Retrofitting an enthalpy exchanger yourself - experience reports?

Hello and good morning to the forum! After long lurking, I have decided to register because I would like to query collected forum knowledge :). A little about me/us: we moved into our house (prefabricated house, timber frame construction) in 2023. So far, the building technology (Viessmann split heat pump and Zehnder Comfoair E 350) worked smoothly over the winter, unfortunately, like many others, we have a problem with too low relative humidity. An inquiry at Zehnder revealed that replacing the standard heat exchanger with the appropriate enthalpy exchanger (we were given the article number) is feasible. Now to my concern: Has anyone already done this with this ventilation system? I only find instructions for the Comfoair Q350 model. I also have an offer from a technician, which amounts to about 1750 euros. That seems quite a lot to me (2 hours of technician time included? Including exchanger). I have already found out that the part costs around +/- 1000 euros ;) but the installation did not seem that complicated to me. But before we mess around here, I’d rather ask first. And if someone has already done this themselves, it would be great if you could share your experiences – was there a noticeable improvement? And one point that still concerns me: The E350 has no pre-heating coil. The heat exchanger from Zehnder is only described for use down to -6 °C outside temperature... what happens if it gets colder? Does the ventilation have to be turned off then so that nothing gets damaged? Thanks in advance for reading, I would be happy if someone can say something about this. Best regards Bubo

Unplug the unit, remove the front panel (4-6 screws), pull out the old WT on the belt, slide in the enthalpy exchanger, put the front panel back on, done. In between, you can vacuum once more. Takes about 10 minutes.

Usually, no preheating register is needed.

Preheating registers are generally not needed.

In winter when it’s cold, however, they are rather needed. My Vaillant I believe goes into "frost protection" mode at -4°C. That means it turns off. But the manual should state how the respective manufacturer handles it. If it is -6°C here, I would assume the system simply switches itself off and won’t turn on again no matter how much you try. Only again when it gets warm.

I believe the average temperature must have been -4°C in the last 24 hours. Otherwise, my Vaillant would have been off repeatedly for a week this winter, but it was only off for two days.

Thanks to you too for the info :). I think we will get one of those and try to install it ourselves.

Unplug the unit, remove the front panel (4-6 screws), pull out the old WT on the belt, slide in the enthalpy exchanger, put the front panel back on, done. You can vacuum inside once more in between. Takes about 10 minutes.

Usually no preheating coil is needed.

This is basically the procedure. But I would still do it myself only after the warranty has expired or make sure, if the main unit unexpectedly breaks down, to reinstall the old block before the technician arrives in order not to jeopardize the warranty.