My plumbing contractor will be installing staple-up tubing on my new construction home.  The 1st floor stapled tubing is over a heated, unfinished basement (tubes in concrete).  My general contractor wants to insulate the joist cavity with foil-lined fiberglass.  However, I want to avoid fiberglass because of the breathing hazard, and my kids have allergies.  Instead, I want to use the commonly seen 1/4" thick bubble-wrap that is double lined with a radiant barrier.  If I staple this inside the 2x10 joist cavity- say 6-8" away from the tubing - will that be sufficient to avoid significant heat loss towards the basement and radiate heat upwards towards the floor?  Has anyone gone with this approach and seen good results?

Nope. It just will not be sufficient no matter what they say. I've used it in some of my earlier radiant floor heating systems and it did NOT work as well as I was told it would by the Mfg. I ended up increasing the supply water temps to an unreasonably high limit, taking a hugh hit on the boiler's efficiency. Mistakes I won't be making again.

Instead use a real insulation with the R-value sufficient to prevent downward loss and promote low water Temps. The minimum R-values can be found in the Radiant Panel Association's Guidelines. You can download the PDF here:
LINK

Bubble foil is junk. worthless cr_p. waste of money, and will add to your heating bill forever.

Foam in place with Icynene or Urethane foam.

A high quality reflective foil with a center core of polypropeylene is more effective, Microfoil, has patented taped edges that you can also staple up and will also give you this highest fire rating.

Hi. I have staple up on a first and second floor house. (We built a couple of years ago using alot of green materials.) My contractor used R-6 foil backed radiant insulation according to the above requirement three years ago. We also insulated with R-13 cotton insulation since I can't stand fiberglass for the same reason as OLPJEB. It is fire rated as well. We put in the cotton for a sound barrier for tile floors. One bathroom we did not do it because we did not need the sound barrier. (this part is heated though). I noticed the bathrooms with the extra insulation are doing better than the one without.

Gary-is this because what you said. It isn't sufficient with a staple up system. If not, why does does the association say it is enough to use R-6 insulation? I am wondering if this is why the floor can't keep up. It can never maintain temperature. Thanks for your help.

There are a lot of possible reasons for that, green talk. Your heat load could be too high, floor area too small, water temperature too low. The bathroom you did not need the sound barrier for.. why not? is it over colder space?

The second question is what exactly is "R-6 foil backed radiant insulation".

Over heated space, fully heated, I normally spec an R13 between heated floors myself, but then all my recommendations are a "step higher" than in the RPA guidelines, typically. For instance, I would have a cow if someone installed a joist system over unheated space with only R13 in the joists. Code in many areas is R30, even without Joist heat!! But, the guidelines do not address climate, system type (above or below floor, operating temperature, etc) and are just guidelines, not hard and fast laws.

NRT Rob, we did not insulate this bathroom since it is the master bedroom bathroom and over offices that are ours. We figured we not need the sound proofing in areas where we would either be in one place or the other. The radiant is via a geothermal pump so the temp can only be no more than 125. How do you know if it is either the radiant pipes are spaced too far away for the amount of floor and heating requirement (which is limestone) or the joists need to be better insulated via a spray in foam at this point? The radiant is to just keep the floor warm and not to heat the space.

It is always fighting to keep its temperature and there seems to be a 9 degrees different between the thermostat and what the temperature of the floor truly is. (We tested it.)

The insulation that I am talking about is the type that is typically put in up under the radiant pipes with the foiled back. If I recall it is only R-6 or R-8.

Typical under joist with foil facing up?

I don't remember, but I think it is facing up to spread the heat of the tubes. The tubes are stapled up and then the foil insulation is next to the pipes.

R-6 radiant foile'd back isnsulation. The best thing that ever happened to that stuff was the introduction of the cotton insulation you used. Too bad the areas you deescribe are under-preforming.
Can you give us more details?

Ditto to the question ........................ " What is R-6 bubble foil ? "

Where does is get this designation from . ?

I've never seen product stamped with approved testing, as other legitmate insulation products are.

