor'. I guess if they don't strap ceilings already out by you, it would add one more step to the install. it is a pretty easy step though.

Gordy

I too

Thought that was a conservative number. Here is an output chart for radiant ceiling using Radiant- trak 12" OC, and 20* DT. Verifying Mark's intuition.



My radiant ceiling which is in the plaster 6"OC usually runs at 115* ST on a design day, and 15* DT.  Surface temps are 87*



What I truly enjoy when she is cranking is laying on the couch or the easy chair, and you can feel the warmth blanket you. Like liquid sunshine.



Gordy

Gordy

Bigger Please

Sorry Can't get it bigger bust out the magnifier

Gordy

Old Days

 My old Chase Copper, and Brass Radiant heating book that came with the house says 150* mean water temp can be used with plaster ceilings. I really don't see the need or care to try.....But I'll bet it would feel real cozy from about a 12' ceiling.



Gordy

Mark Eatherton

Thanks Gordy...

Knowing Tom Tesmar as I do, I suspect that he can back up his numbers with real world data, like flow meters, data loggers etc.



Although I don't agree with his stance as it pertains to heat sources (he promotes the use of water heaters as heat sources) I do have to respect his work as a radiant pioneer.



ME

EricAune

Great info, great comments

Thanks guys, this is great. 



If you want to see the chart better, right click on it and select "open in new tab". Proceed to click on the new tab and it will be more clear and larger.

Gordy

New vs Old styles

 The only thing I can say though is I have NOT experienced the performance of new installation methods for ceiling radiant.



  I would think strapping, and plates would kill performance or raise water temps compared to a tube which is inbedded in plaster at closer centers. Plus what is the r-value of drywall, and keeping good contact with plates against the drywall.



 If I were going to do it using modern construction methods I would have to say Marks method even though more costly in materials would have to yield better performance both efficiency, and comfort wise, Would seem to have better chances of aluminum making good  contact with drywall.



After all who plasters a house anymore.



Gordy

Gordan

Your numbers aren't that far from Rob's

Using the 1.6 BTU/sqft-deg F rule of thumb for 68 deg. F indoor temperature, your 87 deg. average surface temp = 30.4 BTU/sqft, and you get there with 107.5 deg. F average water temperature. Rob figures on 30 BTU/sqft with 110 deg. F average water temperature. Seems pretty close. Now figure in your tighter spacing (6" o.c. vs. 12" o.c.) and different construction detail (embedded in plaster vs. thin plates over strapping) - if you're right in your thinking that embedded would ensure better conduction to the surface, then Rob's numbers don't seem that conservative.



R-value of 1/2" drywall is .45.

Mark Eatherton

Human Physiology Limitations...

The floors are typically limited to 85 dergees F limit due to human physiology limitations, NOT physical limitations. I've had floors in my lab up to 140 degrees F using 190 degree F water temps. If you are not in direct contact with the emitting surface, then you are not limited to the 85 degree F surface temperature, hence you CAN get more btu/h/ft sq out of a wall or ceiling than you can a floor.



Also, the 1.6 that you site is for a vertical surface. It includes radiant emmisions and convective emissions. A ceiling will have ZERO convective emmissions because there is no where for the heat of convection to rise to, assuming a non sloping ceiling surface.



The factor for floors is 2 btu/sq ft/hr per degree F difference between emitting surface and surrounding air. And that number is somewhat subjective, because what really drives the radiant energy transfer is the AUST (average unheated surface temeprature), and it is not heavily influenced by the ambient during recovery.



Bottom line, with a properly controlled radiant ceiling, like a properly controlled radiant floor, you wil NOT be at max temp until you are at design temp outside, then you WANT a hot emitting surface. And you shouldn't be aware of where the heat is coming from to any major degree.



Many of the rumours of "Hot Head" syndrome, and "Shadowed Leg" syndrome come from older, out of control systems. This ain't your grandpas radiant ceiling :-)



For those skeptics about radiant ceilings, try it in your own backyard first, then you will find it easier to promote to your customers. I don't know what the psycological hang up about radiant ceilings is, but it is a hidden barrier to the use/promotion of this excellent comfort delivery system. Once you experience it for yourself, it makes selling the concept to the consumer MUCH easier...



Virtually silent comfort with no floor covering limitations :-)



They have a new radiant ceiling in the RPA's office. It is slated to do the base load cooling as well.

