I'm installing radiant heat in my two story and would like to know where to install an insulation layer.  I've seen a diagram where the insulation is below the floor joists  (I prefer this as I don't have to cut and fit around romex, plumbing drains, etc.)  In that same diagram there's insulation stapled up right next to the loops.  What's the difference?   And how do I decide which is right for my system?  

I've heard good things about the Foil/Double Bubble/Foil and will probably go with it.

Thanks for your help,

Ben

Ben, some people like to put the insulation up close in the box but we suggest you staple it to the bottom of the floor joist (unless the depth is over 12 inches). If you use a product like MicroFoil which already has the self sealing taped edges, you simply staple it to the joists, pull the tape off and stick to the next piece and continue on. this product has a white backing so it is estectially pleasing and has a heavy duty scrim in it for duriability, it gives a nice fiinished look and makes a nice heat envelope. MicroFoil has a 4 ply polypropelyene core to it so it has the highest fire rating as well as a high R value.

Too much of a space reduces the performance of your radiant system. Frankly, I"m not sure why, as air isn't that hard to heat up. But, that's what the studies show. 2" of space is used for suspended tube systems to allow for a small convective loop of hot air. If you are using plates, that or less is recommended. This does make it harder to seal against infiltration, but that's an additional detail worth figuring out (and do not forget to really insulate end and rim joists especially well, with sealant!).

Also, I would typically suggest regular insulation under the reflective, if you use reflective.

NRT.Rob-

I'll be spraying open cell polyurethane on all rim joists, air infiltration will be very low into my joist cavity. 

Looks like I should place the insulation layer next to the loops.  Oh well, I'll get the hang of it I'm sure.

Thanks for your help guys,

Be n

Does the same hold true if I have radiant in the basement slab as well? Will I still need to add a reflective barrier below the plates of the radiant tubing? If so, what is a good reflective barrier?

radiant floor should always have insulation underneath. over a fully heated space, R13 is adequate, typically. Over a cold space, R19 to R30 is typical.

Ben,

I just put in under floor radiant heat and I used the Low-e foil insulation. It should be about 4 inches below the pex tubing.  The idea is to keep the joist bay air completely static. With the air space your R-value is about R12 (insulation itself is R2.9). You can also add reg fiberglass under the foil.  The folks at houseneeds were very helpful. 

Foil insulation: LINK

Yoda - It sounds like you only installed the radiant bubble foil under the staple-up and no additional insulation. If so, what was your experience with only the bubble foil as the insulation barrier? Most experts in this forum (I am NOT an expert) have said that this is simply not sufficient, and you need a 'real' bat or sprayed insulation below the bubble foil. I ask because I am one month away from installing the insulation under the staple-up.

I used "only" the staple up and have wonderful results! I used MicroFoil stapled it to the bottom of my floor joists, used the 4 foot wide with white backing. It was very tight, has patented self sealing tape on both sides. I used my home as a test case. I put it in 3 rooms. one had hard wood, one laminate, one a pad with wall to wall carpeting . All were done with 2 x 6 so I had a 5 1/2 inch air space then stapled up MicroFoil. All rooms and floors are toasty warm!

Staple up Quick Facts


Floor Output at 140°F Inlet Temperature not surface temp of woodfloors: Output in Btu/hr/sq. ft 

No plates, 5/8" air gap  23.5
No plates, 2" air gap  26.2
Plates, 2" air gap  42.0
Plates, 5/8" air gap  46.3

Notice the 2" gap is not a big deal BUT make sure IF YOU can ...
remodel your home w/ (Max R values/Joist) everywhere you stapleup regardless if its heated space below. Remember you want the heat and (mostly walking sounds,conversations,creeking,saturday night etc.) to go upwards not downwards. 
LINK only use 5/8 space if you care.


Make sure use use "IC" rated hi-hats and insulate the tubes (Black pipe foam) only as you pass your hi hats! Your lights will turn off constantly even using cfl's due to the temp. Yeap that sucks! Amityville horror ha... "Read your HI hat temp shutoff".Yes SOME electrical lights (UL rated) will shut down to prevent fire... Not some others from China. I know you can use non IC too but why? Don't chance ripping down your sheetrock TYPE X get IC rated! USA MADE!!! If you live in a freezing climate like NY or have a high heat loss BTU/Hr/Sq.ft do this. Why? because you will need to crank up the temp that's why.


Always use plastic copper tube inserts so that expansion and friction won't scrape your pex against wood. I may be dead when it happens but it's great practice. Usually Black plastic hangers 1 1/4" w/ 5/8 id.

