I'm just getting started with this forum and figuring out where to post these things.


I just posted this question as a blog, but perhaps the "Discussion" format is more appropriate.

I am wondering if anybody out there has run across hard info regarding energy savings from conditioning or encapsulating crawlspaces.


I just finished one and the difference is amazing. Low humidity, very even temperatures and no drafts. It truly does feel like conditioned space. 


But how much energy, if any, is it really saving my client? There doesn't seem to be much information on the web about this. But I know that somebody has to have asked this question before me and done a study!


Any thoughts and suggestions on this are much appreciated. 




Bachi Brunato

Ultimate Home Perfomance





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This is the only study I have heard about... http://www.advancedenergy.org/buildings/knowledge_library/crawl_spa...

Now not to knock your question, but as I was perusing it this statement sums it up for these types of questions / looking for a one size fits all savings number "Baton Rouge results also varied, ranging from a 6 percent savings to a 29 percent penalty. Here, homeowner behavior and the location of insulation and ductwork appears to have caused significant variation."

You have to model it (based on the actual house & orientation), verify it, and the homeowners need to maintain it before one could hazard a guess on what if any savings are seen. The main selling points are the ones you brought up above (i.e. comfort) along with prolonging the buildings life - getting any savings is just icing. Hope this helps

In general, hot, humid locations enjoy more savings while cooler, dryer locations don't seem to save as much.  The Advanced Energy data from Princeville, North Carolina demonstrated a savings in the summer months and a wash or slight penalty in the winter.  Advanced Energy went on to evaluate conditioned crawlspaces in Flagstaff and Baton Rouge with mixed results.  Flagstaff resulted in a net penalty while Baton Rouge showed positive results I believe.  It appears that the reduction in moisture in the warm air made more of a difference to the efficiency of the air conditioner while the added volume to heat in the winter detracted form savings.


Scott Cummings

Dow Building Solutions


Remember that we don't heat volume, we heat surface area.  So look at how cold was the unconditioned crawl and how leaky was the floor between the crawl and house and how much insulation and square area was in that floor. Compare that to the how cold is the exterior and how much insulation and area is in the now - exterior presumably airtight - foundation wall.  Throw humidity in, add a few ducts that may or may not leak and may or may not be well insulated, and a maybe-leaky-now-tight envelope and you can see the variable variables.  It's a similar argument for conditioning an attic, however, we throw in the distinct possibility that we could cause moisture problems as the house's humidity rises into the attic in cold weather.

Ed Minch

You might look into software that uses ASHRAE's Manual J criteria for calculating the heating and cooling load for homes.   The HVAC guy that calculated the load on my house used Elite (www.elitesoft.com) and, based on the analysis he performed using that software, the encapsulated attic reduced the cooling load on my home by about 20%.

Hi Bachi.  I have had lots of practice doing crawl spaces.  You could figure it using math. I just tried to get the homeowner and the general contractor of a home that I did the ICF crawl space walls for to insulate the floor.  You may insulate the sub floor or the dirt at the floor of the crawl space.  They did not want to spend the 900 dollars for foam insulation.  Think about it, the ground temperature is about 50F in the winter to 60Fin the summer, here in western Montana.  In the winter time, the house inside temperature is about 66F.  So this means there is a delta temp differance of 16F ALL THE TIME durring the heating season.  With no insulation the only insulation will be the flooring, which is probably R 2.8.  One divided by 2.8 is the U 0.357 btu/hr/degF times delta T of 16 is 5.71btu's heading for China.  Times this by 24 hours is 137.14 btu/sq ft per day.  2,000 ft2 times 137.14 btu is 274,285btu for a 2,000 ft2 home.  divided by 3413 to get killowat hours is 80kwh per day.  My electricity cost for western Montana is 8.8 cents a killowatt hour.  80 X  .088 = $7.04/ day.  I live at 47deg. north lattitude and 3400 ft above the sea.  Heat degree days here are 7700.  So congradulations to you on doing a crawl space well!  I feel if the home I was describing above were smaller, then the builder and the homeowner would have insulated the floor.  My self personally, I would put 12" of eps foam down on the floor and have a home of 1000ft2 if it were my home.  I like low heat bills.   I have a home here for a client that is 1200 ft2 and $125 dollars for the entire winter heating season.  The insulation cost was around $14,000, R 70 walls and roof.  R 30 slab.  I installed a solar thermal combi system to radiant slab.    


Hi Terry, I do love deep retrofits.  But I have to disagree with your basement assumptions.  Heat that is lost through exposed exterior foundation walls is gone with the wind.  Heat that is lost to the soil will have to travel farther before it reaches the surface and disappears.  The deeper the foundation and the farther the heat has to travel, the slower will be the heat loss and that is by definition (essentially) r-value. 

So, even if the delta T starts out as stated, as the heat sinks into the ground below, the temperature will rise and the delta will fall.  I'm sure you have seen the temperature models that show the temperature bands emanating from below a basement slab and curving up to the surface.  It is only when the heat reaches the surface that it can escape.  All other heat, assuming no moving water, simply builds a plume below the slab and results in an increased resistance to heat loss.  The plume will build until that delta T is spread out so far that it can no longer effectively move the heat.  If you spread out that 15° delta over 15', that would be 1° delta per foot, which would be minimal heat movement.

