Question Part 1. What is the best practices for a typical wall assembly for a $2-$3 million townhouse in Chicago with brick veneer? Question Part 2. What is the best practices for a high R-value to Passive wall assembly for an equally crafted townhouse as the above that would not result in a 18"-20" wall assembly? Lot dimensions are the typical 50' x 160'.

The questions are mayhaps a wee bit too broad to address in any detail.

But equally broad in response:

Air sealing needs to be taken to heart even at the design stage, and followed up on throughout construction. If the architect doesn't or can't spec the primary air barrier (and the transition details), find one who can. Even the best-insulated "wind tunnel" of a town house has high energy use. Multi-story buildings have high stack-effect drives, making air sealing even more critical to thermal performance than single story structures, at ANY R-value.

Buildings need active ventilation, even leaky ones. But in a tight building with high thermal performance specs in a Chicago climate, energy recovery ventilation (ERV) makes sense, more so than exhaust only or heat recovery ventilation (HRV), due to the higher-than-healthy outdoor summertime dew points. An ERV "preserves" some of the air conditioning's dehumidification by taking some of the humidity out of the incoming air stream, giving it up to the exhaust air stream, whereas HRVs exchange sensible-heat only. High performance buildings have fairly low cooling loads, and running compressors solely for dehumidification may be necessary at times.

From a long term sustainability point of view, all brick clad buildings should be using stainless steel masonry ties and good venting both top & bottom on the cavity.

A thermal weak point on brick veneer buildings is often the thermal bridging at the top of the foundation. Make sure the designers/architects deal with that.

When using any foam insulation at high-R, the blowing agents matter. Most (but not all) closed cell spray foam is blown with high global warming potential (GWP) HFCs (most commonly HFC245fa, at ~1100x CO2 GWP). Most open cell spray foam is blown with water. Almost all XPS rigid foam in the US is blown with HFC134a, at ~1400x CO2 GWP. By contrast most EPS and polyisocyanurate is blown with pentane at ~7x CO2 GWP. In a high-R building those differences make a HUGE difference in the 100 year global warming footprint of the building.

At R20 whole wall (all thermal bridging factored in, eg 2x6 w/R20 cellulose cavity fill + R6 polyiso sheathing) or above, the windows begin to dominate the heat load numbers. Pay attention to both the size and U-factors of the windows. A U-0.25 window is an R4 hole in your R20+ wall, with >5x the heat loss per unit area. Rationalize every square inch of glass, and it's U-factor, but also pay attention to it's SGHC (solar gain) numbers. High gain windows on a west facing wall can drive cooling loads through the roof, but may be appropriately used for passive heating when facing south, with overhangs/awnings to minimize summertime gains.

Prohibit use of atmospheric vented combustion appliances of any type. In tight tall houses these are both air leaks and susceptible to backdrafting.

Use drainwater heat recovery heat exchangers on the shower(s), especially any luxury-gusher type showers, since they can reduce showering energy use by 50% or more, and reduce the size of the hot water heater needed to serve the load. In high-R high-performance buildings hot water energy use will usually overtake space heating & cooling on annual energy use.

It's likely that you can hit close to Net Zero Energy at less than half the R-values that it would take to hit PassiveHouse, provided you don't have shading factors cutting into photovoltaic output, and optimal roof pitches. R40 whole-wall is a pretty good standard for getting there in climate zone 5 (Chicago), but is more complicated to hit with brick veneers, since foam thicker than about an inch usually requires custom masonry ties. A 2x6 +1" iso runs only ~R20- it exceeds code-min for zone 5, but isn't exactly high-R for the climate.

Best Practice for any construction is Passive House, by far, and with that budget there is no good reason not to. Walls do not have to be anywhere near 18" thick, but it is not a simple matter of adding insulation. Contact an experienced PH architect; if there isn't one in Chicago, there are others on the east coast or elsewhere who can help you and who have done similar buildings. Go to PassiveHouseUS.com for a list.

So I would imagine typical (to even half the R-value of a PassiveHouse. Though shocking to know that R-values are at 80 for PassiveHouse walls...I had maxed at 55 for a PassiveHouse) would be 4"x8" Brick; 1" Air; 1.5" Rigid Foam; 2"x6" mold and termite treated studs; Spray foam insulation closed cell in stud cavities; 5/8" gypsum. But, I guess my concern is the reinforcing of the brick veneer. Is there typically brick, cmu or simply stud reinforcing on a typical Chicago contemporary townhouse? ...Single family.

