Ask a residential ventilation specialist anything

[robemcdonald]

Like the myriad other similarly titled threads. If you have a ventilation question please ask away.

I have worked in residential ventilation for the past 8 years. I work with building design consultants to design systems for new build projects and less frequently with housing associations to help identify and resolve ventilation issues in existing dwellings.

I do work for a major UK ventilation manufacturer, but any advice I offer here is my own opinion not my employers.

[monkfish1]

Do you have any experience of passive ventilation systems?

[Mabbs9]

Morning. Thanks for the offer. We have a new ish house. It has 4 trickle type extractors that can all be boosted. I believe there is a building reg at construction to check if a house is well sealed? Surely with four vents to ambient it will always show them as not sealed?

I know this overlaps your area rather than sitting right in it but it seems a bit of a conflict.

Likewise if all the extractors are operating in a theoretically sealed building, are they removing air or just very slightly lowering the pressure in the building?

Thanks. Sorry if it's off-piste!

[mrmistoffelees]

Is there an easy(ish) way to work out if MVHR would be worthwhile on an existing house without doing a pressure test? Very much how long is a piece of string, I'm sure - but it's something I'm considering. House is 5 bed, built 2000, and considerable work has been done to replace doors with composite Solidor, window units are triple glazed, loft insulation is 350mm and there's some insulation between floors. Ground is uninsulated slab. If a pressure test is the only way to come up with a yes it's worth it/no it's not then... it is what it is.

[robemcdonald]

monkfish1 said:

Do you have any experience of passive ventilation systems?

Unfortunately not, I work with mechanical extract only.

The only knowledge I have is they don’t work well if you live in a valley and we asked to replace them with mechanical systems on occasion.

I’m not sure they are even listed in the new version of Part F.

[robemcdonald]

Mabbs9 said:

Morning. Thanks for the offer. We have a new ish house. It has 4 trickle type extractors that can all be boosted. I believe there is a building reg at construction to check if a house is well sealed? Surely with four vents to ambient it will always show them as not sealed?

I know this overlaps your area rather than sitting right in it but it seems a bit of a conflict.

Likewise if all the extractors are operating in a theoretically sealed building, are they removing air or just very slightly lowering the pressure in the building?

Thanks. Sorry if it's off-piste!

It’s fine.

Can you post a picture of the extractors, so I know what you mean?

If you had a sealed box and were extracting air continuously then you’d have a vacuum.

Fortunately your house isn’t a sealed box. Unless you are running at high flow rates (if you have “through the wall fans” you aren’t) then your okay.

[robemcdonald]

mrmistoffelees said:

Is there an easy(ish) way to work out if MVHR would be worthwhile on an existing house without doing a pressure test? Very much how long is a piece of string, I'm sure - but it's something I'm considering. House is 5 bed, built 2000, and considerable work has been done to replace doors with composite Solidor, window units are triple glazed, loft insulation is 350mm and there's some insulation between floors. Ground is uninsulated slab. If a pressure test is the only way to come up with a yes it's worth it/no it's not then... it is what it is.

How big is the house Sq.m.?

The biggest headache is where you put the MVHR and route the ductwork.

Cost of materials will depend on size of the house, but could be as low as £2-3k not including installation or commissioning.

[mrmistoffelees]

robemcdonald said:

How big is the house Sq.m.?

The biggest headache is where you put the MVHR and route the ductwork.

Cost of materials will depend on size of the house, but could be as low as £2-3k not including installation or commissioning.

Thanks for taking the time to reply - 240sqm. Would probably put it in the loft. Have what's in essence a riser from there down to the ground floor that could take pipework and distribute it to areas that would benefit most - utility room has a heat pump tumble dryer, kitchen and living room are easy to get to above the ceiling.

[monkfish1]

robemcdonald said:

monkfish1 said:

Do you have any experience of passive ventilation systems?

Unfortunately not, I work with mechanical extract only.

The only knowledge I have is they don’t work well if you live in a valley and we asked to replace them with mechanical systems on occasion.

