Well ... they are going to say that - so if the soundboard warps or developes pressure ridges .. it is easy for any piano manufacturer to say the problem is that the humidity has not been properly controlled ... and therefore not their problem.
Certainly it the humidity of the room is controlled ... then the Dampp Chaser system is not needed.... however I suspect that in Europe - where air conditioning is not common; we have the situation in summer that dehumidifying the whole room (with open windows..) is not practical.... thus the DC system at least should help.

I have had my DC for about a month - the RH inside the piano varies between 53 and 57% ... while the room varies between 40 and 50%... I want to try to do the best thing for the piano - thus I have installed a DC.... maybe this is a waste of money - but at least I know that I am doing the best thing possible for the piano

If it's good enough for my magnificent 1937 Kurtzmann, it's good enough for a Steinway.

Yes, that was why I went with the DC -- because I have no way of controlling the room humidity (no AC, and open windows in the summer). Also, I have an upright, for which the DC is supposedly more effective (compared to in a grand).

The nice thing about having a dampp chaser on an upright is that the cabinet is so enclosed that the internal humidity can really be controlled. I had a dampp chaser on my upright (before I traded up to a grand) and I *really* noticed an improvement in tuning stability. The improvement is present with my grand but not to such a noticeable degree.

I install the fabric undercover on grands. It makes a big difference to help keep air flow isolated under the piano, and yet it's an open-weave fabric that breathes.

--Cy--

Cy, is it true that the tension resonator on a Mason & Hamlin makes the fabric undercover a bad idea?

Not in my experience. The undercover helps the air under the soundboard stay more constant than not. The constant cycling of the system keeps air moving. The undercover cloth has very large holes, like speaker cloth; it's very breathable.

--Cy--

From what I've read, the issue with the undercover on a Mason is more of an aesthetic problem than anything else. The tension resonator forces the undercover to have to hang lower I think.

Whole house humidifiers are powerful, not expensive, and can be run at the silent setting. Little noise. I use a Bemis humidifier, and it works pretty well. Yes, one has to treat the water and clean the unit often and replace the wick. However, the Dampp Chaser unit requires the same maintenance (changing wick, cleaning) in order to remain sanitary. That's the nature of humidifiers.

I also have a Soleus Dehumidifier that is extremely silent. It has only 280 watts, so it isn't a powerful beast, but it does the job. In the summer, we use central air anyway, as it gets to hot here in Southern Ohio, and that very effectively reduces the humidity at the same time.

While the D-C seems to be a great unit, there is nothing better than whole-room control. Not only your piano feels good in this case, but you, the player do, too. That's something the D-C cannot provide, obviously.

I have one concern about the D-C, though. The heating rod does not actually remove moisture from the air (as does a regular dehumidifier/airconditioner), but heats the ambient air to reduce relative humidity. If you use that feature in the summer in order to save on airconditioning cost, your house will already be pretty hot, and the heating rod will furthermore heat up the soundboard.
Say, your house is already at 80 deg. F and the RH is 70% inside after rain, then in order to get the RH down to 50%, the rod will heat the soundboard up to 90 deg F or even higher. In the fall this is no concern to me. But during the summer, I just don't feel comfortable with adding heat to soundboard wood. I'd rather remove moisture in the first place so that I don't have to heat the ambient air.

While the air may be heated by the rod, that does not necessarily mean that the soundboard comes to the same temperature. It has a lot of mass. I typically put no more than 100 watts of heating rods in a piano, so it's not a lot of heat. And recall that the system continuously cycles between wet and dry; heat doesn't build up.

I agree with you about whole-house control, as I've said before. The purpose of the system is to protect the small, critical environment of the piano when it is in harsh ambient conditions. My response to the many "what if" questions about the system is simply that it has has proved its success over many years in many pianos, including my own. And I'm picky!

--Cy--

Oh, you're right, depending on the size of the piano, and where you have to juggle the location of the water tank or tanks. Actually most pianos look better from underneath with the undercover, especially on stage, even if parts of it hang below the rim. The undercover is black.

A side benefit is if you have toddlers or pets, it keeps them from messing with anything from underneath, and possibly harming themselves or the piano.

--Cy--

I have lived in or near Toronto all my life and quite honestly the drastic swings in humidity and temperature will most certainly harm your piano over time. You won't see it happen as it is a slow death kind of like smoking cigarettes, and then its too late. Properly installed you would have no worries with a Dampp-Chaser and actaully it will extend the life of the piano in Toronto especially a drafty home with no A/C.