ME

NRT_Rob

of course it will

you can say that in any case that more coverage, better aluminum, tighter on centers will improve performance.



but the plate and strapping method is a less than a quarter of the cost. it's competitive with medium-temp (140) baseboard. and you can still do a max design temp of 120 and heat nearly any space in north america with it. You can EASILY limit to a 110 max if you do a tighter on center and marginally increase the cost.... and you're in happy geo heat pump land. at $2/sq ft in material costs. Radiant comfort.



Weren't some people asking about easy, cost effective, simple radiant? that's it right there. Shangri-la. basic thermostat, basic outdoor reset, fast install, great output at low temps.



so my question isn't "is roth better"? of course it is. the question is " it is cost justified"? and there, I think the answer is pretty much no. at least, not out here in the east where they are already strapping the ceilings. the benefit is incremental at that point, I think.

Gordan

The way I've seen it...

1.6 BTU/ft^2 F for ceilings, 1.8 for walls (lower portion) and 2 for floors. That chart Gordy attached seems to use the 1.6 slope as well.



Mark, my main point was that Gordy's real-life measurements are pretty close to Rob's "conservative" estimates - much closer than to the charts for Radiant Trak. If ceiling output curve slope is less than the 1.6, then that would favor a conservative view even more: he'd be getting less than those 30 BTU/ft^2 F at 107.5 F average water temp, when the chart says that he should expect 40.



Not knocking radiant ceilings. About finished putting them in everywhere in my home, so I sure as heck hope they work. ;-)

Gordan

Hybrid

How specifically did you intend to do this?



I did hybrid and there are some gotchas, but they may not apply to what you intend to do. My case was applying over an existing plaster ceiling that I really didn't want to heat, so the foam is between the transfer plates and the plaster (with the exception of the tube channel.) It was a lot of work, so much work in fact that I really wish that I knew of a structural product that's a good insulator, that I could have used as strapping - and forget about the foam. Polyiso can also run thicker than its nominal thickness, which was a lesson.

NRT_Rob

I've seen other numbers

that claim 1.2 to 1.4 for ceilings.



all of this is interesting, but let's never forget: even my conservative numbers result in incredibly affordable, powerful, comfortable radiant ceilings.



now, COOLING performance, I'm more shaky on. but our shop ceiling is not ideal for sure...

Gordy

The point is

The power of the ceiling radiant panel.



My Grandparents built the house I live in now. I know from the years they never settled for less than 75* set point, and it was always very warm upon visits not in an uncomfortable way.

When the house was built the attic insulation was 5" of vermiculite thats it. Yeah I know fuel was cheap, but it shows the power of the panel. Back losses are not what you would think with the type of construction used for my ceiling radiant.

In the midwest every other decade or so you will get a week of double the lows of a design day which is - 9* here. I have seen - 27* in my life time, with -20* lows lasting a week. Now if you design around a 68* set point for a design day of -9, and you hit times like those below design days whats going to happen put on a sweater? Not exceptable, and as long as you have enough boiler the ceiling radiant will get you through that because you can have higher surface temps.



At -9* I see an average water temp of about 107* supply 0f 115*, and return of 95* we keep the thermostat at 72* so the chart is valid, and the system can easily overcome those below design days with not exceeding the 120* drywall limitation.  



My point is Robs numbers are conservative to the ceiling radiant panels potential. There is nothing wrong with his number, and its a good number to use as you see buy the chart I inserted. But you could deliver higher numbers if needed, and not be limited by floor temps.

Gordy

Rob

 I'm not saying that everyone should build ceiling radiant like I have. To do what I have today would be cost prohibitive.  All I'm saying is that I see deficiencies in some of the new ways in doing it compared to mine, and they may be anal.  I can't testify to the real life performance of these new methods compared to mine.  You are a designer, and you obviously have very satisfied customers with systems performing as expected. Please don't be offended I do admire your work.



Gordy

NRT_Rob

Gordy

no offense taken at all. great conversation all around I think.

tbone52

describe rad ceiling mounting methods

Rob,

Can you describe your hybrid straping method (s) for rad ceiling?

NRT_Rob

I'm considering

one strap per plate instead of two, with the other side being rigid foam.



siggy shows an all foam detail, but I've never been comfortable with that from a plate or drywall installation standpoint. plus as I've noted, everyone around here already straps their ceilings, so any design I use must accommodate strapping.



the rigid foam should improve performance though.

Gordy

Rob

 When you say "everyone around here already straps their ceilings"  Is this a common practice in construction in general?  Or are you refering to framing practices for Rad ceilings in particular.



Gordy

NRT_Rob

standard construction practice

for all homes in the northeast, practically. makes it easier for the drywallers. might be other reasons too.