<html> <body> Greg, A wool-felt string-cover alone will protect the strings against rust.  That has been well established by grand pianos in (ocean front) beach-houses with string-covers that have brand-new looking interiors after decades as compared to their unprotected neighbors.  Wool has the natural capacity to buffer humidity and any sort of cover probably prevents condensation.  This is the first accessory I recommend. Add a DC system and undercover and you will then reduce the sound-board oscillation to negligible resulting in tunings that last until your next service.  You get to do a concert level tuning each time you return to the instrument.  I have two Sauters on the floor here.  They are fine pianos which are much more stabile than average.  One has a DC with undercover and the other has DC with undercover and string-cover.  The one without the string-cover is noticeably (to me) affected by the weather.  The other one hasn't been tuned in a coon's age and still has a solid tuning on it. YMMV Andrew Anderson At 07:48 AM 2/18/2008, you wrote: <blockquote type=cite class=cite cite="">Patrick, I completely agree. My post, however, was dealing with the prevention of oxidation and/or rust not the promotion of it. A DC unit in a grand won’t do much to prevent it. One could argue that the string cover will retain some of the DC unit’s effects but it seems to me that little is afforded here since the only pass through from the underside of the soundboard to the top side are through the nose bolt holes. I doubt that the amount of air passing through these holes in the board are enough to effect much of a change topside.   Greg Newell Greg's Piano Forté <a href="http://www.gregspianoforte.com/" eudora="autourl"> www.gregspianoforte.com</a> 216-226-3791 (office) 216-470-8634 (mobile)   From: pianotech-bounces@ptg.org [<a href="mailto:pianotech-bounces@ptg.org" eudora="autourl"> mailto:pianotech-bounces@ptg.org</a>] On Behalf Of J Patrick Draine Sent: Monday, February 18, 2008 7:59 AM To: Pianotech List Subject: Re: Whole room humidity control better than Dampp Chaser. ( Right?)   Greg, My (anecdotal) observation is that a standard DC installation on a grand will not promote oxidation of steel strings and copper windings, while usage of a room humidifier often will result in rapid accumulation of rust & dull brown copper windings. If customers are inclined to use a room humidifier I urge them to keep the lid closed when not in use. Customers sometimes blast the mist right into the piano -- sigh -- they think they're "doing the right thing."   Patrick Draine   On Feb 18, 2008 12:36 AM, Greg Newell <<a href="mailto:gnewell@ameritech.net">gnewell@ameritech.net</a>> wrote:  I believe that it's even a bit of a stretch to claim that it helps to prevent rusty strings in a grand as the pictures would seems to indicate. </blockquote></body> </html>