Humidity Factor, workload

[Fred Sturm]

I'm going to throw a revised humidity factor at you, based on feedback
received both on and off list. (And don't worry, I'll compile all these
altered numbers in one document, probably by the end of May so we can
all chew on them for a while before convention).
For comparison:
> 2002 version
> 1.3 - Excellent: 15% maximum variance in relative humidity (or has
> humidity control unit installed and well-maintained)
> 1.0 - Good: 30% maximum variance in relative humidity.
> 0.7 - Fair: 50% maximum variance in relative humidity
> 0.4 - Poor: Greater than 50% maximum variance in relative humidity

revised version
1.2 - Excellent: 10% maximum variance in relative humidity (or has
complete humidity control unit installed and well-maintained, with back
covers on uprights, string and bottom covers on grands)
1.0 - Good: 25% maximum variance in relative humidity (or has complete
humidity control unit installed and well-maintained)
0.8 - Fair: 40% maximum variance in relative humidity
0.6 - Poor: 60% maximum variance in relative humidity
0.4 - Very Poor: variance in excess of 60%

Notes with respect to piano installed humidity control systems:
1) It is likely that a complete system without back/bottom/string covers
can bring a piano into the Excellent category if the variance in the
building is no more than 30%. Some discretion should be used in
assigning categories.
2) "Half systems" (a humidistat with a dehumidifying unit) can help in
situations where ambiant humidity rises above 50% on a regular seasonal
basis. In general, such a system might improve tuning stability by one
step. Complete systems are strongly recommended wherever possible under
most conditions where humidity varies more than 15%.
3) There is a certain amount of maintenance time involved for complete
systems. Most of this maintenance is unskilled, and can be accomplished
by, say, a work study student, thereby freeing up technician time.
4) Systems must have the appropriate wattage and position of components,
as recommended by the manufacturer, to produce the predicted level of
effectiveness.

General note with respect to humidity control: 
	Variance in humidity is by far the largest factor in maintaining tuning
stability, and it has structural effects on the long term integrity of
every piano (particularly soundboards and pinblocks). The effect of
humidity variance is amplified many-fold in modern institutional
environments, due to code requirements for HVAC systems. Modern HVAC
systems exchange the entire volume of air in the building many times a
day. As a result, air is in constant motion (leading to more rapid
movement of ambiant humidity to and from wood), and changes in outside
humidity are reflected almost instantly within buildings.
	Hence, the importance of humidity control to the quality of piano
service cannot be overemphasized. In all likelihood, the multipliers for
"fair" through "very poor" are very conservative, in terms of showing
the effect of large scale humidity change on overall tuning quality and
general long term need for rebuilding and replacement of instuments.

As always, comments and suggestions welcomed and solicited.
Regards,
Fred Sturm
University of New Mexico