Hi, We built an ICF house back in November (FoxBlocks) in Nashville, TN. I was hoping our energy bills would be similar to the ICF houses we toured locally, but ours are still running over $400/month (!). Where did I go wrong?? Here are the details: WINDOWS: We do have massive windows in almost every room, they are Marvin Clad Ultimate Casement windows, which have a U-Factor of .30 & SHGC of .29 with the low-e II with argon glass. Of these windows, we also have 5 that are "splayed" in shape, and were built with a wood surround and then spray foamed to create the angled shape (in other words, the shape wasn't created with ICFs). I checked the spray foam before it was covered with drywall and they did a thorough job. HOUSE SHAPE: Our house is 4700 square feet and I will say it is an unusual shape - picture a long boomerang where half of the "left wing" is only one-room deep, and therefore there are windows on both the back and front of these main-living-area rooms (kitchen, great room, den). HVAC: We have 3 Carrier brand units... CARRIER 15 SEER Two 1.5 ton split heat pumps with 8 kw heat One 2 ton split heat pump with 8 kw heat 2 stage variable speed and two ERVs (I think). The "left wing" has its own unit, the middle bottom its own unit, and the upstairs middle its own unit. OTHER: We have a conditioned crawlspace and attic, all with spray foam. I have not had a blower test, but do not notice any drafts whatsoever at the doors/windows. And on a side note, I feel like the house seems humid alot. Would love any and all input. Thanks very much, Lori

Are those massive windows on the north or west? Is there any shading in front of them? I'm guessing that there's no awnings, but what about trees to block some of the sun?

Have you had a tune up or just a technician look at the heat pumps to make sure they're working correctly? I've heard of malfunctioning heat pumps operating in both heating and cooling mode at the same time. That would be a diagnostic thing. You might have your mechanical equipment checked up first, because with an ICF house and all of that sprayfoam your enclosure is probably pretty darn good.

New buildings can emit lots of moisture, especially from concrete, through evaporation over the first year or so. I wouldn't doubt it if that has something to do with the humidity. I have heard of some people putting a small dehumidifier in the basement and running it all the time for a year to help dry out the building.

It does indeed seem like something is not right. I wish I knew what to tell you. It sounds like you probably have a beautiful house though!

There are a lot of questions here. How high are your ceilings? What is your attic insulation? What temperature do you keep your house? What are your other energy usages? Hot water? Dryer? Lighting? How many people are using all of these things? Was a Manual J calc done? It should have the BTU loss(gain) for the house. All of those 'massive' windows at only R-3 add up. The shape of the house could be a factor as well. A square would have the smallest amount of wall area (actually, a circle does); the more extreme the long and skinny shape, the more wall area there is. A house that was 10' X 470' would be 4700 square feet, and have more than 3 times the wall area of a square.

Our poorly insulated house in FL was 1/3 the size of yours, but the power bills ran $300/month in the summer, with the thermostat set at 78-80 F. If we had kept it at 72, like many do, we would have been well over $400 a month.

Who put the pieces of the puzzle together? If you just did it yourself, or the various subs just designed for you, then that's normally your problem. I've done 5000 sq.ft. homes with energy costs under $ 50.00 month.

You need an energy specialist to review what you have already, possibly make some adjustments and change a few things and get this puzzle balanced and working properly.

I've heard of malfunctioning heat pumps operating in both heating and cooling mode at the same time.

They have three units in total. I'm sure there is a master control system to prevent things like that.

Sounds like the building layout or shape is not real efficient, and window area and exposure could be a problem. It wasn't clear if the main energy expense is heating or cooling either. And anyone aiming for high efficiency in a building should have multiple blower door tests done during construction to make sure the building is being built as well as it can be.

You need a blower test and an accurate Manual J or equivalent. Hiring someone for an energy audit would be easiest. If the results from this don't agree with your actual energy usage, then you can dig deeper.

Posted By rosegirl on 25 Jun 2014 11:53 PM
WINDOWS: We do have massive windows in almost every room, they are Marvin Clad Ultimate Casement windows, which have a U-Factor of .30 & SHGC of .29 with the low-e II with argon glass. Of these windows, we also have 5 that are "splayed" in shape, and were built with a wood surround and then spray foamed to create the angled shape (in other words, the shape wasn't created with ICFs). I checked the spray foam before it was covered with drywall and they did a thorough job. HOUSE SHAPE: Our house is 4700 square feet

Therein lies your problem: "Massive windows in almost every room", "U-Factor of 0.30", and "Our house is 4700 square feet".

Windows will contribute to a huge energy load in the summer due to the solar gain. Ideally the home should have been positioned due south with very limited windows on the west, east and north. The south facing windows should have adequate overhangs and solar shades to help with summer cooling loads.