So.....?

My contractor used something similar to what was on this website (http://www.houseneeds.com/shop/misc/insulation/insulationindex.asp) low e-foiled back insulation. Unfortunately, he died in a car crash so this is why I am asking the forum for help. So my question is how do you know if the pipes were not spaced close enough together or the lack of insulation is the problem? It is a 500 square foot bathroom floor spaces to keep the floor warm but not to heat the room. I have taken an infared gun to see if any of the pipes are putting off less heat, but they are all working.

The geo water is about 98 degrees coming in and 88 degrees going out of the manifold. The floor is set to about 80 degrees but never gets past 71. The sensor is actually on the manifold. The ceiling below the floor is not warm. Did I give enough information this time?

well, that might be part of it. it's probably not "really" an R-6.

At this point, unless you can retrofit more insulation you will probably have to turn up your water temp or add supplemental heat.

I can blow in insulation but will it cause the foil insulation to be pushed up against the pipes? Is that a problem b/c I thought there needs to be an air space. When you do a job how much insulation do you put in the joist given the floor below is heated? My plumber thinks that the load is not enough but I think it is the insulation because all of the other bathroom are doing just fine. What temperature do you usally set the thermostat at to keep the floor warm but not necessarily for heating the space?

if you don't want the floor to heat the space, you set it to room temp. But, that won't feel warm, it'll be cool or neutral. If you want a physically warm floor, you have to raise the floor temp, and then it's adding heat to the space. Running on a floor sensor alone instead of an air temp and a floor sensor is definitely not my recommended method anyway... you can't set one floor temp and leave it all year, because you need different floor temps for different load conditions to meet the load.

Without a load calculation, no one can tell you what the real culprit is here. I would normally spec R13 under this, but that doesn't mean putting insulation under it will necessarily solve the problem. Maybe you're right, but without a load calc I can't tell you that you are for sure. If these bathrooms have less floor area, higher ceilings, more window, more space taken up with jacuzzis, more outside wall then it might be a load issue. If they don't, it's probably insulation. But, that's just educated guessing.

Not sure about pushing up the foil insulation. If it's installed tightly, maybe it'll hold in place. If the tubing is stapled directly against the subfloor, the airspace is just for the reflective stuff anyway, so if you do an R13 blown in you can ignore the bubble stuff entirely. However, if the tubing is suspended off the bottom of the subfloor without touching it, which is a preferred method, the 2" airspace is critical to the operation of the floor.

The only thing that will make the floor surface temperature to your liking is to raise the water temper.

With a geo system you are limited to how high you can raise the water temp. If I recall I think it can not be higher than 125. It is not a boiler. This is why I wonder if it is the load.

Yes you are. But you indicated it was currently running at 98 degrees. That's very low even for a top of the line radiant system. If these rooms have a "real" heat load, that is not warm enough even with proper insulation. Not knowing what your load is, I can't say for sure that it's not warm enough, but it's definitely a prime candidate for tweaking.

The water at the geo is 125, but the temp of the water of the manifold which is right by the floor is 98 and returning at a 10 degree drop as required by the makers of the geos. I can't increase the geo water because this is the highest it will go unlike a boiler. I guess if it is the load then in order to compensate given the lower boiler temp the pipes would have to been closer together? The room itself had regular geo heating and cooling and is fine. I just don't like that the floor always seem cool compared to how high I have the thermostat. I have always read that radiant is very efficient. Would boosting up the thermostat heat to compensate to make the floor warmer increase my energy bill alot more?

If you've got 8" o.c. tubing or so, stop worrying about pipe centers, it's basically irrelevant.

I would want to know why the water is 27 degrees cooler at your supply manifold than it is at the Geo hot water outlet. Either you have a mixing device that could be turned up, or you have some seriously excessive pipe losses on the way to the manifold, or you have seriously restricted flow rates in these loops.. possible air that needs to be purged out. I would suspect that you have a mixing device that could be adjusted (mixing valve, injection pump).

Are your other manifolds at 98 degrees as well?