mathraki

I do have a question about a topic where i am looking for less theoretical answers and more 1st hand experience. Is it ok to install the extract and supply vents on opposite sides of the roof as shown below. I want to do this to assist summer bypass feature. There are opinions of the units struggling to cope with pressure diff. on each side of the roof but , I am sceptical on this.....anyone got experience of this ? thanks,

my observation would be that the warm moist air leaving the house is condensing within the extract ducting. The water trickles back towards to MVHR unit, wetting the filters and other components. I am about to install mine in a un-insulated attic. this will increase the risk of the above happening for me too. I intend to mitigate the risk by : a using solid plastic, insulated ducting for Ingress/Egress vents. Insulate pipes, connectors etc. Fitting a in-line duct condensation trap on each Ingress/Egress ducts close to the unit Where possible allow a gentle fall away from the unit for the exhaust duct/vent draft plan below, welcome observations

i am installing a MHRV into a mid-terraced Victorian house. Over and above the running costs and effort, there are many counter benefits such as you have outlined.... - offsetting the sealing of openings (new windows/doors) - off-setting any airtightness measures added to rooms, floors etc. to ensure there is adequate fresh air ventilation. - allow for windows to remain shut - obvs. preheat incoming supply - reduce heat losses - expel humidity, mitigate damp, mould, condensation etc. - Improve air quality - increase comfort levels Controversially I am not even doing all rooms - just middle and top floors (4 bedrooms, 2 shower/WC rooms); this approach will further decrease the efficiency of the system. I would summarise as follows, I think it is worth it, as I want to reap some of the benefits above and I am limited in what I can do (listed building) and I acknowledge it is far from a model-installation. 'Routinely opening windows' is trite suggestion and not an option for a large house and/or modern family (2 working parents ) that are trying to reduce heat losses and improve comfort and I think a MHRV retro-fit addresses many issues. Best of luck with your installation if you proceed. PS - it helps to try and pick up a good condition 2nd hand unit, I did (Vent Axia sentinel kinetic FHL) and it completely enhances the justification and negates commercial downsides.

@phatboy thanks for the pictures. The Flexible Silencer on the domestic supply side - did you consider rigid v flex silencers when planning ? is one more effective than the other ( they seem similar in price).

"The warm moist air in the home will condense out on these colder areas leading to damp" Potentially, if the conditions are present for condensation to occur. If the house fabric is kept at a temperature above the dew point then the water vapour will not (cannot) condense. If however the localised effect of a draught i.e. cooling the wall in the gap-area between two boards, could potentially cool to the gap-area to a temperature below the dew point and water could condense in these areas. Sealing the gap, avoiding the 'cool' air getting in is a good remedy; the correct insulation is a better solution again and furthermore the dilution and extraction of the saturated air using MHRV or similar is also a mitigation. Pedantic perhaps but i wanted to clarify that not sealing gaps does not automatically lead to damp and in many cases the additional air flow is exactly what prevents it.

But is the fact that it is v. difficult to get an old house (1906 mid terrace, 3 storey in my case ) to the new-build air tightness standards, still reason enough for NOT going MHRV .....when at least, many of the 'big leaks' have been addressed. Won't MHRV still ventilate the spaces whilst removing moisture rich and smelly air and recover 'some' of the heat in so doing ? As I seal up and fix my new Victorian house (room by room), I am reducing the air ingress into the living areas via floor, skirting, sockets, windows, fittings and services. I am conscious I need to provide ventilation and despite acknowledging I may never get all leaks addressed, MHRV is still my preferred option. Further I am only planning on doing MHRV in the middle and top floors, with the MHRV unit in the COLD, eaves ventilated attic: Top: 3 bedrooms and 1 x WC/Shower Room. Middle: 1 bedrooms,1 x WC/Shower Room and 1 x Office. Ground: Entrance Hall & Sitting room (out of scope because too far from Attic and too diff. for ducting) The Kitchen, utility and another WC will all be new-build to rear from the entrance hall ....down 2 steps, you know the type. So whilst my set-up is far from standard, ideal or probably recommended ...MHRV will allow me vents wet rooms with minimum holes punched in the walls whilst refreshing the air in the bedrooms and office without the need for the windows to be opened (often). Cross your fingers for me.