Posted By IM&A on 24 Apr 2013 03:49 PM
So I would imagine typical (to even half the R-value of a PassiveHouse. Though shocking to know that R-values are at 80 for PassiveHouse walls...I had maxed at 55 for a PassiveHouse) would be 4"x8" Brick; 1" Air; 1.5" Rigid Foam; 2"x6" mold and termite treated studs; Spray foam insulation closed cell in stud cavities; 5/8" gypsum. But, I guess my concern is the reinforcing of the brick veneer. Is there typically brick, cmu or simply stud reinforcing on a typical Chicago contemporary townhouse? ...Single family.

I'm not quite sure how to parse all of those sentences. 

Closed cell spray foam in a 2x6 cavity is a travesty- a total waste of foam, and if blown with HFC245fa (like most closed cell), a major net-negative on lifecycle environmental hit.  Foam is not inherently green. Closed cell foam blown with high-GWP agents is the opposite of green.  Save the foam budget for the exterior of the sheathing, where you get the full benefit of it's high-R rather than letting it's performance be cut off at the knees by the thermal bridging of the framing.

At a 25% framing fraction (about right, with typical numbers of windows & doors) the whole wall R of 5" (the thickest practical application, since it's so hard to trim) of cc foam in a 2x6 wall comes in at about R16, and that's including the sheathing & gypsum.  A full-fill 5.5" of trimmed open cell foam in the same wall comes in at ~R14, using ~25% of the amount of polymer, and about ~0.1% of the greenhouse gas damage. Open cell also provide an even better air seal than close cell (!),  all at a fraction of the cost. How much are you willing to spend for another R2?

Cellulose would come in at the same R as open cell foam with an even lower environmental hit, would provide better seasonal moisture management & termite control (due to the lower moisture content of the structural wood and the borate content of the fire retardents in the cellulose.)

If you add the ~R10 of the 1.5" of exterior iso you end up at only R26 whole wall in the closed cell case,  R24 whole-wall in the cellulose/open cell cases. You're not even CLOSE to hitting R55 (even center cavity) with that stackup, or even R40. With something other than brick cladding you can hit ~R40 w-w with 2x6 framing 24" o.c. with 4" of exterior polyiso in a reasonably buildable, not very complicated stackup that's under a foot thick (and still far cheaper than your closed-cell foam cavity fill option.)  For R55 whole-wall you're usually talking double-studs and fat walls.

Most brick veneer construction in the US support the brick via metal ties to the structural studwalls or CMU. I'm not sure if there are conventions in Chigago area that are any different than other places (except seismic zones, which may need their own special-sauce to remain standing.)

How many storys, and how set in stone is the brick cladding concept?  Full basement, slab-on-grade or... ???

Sorry about the syntax in the earlier post. I am only researching conventions. I am not budgeted for a build as of yet. I just thought that 2"x6"s if being used to add for structural support on the exterior walls for a brick veneer would be a sounder choice than 2"x4"s and provide better insulation. 24" o.c. seems unconventional. 2 stories with a full basement with framed flooring connecting the foundation walls. Although I am married to the brick idea...I can reason other exteriors. I am glad that you pointed out custom ties for the masonry to build a better wall to increase thermal resistance. In response to your first post on U-values I would lean towards double or triple pane glazing. I hope that the reveal of not purchasing at the moment doesn't deter you from answering some of my questions. I was hoping that I could pose a few from time to time. I am still trying to wrap my head around iso. Normally an acronym used for "Standards" in building. I know that you are probably referring to rigid foam insulation or sheathing? Surely, to sum up some of your points on high R-value/Net Zero Houses to PassiveHouses, they require a pretty sophisticated mechanical room. I do see some of the components.

