I have two of these units fitted in our small 2 bedroom apartment. I bought them on the advice of the team at iSells, who were brilliant. We are limited on space as the fabric of our building is reinforced concrete & whilst what I specified myself as an amateur may well have worked, these units were perfect.
I fitted them and the ducting myself but my first electrician couldn't cope with connection (he was the problem, not the units) so again with the help of the iSells team I got in touch with the Vent-Axia* service engineer for Cornwall who was also beyond helpful in connecting & endorsing the decision to buy these. They are in permanent use & keep the damp & mould at bay a treat - a huge problem when living next to a Cornish Beach. (After a complete refurbishment of our home the electricians involved had no problem disconnecting & reconnecting these units without incident.)
Sadly I am back on the iSells site buying a replacement as the motor on one, connected to our bathroom so the most heavily used, burnt out today. Again, that's not a criticism of the unit - it had rusted away - again a factor of living in a damp salty atmosphere. (We cannot have anything metal e.g. wire coat hangers, as they almost instantly rust.)
I recommend these to the owners of the many neighbouring apartments & iSells are continuously helpful & knowledgeable when needed, so I am a repeat customer.
I'll keep on buying these devices as whilst I don't understand how these work, they do.
Top Tip - Take care of the heat exchanging filter units & wash them regularly as recommended. They are very expensive to replace.
* There is an identical Vent-Axia model - this is made in the same factory but unbranded.