A year ago I bought a 1916 Steinway O and I had a technician install a dampp chaser. He said the undercover is mainly there to hide the system from view and asked me if I really wanted it. As I did not think the undercover would be a visual improvement I declined. But now I am wondering. We have had some bad swings in humidity here with sustained highs in the last months, and the grand is up by around 15 cent. Not that I can really hear this, what I hear is that not all strings are up equally much (the 15 c reading is from a small tuning device, I don't know how reliable it is).

I'm getting it tuned next week and wonder if installing the undercover would make a noticeable difference.

It's not necessary, but should help keep the piano more stable. Keeping the lid completely closed when piano is not in use will also help with stability.

This is incorrect. While the undercover does hide the system from view, its main purpose is to create a stable environment, which in turn will keep the tuning much more stable. A 1917 Steinway O sits in my living room. Once the undercover was made available, I installed it and the tuning stability improved drastically. I also keep the lid fully closed when the piano is not in use.

There are also new types of undercovers available, which are made specifically for each type of piano. They are easier to install than the standard undercover, and make servicing the system much easier.

It's generally the middle of the piano that will change pitch the most - the octave below E4. Some Clients perceive this as "the bass is out of tune", when in fact, it's the tenor that has changed relative to the bass.

The undercover creates a "micro environment" under the piano, which keeps the soundboard more stable, thus the tuning is more stable. You can also consider a piano cover - which I recommend for schools and churches.

In Sweden, I can't imagine your piano is sharp, now, as you are heading into winter, and your heat must be on, so the middle of the piano should be flat, not sharp - depending on the time of year last tuned.

Agreed. Not having an undercover is a bit like trying to keep a house climate controlled with all the windows and door open. At very least, not having an undercover reduces the effect of the DC system significantly.

Thanks all, it seems installing it is a good idea. Problem is I seem to have misplaced it. Eric, how can I order these new types of undercover? Can I install them myself or should the technician do it?

The new type of undercover is the Barnes EasyInstall Dampp-Chaser Undercover, and is endorsed by Dampp-Chaser. Now sure about Sweden, but technicians in the U.S. can order them from their Dampp-Chaser product supplier.