Posted By IM&A on 24 Apr 2013 07:20 PM
Sorry about the syntax in the earlier post. I am only researching conventions. I am not budgeted for a build as of yet. I just thought that 2"x6"s if being used to add for structural support on the exterior walls for a brick veneer would be a sounder choice than 2"x4"s and provide better insulation. 24" o.c. seems unconventional. 2 stories with a full basement with framed flooring connecting the foundation walls. Although I am married to the brick idea...I can reason other exteriors. I am glad that you pointed out custom ties for the masonry to build a better wall to increase thermal resistance. In response to your first post on U-values I would lean towards double or triple pane glazing. I hope that the reveal of not purchasing at the moment doesn't deter you from answering some of my questions. I was hoping that I could pose a few from time to time. I am still trying to wrap my head around iso. Normally an acronym used for "Standards" in building. I know that you are probably referring to rigid foam insulation or sheathing? Surely, to sum up some of your points on high R-value/Net Zero Houses to PassiveHouses, they require a pretty sophisticated mechanical room. I do see some of the components.

At 24" o.c. the board-feet of timber for a 2x6 and it's structural strenght comes in at about the same as 2x4 16" o.c. construction.  It's pretty common, but not the traditional standard- most 2x6 framing in the US is still done 16" o.c..

At 16" o.c. the additional couple of inches buys you about ~R4.3 in whole-wall performance when using fiber or open cell foam as cavity fill.  Reducing the framing fraction by wider spacing and going full-out on advanced-framing can get you another ~R2, but at a somewhat reduced structural capacity.

In the US building trades rigid polyisocyanurate foam is commonly refered to as "polyiso" or "iso".   Only the architects & enginerds call it PIR or polyisocyanurate.

The mechanicals get SIMPLER, not more complex when you go higher in building envelope performance.  Yes, in a very tight house you end up with an absolute requirement for at least some mechanical ventilation, but it need not always be in the form of a ducted system. But even when it is, the ducts are tiny compared to conventional air conditioning or heating ducts.  Many Net Zero Energy houses are heated/cooled with one ductless mini-split heat pump head per floor, no need for a centralized system or distribution system, and the inverter for the solar array usually hangs on the wall next to the electrical panel (or outside, next to the meter.)   Many PassiveHouses have no air conditioning (a mistake in an IL climate, IMHO) and distribute heat via the ventilation system (a quirky requirement embedded in the German PassivHaus spec.)  There is a US PassiveHouse located near me (alsoUS zone 5) that's heated & cooled with a 2-head multi-split air source heat pump, and the "mechanical room" if you want to call it that is just the water heater closet that also houses the ERV.   They went a bit nuts on the insulation with R100 cellulose in double studwalls, rather than doing the more careful math. I'm sure it could have still made the PassiveHouse spec with R60 walls with a few design tweaks, but the owner/builder was a building contractor, not an engineer, and cellulose is cheap, if you don't mind the monster-thickness of those walls.

At 24" o.c. the board-feet of timber for a 2x6 and it's structural strenght comes in at about the same as 2x4 16" o.c. construction. It's pretty common, but not the traditional standard- most 2x6 framing in the US is still done 16" o.c..

Surely, with a brick veneer using stud backing the use of 2x6s helps with regards to the top plates forming the sill for the 2nd floor (there is more to connect the joists to). I am pretty sure ledgers shouldn't be used for brick veneer with a stud backing. So the extra strength of the 2x6 16" oc is desirable, no? ...as opposed to bringing it back to the strength of 2x4s 16" oc by going 24" oc with the 2x6s.

The mechanicals get SIMPLER, not more complex when you go higher in building envelope performance.

But when factoring in the critically important centralized air exchanger; centralized dehumidifier; air filtration; the possible geo-thermal unit; the backup furnace; the highly recommended solar panel system; tankless water heater; ...I would mention a centralized water filtration system, but, that might be going overboard. Then there are people recycling grey waters for like toilets and what not. It can get complex.

Posted By IM&A on 25 Apr 2013 01:06 PM

The mechanicals get SIMPLER, not more complex when you go higher in building envelope performance.

But when factoring in the critically important centralized air exchanger; centralized dehumidifier; air filtration; the possible geo-thermal unit; the backup furnace; the highly recommended solar panel system; tankless water heater; ...I would mention a centralized water filtration system, but, that might be going overboard.

