Here's what we want to build-how much/what boiler and how much storage?

[Badfish740]

Last night my wife and I were talking in hypotheticals about the home we'd like to one day build. All other things aside let's talk heat and domestic hot water needs. I know that I want a gasification boiler with oil as a backup, evacuated solar tubes, and of course storage, but sizing and configuration are still very much a mystery to me. Here is a basic rundown of the needs of the house:

1. We're planning on about 3500 square feet of living space which takes into account that about half the basement will be finished-however, we plan to build into a hillside the way many raised ranches are so that the garage (two car) is under the house. Given the fact that I now change oil and do all other car maintenance outside 365 days a year, I'd like to heat the garage/workshop as well so let's just call it 4000 square feet.

2. Heat will be delivered via an in-floor radiant system.

3. DHW needs are as follows:

-There will be three full bathrooms. One will be a simple stall shower, sink, and toilet (guest bath), one will be a "kids" bathroom with a regular tub and shower, sink, etc... Then comes the mother of them all-the master suite. My wife is a steam and hot water addict so I'm currently researching all of those crazy steam showers and whatnot, but regardless in the master suite there will be a large soaking tub, steam shower, his and hers sinks, and hot water towel warming bars.

-The kitchen will contain one large sink and one chef's sink for washing vegetables and whatnot. There will also be a dishwasher of course (we are currently dishwasherless and my wife lets me know-every day )

-The laundry room will of course have a washing machine and also a utility sink.

-I'd also like to have a large utility sink in the garage and a hot water hose-bib so that I can hose out the floor with hot water. What I'd also like are hot water hose bibs on each corner of the house to go along with the regular cold water bibs. I've more than once found myself in a situation outside saying "I wish I could pipe some hot water out here..."

Given the DHW needs which are probably more than the average house, am I going to need a larger boiler than one would normally need for a 4000ish square foot home? Would evacuated solar tubes offset the difference? How about oil boiler sizing? I only see the oil boiler being used during extended absences from home (more than a few days) or in the summer for hot water production. Finally, storage. The boiler room will be in the basement and will be accessible by an 8' x 10' garage door first and foremost for easy access to fuel (I can dump a tractor bucket full of wood in front of the door, open it, and start tossing wood into the boiler), but it will also mean that the large storage tanks will be very easy to move in (and out) when needed. Basically, can I have too much storage? What would be too little? 1000 gallons? 2000 gallons? It's a lot of questions, but I'm looking forward to having a discussion about designing the optimum heating system from a blank slate.

 

[joecool85]

With a house that large I would go 2000 gallons in a heart beat, I'd say 1000 or so would be the minimum for effective storage.

 

[Floydian]

Hi Badfish-
I'll offer my opinion on a few things.
Obviously your building envelope comes first. How well you insulate determines the energy usage for the life of the building so you want give this part a lot of attention in the design and construction phases. Windows and doors can be real killers when it comes to heat loss.
Once you know the construction methods, how its insulated, sq. footage of doors and windows, etc. you can get a pretty good idea the heat load at design temp. This overall number should be arrived at using a room by room heat loss calc. This is VITALLY important as it determines everything for your hydronic heating system design.

If you can get your heat loss to something around 10 btus/sq. ft. at design temp you'll be doing well.
Using 10 btus/sq ft as an example: 10x4,000 sq ft=40,000 btus/hr at design. Not likely for 24 hours but lets say it was:
40,000x24=960,000 btus/day. I have seen it said on here that the average heat load is about half the design load so lets say
480,000 btus/hr avg. + your DHW needs. Of course these numbers are total speculation but they could help size your storage once you know some real numbers. Also knowing what temp water you can utilize in your heating system will help size storage. Then you could size your boiler the charge up your storage in a reasonable time.

In your situation I would take a very serious look a Garn.

Good luck,
Noah

 

[joecool85]

At 550,000 btu/hr per day and running the thermal storage from 180 to 140 you would get 14 hours of use on a 1,000 gallon tank, or 28 hours on a 2,000 gallon tank. That is on a winter day, in the spring and fall you could expect 3-4 times the hours. So it depends on how often you want to load your boiler. Basically in the dead of winter you would load your boiler twice a day with 1,000 gallons of storage, or once a day with 2,000 gallons of storage.

 

[joecool85]

Oh yeah, also, to answer your question about too much/too little. Basically you can't have too little or too much, just depends on what you want your system to do. That said, from what I have found generally a house your size would use a 500g as an absolute minimum and 4,000 gallons as a max.

