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Hi all,


First post here and I must say what a great community this appears to be - I wish I had found this forum when I started my self build in 2020 rather than now when I'm a few months off moving in! Some of the posts and level of detail in them are absolutely brilliant!


On topic however, I have a Domus HRXD MVHR unit I purchased from BPC back in April last year. I fitted it and plumbed it up, but the time has only come to get it going this week as we finally have heating on!


I have balanced the system according to the figure provided by BPC with a calibrated anemometer. The system has been on for 24 hours, and my exhaust temperature is reading about 10deg C. According to the manual, this should be reading the temp of the air coming back to the unit from the extraction side. The 12deg C in the attached photo is the intake temp. from outside, which I think is possibly being a bit generous with it being the start of Feb! Room temps are all set at 17deg C, and all rooms are genuinely at this temp.


I have measured the air coming from the supply ducts with a calibrated thermometer and it is reading 12-14degC.

Is there typically a longish heat up time for these systems, or do I potentially have an issue? I have contacted BPC and waiting to hear back from the technical team, but thought it might be no harm to check out some real world experiences here.


Any feedback is much appreciated, especially from those of you with a Domus unit!






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The terminology can be tricky here. Extract and exhaust are opposite sides of the heat exchanger. 


Your supply will always lag the room temperature a bit (in heating climates) as the heat exchanger is less than 100% efficient. 


Beware the internal heat exchanger temp probe may not be too accurate either. Perhaps verify with an external thermometer. 

Edited by Iceverge
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Thanks Iceverge.


I would also have believed that 'exhaust temp' would have referred to the temperature of the air leaving the unit being expelled outside, after the heat exchanger. I think what's throwing me is the depiction of 21degC in the manual illustration, as surely you wouldn't' have 21degC leaving to atmosphere? Your room temps would have to be sky high at that stage surely?


My humidity levels are also quite high at 79%, but I'm putting this down to the length of time the unit has sat idle before being switched on and commissioned. 

I suppose the best thing to do is let it run its course in low mode and monitor my supply temps as I gradually increase the temperatures in the rooms.


The thought of paying to heat the air, and then paying to have it expelled to atmosphere is giving me nightmares ?

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The heat recover % figures quoted are lab based, controlled conditions, best case figures. In reality you'll never see 90% energy recovery. But you also have to bear in mind that the primary job of an MVHR is to maintain good air quality and to recover some of that lost energy. Of you had trickle ventilation or mechanical extractors, you'd have poorer air quality (variable) and more heat loss.


Your humidity is probably high because your Hosur is still drying out. Our last screed pour was end of November and we.have dehumidifiers running 24x7 and humidity sits around 70-75%.

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