"Modern construction does not tolerate large temperature swings, nor does large thermal mass or massive fireplaces, but a basic understanding of thermal dynamics and human comfort levels will help in making long term construction decisions. "

Please explain what you mean by this?

Jmagill,

I'm not sure your comments really make much sense. Badger is saying we can regulate temperature successfully in our buildings, not that the goal should be to maintain a single point temperature for an entire structure. Your arguments against that basically say "you can't make us comfortable anyway". I can't say I really understand that or that I agree with most of your points other than the occupant desire conflict argument (hubby wants hot, you want cold). For instance, you don't usually do heavy labor in the room with your computer. that is an argument for zoning... warmer computer room cooler exercise room.

opening a window only makes sense when the heat is free, of course, though it's still wasteful. and of course I understand in order to reap the benefits of passive solar gain there is a price to be paid in temperature overshoot in high gain areas. I think both badger and I were referring to the COLD temperature issues a prior poster had mentioned, not overages. As in, there is no need to deal with 55 or even 62 degree rooms in any building that would consider an expensive addition like a fancy stove or fireplace.

neither badger nor I were arguing against fires either. simply saying you can use fire and still modulate your heating to achieve comfort.. for a similar, or lower price... by moving the fire out of the living room, into a boiler, and dumping the heat into an insulated tank to be used as NEEDED. and HOWEVER you define comfort, it would be superior with the hydronic method.

again the only exception I can see to this would be a "cheap fireplace" option. I have seen many fireplaces and masonry heaters out there that exceeded the entire cost of my radiant systems, for example... hard to say that makes any comfort or energy sense at all.

If I don't make sense then let me explain.

I am saying that not all of us need a system that regulates the temp. to within a degree of what is comfortable. Some us are perfectly happy with a mainly passive system with free heat and the addition of a little work of our own to regulate that temp. with in a 5 to 10 degree fluctuation. We may be able to then preclude the addition of active systems that require constant use.

I do that 6 months of the year with my SIP home and concrete floors. I open windows to cool the mass during the night and I close them up to keep the cool in during the day. This enables me to entirely cut out air conditioning. During the winter we open all the blinds during sunny days and close them down as the sun sets resulting in no active in house heating during the day.

In my next home I will take that one step further with added mass and passive solar design encapsulated with insulation that will result in needed heat input only on cloudy winter days. With all the money I save on a high priced heating system ( installation and operation costs) I could easily afford that masonry fireplace that will do duel purpose as mass and supplementary heating.

ok, maybe I'm not being clear.

1. Masonry heaters are just as, if not more expensive than active hydronic systems, even wood boiler powered hydronics.
2. Masonry heaters are less regulatable than active hydronic systems.
3. Masonry heaters are less efficient than many wood boiler options.

If you have a house that doesn't need active heat input, such as a masonry heater, great, nice job! But if you're going to add a masonry heater, I just don't see any advantage to it. You can do a Trombe wall far cheaper, and you can do the supplemental heat far better and if not cheaper than darned close to it with a slab radiant or hydronic radiator system and gasification wood boiler.

So what's the advantage of the masonry heater again?

I understand all your points Rob and agree with most.

The difference would be preference. Someone may prefer the the masonry heater to the hydronic radiator system.
Some may prefer the up front costs and smaller future costs. Some may prefer the flick of a switch heating system.
I can see a great case for passive solar with mass and a few baseboard electric heaters but I prefer a fire.

Masonry heaters can be done well and and at a very competitive price especially if you factor in that many already want a fireplace stonework and it's associated costs.

Open window control is great...in Hawaii. If you are like the rest of us in cold climates, humidity can be a real issue at night. In New Mexico and Colorado, two dry places I have lived in worked, too much humidity is not an issue and open windows may work for you (especially if you are home all the time to tend them).

Here in Minnesota I regularly tell my customers to keep the windows closed at night if they want to stay cool during the day, it costs money to condition the air and you don't want to throw money out the window.

People often get confused about comfort and energy efficiency, assuming they are mutually exclusive, thus fiction is made by anecdotal misconceptions and junk science.

"Modern construction does not tolerate large temperature swings, nor does large thermal mass or massive fireplaces, but a basic understanding of thermal dynamics and human comfort levels will help in making long term construction decisions. "

Please explain what you mean by this?

