Besides ordering from zehnder, are there any other filters available that will fit their units? It’s not a question of price but more so of long term availability. If they go out of business will I still be able to source filters? I haven’t had the chance to pull one out of the packaging and go down to the local HVAC supply house with a tale measure.

I’m an electrician and not an HVAC contractor so I don’t understand if these are a common size/shape/build or totally proprietary.