[pianotech] Protection from underfloor heating

[Jim Ialeggio]

Joseph Giandalone wrote:

<Now, Why is it that in my long term observation here in mid-New 
England, pianos in underfloor-heated homes have the most extreme 
symptoms of seasonal humidity variation?

Ok...Lets get some info. How old are these ranch houses? How drafty are 
they, ie how much exterior air is brought in, heated, then "exhaled", as 
new cold, bone dry NE air is brought in?  Are the homes older 
inexpensive construction? Your observations seem to be targeting a 
particular subset of home construction, slab-on-grade. So I'd like to 
confirm the specifics of what the moisture sources are before drawing 
any large brush conclusions.

In addition, your post refers to seasonal fluctuation. So I'd like to 
focus on that. Would you specify what you mean by this. To me "seasonal 
fluctuation" means a 1 time change at the beginning or end of the 
heating season. Is that what you mean, or do you mean instability during 
the entire heating season?

Most of the slab-on-grade ranches in MA that I am familiar with are 
bottom of the line entry homes, with older, inexpensive construction. 
These slab-on-grade homes are generally older, cheap construction, with 
no moisture barrier between grade and slab, and no insulation at the 
perimeter of the slab. A slab with no moisture barrier is very often 
creating a very moist slab in summer. This slab adds a huge amount of 
moisture to the building interior during the summer, AC or not, even if 
there is no apparent wetness on the slab. The most recent building codes 
are very picky about slab insulation and moisture barriers these days, 
so I would differentiate between older and newer construction.

Moist summer slab conditions, in addition to normal summer high RH%, 
means the swing to heating season has to first cook out that moisture 
from the slab. That cooked moisture has to go somewhere, and the 
interior of the home presents the path of least resistance...so it goes 
to the interior. This most likely creates an RH spike at the beginning 
of the heat season, followed by a significant RH decrease while the slab 
is in heating mode. In addition, in a drafty building, the decrease in 
RH will continue to aggressively drop of a high air change rate.

So are you referring to a single fluctuation at the beinning and/or end 
of the heating season, on general instability during the heating season?

Jim Ialeggio

Jim Ialeggio	
jim at grandpianosolutions.com
978 425-9026
Shirley Center, MA