Hi,

I have a Vent-Axia MVHR and although I have grown to love MVHR I have noticed it does have tendency to run continuously on boast on damp rainy days like today. has anyone else noticed this and thought of possible solutions given that they can be loud on boost? Do more expensive brands avoid this some how? I am not sure if the damp air is through open windows being summer time or via damp intake air from outside.

I have a Vent Axis Kinetic. I've got a smart home system and humidity sensors in the bathrooms which set the MVHR to boost above a threshold level using the volt free switches. As you've found there are days when atmospheric humidity is above the threshold you'd normally want your MVHR to boost at - I now have a 'high humidity day' switch in the smart home interface that raises the threshold for 12 hours.

I'm pretty sure my unit also has an inbuilt humidistat but I can't remember if I deactivated it or not but it doesn't seem to give me issues (or the controls from the smart home system over ride it). Ideally you could do with a switch to change the settings temporarily but you might have to do it permeantely -
https://www.vent-axia.com/sites/default/files/439817_ad.pdf

The manual says

Internal Humidity Sensor Screen (if fitted)
The Humidity Sensor screen enables you to switch the Sensor On and adjust the trigger point between 50% and 90%. (default setting 70%).

Humidity Rapid-Rise (RH RR) Overrun
The Sentinel kinetic does not just look for relative humidity levels above a set point, which can be unreliable in products that extract from multiple rooms, but it also looks for rapid increase in relative humidity typically generated by such activities as showering or cooking. This feature allows an overrun of up to 60
minutes from a “Rapid rise” of humidity.

Posted By: RobLI can imagine it's not obvious what to do on a hot humid day - the faster you run the unit, the more humidity it will raise the house to.

I imagine it's something like the same logic as a summer bypass. The system clearly needs two humidity sensors, one sensing internal humidity and the other external humidity, as well as temperature sensors. Then it can calculate the absolute or specific humidity (not sure which) and decide whether it should be increasing or decreasing fan speed. And two control settings - an upper limit and a lower one. But I doubt most units are kitted out that way.

In my HR25-H the threshold is set by a small trim-pot, with a rod fitted to make adjustment possible without tools (though you have to unscrew the faceplate to get that far).

Rgds

Damon