Pex and insulation for radiant ceilings

chew_baka9

Hello All,

New to the forum.

I have a major renovation and addition starting on a home in New Jersey.
We are installing radiant heat under the floors in most of the existing home. We do not have access to the floor below the master bedroom but the ceiling in the master with be all open.

I see some specialized systems in the market for radiant ceilings.
Is it possible to run hydronic PEX loops in the ceiling to heat the master bedroom?
If so what method of insulation and airspace above the loops and/or heat transfer plates would be best?
Ceiling will be standard 5/8 sheetrock.

Thanks for your comments.

Rich_49

Is the space above the master heated or unconditioned ? Insulation is a must regardless but what R value may be different .

I have yet to see a room which radiant ceiling could not heat while , oddly enough ( not really ) , I have come across many rooms where floor heating required supplemental while moving it to the ceiling only eliminated that requirement .

Gordy

There are a few ways to go about the assembly. I like panels with a continuous aluminum skin. Roth has choices of 3/8”, or 1/2” pex, and 12”, 6” tube spacing.

Then there is plates with furing strips. I personally think it’s a little harder to get good contact to the back of the gypsum board for good heat transfer.

SENWiEco

Do you have access to John Siegenthaler's Modern Hydronic Heating book? He talks about options and designs in chapter 10.17 (pg 471). It is very doable, I will be heating and cooling my whole house via ceiling panels made up of pex loops in ThermoFin C plates

bob eck

Can you put the radiant on top of your sub floor. Viega has a product called Climate Panel goes on top of the floor then the finished floor goes on top of it. Check it out.

TAG

We had electric ceiling at a beach house at the NJ shore when I was a kid -- believe it was buried in the plaster vs under drywall. Mention because It was quite common on LBI. Remember manuals with calculations years ago when I was looking into various radiant. You may want to track some down for basic numbers.

It worked very well -- can remember laying in bed and feeing the heat. Have done wall radiant when I needed some supplemental heat when renovating .... in those situations I used foil foam and cut the foam to fit between the studs -- tubes attached to the foam ... works very well. Always do some in my showers.

I have no numbers to back this up -- but the transfer through the drywall with tubes alone seems better than what you get with plates through subfloor and 3/4 finished wood with same temp water.

Gordy

Believe it or not wood is a better insulator than gypsum.
5/8 gypsum which is r .56. So unless you do over the top with a tile overlay, the ceiling would push through less r value than an over the top with wood, or even radiant friendly carpets.

The chase copper, and brass manual from the old 50’s house quoted 70 btus a SF possible, With water temps of up to 160* . I don’t know if I’d ever push plaster to that temp, but they tested, and believed it to be possible. Never needed to though.
Drywall puts an upper limit of 120*. I couldn’t imagine needing that kind of surface temp with a well designed panel.

hot_rod

Here is a simple DIY radiant ceiling detail.

Gordy

hot_rod said:

Here is a simple DIY radiant ceiling detail.

While nice workable panel detail I look at labor costs of doing a multi layer, and fastener system.

1 layer of osb.
1 layer of foam.
1 layer Attaching plates
Extra fasteners for each layer.
1 layer of gypsum.

With something like Roth, or similar.
1 layer of Roth panel.
1 layer of gypsum.
Done.
Also the continuous aluminum skin is superior to the plates.

TAG

I have never used the Roth -- it's foam correct .. w/ AL skin?

It's been a while since I looked at it and I was afraid of putting the wood over the foam w/ long nails (noise) .. Went with Warmboard. They sent me a sample --

On a ceiling -- The Roth looks like a great idea. It was much cheaper vs warmboard

Gordy

There’s is also sunboard. Which offers different tube centers. That’s what I like. With WB you are stuck with 12” centers which is fine, but depending on load it’s nice to have a tube center option.

I think the foam insulation is redundant, and in that particular detail, maybe using foil face in trying to leverage that foil into the output spread.

I think continuous aluminum is superior.

TAG

I thought the Roth was a full AL clad -- my memory is the panels are light weight. Think in a ceiling the foam and light weight would both be a plus ... no ?

