best insulation under radiant heat in a crawlspace

donedeal

So I'm looking to beef up my insulation in my crawlspace that has radiant heat as that room is quite cold. This room was an addition over a crawlspace with poured concrete and no vents. I have suspended tube system and currently from top down, there is PEX, followed by a thin reflective metal, followed by fiberglass insulation with a vapor barrier facing down. Everyone including my inspector told me that the vapor barrier should face up towards the warm space and that I should flip this over. Should this be any different for my set up given its radiant heat?

Is there something better I could be using? I've read fiberglass really isn't all that great as it falls , has gaps and then R value is shot.

Is it recommended to line the walls of the crawlspace with foam board as well?

Here are some pics of the space.

Rich_49

What floor joists do you have , 2x 8 , 2 x 10 ? How much of an air gap is left between the sub floor and the "reflective" metal ?

The FG that's there looks a little thin , is it 3 1/2" or greater ?

Best would be to replace FG with Roxul from the metal to the bottom of joists then attach 1" of foam boards to the bottom of the entire surface to eliminate the thermal bridging of the wood . Those joists transfer heat downward to the crawlspace . Better to get that heat working in the right direction . Make sure the ends of the joist bays are insulated somehow to prevent even more heat from running to those ends and having a band of warm at the siding . Foam boards or spray should suffice at that junction . Now every bit of heat you can send to the living space is being sent to the living space .

BenWoj

A few things come to mind that may help your cold room. It may not be insulation which your looking for, but It should increase your heat transfer to your room so you won't need any additional insulation.

The drawback from suspended tubing is you have to have your joists well sealed. What your trying to create is a convection oven, and with any type of air flow in or out, it will prevent the cavity from warming up which provides heat to the room above.

Do you have the room to place plates to the underfloor of the crawl space? Allowing your tubes to directly transfer heat to the plates, which are directly placed to your underfloor will make a huge difference.

The house my wife and I bought had suspended tubes as well. Didn't heat worth a crap cause there were so many small gaps everywhere. Switched to plates and it's like night and day.

donedeal

So I just had a local energy/insulation company come out. They recommended encapsulating the crawl space floor with a bunch of stuff then foam boarding the walls, and spray foam the rim joists. They said the FG was useless and could be removed. So now nothing would be between the joists but the pex and then the reflective metal barrier. Nothing beneath that. I would think that heat would be lost to space below or it would all heat up together as a space and eventually warm the room? Is this efficient?

Mark Eatherton

donedeal said:

So I just had a local energy/insulation company come out. They recommended encapsulating the crawl space floor with a bunch of stuff then foam boarding the walls, and spray foam the rim joists. They said the FG was useless and could be removed. So now nothing would be between the joists but the pex and then the reflective metal barrier. Nothing beneath that. I would think that heat would be lost to space below or it would all heat up together as a space and eventually warm the room? Is this efficient?

Don't use that company. They don't understand the needs of this particular radiant system. As Ben said, if you can get some good heat transmission plates (not the flimsy flashing metal ones) it will make a big difference in heat transfer, comfort and energy consumption.

If you decide to stick with the suspended tubing, the 2" gap is critical to ensuring proper heat output, at a premium operating costs. Pushing insulation up tight against the tubing will actually result in less heat output because you have killed the convective and radiant portions of the equation.

You must also make certain that the ends of the joist bays are thoroughly insulated to lessen the conductive losses through the exterior rim joist.

ME

Gordy

The company is under the misconception if the crawl space is conditioned the room above will reap the benefits........maybe......not.

In the end it will cost you more because now your heating the crawl space, and the rooms above.

Rich_49

Look at what they want to do this way . If your crawlspace is under a 1000 sq ft home and it is an average of 4 feet deep you will be heating a 500 sq ft room . That room will always be heated first before the rooms in which you dwell .
Tell the next company that Resistance or R Value must be placed below the tubing and the ends of the joist bays must be sealed and insulated well and the airgap must be maintained between the insulation and sub floor .

Dave H_2

With suspended tube radiant, sealing of the joists is critical. If you have 2x 8 joists, go with 6" on insulation. Try to get as much as you can. If 2x10 joists, get 8".......Keep the insulation at the bottom of the joist so that you can maintain the 2" needed air space with the radiant pipes. and tuck it up when you get to the rim joist, that's the largest heatsink along that outside wall!
Vapor barrier faces the living space. It doesn't affect performance of the radiant, just keeps moisture where its supposed to be.
And make sure it seals the joists, if you can because the on-centers of the joists are off, I used the bubble foil that was 4 feet wide and stapled it to the joists to help seal it off.

Dave H

donedeal

Ok thanks for the great Info but I was wrong in my initial posting. I went in there pulled stuff down. It's watts radiant onix tubing stapled In place and then the metal reflective below followed by r21 FG. The rim joists are exposed. So I think I'll foam board and spray foam gaps at the rim joist, would heat transfer plates be Applicable still with this tubing? What's a good brand? And then keep the FG but flip it around and then foam board across the bottom of that between all the joists.

hot_rod

Not much you can do to improve heat transfer from that tube. I have not found transfer plates that fit well. Pulling the tube down and removing thousands of staples would be ugly

Check that the tube is in good contact. Take a 2x4 block and drive the staples against the tube. Any air gap and you lose conduction to the floor

The rim joist seal is critical. At least 4" of foam sealed with expanding foam. Buy a large container like Tiger Foam with a hose and nozzle to control better. The box stores have those kits

Floor coverings can really dampen output also. Keep them lean and hard surfaced