 

[chuck172]

At 550,000 btu/hr per day and running the thermal storage from 180 to 140 you would get 14 hours of use on a 1,000 gallon tank, or 28 hours on a 2,000 gallon tank. That is on a winter day, in the spring and fall you could expect 3-4 times the hours. So it depends on how often you want to load your boiler. Basically in the dead of winter you would load your boiler twice a day with 1,000 gallons of storage, or once a day with 2,000 gallons of storage.

To be clear, you would have to burn the boiler twice as long, use twice as much wood, to charge the 2,000 gallon tank vs. the 1,000 gallon tank. You really gain no efficiency just added convenience.

 

[Badfish740]

Hi Badfish-
I'll offer my opinion on a few things.
Obviously your building envelope comes first. How well you insulate determines the energy usage for the life of the building so you want give this part a lot of attention in the design and construction phases. Windows and doors can be real killers when it comes to heat loss.
Once you know the construction methods, how its insulated, sq. footage of doors and windows, etc. you can get a pretty good idea the heat load at design temp. This overall number should be arrived at using a room by room heat loss calc. This is VITALLY important as it determines everything for your hydronic heating system design.

If you can get your heat loss to something around 10 btus/sq. ft. at design temp you'll be doing well.
Using 10 btus/sq ft as an example: 10x4,000 sq ft=40,000 btus/hr at design. Not likely for 24 hours but lets say it was:
40,000x24=960,000 btus/day. I have seen it said on here that the average heat load is about half the design load so lets say
480,000 btus/hr avg. + your DHW needs. Of course these numbers are total speculation but they could help size your storage once you know some real numbers. Also knowing what temp water you can utilize in your heating system will help size storage. Then you could size your boiler the charge up your storage in a reasonable time.

In your situation I would take a very serious look a Garn.

Thanks for the replies. As for the first point I should have talked a little more about construction from the beginning. We want to built a log home with milled 8" logs. I grew up in a home built with milled logs and can attest to them making up for what they lack in R-value in thermal mass. However, no matter what you do, log homes never seem to be the "tightest" construction, so my next step will be researching heat loss calculations using that type of construction. As for windows and doors we won't be going crazy with any large expanses of glass, except maybe in the family room.

At 550,000 btu/hr per day and running the thermal storage from 180 to 140 you would get 14 hours of use on a 1,000 gallon tank, or 28 hours on a 2,000 gallon tank. That is on a winter day, in the spring and fall you could expect 3-4 times the hours. So it depends on how often you want to load your boiler. Basically in the dead of winter you would load your boiler twice a day with 1,000 gallons of storage, or once a day with 2,000 gallons of storage.

To be clear, you would have to burn the boiler twice as long, use twice as much wood, to charge the 2,000 gallon tank vs. the 1,000 gallon tank. You really gain no efficiency just added convenience.

Here is where I'm still not totally understanding how this whole process works. I do get that the point of storage is so that I can charge the water with heat that is stored in the tanks, but I'm not clear on the process. When you're actually burning are you simply watching a temperature gauge to determine when to stop burning? Do you just burn for a set number of hours? The other big variable is the evacuated solar-I need to do some more research on what to expect in terms of BTUs in summer vs. winter, etc...but at the least I'm hoping to be able to rely heavily on it for hot water in the warmer months.

Oh yeah, also, to answer your question about too much/too little. Basically you can't have too little or too much, just depends on what you want your system to do. That said, from what I have found generally a house your size would use a 500g as an absolute minimum and 4,000 gallons as a max.

I plan on sizing the boiler room pretty generously, so I was actually wondering if 4,000 would be too much. If its not, I figure that four 1000 gallon residential propane tanks (4' in diameter by 16' long) could fit in a rack with two on the bottom and two on top. I had another thought about the tanks themselves. I have seen folks who have insulated them, but would it be beneficial to let them radiate heat since they would heat the boiler room and the space (the kitchen) above?

 

[joecool85]

4,000 gallons isn't too much if you have enough boiler capacity. Bringing 4,000 gallons up from 140 to 180 would take 1,340,000 btu/hr. An Eko 80 running full bore (275,000btu/hr) would take 5 hours to charge the tank. It would take 10 cubic ft of oak to make this amount of btus, I think that would fit in one load but don't have the spec for that.

