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Community and Q&A

New build follow-up (structure, insulation, windows, HVAC)

Matt Anderson | Posted in General Questions on

Hey everyone. I wanted to do a follow up post from my original about our new construction. I took in everything that was said and went back to the drawing board. Here is what I had come up with.

House Overview

We will be building a full brick walkout ranch in Zone 5 (Ankeny, Iowa) which, unfortunately, has most of the window placements facing NE because of the orientation of the views over the pond and not south like I had originally hoped for. In trying to balance our budget and not go over what we can afford, we decided to do a full brick house and more insulation on the exterior. Because of this, we’ve had a hard time deciding on the windows. When pricing the triple pane, we were WELL over budget, so we had to go back down to the double pane. We will have 2 direct vented fireplaces (living room/family room). I’ve listed out the highlights of the build we are proceeding with and wanted to share with the community and receive feedback one last time before the digging commences. I’ve also reattached the next to final version

Wall Structure:

  • Brick
  • 1×3 (¾”) Furring)
  • 2” Foil Faced Polyiso (used to up my whole wall R value)
  • TyVek House wrap
  • ½” OSB Sheathing
  • Siga Wigluv used to tape and seal at joints
  • 2 x [email protected]” OC
  • 5 ½” Dense Packed Cellulose
  • 2×2 (1½”) Horizontal Furring (Wiring Chase)
  • 1/2” US Gypsum XP Board


Exterior Walls

  • 2” Foil Faced Polyiso
  • 5 ½” Dense Packed Cellulose

Interior Walls (2×4) Sound Walls

  • Netting installed on both faces of the wall
  • Spray cellulose blown into each stud cavity
  • Common wall between the Dining Area/Kitchen and the Master
  • Common walls between Garage and house
  • Common walls around bathrooms

Basement Walls

  • 2” XPS (R10)

Garage Walls

  • 5 ½” Dense Packed Cellulose


  • R60

2” XPS (R10) for Under slab and Perimeter

R3 for the following:

  • piping larger than 3/4â€inch outside diameter
  • piping branches serving kitchen sinks
  • piping located outside the conditioned space
  • piping from the water heater to a distribution manifold
  • piping located under a floor slab
  • buried piping
  • piping in recirculation systems other than demand recirculation systems


  • I’ve gotten price quotes from Marvin Integrity/Kolbe/Gerkin. I used to try and find the appropriate windows. Like I had stated above. Most of my windows are facing NE.

NO CLUE………………HELP…………………


  1. Waterfurnace Series 7 properly sized to minimize short cycling, vertically drilled wells. Sizing has not happened yet but will be done this/next week.

Questions Still Open and wanting feedback:

  1. After reading many many many posts about ventilation, I have decided I am completely confused. I got a quote from Zehnder which was around 8K since I will be doing the install myself. I would like to hear what others in the community feel would be a good alternative to the Zehnder 550 HRV. Since I am going to be tighter than most houses, I really need a good ventilation strategy.
  2. Should I be concerned with Foil Faced in the open cavity? I was reading that there were test results showing that the foil faced may not “live” the life expectancy I was hoping?
  3. Since I am insulating the basement walls with 2” XPS, do I need to add more insulation in the cavities? If I do, would cellulose work? I am afraid of it retaining any moisture. Any recommendations?
  4. Based on the recommendations from efficientwindows, I was looking for windows that meet this criteria
    • Double-glazed, Low-solar-gain Low-E Glass, Argon, Non-metal, Improved
    • U = 0.23-0.30
    • SHGC = ≤0.25
    • VT = 0.41-0.50
  5. Since I am going with a GEO system, I am having a hard time deciding on a water heater solution. Do I go with a holding tank? Tankless? DHW? Any thoughts would be greatly appreciated.

Let me know your overall impressions. If I am going down a road I should think twice about, let me know. At the end of this, I will be posting my spec sheet to help others that are in my situation may well rounded choices.

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  1. Nick Welch | | #1

    For water heating, look into a desuperheater. This is an add-on for your ground source heat pump that provides very cheap or "free" hot water. Also look at a drain water heat recovery unit. These are the best options for maximum efficiency.

  2. User avatar GBA Editor
    Martin Holladay | | #2

    You explained that you want to install a ground-source heat pump, but you didn't explain your heat distribution system. I'm guessing that you'll have forced-air ductwork, not a hydronic (hot-water) distribution system. Is that right?

    If you have forced air ductwork, a central-fan-integrated supply ventilation system will be much less expensive than a Zehnder HRV. More information here: Designing a Good Ventilation System.

