Hello,

We are installing a small, basic ground-floor MVHR (Blauberg D-105A) as part of a side-return open-plan kitchen extension to our 1910s terraced house. A full-blown MVHR is beyond the scope of the project.

I'd really appreciate any comments on the attached design. A few notes:

• North is at the top of the page. There is a steel beam running north-south as shown. We can just get some 125mm duct underneath where it meets the column to the south as shown, boxed off above the kitchen units. The beam is otherwise impassable (within the scope of the project).

• East of the beam, the south third of the kitchen has a pitched roof with Velux windows (usual London side-return extension). This also limits valve placement options to the area of the bench seating as shown (hence the proposed directional supply valve to avoid draughts).

• Valves can otherwise be placed anywhere in the kitchen ceiling west of the beam. It is not possible to place valves east of the beam other than close to the south wall as shown.

• The extension is being constructed with best efforts on the insulation and airtightness front but not to a certifiable standard. My main ventilation priority is the utility room, which will have a condenser tumble drier and be used to dry clothes on hanging rails. I have a CO2 meter and CO2 levels in the house are already poor in occupied rooms. The house does not "officially" need an MVHR, but I would like to ventilate in an energy efficient manner and improve air quality.

• The kitchen will have a conventional extractor hood over the hob, vented to outside. Given this, I am questioning the need for an MVHR extract valve in the large open-plan kitchen space and wondering whether having an extract valve solely in the utility room would ensure it is well-ventilated without providing excessive airflow to the 2 supply valves. Would the supply valve location in the south east of the dining area, coupled with the utility room extract valve, set up a drift of fresh air towards the kitchen door to ventilate the kitchen, with the conventional extractor hood used for cooking as required? Such that an extract valve in the kitchen is not needed?

• If a kitchen extract valve is needed, where is the best location for it? I thought next to the door so as to be diagonally opposite the supply valve, although I'm concerned this might work against the utility room extract valve.

Thanks.

P.S. An image file doesn't seem to upload very clearly, hence the .pdf.

When MVHR is used, it would be normal to specify a recirculating cooker hood to clean the air, not an external extractor fan. I'd do that, leaving the MVHR vent as designed.

Posted By: djhHi James,

I think having an extract valve in the kitchen is a good idea, and where you show it seems like a reasonable place. It won't compete with the utility valve because you can set the relative extract rates. This can be done at the valves, or better done where the two ducts separate from each other (will be quieter). The utility duct is noticeably shorter so will tend to have a higher flow rate other things being equal.

All the valves seem to be sensibly placed. Where do the intake and exhaust ducts terminate?

I'm not quite sure what the object in the middle of the kitchen floor is, but I assume it is some kind of central island? You might want to check the clearance between its south-west corner and the north-east corner of the dining table because it seems narrower than all the other passages.

Thanks Dave, that's really helpful.

The intake and exhaust ducts terminate on the external wall above the sloping roof of the kitchen extension, into the sheltered space above the side returns of my and my neighbour's terraced houses - so they would run a short distance south east and vertically upwards to the external wall supported above the steel beam shown.

There's not a lot of space there - I believe we will need to have the exhaust valve above the intake valve, possibly with a snorkel arrangement to separate them. The cooker hood will exhaust in the same area so we will need to make sure everything is adequately separated. Any advice here would also be appreciated (!).

Can I ask how one would set the relative extract rates where the two ducts separate from each other please? Some kind of limiter in the duct itself?

You're right about the clearance between the island and dining table - the table size and location will be slightly different than shown here so the gap will be bigger. I'll update the plan.

For me, two inlets in the lounge, one each side

Cooker extractor to outside rest ok

Posted By: tonyFor me, two inlets in the lounge, one each side

Cooker extractor to outside rest ok

Thanks Tony.