 

[Frozen Canuck]

If you really want the log look might I suggest that you use a log look siding on the exterior of your home, preferably over SIP (structural insulated panels) as these are currently the way to achieve the highest R value, they can be used from the foundation footings up. We use them for the net zero homes we build here. You can easily achieve R 60 & above with these systems. Some manufacturers make very DIY friendly systems as well if that is of concern to you. The thermal mass you spoke of in a log home works both ways as the logs are on the exterior of the home ie. they lose heat to the outdoors, remember HX works both ways here too. Most of the log homes that we do a major thermal renovation on here are younger than 25 years & the owners just finally get tired of being uncomfortable in the home, water freezing anywhere near an outside wall, etc. Whatever system you decide to build with get as high an R value as you can, every dollar you save in energy use in your home will be available to compound over the life of the home, trust me it really adds up over time. When we do a net zero home we look at every system in the home as energy savings here also compound over time. Heat recovery ventilation as well as a host of others which I am sure you will run across in the research stage of you home planning. Btw a high R value home that is tight is easier to cool in the summer if A/C is in your plan. Re: your boiler & storage, sounds like you are looking for a heating system that won't consume a lot of your time, that means a larger boiler with ample storage so you don't have to tend your heating appliance all the time & put other things on hold to do so. Look at the Garn 2000 as well as others in that size with comparable storage. Tend to look away from units that posters report ongoing/continual problems with (lots in this catagory). Why buy a 20+ year headache? You want to use it, not feel used by it, right?

 

[Gooserider]

My take - I wouldn't want real logs, for the reasons FC mentioned - log siding outside and log paneling inside should be quite doable, and would give you the look while still being energy efficient...

I would be inclined to design towards around 2Kgal of storage, maybe even one Kgal if you can get the insulation good enough to make the heat loss reasonable. It takes about the same amount of wood in total to heat 1kgal two times, as it does to heat 2kgal, but you don't want your storage to be TO big, as you will always lose heat from the storage, and you are better off not having so much storage that you lose a lot of the heat you put in before you can use it. From what I've seen, it appears that sizing storage for 1-2 burns / day under "design day" conditions is about optimal. I could see you being very happy with either a Garn or a gasser w/ external storage, each has it's own advantages and disadvantages, but I think either would work well for you.

Insulate your tanks VERY well - yes radiation is nice in the winter, but they will also radiate in the summer, and you won't want that. Better to spend the extra money on plumbed in radiation that you can shut off...

Given a blank slate, I would try to design to have the tanks vertical - this does have slight advantages for better stratification, though not usually enough to justify "heroic" measures to go vertical on a retrofit install - however why not go for the best if starting from scratch? If doing solar, it might also be worth looking at 500 gallon tanks as the "unit size" and plumbing in such a way that your solar setup only has to heat 500g in the summer - since all you need at that point is DHW, 500g of storage should be plenty, and you are better off concentrating your solar output in bringing one tank to peak than in attempting to partially heat several.

Speaking of solar, I've been looking at it for a fairly long time, and I don't see much virtue in evac tube arrays, definitely not enough to justify the huge cost difference between tubes and glazed plates... IMHO a lot of the people pushing vac tubes use advertising that is seriously deceptive, if not downright fraudulent... Yes, a vac tube system will reach higher peak temps, but a flat plate will do as much, if not more total BTU's at a fraction of the cost... If ever we can figure out how to make the money work, I'll be putting a big flat plate array on our roof, doing a closed drainback configuration, but wouldn't even consider tubes.

Here is where I’m still not totally understanding how this whole process works. I do get that the point of storage is so that I can charge the water with heat that is stored in the tanks, but I’m not clear on the process. When you’re actually burning are you simply watching a temperature gauge to determine when to stop burning? Do you just burn for a set number of hours? The other big variable is the evacuated solar-I need to do some more research on what to expect in terms of BTUs in summer vs. winter, etc…but at the least I’m hoping to be able to rely heavily on it for hot water in the warmer months.