In the "good old days" high mass fire places made sense since it was one of the few ways to store heat. Today the modern residence controlls the loss of heat by controlling unwanted heat transfer. Thermal mass by definition does not tranfer energy quickly and can be a great asset in warm climates with cool, dry nights, but in the shoulder months such designs fall short of what the majority call comfort.

I love my little wood stove but don't call it modern, particularly GREEN or "thermally" comfortable. It is nice to have an intense source of heat when one gets the chill but the ratio of fuel savings to comfort come from low temperature hydronic radiation.

"In the "good old days" high mass fire places made sense since it was one of the few ways to store heat."

"Today the modern residence controlls the loss of heat by controlling unwanted heat transfer."


So in my version of the modern building. I combine both and I have less need of a heat source because with my combination of mass and insulation.

My modern building tolerates large outside temp swings very well because I used both mass and insulation.

Thermal mass is great - it's the ability to turn it on, off and isolate it from the interior temperature that some systems lack.

Proper solar and mass design combined with exterior insulation negates the need to isolate the mass. Today it is 32 outside and my heat never came on all night and it is 68 degrees inside. My small amount of mass absorbed yesterdays heat from the sun(Outside temp never got above 55 yesterday)kept my home between 68 -70

I got up in my camper van in 40 degree weather this week (warming to 70s in the afternoon.) Walked into the house and it was 66 in there with incomplete attic insulation and doors wide open all day long. Thermal mass works.

And that is my point about having something to sell. When you are holding a hammer the whole world looks like a nail. The OP wants a passive solar house. Badgerboiler would put him in "modern construction" that is almost guaranteed to overheat. NRTRob would give him a thermostat that, in my house anyway, would be as pointless as... well, pointless.

The fact is that builditsolar.com is replete with people who DIYed masonry heaters, among an amazing list of accomplishments. (My prize for ingenuity and bravery goes to the fellow who built a solar steam generator.) If the OP goes there and says, hey, this isn't me, then so be it. It is not my choice either.

I've written some of this above but apparently it needs repeating:

* People want what they want. If it's 40 feet of window walls and/or a visible flame in the living room, there are lots of ways to get it done in a green manner. Passive solar will always be the exception, because it is a rare lot that has adequate privacy and insolation. Where it can work, it would be nice if pros would help make it work rather tell folks what they really want.

* Passive solar is typically slab on grade, and making things fit is the most difficult design problem. A 200-gallon heat storage tank (principally for DHW) is the best I can do, and it only fits mounted between floors in a vertical chase. Granted, masonry heaters take up lots of real estate, but there is no reason to tuck them away.

* If the solar part works, auxiliary heat will be needed infrequently. The second toughest design problem is deciding how much to spend on something you hope never to use. For starters, a furnace style wood boiler is sure to be four times larger than it needs to be.

* Night time setback saves energy even in high mass homes. http://www.ornl.gov/sci/roofs+walls/research/detailed_papers/thermal/results.html Gets 99.7 percent of the energy savings possible in Badgerboiler's modern construction, in fact.

* So on a chilly morning, do you want a conventional thermostat set point that's going to cycle hydronic dozens of times before the walls are warm again? Or do you pour the heat to your masonry fireplace and get a corner of the room toasty again in 30 minutes?

* "Chilly" is a judgment call. At the design day temp of 10 degrees F, my house should cool four degrees overnight. Is that more or less tolerable than a 10 degree setback in Badgerboiler's modern construction?

Todd, you are mischaracterizing my argument, which is what I'm objecting to. If you're going to dismiss my perspective or my integrity, at least do it in response to my actual arguments.

I've said several times already if you can do the masonry heater CHEAPLY, that might change the discussion. However if you are paying someone for the heater, it's more expensive than many wood burning radiant systems and more limited. You seem to be completely ignoring the very careful qualifiers and explanations I am putting in my arguments and then blaming me for not seeing the whole picture or something. Most people don't build their own masonry heaters, even people who might run their own pipes or low voltage wiring. but if you do/can... great! If that's cheap, then then argument is different. Just as I have already said. Several times.