The ICF wall is not the problem here, it is your "massive windows" in every room. This goes back to the original design. ICF doesn't cure a bad house design. I understand people want "views" but "massive windows in every room" doesn't equal an energy efficient home.

For example:

Your R-23 Wall home with double pane R-3 windows (15% glazing) = R-10 whole wall average

So your home wall is basically an R-10 average wall due to the window glazing you installed. That is not even counting the heat gain that is pouring into the rooms from the summer sun blasting the east and especially the west facing windows.

You can double check my math but I was in a rush when I ran the numbers but that is what it calculated to.

can you post your monthly energy bills for one or more years?
and systems run by them, ie pools, hot tubs, lawn sprinklers, well etc...

Posted By Lbear on 26 Jun 2014 11:55 AM


You can double check my math but I was in a rush when I ran the numbers but that is what it calculated to.

You can't calculate anything without knowing what percentage of the wall is window area.

And I calculated R11.5 whole wall assuming 15% of the wall area is R3 window and the remainder is R23 ICF.

Posted By arkie6 on 26 Jun 2014 01:18 PM

You can't calculate anything without knowing what percentage of the wall is window area.

And I calculated R11.5 whole wall assuming 15% of the wall area is R3 window and the remainder is R23 ICF.

That is why I wrote down 15% and used that to base a general average. Based on what the homeowner stated, "Massive windows in all the rooms", one can assume that there is AT LEAST 15% glazing but probably more.

So basically an R-10/R-11 whole wall average. Which is bad and not to mention the summertime solar gain that is happening with those massive windows all over the home. That is contributing to the cooling loads.

Even if they had an R-50 wall, with all those incorrectly facing massive windows they are using a pale to empty out a sinking ship. I see it all the time. People buying or building homes with massive glazing facing east, west and south with no overhangs and then they have $600 a month A/C bills during the summer and wonder why.

If the homeowner went with R-8 triple pane windows that would have helped out but it still doesn't fix the problem of improper design. The words "massive windows all over the home" and energy efficient doesn't belong in the same sentence.

How much is your elect per kw?

Did you have a competent HVAC contractor do a detailed heat and cooling load calculation before you built? A competent one will use a program like WrightSoft to do the calculations. If, by chance, your answer is no, then that is where you went wrong. If you did have the calculations performed, then how does your energy use compare to the calculations?

Posted By Lbear on 26 Jun 2014 11:55 AM

...Windows will contribute to a huge energy load in the summer due to the solar gain. Ideally the home should have been positioned due south with very limited windows on the west, east and north...

North facing windows wouldn't be an issue with solar gain. In a cold climate north glazing would be subject to cold winter winds, but in Nashville this shouldn't be of much concern should it?

Posted By Jelly on 27 Jun 2014 11:32 AM

North facing windows wouldn't be an issue with solar gain. In a cold climate north glazing would be subject to cold winter winds, but in Nashville this shouldn't be of much concern should it?

Solar gain on the north window will not be a problem but it is an R-3 glass area instead of a R-23 wall.

Where you went wrong? Sounds like you didn’t do an accurate cooling/heat load analysis during the preliminary design phase BEFORE the build phase. Had you done so, you likely would have either made design changes or accepted the higher energy usage as a trade off for something else (e.g., perhaps larger windows showcasing some great view). Actual energy usage should never be surprise…it should be a validation of both the cooling/heat load analysis and the competency of the design/build. It is also entirely possible that there’s something amiss with your HVAC system and high humidity in an ICF building for several months after the build is not uncommon either.

Posted By sailawayrb on 27 Jun 2014 12:55 PM
... high humidity in an ICF building for several months after the build is not uncommon either.

True, there is a whole lot of moisture in that concrete sandwich with no where for it to go.

Also 5 tons of AC seems a little high (leading to short-cycling), but the calcs may have suggested it due to the excessive east/west glazing.

Typical window to FLOOR area ratios are about 15% not wall area. "Massive" might bring that up to 18%, so for a 4700' house is 700-850 square feet of U0.30 window.

But with an SHGC of 29 even a U0.30 window is net-energy-positive in the winter-these windows may add to the peak heating load, but they still trap more heat from solar gain than they lose, provided there is sufficient thermal mass in the house that it doesn't overheat and you end up opening the windows even in cold weather. The amount of gain depends on the local climate conditions- a reasonable energy use modeling tool like DOE2 would give good ballpark numbers, if you wanted to try and simulate it.

when I was in search for the windows
They said this
"some window suppliers do not meet the energy star criteria and
high price is not a sign for good window"
so i did remove some suppliers from my list

If the house is occupied how many freezers, garage refrigerators and wine coolers do you have?

Then there's the added computers and all the other parasitic electrical consumption.

I was surprised at how much my electric bill dropped after I made the wife get rid of the wine cooler and spare refrigerator in the garage.

Out west the electric bills are stepped so just a little more KW makes a heck of a lot of difference in the bill. (lucky us)