    You have chosen to install code-minimum insulation on your basement walls. That will work, but you might want to install thicker insulation there (for example, 3 inches of rigid foam instead of 2 inches). I don't recommend installing cellulose insulation in your basement.

    In general, ground-source heat pump systems are quite expensive. If you chose a simpler (cheaper) heating system, you could use the money you save to buy better windows or more insulation for your basement walls.

    It sounds like you may have natural gas available, since you mentioned two "direct-vented fireplaces." It's hard to beat natural gas as an inexpensive fuel to heat a house.

    Another way to save money on your complicated heating system is to cancel the two fireplaces.

  3. User avatar
    Dana Dorsett | | #3

    I'm wondering if you've found a source/price for the extra-long masonry ties needed for 2" foam?

    For a house with your ~R25 whole-wall R on the above grade portion, Martin has it right- R10 foundation is on the very skimpy side, and is current code-min for zone 5 IA, but doesn't meet IRC 2012 code min:

    Using 3" of polyiso (~R18-ish) would be a better match to your other R-values, and nicer to the planet than XPS (since XPS is blown with very powerful greenhouse gases, most of which escapes in under 50 years, causing it's performance to sink to the R8.5 range to boot.) Alternatively, an inch of polyiso trapped to the foundation with a 2x4 studwall with R15 rock wool batts hits a similar whole-wall R of ~R18. (Rock wool is preferable to cellulose in sub-grade apps, since in the event of a plumbing leak or other flood it won't expand or wick the moisture higher, and can dry-in-place after the tide goes out.)

    In the same vein, R10 under the slab is OK, but using 2.5-3" of EPS (Type-II or Type-IX) would make sense. If you are using the slab as the space heating radiator, bump that to 4" of EPS. EPS is the same polymer as XPS, but blown with much more benign stuff (pentane, instead of HFC134a), with only 0.5% the global warming impact. Unlike XPS, the R-value on day-1 is the same as in 50 years. (At 100 years the R-value of XPS & EPS of identical thickness & density will be the same.)

    In a zone 5 climate the Daikin Altherma air-to-water heat pump can match or beat ground source heat pumps in low-temp-low-load situations for considerably less risk and less up-front cash. Whether it's cheaper than the GSHP after the substantial subsidies allowed for GSHP depends on the contractors and the subsidies.

    The "right" solution to your hot water issues depends on your actual hot water needs. A heat pump water heater is probably cheaper than a DSH solution and runs at about the same annualized net efficiency. (In cooling dominated climates with big cooling loads DSH would be a clear winner though.) I'm partial to the all -stainless Air-Tap series, but the Stiebel Eltrons are pretty good. The 50 gallon GE GeoSpring is a reasonable value too. Tankless electric hot water heaters are less efficient than DSH or HPWH and have output capacity issues at your incoming water temps. Tankless propane is substantially more expensive to run than HPWH or DSH at typical low IA electricity pricing. Tankless natural gas is cheap to operate, but maintenance isn't (especially if you are in a hard-water area). Condensing tank type water heaters can do as well or better than condensing tankless with fewer maintenance issues and lower installed cost.

    +1 on losing the low efficiency fireplaces that usually end up being little more than a pretty air & heat leak in an otherwise pretty-good house.

  4. Matt Anderson | | #4

    Thank you everyone for the responses!

    As of right now, we would have a forced air system. To give any example for budgeting, for the Waterfurnace series 7 5 ton with vertical wells drilled and installed cost, we were at 24.5K. I know that number would be going down once the calculations were done on the system.

    I read a lot about the Poly/XPS/EPS in the forums, but I must have mixed up what I should have seen and also forgot about when looking at the 2012 code. So I could either bump up the RValue on the walls by going 3" Polyiso or an 1" with 2x4 and rock wool. Good to know that and I can do that myself:)

    In regards to the water heater, were you talking about the Airgenerate AirTap?

    I haven't heard of the Daikin Altherma, but will look into it.

    The fireplaces were for my wife who wants them. We will be venting them directly to the outside of the house, no real bends. Any recommendation to help with that?

    Again, thanks for the great feedback.

  5. User avatar
    Dana Dorsett | | #5

    Polyiso and EPS are both blown with pentane (at about 7x CO2 for global warming potential). XPS in the US is blown with various HFC mixtures, the predominant component of which is HFC134a at ~1400x CO2. Polyiso is slightly hygroscopic- can't bury it or it'll become waterlogged, but has a high kindling temp and doesn't melt the way polystyrene (EPS/XPS) will, which makes it a preferred product for wall assemblies. EPS won't take on moisture permanently, and is the preferred product for exterior sub-grade foundation insulation or sub-slab insulation.