Never used the sunboard -- not a good website.

Have had excellent results with Warmboard and wood floors .... it makes for an incredibly strong solid floor.

Depending on insulation -- the OP's load my be low.

RetrosPex

This is a very interesting discussion. I looked at Siggy's design, and I like it except for the detail about leaving one side of an aluminum plate loose to expand. I'd use extruded plates, and fasten them with coarse screws. Or, like Gordy says, use a panel with continuous aluminum. You cannot beat that. They will outperform a floor system. The other aspect I really like about a ceiling system is this: How many times have you changed what is on your ceiling? How many times have you changed flooring? Having it above head eliminates future issues with someone driving a nail thorough it.

In my current project, I have a master bedroom heat plan that is yet to be decided. I purchased a couple European wall radiators, but planned to also go with underfloor plates. I'm considering putting a 2" layer of rigid insulation on the underside of the ceiling, screwing on plywood, and then applying plates. I'll also look into those panels Gordy mentions. Haven't seen them yet.

The ceiling option sounds great. Good luck

CFH

I installed the radiant in a section of my garage ceiling right by the garage door. The first heater i installed was a fan coil. It was not rated correctly by the manufacturer so it was undersized. It still put out around 25000 btus. I had a piece of cast iron baseboard lying around so I installed it as a supplement. My desk was by the garage door and I was still uncomfortable. I noticed a roll of 3/8 hepex tubing nearby and thought it would be easier to install the radiant ceiling instead of installing another piece of cast iron behind my desk. The 1st attempt was stapling up the tubing directly to the existing ceiling with spray foam above the sheet rock. The insulated concrete walls and the slab were too much of a heat loss so I used plates.

CFH

CFH

CFH

I sheetrocked over the plates. When you walk into the garage and the heat is on the 1st thing you notice is how comfortable it is under the radiant ceiling as yo walk back to the fan coil you can feel the chill what ever the air temperature is.

CFH

Here are 2 pictures with an IR camera. You can see in the 1st picture where I cheated on the transfer plates. The second picture is after 5 minutes. Radiant ceilings are the easiest retrofit. It works great. As you walk past the radiant ceiling to the cast iron radiators to the fan coil you can feel the comfort drop. I am running the ceiling supply temperature at 180 degrees because I did not want to install a mixing valve and I have no issues yet. The surface temperature get to 80 degrees. I use the garage as a test bed

CFH

Cast Iron baseboard starting to heat up

CFH

EBEBRATT-Ed

@CFH your on a 5 year old thread

CFH

you looked at it. Some how this thread came up in a search. I think radiant ceilings are good

hot_rod

180F seems hot for contact with sheetrock? It must be some pretty high BTU/ sq ft output.

I think 125F is the max temperature USB Sheetrock® brand recommend. Although I'm not sure what happens to sheetrock exposed to high temperature.

I agree with the comfort and quick warm up of a radiant ceiling.

Here is how I did my "exposed" radiant ceiling in my home. It never was popular with the misses however :)

CFH

The supply temp to the tubing is 180 degrees. The surface temperature of the sheetrock is less than 80 degrees. That is almost the same as a 180 degree cast iron radiator hung on a sheetrock wall. I don't use the heat to maintain 65 degrees in the space. The thermostat always sets back to 45 degrees. At the time of the installation the above ground uninsulated concrete walls and uninsulated slab on a high water table had a great heat loss. It takes about ten minutes for the space under the radiant to get comfortable. The garage is in a flood zone so it took me a while to decide on the insulation I would use. I started installing 2" polystyrene glued to the walls with some Tapcons as necessary. I will stucco over the polystyrene. This was a cheap test installation. Once the insulation is completed and the heat loss goes down I may reduce the supply temperature to the radiant ceiling. My friend installed a radiant ceiling in his split level garage converted to a den because he could not raise the floor and it works great. because he is a plumber and it is in his own home it runs uncontrolled. I recommended radiant ceilings to customers in places they may not want a kick heater and I just wanted to have a place to test the performance and work out any kinks. I keep the garage door open in the winter and the ceiling on and do my paperwork. I appreciate any feedback from any other radiant ceilings. I will plan on removing the radiators on the 1st floor and installing radiant walls. The ceiling is 14' high and sheetrock and spackle will be costly at that height.

hot_rod

Here is a little cheat sheet for radiant panels. Radiant walls have a slight edge over ceilings as you do get some temperature stratification at radiant ceilings.