I would not bother too much with directional valves. The normal ones diffuse well and MVHR air flow rates are generally well below the perceptible draught threshold.
Have you considered acoustics? Best to include inline dampers/mufflers so that there is no crosstalk between the rooms, and the MVHR fan noise does not propagate back into the feed and extract lines.
Since this looks like a branched system, the MVHR unit would have to have intake and supply dampers (on the house side), with additional inline ones for both supplies and the lounge extract.

Posted By: tonyI don’t like that, grease is an enemy of ductwork and you don’t want in your heat exchanger either, recirculation units are not very good at taking grease out of the air.

The MVHR extract vent in the kitchen should be of the type with a built-in grease filter. The better cooker hoods aren't too bad, especially if they have carbon filters.

The extract rate that I require from my cooker while I am frying fish and boiling tatties, is a lot more (5x or 10x more) than the extract rate that I require for the other 23.7 hours of the day.

For that reason I'm happy to have a powerful extraction cooker hood, completely separate from the room ventilation!

@djh My understanding of the fire valve is a BC requirement and I would guess will have to do with smoke distribution fire spreading and fanning the flames. I did not dream it up I had to fit one to our system. Our recirc fan work really well in conjunction with the MVHR but then we do very little grease production. Just to be clear the cooker extractor does not feed into the MVHR but exhausts about a metre away from the kitchen MVHR intake and there is no sign of any grease in that duct. I can easily check all my intakes and exhausts as my valves are "bayonet" fit into the ducting via a galvanised adapter. I can confidently recommend the Lindab valves they are well made of metal and not that much more expensive than the cheap plastic ones.

Posted By: WillInAberdeenThe extract rate that I require from my cooker while I am frying fish and boiling tatties, is a lot more (5x or 10x more) than the extract rate that I require for the other 23.7 hours of the day.

For that reason I'm happy to have a powerful extraction cooker hood, completely separate from the room ventilation!

Yup, I can quite see that and would be happy myself but it would have messed up our airtightness I think. And the MVHR does just fine extracting the general kitchen air after it's been through our recycling hood when necessary.

Thanks for all the advice. TBH I'm a bit concerned about extraction in the utility room. It has no external walls and will be used almost continuously for line-drying clothes on a hanging rail. There will also be a condenser tumble drier and sink which will be used frequently. The room volume is 13.2 m³.

The Blauberg D105-A unit can theoretically do 16, 22 and 29 litres/second on settings 1,2 and 3. I believe this meets building regs for continuous extract in a utility room (8 litres/second) but I do also want it to actually clear the air in there in real usage. My current Manrose extractor fan in my unrenovated bathroom is theoretically 24 litres/second and it doesn't seem like much - takes a while to clear the room after a shower and we struggle with mould in there.

My concern is that if I have an MVHR extract in the kitchen as well as the utility room, I will be diluting the extract capability from the utility room. The extract requirement for the utility room is the primary driver and will determine the setting the MVHR unit is run at. Thus having an additional kitchen MVHR extract with associated duct and valve losses might mean the unit must be run at a higher setting to achieve adequate utility ventilation than would be required if the utility extract was the only extract vent. I don't want the unit running at its highest setting all the time, nor do I want excessive airflow at the supply vents as a result.

I will have a conventional externally-vented cooker hood in the kitchen and am perfectly happy to use that when cooking and using the sink etc., as I would if I had no MVHR. I am wondering whether the intermittent, on-demand cooker hood extract plus the fresh air from the MVHR supply in the living side of the open-plan kitchen-diner would suffice and allow me to omit the kitchen MVHR extract. The kitchen and utility room doors will remain open most of the time and the distance between them is short. If I had no MVHR then the cooker hood extract would presumably be considered sufficient - the only difference with the MVHR in this case would be some warmed fresh air supplied to the room.