There is no argument whatsoever against the comfort issue though, except that you don't value comfort as much. You simply cannot regulate temperatures as evenly without controlling the heat input to various spaces. Some people don't care, which is their prerogative, but it's certainly a factor to consider and one that I personally feel is undervalued primarily because most people have never lived in a truly comfortable home and don't know the difference. again, I'm not arguing against passive solar there. but it is a factor to consider with the auxiliary heating methods.

For SUCCESSFUL solar homes, we usually see a small electric boiler used when hydronics are used as backup. slapping that on some cheap pipe in a concrete slab is a pretty inexpensive backup method that doesn't have any zoning shortfalls, significant time lag problems (if floor sensing is used), or zoning restrictions. Of course, it's electric, not so green. but then again, if it rarely runs... then this system would be cheaper than even most DIY masonry heaters, and better for comfort management to boot.

Not for everyone of course, and some people like JMagill might pay extra for the privilege of having wood burning visible in a living space. no problem. I've seen clients spend $50k on a fireplace: I can't imagine that personally, but it's their house. I tell people to cut down their north glass and reduce floor covering R values for functional reasons all the time and they don't all listen either because different people value different things for different reasons. But that person can see an Economic argument that shows that they are not making the most economical choice and choose something else. That's called informed decisionmaking. That would require people like Badger and I to illustrate an alternative first, though, right? Otherwise there may be a fair number of people who think the masonry route is the cheapest, most comfortable, or even a vaguely economical choice. Now, they might know how and under what circumstances that may be true or not true. Mission accomplished.


so to sum up, in low load homes:

If you are building your OWN masonry heater, and plan to use it a lot, go nuts. Be aware of the comfort degradation as you move out of the masonry heater area, or design your home to facilitate the movement of heat from the heater to other areas. Do the happy dance.

If you are going to BUY a masonry heater, it pretty much only makes sense if you are making the decision on aesthetics. Economically and for flexible heating control/comfort, wood burning hydronics would win *almost* every time. But all decisions are not made on those criteria... so be it.

If you are just talking about periodic auxiliary heat, I wouldn't do anything that costs a lot, like even a DIY masonry heater. again, unless your aesthetics dictate you must. an inexpensive wood or pellet stove, with faster response time, would be better, or a cheap slab radiant system with electric heating/water heater tie in to minimize heat source costs and provide for fully automatic backup and/or comfort control in non-central areas of the home would be a likely choice.


Is that fair in your mind?

Interesting article on mass setback though, I had not been aware of that research. I'll keep that in mind in the future... definitely unintuitive and I've been wrong for quite awhile on that point. Thanks for sharing.

As for your own home, a home maintaining 66 degrees in MAY with 70 degree days is not particularly impressive. My EPS foam insulated shop maintains about 75 degrees on the upper office level with no thermal mass to speak of and only computer energy usage (sleeping computers, mostly, not much draw) during the day this time of year, in maine (even with only two people here) and is rarely below 70 the next morning... with our windows open. so, "no thermal mass works"? You are definitely going to need auxiliary heat if you are only maintaining 66 degrees in may... sounds like you are planning for that, great, but it's not like your auxiliary source should be an afterthought. Of course I understand you're not done and have no idea how bad your current insulation situation is. Maybe you'll be a lot better when you're done. I hope so! I assume you've got modeling or calcs that are guiding your decisions.

Gets 99.7 percent of the energy savings possible ...

You should be clear and add "in some climates". Mass works best in climates where indoor and outdoor temperatures vary above and below ideal on a daily basis. In others, there is little difference that is overwhelmed by losing thermostat setback.

Examples like "this week" and "today"(in your house) mean nothing - it's whole season performance for a specific location that is of interest.

Just wanted to say thank you for all who come and post on these boards with such erudite and thought provoking answers. It keeps me coming back, and provides knowledge and information to chew on as I work on my house.

-Rosalinda

NRTRob I didn't intend to impugn your perspective or integrity. My apologies if it seemed that way. Everyone has a point of view, especially me. A perceptive colleague once stopped me in mid boast about my cars to observe that I had as much self worth tied up in my vehicles as anyone else except that my thing was how little I spend. Touche.

