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Q&A Spotlight

How Would You Insulate My New House?

In chilly Thunder Bay, Ontario, a prospective homeowner looks for advice on how best to insulate the walls and foundation of his new house

Is a ground-source heat pump compatible with an off-the-grid solar system? A prospective homeowner in Canada is hoping so, but wonders whether that issue has a bearing on how much insulation he should put in the house.

Nik Fiorito is grappling with the same issues every owner/builder eventually confronts: What’s the best way of insulating a new house? Only in Fiorito’s case, it gets a little more complicated.

First, he’s building in Climate Zone 7, forty minutes north of the U.S.-Canadian border, on a hilltop where the temperature averaged 3 below zero F (-19.6 degrees C.) this past February. He’s also considering a fully off-grid photovoltaic (PV) system plus a ground-source heat pump for both heat and domestic hot water.

Throw those variables in the mix and Fiorito’s situation is a little more complicated than building, say, a nice little ranch in suburban Cleveland.

“The home has large, south-facing windows with a walkout basement and as Thunder Bay is quite sunny (no city east of us in Canada gets more sunshine), I think we’ll have a nice solar gain into the home during the winter,” he writes in a Q&A post at Green Building Advisor.

What, he asks, should the wall assemblies look like? He’s leaning toward using Roxul mineral wool insulation in the 2×6 stud cavities, with Roxul Comfortboard mineral wool panels on the outside to lessen thermal bridging and a polyethylene vapor barrier to keep water vapor out of the walls.

A second option would include the use of 1 1/2-inch tongue-and-groove rigid foam on the interior over mineral wool batts. “This would allow me to avoid a poly vapor barrier and flash the windows against the exterior sheathing (OSB, most likely),” he writes. “I know this method (interior rigid foam) is less favored here, but I’m thinking it might work.”

Insulating his planned wood foundation is an entirely different issue.

Those are the topics for this Q&A Spotlight.

First, the question of the…

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  1. LucyF | | #1

    I meant "won't get you very far"
    I meant to say that R-28 to R-30 won't get you very far in terms of insulation in a zone 7 climate.

    I wanted to ask when this topic first came up, would Martin be on the grid if he could? Or if he'd had that option when he built his house? I realize that 40 years back grid-tied wasn't an option. Just curious.

  2. GBA Editor
    Martin Holladay | | #2

    Response to Lucy Foxworth
    I have edited the article to better reflect what you meant to say. Thanks for the clarification.

    Whenever someone asks whether to hook up to the electrical grid, I advise them to get connected if at all possible. If you live in an off-grid house, you have to deal with batteries and fossil-fuel-powered generators -- equipment that is expensive.

    I have none of the advantages of the grid -- meaning that I can't use electricity from the grid during long spells of cloudy weather; nor can I sell any of the surplus electricity that my PV panels produce during the summer.

    I don't regret the decisions I've made, however, and I love where I live. I feel blessed.

  3. LucyF | | #3

    Thank you.
    I admire you for doing that. I know that living off-grid especially in a colder environment entails a lot of work and some degree of compromise in comfort that most people in the US would not ever choose.

    And it is a blessing to get to live in a place you love. Thank you for your commitment to making all of our homes better and more efficient.

  4. DavidButler | | #4

    don't go off-grid unless you have to
    Off-grid isn't for everyone. It's a different lifestyle and involves many sacrifices compared to the way most people live. You have to constantly pay attention to when you use power, and you ultimately end up doing without a lot of things we take for granted. The folks who live off grid and would argue that it's not that big of a sacrifice have simply adapted. Which is not a bad thing. But don't assume it's going to be anything like living on the grid unless you have a boatload of money to spend on power systems.

    So, I agree with Martin that if there's any possibility of grid-tie at a reasonable cost, then by all means, that's the way to go. But it's not just a matter of being able to sell your excess power.

    Most folks don't realize how much PV power is forfeited when you're not grid-tied. Whenever the sun is shinning and batteries fully charged (that happen a lot more often than you'd think, and not just in summer), all power generated above whatever load happens to be on at the moment is lost forever. That's why off-grid arrays have to be much larger (than grid-tied) to offset the same annual load. With grid-tied net metering, you get the full value of every kWh produced, up to the annual load.

    From the article (Rich): "Possibly a diesel generator as electric backup just in case the sun doesn't shine."

    No, Holladay replies, "it's nuts to run a heat pump with a fossil-fuel powered generator."