CFH

That is nice thank you.

OaklandNS

Hi All,

Thanks to you all for posting all the information on radiant ceilings. I'm looking at the Siegenthaler detail for a radiant ceiling installation in my remodel. I am also planning to use it for cooling. I live in Northern California where it is generally fairly dry in the cooling months, but can be humid on some days. For cooling, I'm wondering if I need a moisture barrier (perhaps another layer of foam) between the tubing and the insulation above. My installation will be below a vented attic, and I'm not sure if there will be a condensation issue where the air from the attic hits the cool tubes notwithstanding the insulation above the tubing. If you have any thoughts, I'd love to hear them!

Nathan

hot_rod

I'd use a poly-iso board as an insulation barrier that could handle some moisture. But you have the sheetrock to contend with.

the sweating of the tube and plate is related to dewpoint. You could find that data at the local weather station. Maybe look back 5 years or so.

HBX and others have dewpoint sensors built into the thermostats. that would turn off the radiant cooling if you are approaching a condensing condition.

19% humidity, 30° dewpoint here in Salt Lake currently.

OaklandNS

Thanks! It's more about the attic air, which is not going to be dehumidified like interior air, getting into contact with the tubing. So it would be a concern with the moister air hitting the tubing from the backside. I think if I do a layer of poly iso above the tubing it would probably prevent the moist air from condensing.

That is a cool thermostat. I had seen separate dewpoint sensor devices, but not something built into the thermostat.

hot_rod

poly-iso and tape the seams for a tight barrier.

Maybe check at the Building Science site first for ideas specific to your area.

https://buildingscience.com/

DCContrarian

Cooling is really tough. The problem is that any surface below the dew point will cause condensation, which can be somewhere between problematic and disastrous when it happens in your ceiling.

In one of his articles Siegenthaler says something like "with proper controls ceiling panels can be used for cooling." I've always felt this was something like Fermat's Last Theorem, he just leaves us hanging.

The problem with trying to measure indoor dew point is that humidity isn't constant inside a house. For reasons nobody seems to understand humidity rises in a house, the upper floors are going to have a higher dew point than the lower ones. So you can't have one humidity sensor for the whole house.

With an air-to-water heat pump, as a practical matter the water temperature isn't constant, it rises and falls as the heat pump cycles on and off and depending on load. I have a Chiltrix heat pump, and the output temperature will vary as much as 16F with the same setting, depending on conditions. So if you're trying to control the water temperature to stay above the dew point you can't do it just with the setting on the heat pump.

In places that aren't that hot you need dehumidification more than cooling sometimes. Houses that rely solely on air conditioning for dehumidification can sometimes have humidity issues because there isn't enough of a sensible load to get the AC to run enough to remove humidity.

SENWiEco

I have been using ceiling radiant summer cooling for the last 3 years now (North Vancouver BC Canada). It works very well and provides amazing comfort that you just cant get from chilled air systems. The dewpoint control is super easy to manage. I have dewpoint sensors on each floor of the dwelling. I use the worst case scenario to control the mixing valve, to provide dewpoint + 2 Deg F to allow for a safety. As the panel supply temp never dips below the dewpoint, i don't have to worry about condensation on the ceilings or any of the supply tubing.

Now all of my tubing is run in the conditioned part of the dwelling. The OP has the issue that the tubing runs in the attic. I would create rigid foam tunnels over the tubing, that are sealed with caulking (just like you have to do with fire suppression pipes). This should elevate the issue.

Make sure there is no insulation between the tube and ceilings, so that the inside of the foam tunnels is as close to indoor temps as possible. This prevents winter freeze issues when loop is not active.

DCContrarian

https://forum.heatinghelp.com/discussion/comment/1805713#Comment_1805713

Thanks for the feedback. Do you have any dehumidification as well?