You are absolutely correct that electric resistance and hydronic are the answers for the person who is confident that passive solar/high mass will work almost all the time (ie, people who live in the Southwest.) I live in Pa and I am traveling a different road to cover my bets: inexpensive but modern wood stove boiler from Europe; hydronic; some water storage. We have been down this road, you and me, and I have no interest in retracing our travels.

Suffice it to say that passive solar draws an unusually hardy crew. I want to cover my bets on the resale front as well and I would appreciate your thoughts on this approach to automation (with an oil fired tankless standing in for the wood stove.) Seems to me the way out of the slow warmup is to use slab sensors (got 3 of them). If I used a 2 or 3 degree Tstat delta on the slab, the warmup should be quick without excessive cycling or noticeable heat output.

A second question: I am at the point of second floor hydronic under hard wood flooring. Seems to me that cork, or some similar material under the hard wood, would give me the build up I need for aluminum plate radiant plus noise control. Thoughts?

My house is a work in progress but encouraging to me. With zero emphasis at this point on air infiltration or convection, the concrete is capturing heat and holding it through the night.

Jonr, I don't think climate has anything to do with high-mass setback issues. The conventional wisdom is that high mass houses lose heat and recover it too slowly to benefit from setback. That ORNL says the opposite, it seems to me, would apply equally in most climates.

I have a client right now in virginia doing the mass/electric backup scenario.. his models seem to indicate it should work out just fine. but R40/R60 shells will do that, I suppose.

I get a sales benefit from posting and I"m as vulnerable as anyone to the "every problem is a nail" issue... but I do feel you were mischaracterizing my position and I try very hard to fight my biases and presumptions by being thorough in my responses so if my reasons don't apply, the tools to take apart my argument are usually there. It's not like I'm ramrodding a point of view through with no supporting evidence or discussion or something...

anyway. usually people would use plywood or osb on the second floor for infill. cork would be an odd choice..?

Climate has everything to do with the effectiveness of thermal mass in reducing heating/cooling costs and nobody (well, nobody credible) debates that setback is slower, less effective (note: not completely ineffective) and has a longer morning recovery time when passive thermal mass is used. Therefore, which one outweighs the other is climate sensitive. Some will be more, some less.

Read this and note the first 3 words "In certain climates...".

http://www.ibsadvisorsllc.com/_library/ORNL_Thermal-Mass_Energy_Savings_Potential_in_Residential_Buildings.pdf

IMO, exterior or in the middle of the wall (like ICF) is probably the best mix of thermal mass advantages and setback effectiveness (in most buildings and climates :-)).

Apples and oranges, jonr. Yes, the dynamic benefit of thermal mass, its ability to buffer daytime heat and nighttime cool, is climate related as your link states. It's most effective on an annualized basis in places where the average daily temperature is 70ish and the daily swings in temperature are extreme. Note the word "annualized," as in thermal mass works in some months and doesn't work in others. When night time setback comes into play, we can assume, A, that the ambient temp is well below 70 and, B, that the heat is flowing only one way -- out. Ergo the dynamic benefit of mass on those days is zero.
So why does ORNL say setback difference in high mass and low mass homes is "very insignificant"? This is a quote from your own link above:
"All of this supported a common belief that night temperature setbacks in
massive buildings caused a reduction in the setback energy savings. D.
Burch investigated this penalty in setback energy savings and his
research confirmed the fact that such a reduction took place. However,
the magnitude of this phenomenon was very insignificant. For
example, for a typical residence the difference in setback energy
savings in the massive house and traditional wood-framed was
predicted as only 0.3%."

The answer, of course, is that there is no significant setback penalty for massive buildings, counterintuitive or not. And since D. Burch was analyzing results from actual buildings constructed by ORNL, you should either accept it or change your tag to "Just an engineer who likes some answers better than others."

Okay folks, remember the OP wants to build a passive solar home. The thermal mass is an important part of the controlling the temp swing and storing the free heat.

If design properly with the mass inside the insulation the temp swing should be in the range of 60 -80 degrees in the heating environment they wish to build in. Add to that a bump up of insulation from the normal 22/38 to 40/60 and you can reduce that swing to 65-75. This means that no mechanical heat should be needed unless you have many days of no sun. Setback recovery becomes a mute point. I could live with that swing easily if it meant no heating or cooling bills.

I already live that way six months of the year. If I had added more mass, insulation and better solar orientation I could be living that way now.