    I agree it doesn't make sense to use a generator to run a heat pump. But every off-grid home requires a generator, and it does make sense to use it to power the heat distribution system (hydronic water pumps and/or air handler) when batteries are depleted. In that case, primary heat is provided first from stored hot water, then by a fossil fuel boiler (see following comment on mechanical design).

  5. user-2890856 | | #5

    Mechanical Design
    This story is exactly why I have been showing up in various places and trying to offer valuable information . This particular homeowner would be much better off with a combination PV / thermal system . Instead of using vertical bore holes or horizontal loops that rarely get done correctly to install a GSHP solar thermal is an obvious best practice install .
    Is it true that after exceeding a certain temp that PV efficiency starts to decline ? Would a thermal cooling / collection portion of the panels allow them to produce at a higher rate ? Yes to both .
    Is VBH or horizontal heat exchange method expensive as heel ? Yes .
    Could one install properly sized thermal storage tanks for a fraction of the cost ? Yes
    Could you store in that tank at 160*F ? Yes .
    Can you mix that water down to say 70*F and increase the COP of a small water-to water HP and get a COP of 6.5 ? Yes
    Can this tank possibly bypass the HP for quite a long period of time and passively heat the home.until a point that the EWT to HP would be the same as if VBH or horizontal were chosen then use the HP ? Yes .
    Could you use this same system to do sensible loads for cooling ? Yes .
    Can you heat a low load home with radiant tubing with sub 80*f fluid ? Yes .
    Can you install a smallish DOAS system to handle latent loads ? Yes .
    Is it best practice to have seperate Ventilation and heating /. cooling systems ? Yes
    Does this make sense in an off grid home and a grid tied home ? Yes
    Could you continue to heat the stored water after your batteries are fully charged from the PV ? Yes .

    Would one who researches things like this on GBA ever know such things and be guided to making better decisions and get what he wants done better ? NO !

    Why is this ? Because Martin publishes articles like " All about radiant floors" , " Solar thermal is dead " , Solar thermal is really , really dead " .

    Martin ,
    You really should invest some time into seeing what we are really , really doing out here in the wet world . You may be shocked at what we can offer . Especially to the off grid folks who can heat their homes through multi source heat pumps in case something goes awry with a single source system that is cheap at first glance .

    David ,
    Please remember that you possess skills and knowledge that are certainly in the top 1% of the air side HVAC world . You cannot design everything for everyone . Martin , please note that all of David's mentioned systems had a wet component . How big would the tank have to be to store heated air for use later ?

  6. GBA Editor
    Martin Holladay | | #6

    Response to Richard McGrath
    I have been reporting on energy issues since 1999. You are describing a complicated HVAC system that includes a large hot-water storage tank in the basement; solar-thermal collectors sized for space heating, with associated circulators; a water-to-water heat pump located in a basement; a PEX tubing heat distribution system with associated circulators; a PV array; and a variety of temperature sensors and control modules to make these pieces of hardware interact with each other.

    The system you describe requires a skilled mechanical engineer to design; a skilled HVAC installer and plumber to install; and a team of experts to commission, trouble-shoot, and repair.

    Is it possible to design and install such a system and make it work? Yes. Would that be easy or likely? No.

    Would the equipment be cheap? No.

    Would experts be available locally to fix it when it breaks? No.

    Is this system appropriate for an off-grid house? Absolutely not.

  7. user-2890856 | | #7

    Who said the tank was in the
    Who said the tank was in the basement Martin ? Not me . Many homes don't have a basement . Not solar thermal collectors , combination collectors since you are already installing PV .
    The circulators used would require a whopping 9 to 22 watts each , ALL of them . The system I am describing would require 2 of them . One for heating and cooling and one to move the water from our tank to the source or house . Much better than the monsters required for GSHP which do not appear in the COP numbers of machines . Sensors are already in place , you do advise in the monitoring of RH inside a house correct ? Controls are vey dvanced now and what you describe above is quite intimidating but just not so . Yes , one mixing valve for heating and cooling that communicates with RH sensor and Outdoor sensor . Imagine ONLY moving the energy that you require , no more , no less , at all times . that is terrible huh ?