Where the joist trak ends ...cut thick/(thin ok) alluminum plates so that so that your PEX turn will be evenly heated also. Again heat transfer- Physics 101 keep it moving. "The goal is to have the entire Joist Bay a even and better conductor of heat!"
Spare me the rebuttal, Metals transfer heat faster and more efficiently... however having nothing inside your joist bay vs Joist Trak/Insulation Foil/Insulation/ in both examples the temps "MAY" be the exact same depending on your heat loss. Efficiency won't thats for sure, but radiant anything is in my opinion better than everything else if you get your desired setpoint. In short since OIL is 100 barrel F%$^ that.

I want the maximum efficiency for my home. I won't skip this step but you can in your home if you want.

BTW I'm sorry if your mortgage broker hooked you to a Sub-Prime meltdown home. "Countrywide, with a $1.5 trillion portfolio of loans, is so large that its failure may cause a crisis on Wall Street, which over the past few years has tied its fate to the mortgage industry by buying so many of the mortgage-backed securities these lenders produce, said Stuart Plesser, an equity analyst at Standard & Poor's." Washington Post. I was a former CEO on Wall street for 20 years. This is not over by far.

Who cares about radiant heat then? YOU DO. New homes sales may be in a 747 uncorrectable inverted parabolic dive but remodels will continue ...maybe stronger! Why go into clossial debt when DIY remodeling is here to stay.

I will not repeat this again. It's like the big bang theory..... I've seen the el-mexicano sloppy jobs in new home construction.
It's an artist vision only..what is it? How did so many NEW home NOT have complete Radiant Heating Systems? WTF, One bathroom and one room ...then you can list it as a "Radiant Heat Home" and ask over 1 million. No wonder the real estate meltdown. MY advice to all the DIYers BUY the top of the line material first! Give it to your Sub-Contractor or your buddies but don't skimp on material. I have seen enough skimping in the sheetrock homes with 3 nails in the entire house. You know exactly what I'm talking about! To those builders who used quality materials hopefully your homes were sold.  

Joist trak..joist trak ..joist track . or any other precious metal like GOLD as long as it transfers heat!   Stefan-Boltzmann Law Physics 101 LINK you could use other materials like cement but thats not practical. Metals are...were cheap. Gold at 880 ounce? Glad my copper piping is done. ouch.

Cheap ass Aluminum Foil has an emissivity coefficient of .04 while solid wood Oak has 0.91. Thus we can conclude that the solid Oak will absorb the heat like a sponge while the Aluminum Foil will transfer it faster/get rid of/ (reflect) to the wood floor evenly. Otherwise, if you did thermal imaging on your floor without the plates you would see just 2 pipes and maybe some heat transfer of maybe a few inches thats it. However, using the plates would show an even spread of thermal mass energy rather than a concentration in one specfic area. Can you say "Warp" speed ? get it.
 
Did you ever solder pipes with a torch? Did you hold the pipe in your hand afterwards? Did it travel upwards to get your fingers? Try that with oak? The heat will transfer much slower in oak BUT it will transfer over time!!!! Your cold startup time is reduced by my way or the right way. Both ways are correct. yeah yeah haha.


The high temperature MUST be spread evenly resulting in a larger thermal mass area which is now a much greater heating area surface mass. Plus you will reduce your chances of cupping wood and now you can double your BTU output on this step. (See top chart BTU outputs) 

Otherwise your heat loss may be too high w/ crappy windows, poor spacing, or incorrect tube layouts. If you live in a cold climate like NYC this is a must.

"Joist Trak" high quality not from china! Is a must to protect your tubes from idiots with hammers, protruding nail heads and acts as a great transfer of heat evenly. I can testify that Plates w 5/8" space work extremely well and evenly. Also, always double down 8" OC usually two 1/2" O2 barrier Pex tubes per Joist bay.



 Slabs are a BETTER example of evenly spread heat.
LINK

Concrete

0.85

 while Oak has .91

http://www.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12590





In Conclusion,

Energy prices are DEFINITELY rising to nose bleeding situations. IRAQ? More WARs? $100/Barrel? Comodities gone wild thanks to Global demand for them. In my 20 years on Wall Street I have never seen such Inflation on one side and a recession on the other (housing market 1% down crap). Take my advice and GO as Green as the Jets uniforms. Pay now and pay hard and painfully so but pay NOW! You might see ROI of maybe 10 or less years for the Mansion 5000sqft plus. My energy consumption is reduced by almost half of what it was before 2005(steam). I have a very large home. The larger the better in this case. With Radiant heat the bigger the home the more you will save thus ROI is much quicker in larger homes.

Always go as close as possible spacing wise. Supply windows/doors/heat loss areas then middle of rooms. never go closer than 4" to your OUTSIDE walls/ Joist bays. Label your supplys and returns!! One contractor feed his return and returned on his supply line. Really F uped. Always send the hottest supply to the biggest heatloss..windows/doors...then go inwards.

