Air gap or no air gap.

Buchman1

Recently started major renovation on my house. Total gut of ground floor. Installed a radiant system over slab with mud job over that (tile in the near future) Seems to work great and no complaints. Decided with everything open to do a staple up type system under the second floor. Could not use any type of distribution plates because of thousands of wood flooring nails petruding through the sub floor. Hardened steel nails and damaging to wood floors trying to remove. I used half inch pex with talons every 12" to 18" with screws and tried to stay around 8" on center weaving around the nails.( 2 half inch pex per bay) All loops are very close in length and under 275ft.  Was recommended to use double bubble/double foil barrier with a two inch air gap with no insulation except over attached garage portion. As expected it took a few hours at first to produce any heat. Once it reached temperature it seems to hold heat well except I had to increase the mixing valve temperature to 160F. At 140F it wasn't making any real progress. My plumber sized and installed a Burnham Alpine condensing boiler with a indirect water heater. I did all the grunt work (Carpenter by trade) Each zone/ 1st fl/ 2nd fl. has it own manifold and mixing valve and grundfos 3 speed pump. The boiler is set at 180F because of the water heater  and the still functioning baseboard loop on the second floor. I plan on removing the baseboard but only after I'm convinced the radiant will handle my needs effeciently. Is there any other option to make the radiant more efficient?

Zman

Do you have a picture?

My first thought is to run the outdoor reset curve in the boiler. You can put the DHW tank on priority so it won't be effected, if it is plumbed that way. Do you know if your mixing valves are thermostatic?If they are not you could make the staple up loop match the boiler curve (wide open) and the slab loops "lag" at a lower temp. The performance of your staple up will depend greatly on your heat loss.I have seen similar systems perform fairly well up to 15 BTU/square foot. Above that they tend to struggle.

Your title makes me wonder if you have  closed this up yet? If you still have access I would keep the "double bubble" 2" away then insulate the rims very well I would also add at least r-15 ideally r-21 fiberglass underneath. It looks like the lower level is set up really well. You don't want any downward heat loss.

kcopp

too bad...

you couldn't dremmel the nails out. The plates would help A LOT.... especially if you have the mod/con boiler.

The bubble foil is JUNK. I would add at least 3 1/2" of Batt insulation to the bubble wrap. The gap is needed when you don't use plates.

Buchman1

Thanks for the response

I asked my plumber to set it up exactly as the Burnham book illustrates. Its a primary loop with a Taco 0014 Circ. pump. The indirect water heater is plumbed off the primary loop/secondary  with its own circ. pump and aquastat. The aqua stat, I believe is wired right to the internal boiler controls (DHW Temp switch) and not the Taco SR504 "Priority". The mixing valves are not thermostatic. I'm borrowing a thermal imaging camera with thermometer this weekend to know exactly whats going on. I can tell you that with 160F water running above the bubble foil, the bottom of the foil is cool to the touch so it must be doing something. Also the wood floor above thats insulated underneath(garage) does not seem any warmer than the rest of the house that has no insulation. These factors would tend to make me believe that fiberglass insulation added to the bottom would have little effect. I will probably put R15 under it anyway for piece of mind as its not a major expence. Don't have room for R19. If I had to remove the nails, I would rather just keep/upgrade the baseboard. And Yes, sheetrock is coming soon. Thanks Guys.

kcopp

Well don't.....

take my word on it then....  http://www.healthyheating.com/Page%2055/Page_55_o_bldg_sys.htm



good luck.

Zman

Double Bubble

I think it is fairly widely excepted that double bubble as insulation is voodoo. I would never consider it under a slab. I do believe it has reflective properties which are helpful in this installation. Just as foil faced insulation will help reflect the energy in the air space so should double bubble. I would however install fiberglass insulation to reduce downward heat loss. It would have been cheaper to put in foil faced fiberglass, but since you have double bubble what the heck. Don't forget to insulate the snot out of the rim. I would at least put foam in the cracks and snug fitting batts in the bays.

Alan (California Radiant) Forbes

Ultra-Fin

Your job would have been perfect for Ultra-Fin. One run per bay and lower water temperatures.



When this stuff first came out, I was suspicious until I saw a house that was heated with it and I was impressed.  So now I'm specifying it.



http://www.ultra-fin.com/

Zman

How low can you go?

Alan,

Tell me more. I assume you are still doing an air space. How big? Foil faced insulation? Pex al pex?Most importantly how does it do at low temps?

Thanks

Alan (California Radiant) Forbes

Ultra-Fin

Zman:



You need 2" of air space above and below the tubing and then R-12 insulation below - foil face not necessary.  The hard part is when you have 2 x 8 joists - there's not enough room for regular fiberglass insulation and you have to use rigid insulation.



Water temperatures go down to 100F for 7 BTU's/sq. ft. output.  More realistically, 140F will get you 20 BTU/sq. ft. and you can set up your boiler to modulate between the two.