    I'm sorry I have removed all that environmentally friendly (LOL) refrigerant from right inside the homes of folks . That stuff is not dangerous right ? You did catch the part where water could do this for a majority of a season without the use of the heat pump right ?
    I did forget to mention that I can do away with leaky ductwork that can be located in other than the attic . Imagine insulating your ceiling instead of your attic because you have to get garbage inside the envelope .
    Here is the thing Martin . We can heat using cooler mediums and cool using warmer mediums . Geez , that sounds efficient .
    This is not personal Martin , well kinda . People listen to you , they ask you about certain things and you inevitably always , unintentionally , I'm sure make them feel like they have done something wrong . My end goal here is to get rid of the necessity of refrigerants . We do not need them in every house . This is about the environment right ?
    So , in short , my PASSIVE ideas do not fall into your idea of green ? When exactly wa sit that Green began to translate to " spend some money here but not there , and by the way , use as much of this bad stuff as possible so you'll have more money to insulate and air seal . Once you spend this extra money here you can install garbage .
    Can you tell me how installing a 1 1/2 or 2 ton split in a 10K home is efficient ? What is the low end modulation for these things ?

    Experts .

    Do you have an idea of how many easy systems I see that are FUBAR ? Maybe we should be educating experts and fix both our industries .

  8. user-2890856 | | #8

    Reporting is a funny thing Martin . You have to be very thorough in your analysis before writing for the world to see . You should try it sometime. You would not want to end up like the writer from Rolling Stone that is in the news right now . maybe you could schedule some time to take a ride down to Mass or RI and see what the guys from HTP or Taco are working on . That would certainly be enlightening for you . Hell , you may even cross party lines . How about a small modular unit that heats / cools and can use whatever fuel or source one wishes ? Wouldn't that be something ?

    I have been designing and installing systems since 1985 , my family has been doing so since 1915 . In 1970 my Uncle guaranteed no more than a 1/2*F difference from room to room . Can this be guaranteed by any other system than water based to this day ?

  9. GBA Editor
    Martin Holladay | | #9

    Response to Richard McGrath
    I think we agree on many points, and I'd like to emphasize our points of agreement.

    Like you, I think it's a good idea for HVAC contractors to seek out and specify low-power circulators.

    Like you, I think it's a good idea to keep ductwork out of unconditioned attics, and to insist that ductwork seams be sealed when ductwork is required.

    Like you, I think it's a good idea to design hydronic systems that operate at the lowest possible water temperature.

    Like you, I think that passive systems are almost always preferable to active systems.

    I haven't ever preached against any of these principles.

    Richard, I have every reason to believe that you are an excellent mechanical engineer, HVAC system designer, and plumber. I'm not doubting your skills. However, people like you are rare -- so that when a GBA reader in Oklahoma or Wyoming wants to take your advice, that reader doesn't always have access to your troubleshooting skills.

    GBA provides an open forum and invites readers to share opinions and advice. I have presented my advice, and you have presented yours. GBA readers who are convinced by your arguments are free to install the HVAC system you describe -- and they can install the large water tank that you recommend in either a mechanical room or a basement. (The location of this large tank won't change my opinion on whether this type of system makes sense.)

    When I mentioned solar thermal collectors, you wrote, "Not solar thermal collectors -- combination collectors since you are already installing PV." If by this you mean solar collectors that try to combine water heating and PV in the same collector, I am aware of these systems and have been reporting on them for over a decade. None of these has ever been shown to be reliable or cost-effective. But any GBA reader who is convinced by your arguments should feel free to install them (and all of the other components of your recommended heating and cooling system) and report back on the system's performance.

  10. GBA Editor
    Martin Holladay | | #11

    Response to Richard McGrath
    I'm very familiar with the published papers on solar thermal and PV combination panels, and I know that R&D guys get a dreamy look in their eyes when they talk about the topic.

    Now that we agree on those points: Show me the product you are suggesting. I want to know the brand name, model, and price. Then I'll give you my review.

  11. user-2890856 | | #12

    Martin ,
    The links are for GBA readers who may or may not be completely familiar with combination systems . These are also not papers from R&D departments of manufacturers .
    Unfortunately , I cannot give you a single product since every project has different needs and is in a different area . In my world there is no boiler plate equipment package or one size fits all mentality . I'm sure you can appreciate that . There are plenty of combi panels available throughout the world , pick one , pick a few , it is not my intention to have a debate as much as it is to peak folks interest and get them thinking about where we are headed . Do you honestly believe that once much of the country or world is grid tied that this will be a better place or that the utilities and owners of the grid will thank everyone ? PLEASE !
    When consulting and interviewing clients I tend to listen to what they want , need , prefer and dependent on whether their ideas will work without compromising the house as a system concept that I embrace I design what they want . Only when their ideas are completely bogus and won';t work will I attempt to steer their ideas .
    Storage of all sorts is becoming quite a mainstream idea . I'd be willing to bet that neither compression nor combustion will be very popular in several years . Something to think about when speaking of water and how much energy it can store should be QUITE OBVIOUS for discussions of climate change and rising temperatures .
    Seems to me that in the very countries that are the dominant producers of the type of equipment you recommend that they are developing different technology for their citizens .
    I know that you Martin are not promoting the idea that heat transfer and thermal migration happens differently inside of a house as opposed to on a roof , I also do not for one minute believe that you would be bold enough to dispute that PV panels above a certain temp produce as much as when they are below that temp .
    You had a dreamy look way back when also Martin , you kept on believing and look what happened .

