Dendrobium question

[Hatteras]

I have three dendrobiums planted togethor in a large pot, in mostly bark. THey have been doing great until today. Two plants are burana white and the third is burana pink stripe. The first white one started blooming sometime in October, the second in November and the pink just finished opening it's last bud this past weekend.

Today, when I came home, I noticed all the flowers look like they are starting to wilt, every one of them, even the last ones to open.

The only change they have been exposed to is we have been using our unvented propane heater. Could this cause a problem, it shouldn't be any worse than a gas stove or oven. The plant looks healthy otherwise. The humidity is low but they have been getting misted a couple of times a day. Any ideas ?