there are places where what you say is true, but you're talking about only passivehouses, basically, which is a target most people are simply not going to hit... you need a seriously studied and advanced building team to make that happen. A tiny number of PHs are built per year. Meanwhile, in maine, we have thousands of old farmhouses, on the other hand, that have gnarly little rooms all over the place and are never going to be retrofit to a passivehouse standard. and the vast majority of new construction, even if improved on the envelope, would not hit PH standards... the amount of glass used alone would kibosh it for most people. floorplan typically matters.

most of the "passivehouses" I see built have a hedge heating system in them as well. it's possible, of course, to skip that, and if you're going to that level of efficiency it should be strongly considered... that's half the point, at least, of doing envelopes like that.

But considering the airflow rates appropriate for ventilation (i.e. very low) I have some skepticism about "balancing with ventilation air". even 200 CFM from an ERV can't move more than a small amount of heat, unless you crank up a duct heater of some sort, like the original PH spec would assume. without that, all you can really do with that is dump more cold air in a warmer room to blend it down to the auxiliary room levels... ERVs lose heat, you can't raise a room temp with it unless it's significantly below comfort level. But as you note, a plug load can easily outstrip even that. if I had 60 CFM to a main area with a 10 degree temp drop from the ERV exchange, that's 648 BTUs of "balance cooling" available. one person and a computer kills that... you haven't even touched the underlying heat load differential. and you only get that kind of a drop on PH quality ERVs on very cold days.

don't get me wrong: the comfort is likely much better than the non-PH homes here in maine trying to heat multiple rooms with a kerosene monitor heater, and I'm sure people who are believers would consider it quite adequate. but I strongly doubt it is "perfect" with a ventilation air balance strategy, absent duct heating.

I"m open to evidence to the contrary but I doubt I'll see any in other than a truely highly engineered PH home with very close attention paid to glazing ratios on a room by room basis.

If the main goal is comfort (I am always skeptical of other ascertains) then we start with a heating/cooling load analysis. From this all HVAC options are derived.

First, the largest energy loads in any Idaho home will likely be heating, followed by domestic hot water and cooling if in you are below 5000' lets say. With this in mind radiant floor heating is a natural. Boilers are the most common and one of the most efficient heat sources for radiant floor heating and will also make domestic hot water very efficiently with a built-heat exchanger or indirect water heater.

Now 75% of the energy needs and 80% of the comfort has been addressed. The rest of our efforts will come into perspective.

If it is all about comfort and then about economy we may look back at cost and note that radiant floor heating will likely double the cost of a much more common forced air system, as it should. After all, they put forced air in mobile homes...not known for their comfort.

As you are willing to pay extra for comfort putting radiant in a basement or walk-out slab is really a no-brainer. We call it Radiant Floor Ready. If the basement slab is the only floor to be radiated (as it is also the cheapest and the only way to properly heat space below grade that will not need cooling in any case), we often us a condensing water heater to heat floor and domestic water with a sub-assembly to separate the two.

The comfort of upper floors is often compromised for the sake of cost savings. Specious arguments are made about carpet and hardwood flooring not being compatible with radiant floor heating coupled with the "double-the-cost" singsong and no rational person could "justify" the added cost. I used cork, bamboo (floating) and 3/4" oak (nailed) in my recent remodel. If I cared for carpet I would have used that as well. A competent design will help you chose any floor covering you like and make sure it is compatible with the radiant floor heating system you choose.

This same person is definitely going to "heat" there house with solar someday. Maybe in Arizona, New Mexico and other sunny, mild climates. The same goes for geo. Expensive, forever return-on-investment, and you must have duct work, large capital investment and a single heat source...electricity.

ERVs are for ventilation. With any new house, tight construction is a given. Fresh air become a commodity and any energy recovery ventilator (ERV) becomes a necessity. ERVs are a single purpose device, best to keep it that way. They present a load to the heating and cooling system unless the windows are open.

Dana has suggested that the proper mix of architecture and mechanical systems, (window, overhangs, insulation) will make the difference. Rob also makes a argument for good design and installation teams. Both are right, but lets start with a good design and realistic/honest goals.

Keep in mind that with day time temps about 20F higher than night, an air source heat pump will be noticeably more efficient in the day. Not to mention that you might have excess passive interior solar heat in the day (say 80F) that the heat pump can extract heat from. Water makes it easy to store this cheaper heat.

Is water storage worth the complexity and $ - it depends.