    You can research products to determine which are the best and get pricing on them . You are quite capable

  12. GBA Editor
    Martin Holladay | | #13

    Response to Richard McGrath
    You criticized my advice to off-grid homeowners, and instead advised the installation of a complicated HVAC system that included hybrid solar panels that supply both hot water and electricity. When I asked you to tell me what brand of panel you used, and the price, your answer was evasive. I have a strong suspicion that you have never specified or installed this type of panel, which is rarely used and hard to buy.

    Correct me if I'm wrong.

    If you have never specified this equipment, and you are contradicting my advice to off-grid homeowners because you think you can do a better job of specifying and system design, I expect you to describe a system that you have actually specified and installed. Otherwise, this discussion is simply a waste of time.

  13. user-2890856 | | #14

    Half right
    Martin , I will start off by stating that I do not speak nor discuss technologies with which I am not quite familiar with . I also never denigrate something which someone else has asked to have designed or installed in their home .
    i cannot even begin to say how many times someone has come on this site not wanting to be talked out of something but asking for advice that you have told them is the worst thing ever in your opinion . Martin , this may surprise you but some folks want comfort and a healthy house in every aspect . Most of them are already aware that what they have chosen costs more and are willing to pay that premium .
    Several months ago David Butler reached out to me to assist in the design of an ICF house that would have been really quite fine with panel radiators with TRVs but this gentleman insisted on radiant in the slab . Should we talk him out of what he wants ? NO . We design what we are asked and make suggestions based on what we know .

    I have in fact not used the combination panel as of yet . I have seen several that are working better than expected however . I have consulted , designed and specified many solar thermal systems that were commissioned right next to solar PV panels . Many of these did heating , and hot water . Kind of remarkable how people are willing to spend more just because something is not yet mainstream . .Even after being shown that it works , Unexplainable phenomenon I guess.

    It is quite amazing how well that PV can power a Bosch TW025 Water to Water heat pump ( 1.65kW) and a couple of circs using 22 to 32 watts after showing how GSHP is much less effective than solar thermal storage a mixing valve to insure EWTs at 70* for COP of 5.87 . I mean it does not take complicated controls which are so scary to turn the heat pump off during hard times and just power pumps 2 & 3 to use the energy produced by your fireplace to recharge your tank . We can also make a WWHp make DHW . There are so many possiblities to opening up your mind and so many alternatives I'm sure quite soon someone will ask for the combi panels at which time my design changes not really one bit except that it will be integral with the PV array , which will be smaller because it will maintain it's efficiency and it's longevity will be increased .
    Maybe someday I can be of service to you Martin , I'd be more than happy to assist you in your endeavours or projects .

    Would you say an off grid home should be net zero ? Just wondering .

    See # 10 . # 8 is debatable since if you are using solar thermal for hot water for little additional monies one could add substantial storage below ground or in a basement and hedge against an air source heat pump not having any air to draw from or declining efficiencies when you need them most .

    There is always something to learn Martin unless we know it all already . How many times do you see me getting involved in a discussion about insulation and vapors ? None . Know why Martin , because you are better suited to advise on that than I . In the meantime I'll keep heating the houses you advise on with 80* fluid and NOT Overheating the side with SHG .

    One day maybe you'll enlighten me on how you got such a bad taste in your mouth about all things hydronic and fluid based . I am quite interested in what was done and how it went so badly , I really am . I have a good idea but am still curious . You can PM me about it so a snot to do it in an open forum . Did you let a supply house guy perform a heat loss and spec equipment , spacing and the like ?

    you and I have much to talk about , maybe we will someday .

  14. Expert Member
    Dana Dorsett | | #15

    So about that #8...
    " # 8 is debatable since if you are using solar thermal for hot water for little additional monies one could add substantial storage below ground or in a basement and hedge against an air source heat pump not having any air to draw from or declining efficiencies when you need them most "

    OK, show me the "...little additional monies..." in comparable capacity systems!