I’m not sure they are even listed in the new version of Part F.

Thanks.

Not in a valley, so no issue there.

Just exploring my options because, retofit will be hard, and, dont want the noise that a mechanical system will introduce. I wont be concerning myself with building regs.

[robemcdonald]

mrmistoffelees said:

robemcdonald said:

How big is the house Sq.m.?

The biggest headache is where you put the MVHR and route the ductwork.

Cost of materials will depend on size of the house, but could be as low as £2-3k not including installation or commissioning.

Thanks for taking the time to reply - 240sqm. Would probably put it in the loft. Have what's in essence a riser from there down to the ground floor that could take pipework and distribute it to areas that would benefit most - utility room has a heat pump tumble dryer, kitchen and living room are easy to get to above the ceiling.

The riser isn’t the big issue the supply and extract ductwork is.

Based on the building rates you’ll have a continuous rate of 70l/s so you will need a decent MVHR.

How many wet rooms do you have?

Kitchen, utility, bathroom, en-suite, separate W/C etc?

[robemcdonald]

monkfish1 said:

robemcdonald said:

monkfish1 said:

Do you have any experience of passive ventilation systems?

Unfortunately not, I work with mechanical extract only.

The only knowledge I have is they don’t work well if you live in a valley and we asked to replace them with mechanical systems on occasion.

I’m not sure they are even listed in the new version of Part F.

Thanks.

Not in a valley, so no issue there.

Just exploring my options because, retofit will be hard, and, dont want the noise that a mechanical system will introduce. I wont be concerning myself with building regs.

It might be worth exploring the passive stack option in that case.

If you have a loft than PIV is undoubtedly the easiest to fit option.

[mrmistoffelees]

robemcdonald said:

The riser isn’t the big issue the supply and extract ductwork is.

Based on the building rates you’ll have a continuous rate of 70l/s so you will need a decent MVHR.

How many wet rooms do you have?

Kitchen, utility, bathroom, en-suite, separate W/C etc?

Aah, I see. Would it be viable, if it were in the loft, to utilise the gable walls? House is detached and has a decent margin on either side before you get to trees.

Wet rooms: 2x ensuite, downstairs loo, family bath, kitchen, utility.

Reason I'm interested in this is that for instance my daughter's room, she doesn't open the curtains some days. When I inevitably go in to clear the various teenage build up of crap, there is occasionally some black mould building up on the internal window that I just wipe off for now but obviously suggests air quality in there at least is pretty poor.

[FourGears]

robemcdonald said:

Like the myriad other similarly titled threads. If you have a ventilation question please ask away.

I have worked in residential ventilation for the past 8 years. I work with building design consultants to design systems for new build projects and less frequently with housing associations to help identify and resolve ventilation issues in existing dwellings.

I do work for a major UK ventilation manufacturer, but any advice I offer here is my own opinion not my employers.

Hello. I have a Nuaire PIV in the loft which works wonders upstairs. Downstairs however is not so great particarly the extension which was built in the 90s I think. Lots of the houses on the estate suffer with poor airflow. We don't have an external extractor fan fitted but would that make much of a difference? The winter is spent trying to keep on top of the mould in the downstairs loo, utility and the extra room next that joins kitchen to utility (not a clue what to call it!)
What options are there for getting the air moving?

[robemcdonald]

mrmistoffelees said:

robemcdonald said:

The riser isn’t the big issue the supply and extract ductwork is.

Based on the building rates you’ll have a continuous rate of 70l/s so you will need a decent MVHR.

How many wet rooms do you have?

Kitchen, utility, bathroom, en-suite, separate W/C etc?

Aah, I see. Would it be viable, if it were in the loft, to utilise the gable walls? House is detached and has a decent margin on either side before you get to trees.

Wet rooms: 2x ensuite, downstairs loo, family bath, kitchen, utility.