I agree retrofits to PassiveHouse levels are rarely (if ever) practical, but it doesn't need to get that low for point source (or multiple point source) to be cheap easy and comfortable, even if it means cranking the temp up somewhat in the "warm" spaces during colder weather. Even those gnarly Maine farmhouses with U0.1 walls and U0.5 windows can do OK most of the time with a woodstove overheating the common spaces slightly.

Cutting U factors in half increases the season where that still works, but cutting it by 2/3 or more makes point source heating work pretty much all the time, and that's still nowhere near the PassiveHouse standards.

Using ventilation flows to balance temps is only going to work if the spaces without the heat source are very low loss, which (of course) places a constraint on window area for those rooms. In the Worcester 3-family the typical "unheated" rooms have about 10 square feet of U0.18 window. At a design condition delta-T of 65F that window loss is still about half the point-source heat generated by one sleeping human. There is also about 130 square feet of U0.025 wall, so with fewer than 2 sleeping humans there will be a net loss, but it doesn't take a huge ventilation flow from the adjoining space in combination with conducted heat flow through the partition wall & doors from a room even 2-3F warmer to offset that. Leave the doors open and convection takes care of it. Unless micro-zoned and tightly controlled most ducted or hydronic systems would see room-to-room temperature deltas as big or bigger than they're anticipating.

And this at wall/ceiling/floor U-factors roughly twice that of typical PassiveHouse designs, and about the maximum U-factors anybody thinking seriously about solar space heating should be considering in Frank Scheubel's northern UT location.

Of course you don't have to design a new house that way, but it doesn't take rocket-science design teams to get there. It does take some careful planning and attention to detail though, which is where tools like BeOpt (not the PassiveHouse tools) become useful.

Radiant floor + hydronic heat pump + air conditioning is more than a 3x cost multiplier compared to a simple ductless air source solution. A propane or electric boiler would take some of the initial bite out of it, but at 3x the operating cost. (And this isn't even starting on the potential upfront costs of active solar with hydronic thermal storage.)

But I'm not sure if Frank Scheubel is even following any of this.

Using ventilation flows to balance temps is only going to work if the spaces without the heat source are very low loss, which (of course) places a constraint on window area for those rooms

And very low gain.

Dana... I live in old farmhouse with a woodstove and I've been in and around them most of my life. let me tell you "do ok" is something they DO NOT. You have a hot and comfortable main room and colder other rooms. we are just conditioned to expect and accept that... "comfort" is not an expectation of most people in old farmhouses without a heating distribution system. if you're designing a heating system you can't design it with 60 degree bedrooms.

I think you're severely glossing over both comfort issues as well as the level of technical acumen (and willingness to subvert aesthetics and lifestyle to technical issues) that most buildings will require to achieve good results. Fact is in most multi-room homes point source heat is a cheap way out with fairly severe tradeoffs on comfort.

as you increase the distribution costs, hydronics gets to be less of a cost delta. maybe not radiant floor in all cases, but radiant ceiling can be quite cost effective as can panel radiators. I just quoted an air to water heat pump and radiator system vs multiple head minisplit system and the costs were actually similar. AC would have changed it, but you can spot-add AC pretty inexpensively to discreet areas in hydronics as well.

I'm not downplaying the role of air to air... it's important and fits a lot of homes well. but it's simply not accurate to wave your hands and say that ventilation air will balance out most buildings being lived in and built today, or that you can get a building built for which that is true very easily.

The outdoor temperatures at which ot begins to be not OK start higher in an old farmhouse than in a high-R house.  Cut the U-values by 2/3  and outdoor temp at which discomfort begins drops, and by more than just a little bit.   With responsive modulating systems like mini-splits the overshoot/undershoot you get with wood stove point-source heating goes away too.

It would be interesting to interview the occupants of the KatyWil/Colrain MA house (p. 32-34 in this document ) make out for comfort, heating with a 2-head multi-split.  Again, merely R40 walls, not R80 PassiveHouse style. Outside design temp= +2F.  I suspect it's zoned one head per floor too.

Most multi-room homes aren't in an R40-wall type envelope, but it's not particularly expensive nor difficult to hit that in new construction (compared to retrofits).  Anybody in northern UT thinking seriously about heating with hydronic solar should be looking at R30 whole-wall as an absolute minimum (and U-0.25 max windows, except for passive-gain windows) to get the size of the thermal array to where it might actually fit onto the house.   Bumping that to R40+ would usually be cost effective in further reducing the size and cost of the active solar.  But it depends.   I'm assuming if it's not at least an R30 house, it's not going to be a solar-heated house in any signficant way.  And if it's an R40 house, the temperature balance issues can usually be designed out.