    I find the 32F temp buried plastic storage tanks with internal heat exchangers for low-temp solar using the heat of fusion + W-W heat pump concept, intriguing, but have yet to see any type of ballparking of what a Rube Goldberg contraption like that costs (either installed, or just the hardware.) Even the smallest most stripped down version of these can't be all that cheap:

    Yes, you CAN get pretty good mid-winter efficiency out of solar thermal at fluid temps of 32F, and you can get pretty good COP efficiency out of WWHPs at 32F. But aside from the design risk when employing creative-idiots, what does it all cost, and what is the all-in net COP?

    It would be clearer if you leave the PV out and talk straight kwh, since the lifecycle cost of PV is greater than grid-power in some areas, cheaper in others. During the heating season there's no significant additional benefit to the PV output in a hybrid panel system, the way there is during the cooling season, but if it's impossible to separate, it makes it harder to figure.

    If you can point to specific single-residence sized system (in any climate, but please not a 5000'+ mansion) that has measured performance and a known installed cost, I'd be much obliged!

    "System in a can" ductless air source heat pump performance is a well understood well documented commodity at this point, easy to spec, easy to install. I'm not completely convinced you can even DESIGN a 2-ton WWHP low-temp solar thermal system with buried storage for the installed cost of 2- tons of ductless, let alone install & commission that system for "...little additional monies..." . I'd be thrilled to be proved wrong on that! Conceptually it's pretty cool (literally and figuratively) but I don't see how you get there on the cheap, and it's not clear what the all-in COP & lifecycle costs are, or if they can be financially rationalized against commodity ductless air source heat pumps.

    So, show me how to get there from here, with some credible budgetary numbers! In fact, why not write it up as a guest blog piece or something!?!

  15. wjrobinson | | #16

    Dana, the system you posted
    Dana, the system you posted looks like 10 times the cost of a mini split system.

    Richard, you and Martin are agreeing more than you realize. Hydronic costs more and can please some customers who prefer it. I think we all agree more than not.

  16. user-2890856 | | #17

    Ask Thorsten
    You can probably acquire numbers about this house . The one that got me thinking about the idea I was toying with for some time .

    Radiant floor designed properly probably does work .

    I see you have discovered the Multi Source heat pump drawings of the system done by Antonio Poccia in the Mendham , NJ project . There are others in Montana , Wyoming , many places . Please don't confuse what I am talking about with these systems , they are a bit more complicated and using a cold tank on purpose . I have spoken with these gentlemen for years and while their systems certainly work since Ice stores 142 more BTU per pound it is not conducive to keeping the costs down while still being effective .
    I speak of storing higher temp water and increasing the capacity of that water by mixing it down to 70* to enter a WWHP . I also am recommending that this route be taken as opposed to GSHP to eliminate the high install cost and the large pumps and power usage that is oft omitted from power usage models for those systems . The system can also be controlled to recognize that heat is being added and bypass the HP altogether for a truly Passive strategy . In a home that is already discussing PV the installed panels with thermal removal can add 2.50 per watt according to Boss Solar out of Toronto . You are also aware of Sun Drum and their add on for PVT .

    Tanks can range in size from 100+ gallons to 2014 gallons and they act as the drainback tank also . They can be buried , located in a basement or in an outbuilding of sufficient size to to house them and kept at 40*F .

    The houses we often discuss here can also be heated and supplied with DHW utilizing a WWHP that consumes 1.65 kW in the systems I am able to design . Some folks are willing to pay this type of money which is not as great as you all seem to think as a hedge against many things . Many of these homes also have , as mentioned many times by many parties , a woodstove of one type or another . Any of these can be made to add wasted heat energy to the tank also in times of low sun

    HTP located in East Freetown Mass is also working on may exciting things to be placed in the tight houses , some should be readily accepted by many here but probably won't . They also acquired Solar Skies and their operations have moved from Minnesota to East Freetown and due to the technology that exists in that plant are assembling thermal panels that are far above and beyond what anyone else is producing . Here is a short video of the owner introducing some ideas , the stuff that will interest you and others from this site start at around 18:00 . But feel free to look at the whole thing , some other products may stimulate your head and thinking .

    Just to be clear , I am working on solutions that may at some point be affordable for many more than at present . These ideas include multi family enclaves with district heating and hot water and energy metering to each unit with separate billing for each . Something like that could GREATLY decrease the first cost while allowing more folks to enjoy very low energy usage and real comfort .

