We are putting in radiant heating in our basement (pex tubing in the concrete slab). They are putting in Reflectix concrete slab insulation under the tubing. It has an R-value of 1.1. Is this a good product?

Also, we have a sunken portion of our basement. Should I make sure they they run the insulation on the vertical sides (about a foot) of the sunken portion?

that's a junk insulation product. if you are in an actual cold climate, do not allow it to be used.

USE Crete-Heat---- it will give you R 10 see www.GreenInsulationProducts.com using R 1.1 is not worth putting down.

Thanks for the replies. We live in Iowa. What is the price difference between a product like the Reflectix and something like Crete-Heat? What is the most cost effective way to put down an effective floor insulation under a concrete slab.

ARe you talking about cost now or savings forever? are you trying to be cheap now or be energy efficient for the long haul? assume since you invested in radiant you want to conserve energy. have you heard the old saying, you get what you pay for? if you put junk under radiant, might as well flush $ down the toliet! people take the time to write on here trying to educate others about the benefits of radiant and the necessity to do it right. If you put junk under radiant, you will not get the best performance out of your system and end up spending a lot more money and using a lot more energy.

That's what I'm asking. Yes, energy savings is very important to me -- we also have a geothermal system getting installed. But we're installing a geothermal because we are going to be saving money in 10 years or less, not 30 years. Are there any studies or articles out there that quantify the benefits of upgrading the insulation? Why would they even suggest putting down the Reflectix? What are the benefits?

Rob is right of course. There are no benefits other than perceived cost savings. By the time you tie tube to wire you are behind. R-value matters. Most of the silvery stuff is fools gold...silver. You get the idea. CreteHeat is the real deal and has a confirmed and honest R-value (I have a sample in my hands). And as Rob has pointed out in past posts; it is very fast to install and makes tube installation as easy as can be.

Insulation in heat pump applications is even more critical as your low design water temperature is more affects system efficiency. Investments in insulation returns are immediate, permanent and guaranteed, as they will not go down with maintenance costs.

Why don't you just put in 2-4" of  XPS under the slab?  It is not that expensive and works well Now you are talking R10-R20 under the slab. 
Don't spend big bucks on a geothermal system UNLESS you do a great job of insulating first.    The payback of upgraded insulation is much higher then geothermal will ever be. 
Besides, if you insulate very well, you need a  smaller geothermal system and overall system cost is lower.  If you realy build an efficient house, geothermal is not worth it because your heat load is very small and youre heating bills are low anyway

The cost/benefit of upgraded insulation are easily calculated when the delta-Ts (temperature differences), surface area and unit-cost for energy is known.  Double the insulation R-value, only half as much heat is lost.  With 10x the insulation, the heat loss is cut 90%. Double the delta-T, twice as much heat is lost. Triple it, 3x as much is lost.  Only when the delta-T is zero does the heat transfer stop, independent of R-value.  This isn't rocket science or high-math.  If your sub-soil is already 65-70F, go ahead with the Reflectix (but were that the case you probably wouldn't need/want a radiant floor- you could heat it with 75F water on the coldest day of the year, or just put on a sweater instead. ;-) )

In fact, in new construction if you do some iterative calculation of the cost/size/efficiency of heating systems against what envelope upgrades cost, in many cases  it's hard to rationalize spending the money on geothermal vs. more insulation (or other building-envelope upgrades like air-sealing, or even better windows- which usually have very long payback) and an smaller air-coupled heat pump or other cheaper, less efficient heating system.  If in the end you use less energy with the better building envelope & cheaper heating system, for the same capital investment it's a net win. (The insulation won't usually wear out and need replacement in 20-30 years either, eh?)

If you reduce the heating/cooling loads sufficiently the efficiency of the systems supporting those loads become irrelevant.   That's how the Urbana IL superinsulated PassiveHouse can use a 1kw heating element (about a toaster's worth) in the ventilation as their heating "system", and still use less than half the national average for total annual power use (all power use, not just heating/cooling.)  It's hard to cost-effectively get R50+ walls/R70+ roofs as a retrofit, but most places can be improved significantly with the kind of money it takes to do a mid-sized geothermal sytem.