The idea is that your storage is mostly an "impedance match" between the house load and the optimal wood boiler performance.... Your house will (hopefully) want a fairly small number of BTU/hr, delivered at a pretty constant rate, as you replace the heat that is lost to the outdoors through the heat envelope... The "perfect" heater would be one that converted fuel into heat energy at exactly the same rate that your house lost energy, no matter how fast (in cold weather) or slowly (in shoulder season) it did so, as BTU's are best "stored" in the form of unburned fuel. However, a wood boiler will burn cleanest and most efficiently if it can burn a full bore, flat out maximum heat fire, with no idling... This kind of fire is going to put out WAY more heat while it is burning than your house needs, especially during better than design day conditions - even if a boiler is "perfectly" sized for design day, it will be over-sized all the rest of the time.... So we stuff the surplus heat into a storage tank, and let the fire in the boiler burn out, while we live off the stored heat until the tank has cooled to the point where it is no longer useful, and we repeat the cycle... Theory says the tank needs to be "big enough" to store the heat output of burning one load of wood, with no house load drawing on it. In practice, you almost always will be drawing at least some heat from the boiler / tank to heat the loads while the fire is burning, so if you want to fully charge the tank, you will want to burn more than one load at a time. If your tanks are "oversized" in respect to the boiler output, you would also need to burn more than one load to fully charge them. What this means in practice is that every system is different, but you will learn to look at the weather and the current tank temperature, and estimate how much wood you will need to burn in order to bring the tanks up to full temperature, and plan accordingly. What you end up doing is really not that different from when you are driving, and have to plan your gas station stops.... You know from the gauge about how many miles you have left, and what the tank will take for a fillup (you can also decide to just put a partial burn / fill) and then decide can I make it to the next town (or morning) or do I need to tank up now...

The advantage is that unlike a wood stove where you pretty much have to feed it on schedule to keep the temperature constant, with a boiler / storage setup you can "time shift" the burn to fit your schedule - i.e. look at the tank temperature and estimate how much "heating time" you have stored, and decide whether it works best for you to build a smaller fire now, or a larger fire later to refill the tank... The trick lies in sizing the entire system so that your personal schedule matches your needed firing schedule, without being so big that it becomes a major challenge to charge the tanks when they run low....

Gooserider

 

[101x81]

i agree with fc and goose,

do a good heat loss calculation with the coldest degree day in your area.
here in quebec, most designs are at 25btu/sq.ft

after you can size properly your boiler and storage.

in your case, for a new construction i will go with a garn in a building attached to the house including the wood storage with a direct door going in the house.

my dream

 

[Nofossil]

I noticed that somewhere in the calculations above, a design load (worst case) of 960,000 BTU/day got translated into an average load of 480,000 BTU/day, which is fine. However, that then got translated into 480,000 BTU/hr.

If the 960,000 BTU/hr number is right, then the average load would be about 40,000 BTU/hr. That does not take into account solar gain. In our case, the heat load is about 0 if the sun is shining and the outdoor temp is above 15 °F. In sizing storage, a reasonable goal would be 24 hours worth of stored heat at average load. The amount of stored energy depends on the minimum usable water temperature, the maximum readily attainable storage temperature, and the size of the tank.

A 1000 gallon pressurized tank heated to 180 degrees and drawn down to 120 degrees would provide 500,000 BTU.

I don't see where you're located, but getting a good heat loss calculation is a pretty important step.

 

[ewdudley]

I noticed that somewhere in the calculations above, a design load (worst case) of 960,000 BTU/day got translated into an average load of 480,000 BTU/day, which is fine. However, that then got translated into 480,000 BTU/hr.

If the 960,000 BTU/hr number is right, then the average load would be about 40,000 BTU/hr.
...

Thanks for straightening that one out nofossil.

I've found the GNU 'units' program very handy in keeping these kinds of calculations correct. It will not allow errors that come from slipping up with dimensional inconsistencies.

Wikipedia has a decent introduction to the program: http://en.wikipedia.org/wiki/Units_(software) [As is too often the case, the URL needs to be copied and pasted.]

And here's a good on-line version: http://www.unitsconvert.com/

It's very nice for stating what you know in terms of the most convenient units, and the program will do the conversions automatically into the units you would prefer for the answer.

For instance, what is the rate of flow in gallons per minute for water flowing through a 1.5 inch diameter (0.75 inch radius) pipe flowing at four feet per second?

Using the online version, we input:

You have: 0.75^2 inch^2 * pi * 4 feet / second
You want: gallon / minute

And it spits out:

0.75^2 inch^2 * pi * 4 feet / second = 22.03194848 [gallon / minute]

What is 40000 btu per hour expressed as kW?

You have 40000 btu / hour
You want: kW

And we get:

40000 btu / hour = 11.72284281 [kW]

Or heat storage of a 1000 gallon tank with a 60F delta T?