    One thing I noticed above is that many are still not aware that we can provide cooling with radiant in the floor , ceilings or walls . Sensing dewpoint allows us to mix cooling water to 3* above dewpoint to avoid condensation and the latent is handled by DOAS . We can collect the heat of the returning water and use it to warm DHW , pre heating device to use even less energy .

    To Martin and others . Being frugal and trying to do everything cheap is what gave us as a society every crummy system that we have now been combatting for years . Don't perpetuate that nonsensical mindset and discount ideas others have come up with or are developing because you are unaware of it or don't agree with it . While you do a very fine job here of guiding people through mis information they have gained elsewhere and pr4event them from doing things you know are bad . You must stop and genuinely look at what others are doing and attempting and have an open mind if we are to continue to make a better world for ALL . Glad I had the time in my busy schedule to write this and sound as crazy as Thorsten , James , and even Marc R. who states that solar thermal DHW is a good idea in an NZE .

    With a bit of support on sites like this and not a total discounting of ideas some of these products and methods can become mainstream and off the shelf which will make it more affordable . It is all science based as opposed to computer model based and it works , ask the guys who have written guest blogs that I mentioned .
    Another question would be , What is Greener , Site generated or site derived ? Which will be lore acceptable in 10 years ? Which is easier and less expensive to store ?

    Nik , If you are still watching , you should contact me .

  17. user-2890856 | | #18

    In addition
    It'll never work . Although these are not the same tanks I mentioned . Mr Hyatt will make a 12" wall tank and is also in Utah .

    Very good article about good insulation and building design trumping Green gizmos . This was only written by a GBA regular . Note that if the solar thermal systems stored load was connected to a heat pump that would be much better than GSHP for the reasons I have already mentioned . The problem with most of the installed solar thermal systems is the fact that not enough people design using drainback systems . Some people learn from mistakes and avoid those same problems as systems evolve .

  18. nfiorito | | #19

    Thanks for all the input, everyone! I actually just found that my Q&A was made into this blog post, so I'm a little late to the party.

    Updates on the project:

    -We're about 2 weeks from breaking ground (still ~2 feet of frost up here, folks are still ice fishing!).

    -I have decided against being fully off-grid, as Martin on GBA and even the local solar company have advised me. My wife and I met with them and they took a look at us and our 4 children and said, "you don't want this."

    -We are likely going to enter the microFIT program and install solar panels that operate independently of the house. The way it works in Ontario is that you enter into a 20 yr government contract to sell your power back to the grid, but you yourself use none of it. Every month you get a bill AND a cheque.

    -The quote for installing power poles and lines was less than we were originally advised, about 30% of the number we were first told, so this made off-grid even less appealing and allows us to sell back to grid.

    -We met with the local geothermal rep a couple days ago, and his quote should be coming in tomorrow. Other heating options are Outdoor Wood Boiler or propane boiler/furnace. Most neighbours seem to be using OWB

    -Basement walls (PWF) are 2x10 to account for the high pressure of the fully backfilled walkout basement; as per recommendations on this site and my own thinking these walls will be spray foamed to R35, we have a quote for this and even though it's expensive I think it'll be the best long-term below-grade option. Basement floor is 4" concrete with 2" XPS rigid underneath.

    -above-grade walls will be R24 mineral wool in cavities with 2" EPS externally. I'm going back and forth between putting housewrap over the rigid with outie windows, or putting drainwrap UNDER the rigid (against the OSB sheathing) to ensure any below-dew-point frost on the sheathing can dry out easily in the summer; I think - and someone correct me if I'm wrong - the drainwrap + EPS will pass vapour nicely and dry out without worry.

    -My better half has given me the green light to buy a tractor with a bucket, backhoe, mower, and snowblower, so that might be the most exciting thing out of all of this :-)

    Thanks again, I look forward to hearing more ideas from y'all!

  19. GBA Editor
    Martin Holladay | | #20

    Response to Nik Fiorito
    You wrote, "Above-grade walls will be R-24 mineral wool in cavities with 2 in. EPS externally."

    You're in Climate Zone 7, so that won't work. In your zone, the minimum R-value for exterior rigid foam on a 2x6 wall is R-15 -- and your EPS will have an R-value of only R-7 or R-8, about half the R-value you need. With foam that thin, your wall sheathing is at risk of accumulating moisture.

    For more information, see Calculating the Minimum Thickness of Rigid Foam Sheathing.

