Ceiling Insulation above Radiant Floor System

[Ezzie]

I live in Ontario so winters can get down to a continuous -20C for sustained periods with a week or two that might see -30C. I am getting ready to fire up my new hydronics installation in the shop. My ceiling height is 16'-6" above the floor. The building is framed with 2" x 6" and so I insulated both the walls and ceiling in the shop with R19 fiberglass batts. That was covered with 6 mil vapour barrier (taped and sealed envelope) and 7/16" OSB over that.

My question is, if a radiant floor is the only source of heat, do I need much insulation above the ceiling or is R19 OK?? It's not like I will be working 16' in the air.

 

[jayoldschool]

I'm in Ottawa, so it will be a pretty good comparison. My garage has the same height inside. The walls are insulated the same as yours, and the ceiling is R40, done with blow in insulation.

 

[ScaldedDog]

Mine has R38 batts. So far - this is the first winter I've had the heat working - it's been great. Heat, from whatever source, rises, so I'd think you'd still need to insulate the ceiling well.

Mark

 

[VHF]

Heat, from whatever source, rises, so I'd think you'd still need to insulate the ceiling well.
Mark

To get technical, warm air (or warm water, etc.) rises. Heat conducts and radiates in all directions.

Ceiling insulation is less critical with a radiant floor system where the focus is on warming the surfaces in the room rather than the air. So you may be OK with only R19 in the ceiling.

When you are blowing 120F heated air into the room with forced air, it is going to rise up to the ceiling (and then loose its heat to whatever is above the ceiling by conduction and radiation), so good ceiling insulation is much more important.

 

[ScaldedDog]

To get technical, warm air (or warm water, etc.) rises. Heat conducts and radiates in all directions.

Ceiling insulation is less critical with a radiant floor system where the focus is on warming the surfaces in the room rather than the air. So you may be OK with only R19 in the ceiling.

When you are blowing 120F heated air into the room with forced air, it is going to rise up to the ceiling (and then loose its heat to whatever is above the ceiling by conduction and radiation), so good ceiling insulation is much more important.

Agreed. But I'm still happy with my R38 ceiling.

Mark

 

[Dragster Racer]

I'm not sure I agree totally with that statement. While heat does radiate in all directions, the air will eventually be heated (naturally) and it will rise. That is where much of your heat loss will be, and I would recommend more than what you have for insulation on the ceiling.
Also, expierience with any radient heat still warrents a ceiling fan to get the hot air down where you can enjoy it. Just my experience and opinion.

 

[Ezzie]

Also, experience with any radiant heat still warrants a ceiling fan to get the hot air down where you can enjoy it. Just my experience and opinion.

Is this right?? Someone else stated somewhere here (I'll see if I can find the post) that you never use ceiling fans to circulate the air in a room that is heated by a radiant floor, I think the poster was making the point that it will only accelerate the heat dissipation thus leading to a less efficient system. The idea is NOT to heat the air, the system only warms objects near the floor. Am I likely to still need to dress warm but that everything I touch (tools, car, etc.) are warm so it won't FEEL as cold in there?

Since this is the first experience with a radiant floor, I currently know very little about it from an experiential point of view, this I am relying on what existing users have said.

 

[VHF]

How you FEEL is a combination of the air temperature and the average temperature of surfaces in the room. A room with radiant heat (i.e. warm surrounding surfaces) will feel comfortable at a lower air temperature than a room with forced air heat (which has cool surrounding surfaces.)

With a well-designed radiant system in a well-insulated and well-sealed building, the temperature difference between floor and the ceiling will be small, and no fan should be necessary.

Your body radiates heat to the surrounding surfaces... it as if cold floors, walls, cars, and tools are sucking heat out of your body. Just closing the drapes in front of a cold window makes you feel warmer because there is no longer a line-of-sight path for radiant energy to travel from your body to the cold glass.

Have you ever walked into a unheated metal building on a winter day and felt colder inside the building (even though you are now inside out of the wind)? This is because your body is radiating heat to the surrounding cold metal surfaces.

Disclaimer: Offered as opinion only, and based more on theoretical than practical first-hand experience.

 

[jeff5295]

I'm on my second "home-built" radiant-slab workshop (sold the 1st one last year). My experience says; definately no need for a ceiling fan with radiant slab heat. You'll be within a couple of degrees difference from floor to ceiling. The fan moving air around would likely make you feel cooler. When heating a slab, the heat is already where you need it. Maybe using a radiant tube heater provides different results

VHF is correct. You'll feel a lot warmer with a lower temp on radiant vs forced-air heat. I found 58-60 to be pretty comfortable.