You have: 1000 gallon * (8.33 lb / gallon) * (1 btu / (lb * degF)) * (180 - 120) degF
You want: btu
You get: 1000 gallon * (8.33 lb / gallon) * (1 btu / (lb * degF)) * (180 - 120) degF = 499800 [btu]

 

[Badfish740]

A lot to think about-thanks! At least now I feel like I have an understanding of how it all works together and from there I can come up with a design that makes the most sense. Gooserider, as usual, your explanations were extremely helpful. Also thanks for the idea with regard to having a bank of 500 gallon tanks for DHW purposes in the summer. I never thought of it that way.

i agree with fc and goose,
do a good heat loss calculation with the coldest degree day in your area.
here in quebec, most designs are at 25btu/sq.ft
after you can size properly your boiler and storage.
in your case, for a new construction i will go with a garn in a building attached to the house including the wood storage with a direct door going in the house.
my dream

Here's my idea to that regard. As I said before the basement of the house will contain the garage/shop, a family room, and the boiler room. Next to the garage (totally separated by a wall/doors, etc...for safety reasons) will be the boiler room. From the outside it will appear as though it's a multi-car garage (from the left, one 8' x 10' door, then one 8' x 14' door) with two doors. The 8' x 14' will open to the garage. The 8' x 10' will open to the boiler room. This way, as I mentioned before, I can either put the stacks right outside (the entire area will be covered by a deck off the kitchen above) or simply make it so that I can dump tractor loads of wood right outside the door.

Finally, I will say that we're both stuck on the idea of a traditional log home. As I said, I grew up in one and my parents have been in it for 25 years. They have gas forced air heat and central air and have never had a complaint. I think a big factor in log home construction is milled logs vs. "natural" logs. My parents' logs are milled with the grooves on top and bottom. During stacking, lots of caulk and expansion joint were placed in each groove. Even after the logs shrunk and checked they never had a problem with cold walls, etc... I'm not saying that any of the concerns anyone has raised are not valid-we're certainly not going to get the R-value of SIPS or a similar type of construction, but I think as long as we follow best practices for log construction, make sure that windows and doors are airtight and insulated, and insulate the roof well, we'll have a home that isn't a huge energy waster.

 

[Frozen Canuck]

Just to give you a little more info as you seem to be set on a log const for your home. Average R value of most softwoods is R-1.41/inch, most hardwoods R-0.71/inch. If you choose 8" milled logs & use a softwood species you will probably have R-11 walls. If you are firm on the log house decision might I suggest that you oversize your boiler & storage to a very large degree as you will be sending millions of BTU's to the great outdoors on an annual basis. Kind of sheds some light on the thermal renovation of log homes I mentioned earlier. Not trying to scare you off your decision, just trying to inform you so you are prepared for what will be ahead. Unless of course you can source out some 45"-50" logs to build with. ;-) You see we all forget that when the pioneers built their log homes (that we all love the look of) the built small for a reason & it was not that there was a shortage of logs.

 

[pybyr]

Just to give you a little more info as you seem to be set on a log const for your home. Average R value of most softwoods is R-1.41/inch, most hardwoods R-0.71/inch. If you choose 8" milled logs & use a softwood species you will probably have R-11 walls. If you are firm on the log house decision might I suggest that you oversize your boiler & storage to a very large degree as you will be sending millions of BTU's to the great outdoors on an annual basis. Kind of sheds some light on the thermal renovation of log homes I mentioned earlier. Not trying to scare you off your decision, just trying to inform you so you are prepared for what will be ahead. Unless of course you can source out some 45"-50" logs to build with. ;-) You see we all forget that when the pioneers built their log homes (that we all love the look of) the built small for a reason & it was not that there was a shortage of logs.

Anyone ever done a double-log-layer house? I am thinking of some old brick houses I'm aware of (on an old military base) where there were actually two separate walls - inner and outer - with a void in between. I am sure that there were still some convective and radiant losses between the inner and outer brick walls walls, but at the same time, there must have been a lot less conductive heat loss. Especially with modern insulation in between an inner and outer course of logs, it seems as if you could have a fairly efficient building envelope.

 

[joecool85]

Just to give you a little more info as you seem to be set on a log const for your home. Average R value of most softwoods is R-1.41/inch, most hardwoods R-0.71/inch. If you choose 8" milled logs & use a softwood species you will probably have R-11 walls. If you are firm on the log house decision might I suggest that you oversize your boiler & storage to a very large degree as you will be sending millions of BTU's to the great outdoors on an annual basis. Kind of sheds some light on the thermal renovation of log homes I mentioned earlier. Not trying to scare you off your decision, just trying to inform you so you are prepared for what will be ahead. Unless of course you can source out some 45"-50" logs to build with. ;-) You see we all forget that when the pioneers built their log homes (that we all love the look of) the built small for a reason & it was not that there was a shortage of logs.

