Forum / THE MAIN WALL / Heat loss for logs?

## Heat loss for logs? (17 Posts)

• ### Heat loss for logs?

Completed a heat loss calculation using the Slant Fin software. The only thing that was noticeably missing for me to use doing the calculation for my house was the heat loss factor for logs. I live in a log home with the first floor being 6 inch logs and the second floor being 2x6 construction. I searched multiple sites and found "U factors" for logs. I entered .111 (that's point, 1-1-1) for the logs. Does that sound right? Anyone with experience doing calculations for log homes? If the factor is way off, it could significantly change the final numbers.
• ### R value

The average r value is about the same as it would be for the thickness of bat insulation. In other words, a 6 inch log has an R value of R-19. This assumes the chinking is tight.
Bob Boan

You can choose to do what you want, but you cannot choose the consequences.
• ### Yeah

Chinking is tight is just the beginning. Full log homes are an ever changing envelope over years. If not maintained properly they turn into a submarine with screen doors for hatches.
• ### R-19

Bob,
Where do you get r-19?
I was coming up with about 1.4 per inch for softwood. Which was pretty close to the u-.111 he had.
The air infiltration is a mystery unless you do a blower door. In some climates the thermal mass may come into play.
Carl
• ### Say R what??

R-19?

I'd heartily disagree with that statement.

Wood has an average R value of roughly 1 to 1.1 per inch thickness. So if the log is 6" thick, then its average thickness is 3". (0" for round logs at each junction, 6" thick in the middle, so 0 +6 / 2 = 3) hence, Id say R value = 3.

And if you ask the log home manufacturers, they will tell you that the R value doesn't matter... "It's the MASS effect of the logs that really counts..." Yeah, right. And who should I cal when the heating system doesn't work right when it gets cold outside???

As for infiltration, guess high, because if the chinking is not properly maintained, and it rarely is, then you can expect it to rise over time.

ME
It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.

That was the correct number that I had confused in my aging mind: R value of 1 per inch.
Bob Boan

You can choose to do what you want, but you cannot choose the consequences.
• ### Basic rule of dumb

Basic rule of thumb that allows for settling and wood movement. Off the top of my head, I can't remember the source.

We do a lot of log homes and that was the number we would input if the program didn't have a factor for logs.
Bob Boan

You can choose to do what you want, but you cannot choose the consequences.
• ### Zman

is good . Pine is 1.3 R per inch . But it can cut both ways being a thermal bridge .
You didn't get what you didn't pay for and it will never be what you thought it would
• ### Mark is being generous

you would be likely moneyy in the bank estimating logs at .5 per inch because "We dont need combustion air with the air infiltration through the cracks in the logs ...lol
Ok ..Ok..Ok... three sided , Milled , Turned< Kiln dried? pegged , screwed , Spiked , lock joints , caulked, Rounds tapered , maybe i know too much about these logs ...ok forget i said anything..
*~//: )
seriously , sight unseen . 5
not 5 ,
not 50 ,
point five.
• ### What I would like to see...

is a shot from a thermal imaging camera on a cold night
• ### Log description

The logs are "D" shaped...that is, they are flat on the interior of the house and rounded on the outside. The top and bottom of each log is flat with two "tongue and groove" deals running the length of each log on each side. At the thickest spot the log is 6" thick down to 5" at the top and bottom of the curve. The house is pretty tight (we do not feel the wind through the walls) but I am planning to clean, chink and stain the exterior next summer.

I have also read about "thermal mass" versus the R-factor of the logs, but have not really searched for an explicit explanation. I have lived in NH for years and have experienced some cold, windy nights and the house has been comfortable with only the Jotul burning.

Can anyone else confirm the .111 heat loss factor?

I attached a photo from a couple of winters ago.

Thanks for the responses.
This post was edited by an admin on October 18, 2013 5:29 AM.
• ### 3 sided ...

k , 3 sided logs , over the windows and doors do you have hefty headers made from 4X6 or an insulated space,or simply notch outs in the logs? reason i ask that is not all 3 sided builders build the same way.
do your logs have bark on them ?
seasoned logs are slightly different from kiln dried , because moisture content messes with trying to nail down r values in materials as well. some of the siding we have these days might be said to be of higher insulative value . some log construction i can hand you a cup of coffee thru the wall to the Yard while we ponder further and plumb the depths on the subject.
my thinking is it is somewhat like 5/8 ths T-1-11 with 3 sided though you have a chance to "build out" interior partitions that have flat surfaces to install kitchen cabinets which you may a well wire ,insulate ,plumb a vent for the sink insulate and vapor barrier ,sheet rock, tape and prime and tile cabinet counter tops and back splash. then just treat the log portion as any other wood siding basically.
i plate the deck and top course of 3 sided with 3X6 some guys build like a pony wall about 16 " high to mount electrical boxes and install convective baseboard with copper tube elements that way the surface is flat and they can count upon the wall having a known r value at that height of the wall off the deck.
logs pose a bit of a challenge to plumb and we do not put plumbing IN outside walls although venting is permissible. i roll this by you to gain my perspective on why i consider the r value to be so low. i hope that it helps. i am off to spin in the water side of the super store off an MPO and am giving the grunfoss recirc a go ,it has a niffty temp by-pass located under a sink. The branches to the upstairs bath rooms is just after that branch within inches. it has a timer and that seems like a fairly coherent idea . : )sorry i digress of into things from time to time , like me though you should not be overly optimistic , ... there are probably hidden variables that are overlooked that have to be taken into account . logs though are like siding, ... cosmetic not much r value.

There are logs over the windows, not 2 x 6 construction...
No bark on the logs...

We wondered about the logs and R value...but, it seems to me that the thermal mass plays an important part in all of this. I remember a brick wall at a house in Denver that would get heated up by the setting sun and in would throw heat into the house all night. The house actually feels (to me) to be pretty efficient. The Jotul has heated the house plenty over the last couple of winters...even on cold night we sometimes have to open a window or two to keep the house comfortable...

.111 seems reasonable to me, but again, I am no expert.

Is heat loss factor the same as U Factor?
• ### Thermal mass and thermal bridging

Rich kinda grazed it in his post.

When trying to create a super insulated home thermal bridging is avoided at all costs this would be the studs in the exterior wall.

Thermal mass is something that can absorb, and store energy then release it preferably when you need it most.

So somewhere with in the log is the Mason-Dixon Line where thermal bridging stops, and thermal mass starts. This all depends on the difference, or delta t of the inside , and out side temperature. The moisture content of the logs which will vary through out the seasons depending on how the logs have been treated, or finished.

So what I' m saying is the r value is a floater. You have what you have, but favor the low side of r value per inch.. Infiltration is a log homes biggest enemy. They are near impossible to make a tight envelope as with other wall assemblies. So favor the high side of infiltration. A blower dor test tells loads, but it may be a different result year after year.
• ### Good envelope...

It seems that we have a pretty good envelope with our logs. There is one corner where two walls and the roof meet that will be getting some attention, but other that that it is pretty good. I have rented places and been to homes that the blowing wind will move the curtains and you can feel the cold seep through the walls. The builder must have done a solid job with the seems and sealing. We will be updating the seem sealing and the exterior staining next summer so it should get even better. My guess is that if the house got very cold (the boiler went out) and we had to heat the house back up, it would take a very long time due to the the logs being so dense. We would need to "push" the cold back out...
• ### Now theres a name I've not seen in a coons age...

I thought you'd fallen off the face of the Earth Weezy :)

Good to see you're verbiage.

ME
It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
• ### Ditto

To the weezbo!

Thought a bear got his internet connection.
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