Reason I'm interested in this is that for instance my daughter's room, she doesn't open the curtains some days. When I inevitably go in to clear the various teenage build up of crap, there is occasionally some black mould building up on the internal window that I just wipe off for now but obviously suggests air quality in there at least is pretty poor.

MVHR might be overkill. PIV would be a simpler option.

[robemcdonald]

mrmistoffelees said:

robemcdonald said:

The riser isn’t the big issue the supply and extract ductwork is.

Based on the building rates you’ll have a continuous rate of 70l/s so you will need a decent MVHR.

How many wet rooms do you have?

Kitchen, utility, bathroom, en-suite, separate W/C etc?

Aah, I see. Would it be viable, if it were in the loft, to utilise the gable walls? House is detached and has a decent margin on either side before you get to trees.

Wet rooms: 2x ensuite, downstairs loo, family bath, kitchen, utility.

Reason I'm interested in this is that for instance my daughter's room, she doesn't open the curtains some days. When I inevitably go in to clear the various teenage build up of crap, there is occasionally some black mould building up on the internal window that I just wipe off for now but obviously suggests air quality in there at least is pretty poor.

Rooms off of rooms are the one in a PIVs armour. How old is the Drimaster? Do you know what setting it’s on?

[OutInTheShed]

FourGears said:

Hello. I have a Nuaire PIV in the loft which works wonders upstairs. Downstairs however is not so great particarly the extension which was built in the 90s I think. Lots of the houses on the estate suffer with poor airflow. We don't have an external extractor fan fitted but would that make much of a difference? The winter is spent trying to keep on top of the mould in the downstairs loo, utility and the extra room next that joins kitchen to utility (not a clue what to call it!)
What options are there for getting the air moving?

An extractor fan in the kitchen makes a huge difference.

[robemcdonald]

FourGears said:

Hello. I have a Nuaire PIV in the loft which works wonders upstairs. Downstairs however is not so great particarly the extension which was built in the 90s I think. Lots of the houses on the estate suffer with poor airflow. We don't have an external extractor fan fitted but would that make much of a difference? The winter is spent trying to keep on top of the mould in the downstairs loo, utility and the extra room next that joins kitchen to utility (not a clue what to call it!)
What options are there for getting the air moving?

You could try increasing the flow rate on the PIV as a first step if that doesn’t work you could look at adding an additional extract fans in the affected rooms.

The key would be to make sure they are a continuously running type and run at a low trickle rate 24/7 instead of just when you turn the light on. You only need a few litres per second for it to work.

It would help if you could provide a rough sketch of the layout and highlight the areas with mould issues.

[LocoBlade]

I've got a general house ventilation/humidity question. I've read in a few places that the ideal house relative humidity should be between 30% and 60%, but although we have zero issues with condensation or humidity, our (~230sqm) house that's heated with UFH downstairs and radiators upstairs seems to be naturally settling between 65% and 75%. We open a window after a shower etc, put the cooker hood extractor on when cooking and have open trickle vents on several windows so the question is, do I need to do anything about this and if so is there anything else other than run a large dehumidifier that we can do to reduce it?

[AndrewT1275]

What MVHR setup would you recommend for a 3 storey house with approx 380m2?

GF is 190m2 inc garage which is inside the thermal envelope, with kichen, utility and wc.
1st floor is 140m2 with 4 bathrooms.
Top floor is 55m2 with wc.

Would 2 smaller units make more sense than one big single? And if so how would you split them?

[robemcdonald]

AndrewT1275 said:

What MVHR setup would you recommend for a 3 storey house with approx 380m2?

GF is 190m2 inc garage which is inside the thermal envelope, with kichen, utility and wc.
1st floor is 140m2 with 4 bathrooms.
Top floor is 55m2 with wc.

Would 2 smaller units make more sense than one big single? And if so how would you split them?

I’d go for two MVHRs. You could do it with one, but you’d need larger duct to reduce the pressure / velocity.

The problem is with multiple floors you always seems to get loads of pressure in the risers. One of many of life’s little frustrations.