SENWiEco

I have a hydronic coil (https://thermatlantic.com/3-ton-cased-coil-with-condensate-pan/) that is installed on the air intake for the HRV (I did not install additional fans, as the pressure drop through the unit is low and the HRV fans keep system ballanced). I have not calculated the exact efficiency, but based on the temp differentials through the coil, it is doing well. It is fed with unmixed chilled water straight from the buffer tank, so this loop was well insulated and sealed with Armaflex rubber pipe insulation.

I have full control of this, and the rest of the system, using the ThermAtlantic supplied ControlCorePro software. They use this software and PLC thermostats, to control the DX2W (https://thermatlantic.com/dx2w-ex3-36-48-residential-air-to-water-module/) and the Gree heat pump. I have full control of the programing, and have made several changes to advance to logic.

All in all, it has been an amazing system and uber comfortable.

Big Ed_4

It would be best to increase the mass of the panel .

DCContrarian

https://forum.heatinghelp.com/discussion/comment/1805744#Comment_1805744

Thanks, this is very helpful. Do you know how many CFM the HRV provides? Just trying to get a feel for the scale.

SENWiEco

On low continuous - 85 CFM. This is for around 3000 ft2 of conditioned space. Ducts were air tight (tested) and house also tested under 0.3 ACH @ 50 Pa (so no infiltration loads)

DCContrarian

https://forum.heatinghelp.com/discussion/comment/1805902#Comment_1805902

Thanks. And kudos on the 0.3 ACH50, that's impressive.

I'm going to guess at some numbers. If the house is at 75F, 55% RH and the coil in the HRV is at 50F, it would remove about 1.1 pints per hour of humidity by replacing 85 CFM. Each occupant generates about 0.2 pints per hour so that would work for up to about five occupants. The inside dew point would be 58F, which means you could run the ceilings in the low 60's and get about 10 BTU/hr per square foot, so about three tons in a 3500 SF house. Assuming the rest of the house is as efficient as the air sealing that's probably more than adequate.

Does the chilled air go through the HRV for rewarming or is the coil after the HRV?

OaklandNS

https://forum.heatinghelp.com/discussion/comment/1805744#Comment_1805744

@SENWiEco I've been trying to figure out the best dehumidification option, and this sounds very interesting. When you say that the loop to the chiller is unmixed from the buffer tank, what do you do to mix the water going out to your ceiling panels? Is there a smart mixing valve that interacts with the dewpoint sensors? Is the warmer water just the return from the panels, tap water, or something heated?

Thanks!

SENWiEco

In cooling mode the buffer tank is just set to 50F (in heating mode the setting is smart and looks at outside temps and adjusts accordingly). So there is 50F going to the dehumidification coil located in the HRV outside air intake duct. For the feed to the panels, the code in ControlCore pro maintains the panel feed temp to 2F above the worst case dewpoint. This is done with a three way valve controlled by a PID function block in control core. The three way valve is either taking straight from buffer tank, straight from panel return, or a combination of the above. I have 'tuned' the PID code so that the actual supply temp very closely mirrors the desired supply temp, removing all the large fluctuations in supply temps. This does mean the 3-way is adjusting a lot more often, but we get a much better consistent temp coming out of the panels. This reduces the cycling of the thermostats, and when I have adjusted the code properly, the zone actuators stay on for most of the day or night (regardless if in cooling or heating mode). We are always trying to feed the system with the temps needed to match the current load on the dwelling. I should mention that most of this is only possible because of the phenomenal building enclosure. For close to 5000ft2 of conditioned space (which includes a garage) our total load is 18K BTU heating and 16K BTU cooling

OaklandNS

Thank you Sean! I'm trying to decide if I should go with a ventilating dehumidifier or something along your lines. I'm in Northern California, so the loads are quite low and the air is mostly pretty dry during hot days. I mostly need cooling to take the edge off on hot days and/or maintain sanity on hot and smoky days when our whole house fan isn't an option. Your approach seems like it could work, except I might need to take the tank temp down further to get water sufficiently chilled to reach dewpoint. And I'm not seeing any US suppliers with similar chilled coil setups readily available.