I certainly wouldn't assert (hand waving or otherwise) that ventilation flows would "...balance out most buildings being lived in and built today...", but it remains to be seen if "...you can get a building built for which that is true very easily."   Designing such a house shouldn't be hard, but finding a contractor who can build it turn-key without a lot of owner/designer monitoring might be.  Few people interested in solar heating their home are going to just buy plans mail order, hand the prints to the low-bid contractor and hope for the best.  I suspect there is at least SOME local talent for designing both the passive and active solar aspects of a new house in UT, given the better than average wintertime insolation for the climate.  Thinking about room to room balance issues in a solar home is par for the (design) course whenever there's a significant passive solar aspect.

the difference between R40 and R80... as you know quite well... is very small. all the heavy lifting is done by R20 and R40 is the coup de grace for high efficiency living... anything over that is vanity or trying to hit a standard, not anything driven by comfort, efficiency or economics unless you do in fact hit the "no heating system tipping point" somewhere in that extremely thin marginal improvement. our own walls here in maine are only R25 and you cannot tell the difference in surface temp between walls and R50 ceiling... radiant heated, of course, with nearly no daytime demands... on a cold day.

I nitpick on this because an R40 wall is not 'merely' R40. it's practically equal to R80. and R value is important but even with good glass, glass racks up deficits very quickly. until that changes substantively, you need a very good thermal analysis to deal with the solar issue. How many designers do you know using AUST or MRT? heck, even I haven't transitioned over to doing that yet. some do. but they don't grow on trees. I could probably only name about a half a dozen designers I know who even know what both of those acronyms mean and why they are relevant to this discussion.

again, not saying you can't engineer a box that can be heated point source acceptably. just saying it's about a lot more than Rvalue and Rvalue alone doesn't determine success there: and the days are far from here were most even "very green" homes are going to be optimally served in that fashion. and many homeowners, even in those communities, are not willing to make the tradeoffs necessary to make an Ecobox work. it's not a slam dunk solution for any but a very, very specific subset of current green buildings.

someday if it's available as a modular, cheap deployment, you'll find the frugal signing on. but as long as it requires custom design and engineering, it's the high end market, and high end homeowners have desires...

Designing the glazing is job-1 on a passive solar design, no doubt, but it need not be perfect to be "good enough" for point source (or "few-points" source).

In warmer climes than N.UT there are existence proofs of quite comfortable single-head ductless heating even in not-so-insulated but tight retrofits, my uncle's place on Whidbey Island being but one. His relatively open floor plan make it easier, but the doored off rooms don't have comfort issues even with the doors mostly-closed.

Mind you, the design temp delta-T for him is about 45-50F compared to ~75F for places inland from Penobscot Bay, but his isn't anything like superinsulated, with ~U0.075-0.08 timber framed 2x6 walls and U0.4-0.5 windows. Most of the glazing in the larger common-area, but the other rooms do have daylight.

What's AUST?

so he got lucky. I've been in many, many homes that would not rank so high on the comfort scale. I would simply encourage you to not be so sanguine about the issue. most people are just used to crappy homes. check out satisfaction ratings with home heating systems sometime

Average Unconditioned Surface Temperature... the second temp (after the conditioned surface temperature) that tells you to what degree heating a surface is an improvement or not.

MRT (mean radiant temperature), it was on the test ;-).

More proof that radiant is the bomb!

MRT (mean radiant temperature), it was on the test ;-).

More proof that radiant is the bomb!

The problem with MRT is that it's a mean. People don't like a cold surface on one side and a warm one on the other. A cold wall of windows is a good example - you want radiant heat coming from that same direction (I know the radiant guys know this but it might be useful to others).

not exactly true. you feel comfortable at a campfire with a cold back and a hot front.

there are temperature asymmetries that people do not tolerate well: namely hot heads, cold feet. but people tolerate a horizontal plane assymetry (hot/cold walls) very well actually as long as they are not losing enough net heat to feel chilly. this is why people like woodstoves or other very hot objects, but do not like very hot ceilings.

the problem with cold windows is not that MRT doesn't work, is that the MRT is actually low. technically you also have to calculate the MRT at a given point, and if you're close to the window, the cold of the window could overhwelm the "warm" of an object further away (radiant intensity varies with distance), so the apparent MRT at a point close to the window is not the same as the apparent MRT at a point close to the heater.

that gets pretty complicated, of course, which is partly why most of us are not yet using MRT in our designs... there is more to it than just averaging all the surface temps in a room. unless you are only concerned with center of room comfort, I suppose.