  20. nfiorito | | #21

    Re: exterior foam
    Hi Martin,
    I realize that's the best case scenario according to this site, and I want to create a cross section that is durable and tight, but I'll tell you that NO ONE up here has gone with 4"+ thick exterior foam. People look at me like I'm crazy for suggesting so! Namely the insulation company and my building inspector.
    Everyone here is going with 1 1/2" - 2" on exteriors. Will all their walls be soggy messes in 5 years? Maybe? I don't know, but the budget and the flashing details are making it hard to take that leap for me. That's why I was thinking of the drainwrap against the sheathing, coupled with EPS, to allow for drying and drainage.

  21. GBA Editor
    Martin Holladay | | #22

    Response to Nik Fiorito
    There may be lots of reasons why you don't want to accept the advice of North America's leading building scientists ... but I must say, "Nobody around here builds like that" is a weak reason.

  22. nfiorito | | #23

    Martin, I definitely agree, I'm just trying to convince all of these people (myself and my wife included!) that it's the best way to go all things considered.

  23. user-2890856 | | #24

    These BioMass boilers are very good things to have also . Be sure to look at those that offer closed system technology as opposed to open to atmosphere units that WILL rot out . You don't even require a constant burn with a bit of properly sized storage .
    If you will have a hydronic based heating , hot water system I strongly suggest you locate a talented designer . Recommendations for these folks should be researched . It is very easy to find people that sound good until the time for heat is at hand . That is when you gain most of your insight into their true capabilities . There are many online resources also dealing with the specific technologies you are talking about . Try Coffee with Caleffi Archives .

    Many here have called me nuts but if you are going to have an OWB you may very well do best to have storage and even possibly forego the GSHP . You can make much more heat with 70*F EWTs than with 50*F = > EWTs while enjoying COPs north of the 5.5 level I spoke of . These systems can also be added onto later freeing up more of your dollars now allowing you the luxury of not settling .

    I gladly come here and take the beating that I do to help folks like yourself get real information to help them realize their thoughts without sacrificing . The thoughts by most here about hydronic systems are well deserved but there are many who are capable of designing , consulting and installing hydronics very well . Avoiding the guys that gave so much of this valuable technology is the hard part .

    If interested I can give you the names of a few that are more North than I and even in Canada . These would be folks who are thoroughly vetted and respected who will do the job right with no excuses later .

  24. Expert Member
    Dana Dorsett | | #25

    If you're going to cheat the foam... (for Nik Fiorito)
    ...install MemBrain or Intello as an interior side air & vapor barrier. These products are class-II vapor retarders when the proximate air is dry which it will be, in winter. They become more vapor open when the proximate air is humid, which will happen in the springtime when the sheathing releases it's winter-accumulated moisture burden into the rock wool layer. The result is that moisture accumulation rate is slow, and the drying rate is many times faster. (MemBrain costs about $100 USD for 8'x 100' sheets at Menards, and can be detailed just like the 6-mil poly vapor barriers commonly used in Canada.)

    At 2" you're only at about half what the IRC considers the minimum to be able to use only class-III vapor retarders (latex paint), but by putting the R8-8.5 EPS there you've effectively moved the average temp at the sheathing a bit south of Minneapolis. With MemBrain or Intello Plus between the fiber and wallboard it should be very moisture resilient. At 2" Type-2 EPS is only about 1-1.5 perms- which is kinda marginal for 3-5 perm paint as the interior vapor retarder, but with sub-1-perm smart vapor retarders it'll be just fine, since the wall can dry in both directions. With a poly vapor barrier it wouldn't have even half the drying capacity, and would require perfection on the installation. Smart vapor retarders are MUCH more forgiving. See:

    Like poly vapor retarders/air barriers, it's important that the seams between sheets over lap and are taped, and only occur where supported by the framing so that they don't leak air over time from flexing at the seams.

    Richard: I was asking about "....the smallest most stripped down version...", not the full-blown diagram I posted. Thanks for the info on the cool (not frozen) storage stuff. How far can you simplify and cost-reduce those systems?

  25. DavidButler | | #26

    further thoughts on mechanical and envelope...
    Nik, glad to see you decided not to go off-grid. That changes the metrics for your mechanical systems. Without knowing the cost of your GSHP system, I can't say whether it would have lowest lifecycle cost, but I can tell you with certainty that the other heating options you mentioned should be done in combination with an air source heat pump. Keep in mind there are more annual heating hours above freezing than below, and depending on relative prices for electricity and propane, an ASHP will cost between half and a fourth as much to operate as a propane furnace or boiler.