All floors tend to collect the coldest air, due to gravity, so reducing infiltration and heat loss through the side walls and above is the best investment.





I'm on board with everything you said except for one thing:

"All floors tend to collect the coldest air, due to gravity, so reducing infiltration and heat loss through the side walls and above is the best investment."

This is a misleading simplification.  If a duct system is operating properly, the temperature will be very close no matter where you measure it in a room.  The ducts have to deliver not just enough air, but enough speed to mix in the room.  Only those duct systems that are not performing well will result in a cold floor.  It is not really by gravity unless you spin the convection that happens when cold air falls due to its density as being weight related.  And this can overcome a good bit of air leakage.

But it is true that reducing air leakage will make a room more comfortable


Hi Ed,

You say "Only those duct systems that are not performing well will result in a cold floor." I think that describes 90% of the homes I visit.  The bedrooms over a garage or the family room over an unheated crawl, always seem to end up with very cold floors.  My thoughts have always been the flood of cold air falling to the floor and the warm air being pushed up leaves those floors with little or no source of heat.  Baseboard heat relies of convection and forced hot air fights it.


The problem becomes more extreme when we look at most basements with colder air cascading to the floor and a couple of vents cut in the side of the FHA trunk at the ceiling.  I agree that a properly designed and constructed air system could mix the air and keep a room comfortable, but they are few and far between here in Maine.

Sealing and insulating the rim area and then the exposed concrete down a foot or so below grade makes for an excellent return on investment.  Below that and or the floor requires a sharp pencil to find much return.




Hi Bud.  I was actually talking about a crawl space under a wood sub floor, quite typical here in western Montana.  I was interested in insulating the I-joist floor system to cut down heat losses to the ground.  I agree that the air tightness works but it must work in combination with other things to achieve energy efficiency.  Moving heat through cold ground is still a mystery to me.  I just got backfrom a camping trip to the Big Hole valley and visuited Jackson hot springs where I read that the ground temperature increases by 15 deg. F for every 1000 ft down you go. I still think it is a good dea to insulate the floor because of  heat flows to cold.  So how long would it take for the plume to build up and would'nt the plume loose heat under the footings and back up to the cold surface?  I do know that in the book Details For Passive Houses on page 64, it shows a detail for a slab that uses 20 cm of xps insulation under the slab.  I think 20cm is around ten inches and at R 5 per inch is  R 50.  I wish I had that much insulation under my homes slab.  And it is very difficult to add more insulation under a concrete slab.  the Walden house has 7 1/2" of eps under slab rated foam.  Theair tightness, is 0.49 ach 50.  My best ach 50 on a sips pannel home is 0.269.  I would say everything is important for energy efficiency.  And a small house is the best bang for the buck.

Hey Montana!  As a kid we used to stay at the cabins in Sula and visit a hot spring somewhere nearby.  Been many years.

Yes, the plume does build and ultimately finds its way to the surface around the house, but the farther it has to travel the longer it takes and that translates into r-value.  Unfortunately, I have never seen a number applied to it.  My guess is too many variables, ie soil and moisture conditions.  New construction, definitely.  Retrofit, hard to justify.  Deep retrofit, everything doesn't always have to have a short term payback :), some things are just fun.

To put the r-value of soil in perspective, think sheetrock.  That's approximately r-1 per inch, and soil can't be all that different.  So, heat that enters a concrete floor and has to travel 6 feet to reach the surface might exhibit something like r-72.  Make that the center of the floor and now the heat might have to travel 15 feet.  I know we have some number crunchers here, so perhaps they will give us some real numbers, but whatever the actual numbers are, my guesstimate is a rather high r-value.



I think your R-1 an inch is a good number although the people at:


Says brick and concrete are .2 or so.

A good way to generalize the ground temperature is to look at ground water temp.  Here in the Mid-Altlantic it is about 58°, where a further north it is in the low 50's.  Montana might be down a few from there and Florida and Southern California are up from that.  So you can see that the colder the climate the more protection you need, but the deltas are not huge.  The edges of a slab, especially a crawl space as opposed to a basement, are the most susceptible to ground temperatures so might be where you insulate first, but what the heck, why not do the whole thing with an inch or two of EPS as many experts are now calling for.  And in Florida, you don't need any insulation because it is almost always cooler than your air temp and it is not cool enough to materially affect your heating.  

I would be curious to see experiences in conditioning crawl spaces in very cold climates like Montana - theory is one thing, but actual data is another.  It works very effectively here.

Ed Minch


I do a lot of free consulting to offset my extremely bad hearing, can't use a phone so I go to their home and talk to them as I can still get by face to face.  But I always take my IR camera, it impresses people and even all by itself, it provides a wealth of information.

Anyway, at one home the perimeter of the family room was showing about 6" of a cold floor, it really looked strange.  It took a few questions, but it turned out that the now family room used to be a garage with a frost wall.  The slab was poured inside the walls and just the natural break between the frost wall and the slab made a huge difference.  The images were so impressive and their complaint was that room was always cold lead them to excavate the perimeter and install edge insulation against the slab and 4' of 2" rigid sloping away just below grade.  Major fix but with great results. 


Terry, my mind finally kicked in and it was Lolo hot springs we used to visit.



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