Anyone ever done a double-log-layer house? I am thinking of some old brick houses I'm aware of (on an old military base) where there were actually two separate walls - inner and outer - with a void in between. I am sure that there were still some convective and radiant losses between the inner and outer brick walls walls, but at the same time, there must have been a lot less conductive heat loss. Especially with modern insulation in between an inner and outer course of logs, it seems as if you could have a fairly efficient building envelope.

I'm sure you could do that, but it would be VERY expensive.

 

[Gooserider]

Just to give you a little more info as you seem to be set on a log const for your home. Average R value of most softwoods is R-1.41/inch, most hardwoods R-0.71/inch. If you choose 8" milled logs & use a softwood species you will probably have R-11 walls. If you are firm on the log house decision might I suggest that you oversize your boiler & storage to a very large degree as you will be sending millions of BTU's to the great outdoors on an annual basis. Kind of sheds some light on the thermal renovation of log homes I mentioned earlier. Not trying to scare you off your decision, just trying to inform you so you are prepared for what will be ahead. Unless of course you can source out some 45"-50" logs to build with. ;-) You see we all forget that when the pioneers built their log homes (that we all love the look of) the built small for a reason & it was not that there was a shortage of logs.

Anyone ever done a double-log-layer house? I am thinking of some old brick houses I'm aware of (on an old military base) where there were actually two separate walls - inner and outer - with a void in between. I am sure that there were still some convective and radiant losses between the inner and outer brick walls walls, but at the same time, there must have been a lot less conductive heat loss. Especially with modern insulation in between an inner and outer course of logs, it seems as if you could have a fairly efficient building envelope.

Double layer log houses would be a VERY expensive way to build, as it would require twice as many logs, and logs are already a very inefficient method of building - think how many 2x's you could make out of a log, and how much wall you could make from those boards, (admittedly with a lot of other stuff added to them) and then how many logs go into one wall... You could just about frame an entire stick built house with the lumber from one wall of a log construction house! If I had the option to build from scratch, I wouldn't go with logs, but if I really wanted the log "look" I'd consider splitting the logs in half and putting SIPs in between them... Although I will say that the traditional construction method that makes me really drool is timber frame. Assuming I ever get the money those dead Nigerian's keep offering me in my e-mail, I'd be really torn between doing something with that, or one of the Monolithic Dome style houses... I've always thought logs were more the mark of "field expedient" construction rather than deliberate engineering mastery....

Gooserider

 

[joecool85]

Just to give you a little more info as you seem to be set on a log const for your home. Average R value of most softwoods is R-1.41/inch, most hardwoods R-0.71/inch. If you choose 8" milled logs & use a softwood species you will probably have R-11 walls. If you are firm on the log house decision might I suggest that you oversize your boiler & storage to a very large degree as you will be sending millions of BTU's to the great outdoors on an annual basis. Kind of sheds some light on the thermal renovation of log homes I mentioned earlier. Not trying to scare you off your decision, just trying to inform you so you are prepared for what will be ahead. Unless of course you can source out some 45"-50" logs to build with. ;-) You see we all forget that when the pioneers built their log homes (that we all love the look of) the built small for a reason & it was not that there was a shortage of logs.

Anyone ever done a double-log-layer house? I am thinking of some old brick houses I'm aware of (on an old military base) where there were actually two separate walls - inner and outer - with a void in between. I am sure that there were still some convective and radiant losses between the inner and outer brick walls walls, but at the same time, there must have been a lot less conductive heat loss. Especially with modern insulation in between an inner and outer course of logs, it seems as if you could have a fairly efficient building envelope.

Double layer log houses would be a VERY expensive way to build, as it would require twice as many logs, and logs are already a very inefficient method of building - think how many 2x's you could make out of a log, and how much wall you could make from those boards, (admittedly with a lot of other stuff added to them) and then how many logs go into one wall... You could just about frame an entire stick built house with the lumber from one wall of a log construction house! If I had the option to build from scratch, I wouldn't go with logs, but if I really wanted the log "look" I'd consider splitting the logs in half and putting SIPs in between them... Although I will say that the traditional construction method that makes me really drool is timber frame. Assuming I ever get the money those dead Nigerian's keep offering me in my e-mail, I'd be really torn between doing something with that, or one of the Monolithic Dome style houses... I've always thought logs were more the mark of "field expedient" construction rather than deliberate engineering mastery....

Gooserider

I agree about timber framing being wicked cool, check this site out: http://www.housesandbarns.com/

Granted, most of his work are multi MILLION dollar homes, but it's fun to look.