    I'm curious why you would spend big bucks for R-35 spray foam on your below-grade walls while your above grade walls at R-32 are exposed to MUCH greater temperature extremes.

  26. DavidButler | | #27

    thoughts on mechanical design for off grid...
    No one would argue that a heat pump can provide all the heat in an off-grid home in your climate. You gotta have fossil fuel heat no matter what. But a water-to-water heat pump can provide the lion's share of the heat, and likely with a much lower lifecycle-cost.

    A huge advantage of a water-to-water heat pump (or air-to-water, for that matter) for off-grid is the ability to load-shift by storing energy in the buffer tank. For this reason, the tank needs to be larger than in grid-tied applications where the buffer's only job is to protect the ground loop pump from short cycling.

    I know Rich won't agree on this point, but in low-load homes, I favor a forced air distribution system (hydronic fan coil in this case) rather than radiant distribution. Radiant is a lot more expensive and any advantage radiant may offer in terms of comfort goes away in homes with a super efficient shell. The additional cost of radiant would be better spent on more PV or storage capacity.

    Either way, a small propane sealed combustion boiler is easily integrated with a hydronic heat pump for seamless supplemental heat compared to relying on a space heater or wood stove.

    Lastly, the key to keeping PV and storage costs to a minimum is smart controls. For example, there will be times when it makes sense to increase the buffer tank setpoint (at the expense of COP) to avoid the use of expensive fossil fuel heat. Similarly, interlocking controls for any significant electrical loads (especially a well pump) are essential to get the most out of an off-grid power system.

  27. user-2890856 | | #28

    As to the expected heat loss numbers for this home . Are you truly entertaining the thought of an outdoor wood boiler Nik ?
    David , would it be true that a WWHP may have better longevity being that it is indoors then an ASHP ? Maybe we could get a load number from Nik to truly help him make an informed decision on which would actually offer his family the greatest benefit as opposed to the guessing .
    could you provide such a number Nik for a comparison with some meaning ?

  28. nfiorito | | #29

    Update #2
    Thanks for the continuing insight, all!
    My GSHP quotation came in today so I thought I'd share that. $23800 + HST (our sales tax, 13%) for a hydronic-only system; radiant and DHW. $28500 + HST for a forced air system which would provide heat, cooling, DHW, as well as radiant. So a $5k upcharge for that. This is of course for everything installed and ready to warm, but stops short of the radiant manifolds and tubing, which I'll do myself.
    These are energy star certified units, but I'll have to update the model numbers and such tomorrow when I take another look at the quote.
    This quotation's dollar amount is just enough to make the decision difficult!
    Note* - the heat calcs were based on the mix of spray foam, batts, and rigid I described previously.
    David B, the reason I'm strongly considering spraying the basement is to account for 1' stud spacing on the back wall of my PWF foundation. Also to avoid condensation issues, as Martin suggested.
    I'll keep updating as I get more info and make decisions, thanks again!

  29. user-2890856 | | #30

    sound suspect Nik considering what you state you will be doing . I offer a discussion and assistance for N/C if you'd like . I am curious as to what these quotations include . How many feet Vert bore Hole , what equipment and sizing also .
    The radiant and DHW number especially even with install and near boiler piping , you're doing the work that nobody wants to .

  30. nfiorito | | #31

    GSHP more details
    Here are more details on my Ground Source Heat Pump quotation. There is another outfit in town I am in the process of getting info from, but here are the numbers from the first guy (two options):

    $23932.48 + HST - GEOSMART Premium H Model HSO75R, 410A, with DHW, Energy Star, 80gal glass-lined storage tank. This is a hydronic only system. 3000' of 1 1/4" 185psi loop pipe.

    $28882.98 + HST - GEOSMART Premium Q Model QT072TR, 410A, with DHW, ECM fan, 2 staged forced air heat and a/c. 15kw internal emergency element. 3000' of 1 1/4" 185psi loop pipe.

    Please keep in mind that being in Canada our labour and materials costs are generally higher than the US (hence the initial sticker shock for some of you). These are field/trench based loops, not bore hole. We also have "red clay" on our property where it will be buried, which the installer says is great for geothermal loops as it surrounds the pipe like after it settles and gets some rain in it.

    I've installed all the pumps, valves, thermostats, switches and pex that the hydronic system requires myself in my previous home, so I'm comfortable doing that and can save money there.

  31. user-2890856 | | #32

    What will your entering source and leaving load temps be Nik , also flow in GPM ? What is the heat loss of the home too ?

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