In a high-R house nothing needs to be centralized, not even the ventilation (though it often is.)  Room to room temperature differences are pretty small in US zone 5 homes with R40 whole-wall with U0.20 windows, and R60 roofs, no matter where the heat sources are.  Multiple point-sources work just fine, and any temp deltas can be tempered by design by how the ventilation is routed.  (Rooms doored off from the point sources get exhaust registers, with ventilation source from the common areas via jump ducts or transom grilles, etc, and spaces WITH the point sources get supply-air only. )

For very low loads, there is NO rationale for the expense of geothermal heating  & cooling.  In a zone-5 climate ductless mini-splits are only slightly lower than a best-in-class ground source heat pump on efficiency (and higher efficiency than not-so-well implemented geo designs), but a fraction of the upfront cost.  When you're looking at high-R houses and heating/cooling loads under three tons it's very hard to make the case for geo.  One mini-split series (Daikin Quaternity) can dehumidify to an independent relative humidity set point, in both heating & cooling mode- there is no need for a separate dehumidification "system" either.  ERVs come with high quality air filters, there isn't really a need for separate air filtering system, and some mini-splits have UV air sterilization plus quality filtering built-in too.

Tankless water heaters are pretty much a waste of money unless you have a massive tub to fill.  A condensing tank-type water heater and a drainwater heat recovery heat exchanger downstream of the showers can operate at "apparent efficiency" greater than 100%, in a high showering-use envirnment, where an 0.98EF condensing tankless would struggle to break 90% (unless the drainwater heat recovery was used there too.)   Even a pretty-good 0.68EF tank can beat a condensing tankless with the benefit of drainwater heat recovery.

Filter your water if you like, or not- it's impact on the thermal efficiency of the building + mechanicals is negligible in the bigger picture.

But the "critically important" list is in fact a lot shorter than what you seem to have in mind, if you take a R5/R10/R20/R40/R60 approach to windows & doors/slab/basement wall/above-grade wall/attic in this climate.  Some New England builders are calling those prescriptive values the "Pretty Good House", and with favorable shading factors can usually be made Net Zero Energy, (or nearly so, if the occupants aren't plug-load hogs).

Last year I helped out a friend on a Deep Energy Retrofit on a 3-story + full basement 1890s antique and finished out to roughly those values. It's heated & cooled with one ~$4KUSD mini-split per floor, and one small ERV system per floor (to eliminate the need for duct chases between floors), and it's one of the most comfortable homes I've ever spent time in.  The heating costs are barely discernable in the power bill, we'll see how it fares come July, (it's only been occupied since September), but I suspect that will be similarly miniscule, given how comfortable it was inside LAST July, while still under construction.  It could be made Net Zero but for unfavorable shading and roof angles (I suppose we could we rotate the building 45 degrees, and knock the building next to it down, eh? ;-) ).  The biggest single energy-use function in that place now is hot water heating, followed in short order by plug loads & lights. (He neglected to install the drainwater heat recovery, despite my prompting, not that it's a deal breaker.)  It's not PassiveHouse, but it IS a pretty good house. 

The "backup" heat for this place is two $50 oil-filled radiator type electric space heaters per floor, but in a higher-budget could spring for hard wired electric panel radiators or cove heaters, etc.  The 99% outside design temp is +5F, pretty similar to Chicago's +3F design temp, and the mini-splits can handle the whole load even when it drops to -15F (which it does once every 20 years or so.)

Solar isn't always highly recommended, but if the site conditions are right, it's often a pretty good investment for long-termers, made even better where heavily subsidized.  In the city tall buildings or even old street trees can cut into it on 2 story homes, but keeping the angles and shading factors in mind when you design is probably worth keeping in mind until it's ruled out.

I have researched typical R-values at:
R-38 for ceilings
R-49 for ceilings in cold climates
R-30 to R-38 for vaulted ceilings
R-25 for floors
R-15 to R-24 for walls
What are the current trends or goals on those R-Values? I saw that you had exterior walls at R40. Sorry I think you already answered that with the statement prior to the New England sentence.

Multiple point-sources work just fine, and any temp deltas can be tempered by design by how the ventilation is routed. (Rooms doored off from the point sources get exhaust registers, with ventilation source from the common areas via jump ducts or transom grilles, etc, and spaces WITH the point sources get supply-air only. )

Then, would zone dampers be a viable green case for centralization?

Ducts add to air-handler power, and lower the net whole-system efficiency of air-based heating & cooling systems. Zone dampers only increase the duct impedance, adding slightly to air handler power. The MOST efficient systems (either ductless or ducted) use fully modulating blower speeds and highest efficiency motors to minimize the power used for moving air, but without the inherent duct impedance ductless designs tend to be more efficient overall. All high efficiency ductless heat pumps use variable speed blowers and compressors.

