Has anyone installed a Double Flux VMC?
The Double Flux variants remove heat from the outgoing stale air to warm the incoming air and push the warm air back into other rooms so all of the heat in the house is not sucked out.
Does anyone have experience of such a system ? I am looking to install one shortly and still looking to understand them fully before ordering one plus all of the ducting etc.
Yes, I’ve installed a few, & have one myself.
The biggest problem is finding/making routes for the ducts, even if you’re doing a new build.
Insulated 160mm duct is quite tubby….
We are currently in the process of adding doublage to all rooms so have a cavity to work with. We can make a larger cavity if needed for the bigger ducts.
I trust as you have one you consider them to be worthwhile?
We have fitted them in seven of our apartments and the two cottages, but we were working from scratch, so hiding the ducting was not as difficult as it could have been. We have received reports from our tenants that they are very happy with how the system works and what it saves them in additional heating.
In our opinion it is a worthwhile investment.
That’s good, but you might need to consider lowering ceilings too.
Yes, I do.
AFAIR they are now obligatory for new builds or, rather, in order to achieve the right energy rating they are necessary.
What about in summer, where the external temperature may be much higher than the internal temperature. With a VMC-A you’re drawing air in from the outside, heating the house up, but with a VMC-B you’re drawing air in from the outside and recovering heat, making the house even hotter. Is this the case, or am I missing something ?
I have a VMC-A and it would be fairly easy for me to upgrade as I have a single storey house with a fully open attic space and suspended ceiling and half the pipework is already there.
Not sure what I have on this new build but there are two of those little turret caps on the roof, one either side and the roof space that we have seen via camera has lots of big silver tubes running everywhere to a box in the middle. The vents in the ceiling that come on automatically when you approach them are over all water sources and in the utility room
If you have two then it’ll be a VMC double flux (VMC-B). You should have vents drawing air out of rooms that have water in them and vents replacing the air in other rooms. You should not have any air vents in the windows.
Yes doing this on the ground floor - currently 3.7m sp plenty of height to play with.
Some seem to have summer mode to take account of this and can suck in cool air.
I’ve gone off the idea of VMCs TBH.
When we bought we were advised to leave them running to ensure ventilation and that was OK for a good few years. Well apart from the power consumption - 2/300W builds up rather a lot when it’s 24/7
But with the long absences due to Covid we started to have quite a serious mould problem - which persisted even when we were making more frequent visits.
Until I turned the VMC off that is - since then, minimal issues.
It’s Brittany. I think a lot of the time they just bring damp air into the house.
Thats it then. Thanks for clearing that up for me so I know now. Have to say it did not get hot indoors during the high summer temps here at all and I did not have the clim going all the time either so it must work and even this morning with the temp dipping to 10°C, it was still 20°C in the house with no sort of heating on anywhere.
I had mold on most things in Brittany even with heating on and a big stove going every day in winter, double glazing and ventilation in WC and bathroom and windows and veluxes open all the time in summer. Its just par for the course living there and evryone around me suffered the same with the old granite, no foundations longères. I no longer suffer with aches and pains down here in the warm now as well!
Isn’t that quite high for a VMC ? Ours is I think only about 50W but it’s a VMC-A.
To be fair that’s the VMC plus the standby for the heating and it’s more like 100W overall if I think about it - ~2-3 kWh/day
The 200W figure is actually the dehumidifier that I’ve started to leave running in place on the VMC, though I’m hoping it will not need to run the compressor continuously. that said it’s pretty underpowered compared with the volume of air that I’m asking it to keep dry (the house is very open plan so the kitchen, dining, lounge and upstairs landing are all one volume) but with limited exchange of air from outside it does seem to be able to keep the RH about 60-65% which is enough.
I just checked & a randomly chosen modern Sauter double flux VMC draws 22W on low speed, 68W on high.
As I said about 100W in total with the heating - I mentally transcribed 2-3kWh/day to 2-300W which is incorrect.
Learned somthing today - VMC.
I have this in my loft.
Held up with string! It ran 24/7 until I started zeroing in on consuption of electricity and the constant dripping from the three vents
The elbow at top right runs to a vent in the salle d’eau. This space includes the w/c and shower cubicle. The vent is directly above a towel rad. The elbow bottom rt runs to a vent above the basin in the ‘buanderie’ . [‘agent speak’ - there used to be a washing machine in the bottom left corner]
I removed the wall between salle d’eau and ‘buanderie’ The total area is is 6 sq m: volume +/- 14 cu.m. The two vents used to drip all the time, as did the one in the kitchen ceiling.
Investigating what this contraption is [I had no idea about this VMC biz] I found the elbow at bottom rt full of water. Removing the end going into the machinery I decanted 5+ litres. Good job I got to it before weight of water pulled it off the gubbins and dumped a deluge onto the floor.
I was going to put a timer on the mains feed but haven’t got round to it yet 
Meantime, I turned it off at the fuse-board. Since then [+/- 3 years] - no drips. Last time I hefted the elbow in my hand I felt no water there.
It seemed dotty to me to have a vent pulling warm air 24/7 - or any time at all - from <1m above the towel rad straight out of the room and another +/- 1m away doing likewise, meanwhile constantly dripping condensation back into the room.
Life in this valley of the Vire is damp. Rue Olivier Basselin is cut halfway up the side of a veritable cliff. The river, as it turns north around the base of the castle rock, runs steeply down, often white water, straight towards my house. The opposite side of the valley is thickly wooded.
The humidity of this valley is therefore considerably elevated above some form of mean.
The result is that the kitchen, with a rad set at 18C, is 21.7/56 humidity. The vent, presumably by natural flow, vents warm air out without mechanical assistance.
The bedrooms and sitting room - no heating, no vents, are +/- 12C/85+ humidity. I can’t afford to heat them. The house is a glorified plywood shack
I have no idea what the ‘regulatory’ state of this set-up is. I expect it’s way away from ‘conform’.
That’s also an issue I’ve had with my VMC (and, unlike you I’ve not been able to access it to check there isn’t a pool of water somewhere).
Plus one of the exhaust vents fell off and just dumped damp air onto the back of the loft access hatch - with resultant condensation until I reattached iit to the vent to the exterior.
Mine is largely held up with string as well.
Normally suspended so you can’t feel any vibrations and cuts the noise down (baling twine is betterthan string😉)