I'm aware that a conventional MVHR system needs an extract in the kitchen and a recirculating cooker hood. I feel like I'm in a bit of a halfway house situation as I dont't "need" and MVHR and plan to use my externally-exhausted cooker hood normally. I'm just trying to ventilate the utility room adequately, capture some of that otherwise wasted heat and provide a bit of warmed fresh air to the TV room and the living side of the open-plan kitchen. I'm not aspiring to a "full" MVHR system, just trying to make a reasonable effort on the energy efficiency and ventilation fronts within what is practicable.

There's a big jump in price and complexity from the £335 Blauberg D105-A to the next sized unit (in terms of total price for the system), which I feel would be significant overkill for the intended purpose and not justifiable. On the other side, the alternative is no MVHR, a regular inline extraction fan in the utility room and the extractor hood and trickle vents in the kitchen, which seems like a bit of a waste.

It seems quite difficult to get advice for a basic system like this. It's a bit like it's a case of no MVHR at all or 100% "full monty". I called a company today and asked them for some info on one of their directional supply valves. They sounded quite offended that one of their valves might be connected to 125mm rigid plastic duct!

Posted By: JCBGFThanks for all the advice. TBH I'm a bit concerned about extraction in the utility room. It has no external walls and will be used almost continuously for line-drying clothes on a hanging rail. There will also be a condenser tumble drier and sink which will be used frequently. The room volume is 13.2 m³.

The Blauberg D105-A unit can theoretically do 16, 22 and 29 litres/second on settings 1,2 and 3. I believe this meets building regs for continuous extract in a utility room (8 litres/second) but I do also want it to actually clear the air in there in real usage. My current Manrose extractor fan in my unrenovated bathroom is theoretically 24 litres/second and it doesn't seem like much - takes a while to clear the room after a shower and we struggle with mould in there.

An MVHR behaves very differently to an extractor fan. It is always on, so you need a much lower extract rate to clear humid air. I think it is worth making sure that your wall and ceiling surfaces include some humidity buffering.

I believe that tiling a bathroom, or using any other non-absorbent surface over most of the walls, is best avoided. Between humidity buffering in the walls and continuous extraction by an MVHR should easily control humidity well enough to avoid mould problems.

I don't know much about using MVHR in just a few rooms though. I suppose it depends on how much the air in those rooms interacts with the air in other rooms.

My concern is that if I have an MVHR extract in the kitchen as well as the utility room, I will be diluting the extract capability from the utility room. The extract requirement for the utility room is the primary driver and will determine the setting the MVHR unit is run at. Thus having an additional kitchen MVHR extract with associated duct and valve losses might mean the unit must be run at a higher setting to achieve adequate utility ventilation than would be required if the utility extract was the only extract vent. I don't want the unit running at its highest setting all the time, nor do I want excessive airflow at the supply vents as a result.

The standard ventilation figures in building regs are pretty well chosen for the mst part, and I wouldn't try to second guess them too much. Design the ventilation to PH specification if you want to be sure.

I will have a conventional externally-vented cooker hood in the kitchen and am perfectly happy to use that when cooking and using the sink etc., as I would if I had no MVHR. I am wondering whether the intermittent, on-demand cooker hood extract plus the fresh air from the MVHR supply in the living side of the open-plan kitchen-diner would suffice and allow me to omit the kitchen MVHR extract. The kitchen and utility room doors will remain open most of the time and the distance between them is short. If I had no MVHR then the cooker hood extract would presumably be considered sufficient - the only difference with the MVHR in this case would be some warmed fresh air supplied to the room.

I'm aware that a conventional MVHR system needs an extract in the kitchen and a recirculating cooker hood. I feel like I'm in a bit of a halfway house situation as I dont't "need" and MVHR and plan to use my externally-exhausted cooker hood normally. I'm just trying to ventilate the utility room adequately, capture some of that otherwise wasted heat and provide a bit of warmed fresh air to the TV room and the living side of the open-plan kitchen. I'm not aspiring to a "full" MVHR system, just trying to make a reasonable effort on the energy efficiency and ventilation fronts within what is practicable.

I think you're in danger of overthinking the issue.