The continuously variable very quiet scroll compressors and implementation of variable refrigerant volume valving allows it to sip power, and maximize efficiency, modulating with the load. The part-load efficiency of these things during the shoulder seasons when the outdoor temps are moderate and the loads are low are truly astounding, but their efficiency at the mid-winter average temp & load is a far better indicator of where your seasonal average will be. For a zone 5 location that would be an average heating coefficient of performance (COP) of ~2.7-3.0. A typical geothermal system may have a COP of 4-5 measuring only the heat pump, but the full-systems typically come in around 3.5 when the pumping and air handler power gets factored in. There are existence proofs of systems exceeding a COP of 4 in comparable climates, but those are the very rare exceptions to the rule, and there are many running seasonal average COPs of 2.5 or lower. A lot is in the hands of the system designer with geo, whereas with ductless systems they're pre-engineered "systems in a can", and it takes truly creative idiots to screw them up (but there are existence proofs of said idiots too, eh? ;-) )

Most state building codes are currently based on IRC 2009 insulation levels: http://energycode.pnl.gov/EnergyCodeReqs/?state=Illinois

Those are center-cavity R values except where noted. An R20 studwall at center cavity is only about R14 after thermal bridging. An R13 studwall runs about R9.5 after therma bridging, but R5 in exterior foam brings it up to about R14.5, which is why the R13+ 5 is spelled out as an alternate. A code-min house circa 2013 is nowhere near the energy pig that code-min was in the 1970s, but it's still nothing like a high performance house.

Under the (not yet adopted by many states) IRC 2012 code, homes in would need to be blower-door tested and in climates zones 1-3 would have to be no more than 5 air exchanges per hour at 50 pascals (ACH/50 is the usual shorthand), homes zones 4 & higher (all of IL) would need to come in under 3 ACH/50. Elsewhere it stipulates that all homes that test under 5 ACH/50 are required to have mechanical ventilation that can meet ASHRAE 62.2 ventilation rates (though the occupants are not required to run it there), so in effect it's a requirement that ALL new homes have mechanical ventilation that can be cranked up to a fairly high rate when needed. This level of air tightness is new for IRC 2012 (under IRC 2009 it was 7ACH/50- more of a stripe on the floor than a hurdle to clear), as is the ventilation requirement. Most high-performance houses test out under 2ACH/50. My friend's deep energy retrofit was a hair under 1ACH/50. The PassiveHouse spec demands <0.6ACH/50.

It's often pretty easy to hit 3ACH/50 even with retrofit air sealing, and dead-easy in new construction when the primary air-barrier is spelled out with transition details on the architectural drawings, provided someone on the construction crew is charged with following up on all of those details as construction proceeds. Getting it under 1.5ACH/50 usually takes a well trained crew and a bit more diligence, but it's not rocket science, nor particularly expensive.

R40 whole-walls in a 16" o.c. framing would be 2x6 with cellulose or open cell foam cavity fill, and ~4" of exterior polyiso (preferably in two layers, with overlapping seams for better air tightness.) That's buildable using fiber-cement or wood siding, but for a traditional brick-veneer it would take some full-custom & expensive masonry ties, and would add about 3-4" to the overall wall thickness (bricks have lousy R value, and they are about thick as bricks, eh? ;-) ) It's possible to do traditional hard-stucco without adding the thickness of the brick, but most stucco guys haven't quite figured out how do deal with foam sheathing thicker than about an inch (but some have.) Most "pretty good house" foam-overs I've seen use fiber cement siding or traditional wooden clapboards to minimize thickness, and do not need more than 24" o.c. spacing for the fasteners for the furring holding the foam in place, on which the siding is mounted. These designs also don't have the thermal bridging masonry at the foundation to deal with that you always have with brick veneers, simplifying the foundation insulation issues.