Pumping 80-120F water into a slab above another 50-55F slab/dirt is a huge delta-T, and with R1 (or in reality less, since it's significantly compressed during the pour, and loses gas flattening further over time) between it, creates a HUGE heat loss.  R5 is significantly better, but R10 is still cost effective in a 10 year NPV, no matter how you're heating the water.  Putting only R1 between the heating slab and the soil is akin to putting then distribution plumbing to your forced hot water systems in the exterior wall stud bays on the outside of the insulation- any efficiency you've gained by going with geothermal is being squandered in the distribution system.  In the grand scheme of things insulation is cheap & effective- don't skimp!

Reflectix might make sense in an attic in some regions, but NEVER under a slab. (It borders on fraud to sell it as slab insulation IMHO.)  In contact with the slab there IS no radiant heat transfer to speak of- it's 99.9%+ conducted.  Without an air gap between the Reflectix and concrete (either above or below) you would do just as well with cheap non-reflective bubble pack- it is barely more than a glorified vapor-retarder.  (Which you may still need, but use 6-10mil poly instead.)  The industry standard is extruded expanded polystyrene (XPS), 2" thick (R10). It works, it's proven, and well worth the money.  As for why anyone would even suggest using Reflectix instead of XPS I can only speculate (outright ignorance on the contractor's part comes to mind, reducing sticker-shock & counting on client complacency is another possibility- it only gets worse from there, but I'm not very imaginitive...)  For sure it's a lot cheaper than real insulation, but this is an instance of really getting what you pay for.

The fact  that they did recommend that type of slab insulation gives me a jaundiced eye toward the rest of their work as well. Did they do a full Manual-J type heat load calculation before specifying a system.  It's typical to find systems oversized by 20, 50, 100% when they just ballpark it, which makes for significantly higher up front costs and forever after in lower operating efficiency.  It might be worth having an independent energy auditor do a whole-house Manual-J on the place (as well as making other non-heating-system building improvement recommendations.)  Even if it costs you a grand, and even if the size of the geothermal doesn't change, odds are near 100% that you can save the cost of the audit over 10 years with the top 3 most cost-effective recommendations.  (Odds are you can reduce the compressor size at least a half-ton by going to R10  XPS instead of Reflectix under the slab alone, with correspondingly less geothermal heat exchanger. The less heat you throw away, the less you have to pump.)

These are excellent and very informative responses...thanks so much. I agree that adding insulation is the most cost-effective single thing we can do for our home. I will be insisting on adding at least an inch of XPS under the slab. The manufacturer of the radiant equipment (Watts) recommends an inch, but I willl look at two inches, too.

We did have a Manual J ran to size our equpiment. It is a large house and we are going with an 8-ton unit, which is a little higher (less than a ton) than the Manual J but they told me they needed the extra tonnage to move the air through all that square footage and through all the registers. (Of course, they wanted to put in much more -- they started at 11.5 tons!!!) We are zoning our house, too. With a large house (and we're going to be in it for many years), I still believe geothermal is a good option for us (especially with the current tax credits).

The Manual J did not take the basement into account, so having the radiant in the basement won't effect the size of the equipment (although we should have to run it less often as the heat rises throughout the rest of the house).

Thanks again for the responses.

It seems like a good number to shoot for to get a moderately efficient house is around 250 btu/degF per 1000 ft^ of house The bigger the house, the more efficient it should be because external surface area to volume goes down.
Assuming you are designing a house with a design temp difference of 70 deg, this works out to be around 17500 btu/1000 square feet. This is a fairly easily obtainable value. I would think you would need to be talking about a 6000 ft^2 house to need that large a geothermal system if you are insulating it well.

I think a realistic number is about 10% of the cost of a house should be insulation, airsealing and upgrades to windows and doors.
I would shoot for R10 slab using XPS
R12-20 basement wall insulation
R25 walls and rim joist
R50 ceiling
triple pane windows

If you do all that, then geothermal is worthwhile.

2" XPS is the standard for a reason.
You do not need foil underneath a slab. Nothing radiates through 2 inches of more of foam. Period!

Foam also affords you a physical decoupling from the subgrade. Please do not buy anything that makes extraordinary claims for high R values.
The highest insulation values come from foams and that is 5-6 per inch. Everything else, except for aerogels is less.

Unless something has changed, triple pain is for the artic. 2" XPS is the most common sub-slab insulation.

