Log Cabin Heat load design

Wayco Wayne_2

I;ve been asked to help design an old log cabin's heating and cooling system. It may be 200 years old but has been updated with drywall on the inside and siding on the outside. There is also a kitchen addition on the back where they left the beautiful old cabin wall exposed. Very nice. I've read that the R-value of wood can be anywhere from 1 to 1.5 per inch, but that the excellent thermal mass properties of wood should also be considered. I own Wrightsoft heat load software and am wondering how to accurately simulate the R-value plus the thermal mass of these walls. Should I go the the masonry screens for wall materials? Inquiring minds want to know. Thanks for your shared knowlege and opinions in advance.

Zman

What climate?

Where are you. I believe the "mass" of the logs is only a factor on shoulder season days. The mass will help when the outdoor temp is warmer than your indoor temp during the day and colder at night. Kind of an averaging. I do not believe it is a factor on your coldest design day.

I would use 1R per inch and a fairly high infiltration rate. I could stand corrected on this. 

SWC

R 1.5 per inch

Hi Wayne



The last one I did was a new 6" tongue and groove white pine log.



Wirsbo/Uponor did the tubing layout and heat loss based on the R 1.5 per inch, so R 9 for this assembly.



The heating system has worked flawlessly. Absolute comfort. Utterly silent and invisible.



Forget about the thermal mass issue, far more important to evaluate infiltration as log homes are notoriously leaky sieves. A blower door test would be essential for something this old even with the additional layers on it.



HTH



Stephen C

Wayco Wayne_2

Thanks guys

It's an interesting cabin. When we got out to the job site it was already a fairly hot day. We were sitting in the kitchen chatting, eating muffins and sipping tea. The Kitchen is the added space with stick framing, insulation and drywall. When we walked into the living room, which is the original cabin you could feel a drop in temperature, which I attributed to the thermal mass of the logs. There's probably a nice flywheel affect where the logs absorb the heat all day long and then transfer it in the evening. I think I might play with using a masonry wall construction and compare it to more normal stick framing and an assigned R value, just to see what the difference would be with the thermal mass issue.