It may be possible to build an insulated foundation with minimal thermal bridging using 12" autoclaved aerated concrete (AAC) blocks, provided it can handle the dead-weight of 2 storys of brick (TBD.) I've never seen one done that way, but there may be details on European website on just how that can work, since AAC construction is fairly common there. The R--value of a 12" AAC block is only about R10 in the higher-density versions more likely to handle the weight, but that's a LOT better than poured concrete or CMU block, and could be brought up to snuff with a couple of inches of interior foam or an interior studwall with unfaced rock wool batts. This inherent thermal bridging point with brick veneers is a tough one, with no cheap or easy solutions. Joe Lstiburek of Building Science Corp has attempted to fix it with an AAC approach, but is less than sanguine about it. See the italicized text regarding figure 5 in this document:

http://www.buildingscience.com/documents/digests/bsd-103-understanding-basements/?searchterm=bsd-103

If you're going for high-R, and insist on the brick, it's up to you and your architects to solve this one, and leaving it in would be like leaving the front door open, severely undermining the thermal performance of what could be a very high performance house.

Not to nit-pick ,but.

"Tankless water heaters are pretty much a waste of money unless you have a massive tub to fill." You will be disappointed in filling any large tub, since the tub-filler will be at 8gpm or higher and the tankess stuck at 4gpm in warm climates.

In my own home and many others the duct chase for ERV is a foot square. Two six inch ducts to serve three bath fans and three fresh air terminals.

As for solar thermal heating: If you had an extraordinary panel at peak DNI yielding say, 7500 Btuh, you would need a lot of panels and storage to make dent anywhere heat is really needed. ROI in the negatives.

My home at three stories with the walk-out amounts to a town home configuration an with the mini-split mounted at the top of the open staircase cools all three floors nicely.

Posted By BadgerBoilerMN on 25 Apr 2013 05:18 PM
Not to nit-pick ,but.

"Tankless water heaters are pretty much a waste of money unless you have a massive tub to fill." You will be disappointed in filling any large tub, since the tub-filler will be at 8gpm or higher and the tankess stuck at 4gpm in warm climates.

In my own home and many others the duct chase for ERV is a foot square. Two six inch ducts to serve three bath fans and three fresh air terminals.

As for solar thermal heating: If you had an extraordinary panel at peak DNI yielding say, 7500 Btuh, you would need a lot of panels and storage to make dent anywhere heat is really needed. ROI in the negatives.

My home at three stories with the walk-out amounts to a town home configuration an with the mini-split mounted at the top of the open staircase cools all three floors nicely.

I was  tankless/tubby thingy is tough, but it takes a seriously large tank to fill spa-sized tubs, and higher BTU/hr commercial tankless &  ganged-tankless units are growing in popularity to overcome the gpm limitations without having to build a tank-farm in the basement. (I personally don't get either the mega-tub craze or the 6 side-spray monster showers, but they're out there.) They're not a great solution, but they take up less space, and don't run out of water. The main point was that there's no real payback on efficiency with a tankless- they cost more up front, have more maintenance issues, and don't have sufficiently higher efficiency to break even on the PITA factor, let alone fuel savings. Where efficiency is primary, for the money you get more showering performance & efficiency out of drainwater heat exchangers, but they do nothing for tub filling efficiency/performance.

The ERV issues on my friend's place were more complicated than just the chase, so that was an extreme oversimplifiction on my part. (The fact is, it's a rental broken into three units by floor, which has other local code issues when combining ventilation, but the routing would have been very awkward no matter what.) In new construction the additional cost of multiple ERVs wouldn't be justified for gaining back the floor space, and it could be done as a central system, but that isn't an critical requirement, which was part of my very fuzzy point.

Nobody's been talking solar thermal here- the ROI just isn't there (as you correctly point out, it's usually negative.) PV is much lower maintenance and higher return, especially where subsidized & net metered at full retail, and makes more sense for houses heated & cooled with heat pumps.

What, you don't need at mini-split head PER ROOM to keep comfortable? NEVER HEARD of such a thing!   (Try selling that over on the "Geothermal" forum on this site- some of them think I'm crazy, clueless about comfort.) That may have worked at my friend's DER with a lot of re-configuring of the house, at least for the cooling season with some cooperation between the tenants. I still suspect multiple heads would be necessary in the heating season unless you lay it out VERY carefully.  One head per floor seems to work for most high-R houses in my neighborhood, but my uncle is both heating & cooling a 2 story with reasonable comfort with a single head mini-split in the full-height Great Room (in a ~1990ish code-min house, no less, but in a more temperate climate- his 99% outside design temp is in the low 20s F.)