Think manfold controls-expensive( if you have seperate rooms..large rooms 5 loops of <300 use seperate zones. The more Zones you have the more temperture control you will have rather than one large mainfold 18 million loops on it. The number 18 million loop will get cold water while the number 1 will get hot water. got it? The cheap way works fine but for the deep pockets and office buildings seperate zoning is a must.

Try to go 200 250 maybe 300 but avoid uneven tube lenghts. Think future..future...future once the tubes are down game over.

I have a dream.... that Solar hot water heating will become mainstream replacing/supplementing fossil fuels!  I only hope that my PEX tubes are so tightly spaced that I can get a setpoint of 73 degrees. You can't even dream this if your spacing is far apart unless you pump one billion gallons per minute where your electric co. WILL get you.

Think Future first, Efficiency now, save later ROI.

To all the Radiant heat guys you are the future but still in the minority now. Have you noticed Radiant Heating prices climbing especially for copper products? Radiant heat is going to get capitalized on by the mass influx of contractors/DIY who see opportunity while the glass is 1/8 full. Radiant heat has a long way to go by European standards. Guess what more and more people will command Radiant Heating and solutions to higher inflation in the commodities sector.

Radiant Heat is above all other heating systems. There is no other option for me or any customer. Fix the heat loss. Get the Radiant Heat. Enjoy. Man that was too long. Ok I'm going to lay down on a nice heated tile hydronic floor and watch my big screen lcd. Energy star of course.


here's a few pics before the insulation and AL wrap spaced 5/8" AIR GAP.

there are people out there with uninsulated systems that are "working beautifully" too. I do not take anecdotal evidence (especially from a seller) as very conclusive. Some people think if a space is warm, the system is "working beautifully". I have had clients in the past that had entire zones unconnected, ten degrees below setpoint temp, that were "working beautifully".

Just because you successfully got some heat into a room does not mean that anything is "working beautifully". Water temps and heat load tell a much more interesting story. If the rim/edge joists are well insulated, then perhaps you'll do ok with reflective underneath over a heated space with nothing else... I'm personally still not going to trust it long term, but others do, and I'll say I disagree but not that they are wrong.

Radiantbarrier,

You have 2x6 floor joists???

"The goal is to have the entire Joist Bay a even and better conductor of heat!"
Spare me the rebuttal, Metals transfer heat faster and more efficiently... however having nothing inside your joist bay vs Joist Trak/Insulation Foil/Insulation/ in both examples the temps "MAY" be the exact same depending on your heat loss.




I knew someone would try to rebut this. In your case again, as I stated above......"MAY" be the same temp...

Yes, I agree (if) you can achieve your setpoint with nothing inside your joist then ok by customer standards. I'm not knocking anyone in the Radiant Heating Industry. You must be working on Air Tight low heat loss homes...God Bless. In very cold climates this is a not feasible unless global warming is real?? I think it may be...

However, with shoddy windows and higher heat loss this might not be practial. 

Don't beat me up ....if you have Air Tight low heat loss...your good to go w/ nada inside. 

In both cases you may be able to achieve the exact same temp as a fully loaded Joist bay. Oh by the way 2x6 is a no no sister them up immediately w lag bolts and fender washers! min 2x8 otherwise grand master flex syndrome.

Mike 

Mike, who was rebutting you?

Standing ovation to Mikeinnyc! I believe their is a LOT of hype about heat transfer plates, foils and bubble wrap insulation in terms of the old fashion ROI (return on investvent for those who have never thought about it). Pink bat insulation works great, has varying r-values and costs far less than fancy aluminum plates. If you are worried about the distribution go to a wider conductor of heat. PEX tubing is pretty narrow even if you double trace it in each floor joist, not to mention a pain to work with. I have resorted to flat electric conductors that simply staple up between the joists and can be as wide as 24". They are relatively cheap, EASY to install and don't require pumps, manifolds or anything else to support them. Super wide distribution of heat without the extra expense of little aluminum devices (also more time to install) or fancy bubble wrap. I source this product (RETROHEAT) at Warmzone.com. They even have a cool calculator at the Warmzone site to get a materials price instantly. Think Green Go Jets!

as long as you are willing to lock in to electric for the life of the home, go crazy.

I've replaced countless electric systems from the late 70's and early 80's though, which is why I like hydronic. If electric makes that much sense, you can always throw on an electric boiler. If something happens and electric doesn't make sense anymore, you aren't locked in either.

Insulating your envelope.. with something more than just fiberglass, hopefully... is always the first best place for ROI. Followed by windows. Everything... everrrrryyyything... else is secondary. Get your load low enough, and your method of heating may well become a moot question...

Bingo! SIPS, ICF's even bales of hay! Super Insulate and save for life.

though, in my own experience, we've radiant heated all 3 types mentioned there jc and the clients have been very pleased in all 3 cases ;)