    Yes, I was talking about the Airgenerate AirTap series. The cool-air output of the heat pump is designed to be ducted (within reason) to where the cooler air is either actively useful, or less of a chill-problem, which makes it easy to place where the hot water distribubtion pluming is optimal, sending the chilled air elsewhere. Other heat pump water heaters need to be placed where the temporary room-chill isn't a problem.

    Didn't find a Daikin installer within 100 miles of Ankeny using the online contractor-finder:

    But there are four distributors in IA, who may be able to point you to a competent contractor:

    CFM Dist - Des Moines
    4137 109th St
    Urbandale, IA 50322
    Phone: 515-331-4137

    First Supply - Dubuque
    4949 Chavenelle Drive
    Dubuque, IA 52002
    Phone: 563-582-1895

    United Refrigeration, Inc. #429
    927 8th Street
    Des Moines, IA 50309
    Phone: 515-288-7211

    United Refrigeration, Inc. #430
    515 8th Ave. S.E.
    Cedar Rapids, IA 52401
    Phone: 319-363-8219

    It'll still be 15-20 grand for most Altherma based systems, but there is no dirt-work and less design risk than with ground source heat pumps (where every system is a custom build, with the efficiency in the hands of the system designers & installers.) It might be possible to reasonably heat the place with ductless air-air heat pumps if the bedroom loads pencil out to be able to split the output of a mini-duct cassette, but it's not the most ideal layout for a ductless approach. It would be less money than a hydronic solution if it works, and almost as efficient.

    A ducted combustion air wood stove with a nice viewing window or direct vented gas-fired variants thereof are generally tighter and more efficient than gas fireplaces (eg: ). The stove-type gas burners are generally in the low 80s for efficiency, whereas many direct vent fireplaces struggle to make 65% efficiency, those some will nose a percent or two over 70%. Did you have a particular fireplace model in mind? Key to making them as efficient as possible is to air-seal both the bottom & top of the flue chases and insulate where it penetrates the exterior of the house. You'd be amazed at how much air a leaky flue chase with a hot stack can suck out of the house, whether the thing is firing or not, and how poorly they tend to be installed.

    The roof pitches aren't shown, but in ANY new construction it's worth keeping in mind the potential for photovoltaic panels. At current average IA grid pricing vs. PV pricing it's a tough sell, but 20 minutes from now the price of PV will have fallen, and by 2020 it's likely to hit the price point where the lifecycle per-kwh price is sufficiently below the residential retail price that third party companies will be interested in making that investment and giving you a lower than retail rate on the electricity you use, if you don't want to spend the money yourself. But if you don't have much roof area facing somewhere between SE and SW (due south would of course be better), the hit in annual uptake would be pretty big, making it a less than ideal setup. At your R-values you'll never hit net-zero-energy with an array that fits on your house, but you might be able to cover half or more. (A SW orientation is more valuable to the grid operator than a SE orientation, since it's output delivers more during the peak-demand hours.)

  6. Richard Patterman | | #6

    I am lost on a couple points.
    1) If you have 2x6 exterior walls plus 2x2 wire chase, couldn't you upgrade cellulose to 7" at very little additional cost?
    2) I assume you have natural gas available for the two fireplaces. Why not drop the over priced geo system and buy better windows and go with gas heating? One of the biggest advantages of heat pumps is eliminating the need for two fuel sources and metering charges.

  7. Matt Anderson | | #7

    Thanks for your comments Richard.

    1) We do have the wire chase, just haven't decided on whether to fill it with cellulose or not, maybe batt. Reason we have the chase is so we could run wire and utilities without breaking the envelope. But you're right, we should insulate there as well

    2) We do have Natural gas. I have a meeting scheduled this next week with our HVAC tech and will be bringing this up to him as well. The rage today is Geo, but I agree with you, buttoning up my enclosure would really warrant looking at my heating/cooling system again. With the suggestions of Martin/Dana, I think I really need to re-evaluate windows and enclosures. I will update this post with what I find out.

    Regarding windows, any recommendations for the triple panes?

  8. User avatar GBA Editor
    Martin Holladay | | #8

    You wrote, "The rage today is Geo." I assume that by "geo" you are referring to ground-source heat pumps.

    I don't know who you have been listening to, but among green builders, there is a strong consensus that ground-source heat pump systems are so expensive that they are unlikely to be a wise investment for a single-family detached house. Among green builders, they are not "the rage."

    For more information, see Are Affordable Ground-Source Heat Pumps On the Horizon?

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