You've thrown a lot of good science at me. It will take me some time to process much of the specs. I was looking for your "plug-hog" reference because it was a good point. But, even the concept of the backdraft risk that you mentioned with the building envelope principle, though a natural use of convection still a complexity to consider the clerestory could in effect turn the envelope into a flue that causes the house itself to act as a fireplace. That is still a mechanical system though not in the mechanical room. I am struggling with identifying the component for the air exchange in a ductless house. But, again, I am just a beginner and doing research. So no need to answer that one. :) [Sorry...I was referring to the old school double building envelope with the building cavity, and the solar greenhouse, clerestory, the current flowing around the house, etc. I'm still pretty textbook about it.]

The HRV or ERV system (Heat or Energy Recover Ventilation) provides the active air exchange. While usually ducted (tiny in comparison to heating/cooling ducts) there are non-ducted variations on the them. These are pressure-balanced system with air-to-air heat exchangers to recover the sensible-heat in the outflow. An ERV also preserves some of the latent heat via a humidity exchange, which is useful in rejecting some of the latent cooling load of summertime ventilation air. The power use is fairly low even at the full ASHRAE ventilation rates, but most homes can run them at a fraction of that rate and still retain excellent indoor air quality.

As long as you're not poisoning your indoor air with volatile aerosols, toxic cleaning agents, smoke, or insecticides, excess moisture is the biggest indoor air pollutant in most homes, and in winter when the outdoor air is dry running the ventilation under dehumidistat control is usually sufficient for purging the other indoor air pollutants.

The double building envelope approach to passive solar was popularized in the late 1970s, but tends to be more complex to build, and eats up more interior space than simply going high-R to achieve the same energy-use performance. It can work pretty well in more temperate climates, but it's probably not a great approach for a Chicago townhouse where space is at a premium and the seasonal solar input is so modest compared to the heating loads.

The stack effect drives on a 2-story with full basement & attic are high, which makes air sealing more critical than on a 1-story slab-on-grade rancher. The 3ACH/50 code-max is still too high for a high performance building, especially if the air leaks are at the foundation and attic, maximizing the stack effect infiltration. Depending on the roof/attic design, it's often much easier to achieve high air-tightness by insulating at the roof deck rather than at the attic floor.

The HRV or ERV system (Heat or Energy Recover Ventilation) provides the active air exchange. While usually ducted (tiny in comparison to heating/cooling ducts) there are non-ducted variations on the them...

The double building envelope approach to passive solar was popularized in the late 1970s...

Very informative. Much appreciated.

Tankless water heaters are pretty much a waste of money ... A condensing tank-type water heater ...

As I see it, the latter will cost you more to buy, take more room, be equally complex, lose heat from the tank and probably have a steel tank that will rust out. It will provide lots of gpm for a short period - but where do you need that?

You can add DWHR to any water heater (it's an orthogonal issue), but in most cases the numbers or practical matters don't work out.

The installed cost of a condensing tank is almost always lower than that of a tankless, the maintenance is lower, and the "personality" quirks far fewer. In low-water-use homes on the gas-grid a standard atmospheric drafted tank might be "right" from the pure economics of it, but in tight homes it's better to have something power-drafted, if not fully direct-vented/sealed combustion.

Do you have an example of a good condensing tank heater?

The smallest stainless steel Polaris runs ~$2700, has a good track record, and would last at least as long as the best tankless. The smaller-burner Vertex runs ~$1700 and has of similar design, but would only last about as long as most standard tanks. Either has far fewer maintenance issues as a tankless.

A condensing Rinnai or Noritz tankless may run $1200-1500 for the basic unit, but requires fatter gas-line plumbing, and usually have custom venting pieces adding to the initial installed price, and more labor-intensive annual maintenance that adds substantially to the 10 year & 20 year costs of ownership, even in case where it's break-even on installed price.

The internals of a condensing tank are just plain dumber and more reliable than a tankless, which of necessity needs a much bigger, and MODULATING burner.

I don't hate 'em, but for most situations a tankless isn't worth the upcharge unless you have no space, or need truly "never-ending" hot water. For as-used efficiency they only beat a condensing tank in either very low volume applications (where standby losses eat into the tank's efficiency), or in truly continuous burn applications, where their very modestly-higher raw combustion efficiency gives them an edge. In most 2-3 person household apps a condensing tank will outperform a tankless on average efficiency, due to the short-cycling losses of the tankless on the more frequent low-volume draws.