While I don't agree about campfires being comfortable (except when compared to no fire at all), I agree about MRT changing with position. Radiant heat in one area does not consistently make up for a cold surface in another area. Putting radiant heat near windows also addresses this issue.

perhaps at the extreme I'd agree with you, but you talk to someone who heats extensively with a woodstove and I doubt you will get much complaint about the temperature asymmetry it presents, though people will adjust their proximity to the woodstove to modulate comfort in many cases of course.

would be interesting to compare that to typical MRT targets for comfort sometime. ooooh, shiny....

Yes, the last time I was sitting with my back to the windows and my face towards the stove, I got up and moved to a more comfortable position.

maybe you're a wuss I've never had that problem, woodstoves were always good for me until I, myself, were overheating.

really would be interesting to test this.

We in fact are using MRT and AUST if we design radiant floor heating systems or HVAC systems or building envelopes for that matter. Any radiant panel works to raise the mean/average surface temperature (MRT) of the room which it serves. The heat flux/output, in turn is affected by the design water temperature, tube spacing and floor covering.

So, AUST is just cold walls absorbing heat energy from warm floor, walls or ceilings. Human comfort is the result. If a surface in the home is too cold and there is no heat source to meet the "load" presented, the humans therein will feel the load. With a surface temperature around 86°F humans are radiators and must give off a certain amount of heat energy to be comfortable – about 200Btuh.
My software programs certainly produce comfortable MRT numbers as this but one of many factors used to predict comfort system design.
As Rob aptly states, we humans are comfortable in a certain range, not of air temperature, so much as MRT.
The difference in radiant vs. forced air heating or cooling is radiant panel efficiency. It is simply easier to address the challenges of AUST with a radiant panel than with forced air. The nature of radiant energy makes it more efficient at transferring energy to and from the interior of any home. This is why the performance is always better when radiant panels are properly designed. More comfort, less cost of operation.

Humidity is another factor affecting human comfort, which is why we need a minimum air exchange (all movement of air costs money) and will usually require efficient exhaust in dry climates and dehumidification in wet ones. Thus the use of an ERV, which exchanges sensible (read at the thermometer) and latent (hidden/humidity) heat maintaining stable indoor environment.

The reason we put heating ducts at the perimeter and under windows in warm air designs is simply to overcome the inevitable thermal imbalance created by the cold window and the intrinsic inefficiency of forced air heating systems. With each heating cycle the outside walls and windows go cold. AUST then, gets out of hand and comfort suffers as MRT drops. This is why people talk about the furnace feeling good when it is running.

With properly designed radiant floor heating system, the "heat" is rarely off. With the proper controls - and floor coverings - coupled with a reasonable architecture, the heat loss and all-important MRT are kept in perfect balance regardless of outdoor conditions, e.g. the colder the weather, the warmer the walls.

We design a lot of radiant systems using all sorts of radiant panels, from wall-hung Euro-style to wall, floors and even the much neglected radiant ceiling system. This reminds me of another perfect example of MRT. Even though all the heat in a room or home may come from the ceiling, the surface temperature of the floors in a radiant ceiling heated space, very often matches the ceiling surface temperature, with outside wall and window surface temperatures being lower than floor or ceiling.

It is all about the average/mean surface temperature of the surfaces in the room.

While I don't agree about campfires being comfortable (except when compared to no fire at all)

Ha Ha. Comfort is a relative thing. Faced with the alternative of exposure, hypothermia and death, a campfire is pretty nice any way you slice it.

I always cringe when the subject of comfort comes up, particularly where it relates to tens of thousands of dollars being spent over and above what will do the job. I have seen that ploy work around here on numerous occasions where a well-heeled new homeowner is sold a $120,000 or a $150,000 heating and cooling system because "comfort" is important. In all those cases, a $40K or $50K system would have been perfectly fine. I have friends who gained comfort by installing a 2 head mini split in a 100 year old leaky farmhouse, replacing a wood stove. They didn't even put one of the units upstairs. Both went downstairs and the "comfort" was fine. Once they spent less than a thousand sealing and insulating it, the "comfort" was every bit as good as brand new $750,000 executive homes with all their ridiculous ductwork, thermostats, bad balancing and poor efficiency.

I feel sorry for the people who feel a whiff of cool air and start to have a bad day.