Also correct that you may be ok with your current insualtion. I'd say give it a try. If the snow is melting off of your roof while heating, that's a good indication you do not have enough insualtion. I've got only 2" of closed cell spray foam on roof and walls. This is my first winter with it so we'll see how it goes.

Insulation provides a buffer between two different temps. The greater the temp differential, the greater the need for higher R value. I keep my shop about 58-60. For argument sake, lets say it's zero outside. I would have a 60 degree differential (because my ceiling is only around 60 also) requiring "X" amount of insulation. Same scenario with forced air, I have 120 degree air collecting at my ceiling and 0 outside. Now I have a 120 degree differential, requiring substantially higher R value compared to the 60 differential.

That's probably an over-simplified explaination, but I think you get the point. More insualtion can't hurt, so if it's financially feasible to do so, you could add some. If the budget is tight, give it a shot with what you have and see how it goes. Personally, I'm thinking you're ok or really close to it with what you have.

 

[flyguy330]

Just food for thought with the ceiling insulation. I'm in the process of building a 2 x 6 stick frame 1932 sq ft building with 15 ft ceilings. I'm quite sure that the more insulation the better. I'm planning on R-50 though the minimun you should go is R-40. Most of your heat loss with definitely be throught the ceiling. My cousin has framed over 300 large shops with in floor heat. His own building was just completed and he used R-50. He also said something interesting about ceiling fans! I had anticipated putting approx 4 fans to esnure circulation of the heat. He stated that this is a big no-no with the floor heat!. A fire hall that they built last year with radiant heat (16ft ceilings) has a difference in temp. of only 1 degree C between ground level and ceiling height. Climate wise I live just North of Winnipeg where we always see at least -35 every winter, and often -40. As long as you have good attic air ventilation, lots of insulation will serve you well. Cheers

 

[Dragster Racer]

Just for the sake of argument: It was already said that even if the floor is warm, if the air is cold, so are you. But the good news is that the warm floor will warm the air too. So you will feel warm. Where will that warm air go?

 

[jeff5295]

Just for the sake of argument: It was already said that even if the floor is warm, if the air is cold, so are you. But the good news is that the warm floor will warm the air too. So you will feel warm. Where will that warm air go?

The warm air will rise, that's a fact. However, my shop is only a degree or two warmer at the ceiling than floor, while a forced-air heat shop will have air twice as warm as mine collecting at the ceiling. More hot air rising, more heat to lose out of the ceiling. It's still a temperature differential situation. That differential is greatly minimized with radiant. Forced-air systems have to over heat the air to bring it to a much lower desired air temp. Also the building is being pressurized which forces the warm air out of any unsealed crevice in the building. With radiant, there is no pressurization. Radiant is constant, even heat, while forced-air is constantly spiking as it overheats then cools, over and over again struggling to maintain a desired temp. All that wasted overheated air collects at the ceiling.

I had 4 ceiling fans in my last shop for cooling aid in the summer. I never felt a need to turn them on during the heating system. The moving air would have made me feel cooler and wasted electricity.

 

[Dragster Racer]

I can certainly understand the even heat statement. One souce with most hanging heaters, so the heat has to be mixed. Not sure where the presurization would come from though. Forced air comes from inside, and stays inside. Combustion air escapes through the flue. Unless it's electric, wouldn't you have a combustion source heating the water for the floor?
I'm not trying to make a case for or against any particular heat source. They all have their strong points and weak ones. I like to turn the stat way down when I am not in there, which frankly is most of the hours of the day. That keeps the delta T down, and reduces heat loss. Then kick it up when I am working in there. That just won't fly with radient. If I was using my shop all day every day, and kept the doors closed, then floor heat would be the way to go. In fact, I am going to be using it in my basement eventually, and the attached garage for keeping it above freezing. Very nice for the basement.

 

[Ezzie]

... wouldn't you have a combustion source heating the water for the floor?

Yes, there is a boiler that heats the fluid that flows through the in-floor tubing (a 50/50 mix of water and propylene glycol). The boiler is a high-efficiency modulating, condensing, direct vent unit from Traingle Tube (Excellence model). It has an AFUE of 92% so there is not much heat transferred to the air in the room in which it is located.