MHRV design & supply wanted, or DIY advice...

[jemhayward]

My first post on this forum, so, apologies if this has been covered before.  I want to install MHRV in an old thatched cottage for condensation control without excess heat loss rather than try to go passivhaus!

I want to extract from kitchen via extractor hood (with good grease filters), from the bathroom, and then supply air to three bedrooms on the first floor.  I have a huge loft space so plenty of room to hide everything, though I will have to duct the kitchen outlet up through a bedroom.

Ideally I'd like someone to come along, design and install within my £2000 budget, but finding someone offering this is proving difficult.

Otherwise I will DIY, as I have done this before with a smaller installation in the adjacent barn.

I think I want a unit with low power consumption, boost facilities and maybe a summer bypass (I could do this manually by swapping pipes around if needed) - It would seem that you pay a a big premium for high efficiency, would be nice, but I'm not sure I need that as such.  I'm concerned about negative pressure buildup causing fumes problems with my woodburner and I'm unsure how I calculate my capacity.

Any advice / experience gratefully received.

Jem Hayward

[dhaslam]

The air flow is  very low  through a heat recovery system  but even so it is as well to balance the air in the room where the stove is and have both inflow and outflow vents in that room.   You need to think carefully about the place for the unit, they transmit quite a lot of sound through the ducts so the bedrooms  ducts should be fairly long and  short duct to the bathroom.   I would put two vents in the bathroom, one over the shower.  The ducts that take in moisture need to go  rise  gradually near the vent  so that condensation moisture doesn't  lie in the duct farther on.    The   normal ducts have only tiny  openings which is a lazy way to balance  the system,   large pipes and  small openings means  they all get roughly the same air flow.     I am adding separate  vents in the kitchen and bathroom with small fans, humidity controlled, because the original vents are too small and in the wrong places  but I am not sure how well they will work.  At present there are  seven  inlets and  six outlets.   

[jemhayward]

main problem is the lounge, where the woodburner lives is almost impossible to get ducts into, though the bathroom is only one leaky door away, as is a bedroom, up an open staircase - the relatively open plan and unsealed nature of the house would suggest that pressure differences would be small.  I have seen a unit that offers positive pressure, which seems sensible.
Above the bathroom would be a logical site for the unit itself, which would suit the noise model, though it does make the kitchen to unit run rather long, with a 2.5m vertical, then 7m horizontal - would I get condensation issues?

[marshman]

Hi Jem Hayward,

A few years back (about 7 IIRC) I installed a Rega Ductex, http://www.rega-uk.com ,  system in my house. It did the whole house. They offered a design service which I used and then modified. The itemised all the components and supplied on a sale or return basis. I actually installed it myself though I think at the time they did offer an installation service - or maybe it was a service for an engineer to balance the system. It worked well and virtually eliminated condensation.

I had three accoustic dampers and the system was virtually silent - I had it running 24/7 and no one complained about any noise in the bedrooms. Originally they only designed in two but the extract ducting transmitted too much fan noise for my liking so I installed a third.

The installation is quite straight forward. I would recommend doing it yourself as you will be a lot more careful about hiding ducting etc.

You need to be very careful if you have a wood burner. Make sure the system is balanced so that there is nore air going in than out so the house is slightly pressurised. This was you ensure that you don't draw any dangerous fumes into the house from the fire.

Good Luck

Roger

[jemhayward]

How do the acoustic dampers work?  Are they a type of ducting or something fitted to the ducts?  I do worry about the noise aspect.  My HR100 ventaxia unit in the barn is relatively noisy, but as the room is sporadically used, we run the low speed fan via a timer, so its not on when we are watching TV...