IF you build an efficient well insulated house, triple pane windows that  are airtight make alot of sense.

When I was crunching the numbers, in my own house the heat loss difference between minimum "energy star" double pane windows and double lowE triple panes was about 10% difference in total heat load.  You have to crunch the numbers to see if this is worth it to you in your area.  I have ~ 9% glazing area.  It is at least as important to make sure the windows and doors are airsealed properly so infiltration stays low.

What is the cost diff between a 6 ton and a 8 ton geo system?

If you insulate under the foundation, add 1" xps the the exterior of the house, use celulose in the walls 2X6?  go to triple pane windows and blow in R50 or more in the attic what does manula J calculate your heat load to be? 

I bet you will find it is more economical to add more insulation and downsize the heating system.  If fact I would give up the geothermal  if it ment I could add more insulation.     

Cheers,
eric

If you need more heating than cooling, I would install a condensing boiler, indirect-fired water heater and put $10,000 back in my pocket, paying for gas with the interest (the market is bound to come back in about 4 years) I made I my immediate savings.

this is a lot of speculation for people who have no idea what this fellow is paying for electricity and gas (isn't electricity cheap in Iowa?).

on a big heat load, low temp system, geothermal can make lots and lots of economic sense, especially if power is relatively cheap.

The lower the heat load, the less geothermal's upfront cost makes sense. Lowering the heat load is of course always the best bet. But that can only go so far economically. After that, if the load is still large, geothermal can make sense.

$10k in fuel costs isn't much for a lot of homes over a 10 year period. on THOSE homes, geo makes sense.

In this case, he's putting in 96kBTUs of capacity, derated for heating, call it 85. In Iowa, with 5500 degree days, he's up around 200MBTU/year for heating as a ballpark.

with a 95% efficient mod con, 2250 gallons of natural gas, roughly, a year.
COP 3 geo: 20,000 kwh/year
COP 4 geo: 15,000 kwh/year

with that, a simple payback rate can be calculated.

Cheap electricity? Where?

We have to factor in domestic hot water, unless he is truly "off-peak" (rare), he will be paying full price for 25% of his fuel load. $10,000 is probably light, but we are all making assumptions, as this is really a question for an experienced designer/builder, whom has collected all the pertinent facts and is paid to design an integrated system.

Payback is valid, but I was speaking to return on investment.

domestic is nowhere near 25% of this fuel load.

I don't know what the cost difference between instalation of geothermal and gas mod con.

given you numbers, where I live in connecticut  Electricity is 19.6 cents/kwh
15000 kwhX0.196 = 2940$

If you have a 200 mbtu load  Propane at 95% efficiency.  I paid 1.49$ gallon for my last fill up  cost would be 2263 gallonsX1.49= 3256$  (natural gas is not availible where i live). 
 
Net diff =316$ year =Not too good.
Of course I would want a large enough tank to go through the winter without filling up so I could buy propane in the summer when it is cheap so figure in 2 underground 2000 gallon tanks in to the cost ~ 8000$+ for the tanks which takes some of the fun out of propane

Now in areas that you are paying 6 cents/kwh  geothermal may make alot of sense. 

On the other hand,  where I live, if you  could spent 40 K$ in building upgrades to the building envelope and cut your heat load in 1/2,  changing to a smaller propane system saves you at least 10,000$ up front costs now you have a net savings of 1312$ year in heating but it cost you 30K more to build 30000/30 year morgage = 1000$  payback+ 0.05*15000 intrest = 750$  or 1750$ total.    Now you are spending 400$ year more for total costs.  On the other hand your house is twice as efficient and when energy costs rise you sudenly look briliant. 

wow, I wish I had access to $1.50/gallon propane. it's almost double that just up here in Maine. and my electricity is less. So up here, the comparison is much more favorable, though to meet oil you need a COP of 3.

Cutting your heat load in half doesn't knock $10k off of any heating system I'm aware of, typically. It may very well have better payback characteristics, but let's not get into hyperbole with 6 cent electricity and $10k system downgrades on a drop from 85k to 40kBTU/hr peak load systems. That just makes good numbers look bad.

never mind whether or not $40k is even remotely close to enough to cut an 85kBTU load to 40k, which in the case of a house large enough to have an 85kBTU/hr load to begin with, I would doubt.