Kitchen smell transfer via MVHR fresh air vents

[readiescards]

My partner started frying some onions in the kitchen, while I was upstairs, I was amazed that the onion smell came out of the fresh air vent in the room I was in.  (my partner had previously commented that when I burn the toast she can smell it from the fresh air vent in her ensuite bathroom with the door closed)

 

Anyone else experience similar?

 

note my own investigations of my MVHR suggests there a sealing issue allowing some 'cross-talk' but before I fix it I was wondering if this smell transfer is normal?

[ragg987]

Yes we have experienced something similar, but it has been intermittment nd I suspect that one source of the "cross-talk" is the external inlet and outlets. In our case they are both on the same external wall about 2.5m apart. Also the MVHR does not seal 100% - I think some of the manufacturers publish figures about this, I recall seeing figures in the upper 90% for sealing against cross flows.

[Dee J]

If there is 'cross-talk' between exiting air and fresh air input then either there is a leak within the unit or exhaust and intake are too close together on the outside of the building.

[jack]

No, I've never noticed this with ours.

[Adsibob]

I’m in the process of designing my MVHR layout and this is definitely something I want to avoid. What are the recommendations for siting inlet and exhaust? How far apart should they be and can they both be in the same side/orientation of the house?

 

@readiescards, did you ever solve this?

[PeterW]

Just now, Adsibob said:

I’m in the process of designing my MVHR layout and this is definitely something I want to avoid. What are the recommendations for siting inlet and exhaust? How far apart should they be and can they both be in the same side/orientation of the house?

 

@readiescards, did you ever solve this?

To ensure they aren’t off balance they need to be on the same wall. Try and get a minimum 1200 horizontal distance between them and vertical separation if possible. Also make sure they are accessible (or don’t have fine mesh on the intake) as you will need to access them to clean them otherwise. 

[Nestor]

11 minutes ago, PeterW said:

Also make sure they are accessible (or don’t have fine mesh on the intake) as you will need to access them to clean them otherwise. 

Supply and extract on same external wall. 2.5m apart, extract 1.5m higher. Never had any cross contamination.

Fine mesh supply clogged after 9 months.

 

 

Edited February 6, 2021 by JamesP

[Adsibob]

Brill. Thanks @PeterWand @JamesP

[readiescards]

The 'cross-talk' I put down to the internal leaks within the MVHR - there are plenty of routes for the stale air to be sucked into the fresh air feed within the device.  Mine you havn't noticed it recently

[Jolo]

Not sure whether to start a new topic or resurrect this one after 4.5 years, but as I have the same problem I suppose it's best to comment here...

 

But I need a bit of a sanity check from those with experience of MVHR systems!

 

We have a Brink Flair 200 unit (it's the Dutch version, the same as the UK Flair 225, but without the screen) with enthalpy exchanger, and have noticed the same issue as described here. Except it's not just kitchen odours, but even less pleasant ones..!

 

To rule out our internal ducting, we even tested it by disconnecting the house entirely and just attaching two lengths of ducting to the unit. Smells which are sucked into the extract duct (shower gel, cream cleaner, coffee, whatever) come out of the supply duct almost immediately. It's really noticeable and strong. 

 

It's also not due to cross-flow outside -- Brink came out earlier this week and had a look, our installation is within spec. (Plus the effect is too strong and immediate to be external.) They swapped the exchanger core for a replacement, but the problem persists. (Not a surprise, as the smells also transferred with bypass mode on.) Their next plan is to do a smoke test.

 

I'm pleased that Brink seem to be taking this seriously, and the company that sold me the unit has been helpful.

 

Am I right in thinking that this just shouldn't happen? This isn't normal with MVHR or ERV, right -- nobody would want a ventilation system which spreads smells around the house! I clearly have a defective unit, right? Some seal must be missing or loose, otherwise this just wouldn't be occurring.

 

Both my supplier and the man from Brink said they've never experienced this before, just my luck to get the one defective unit! 

 

I wonder what model MVHR @readiescards has/had which exhibited this same behaviour?

[JohnMo]

A normal heat exchanger the air and moisture simply cannot mix, they are two flow paths, the heat exchanger is just a heat exchanger.

 

Enthalpy heat exchanger are different but should only allow humidity cross over between the two streams.

 

So would suspect an internal leak within the unit 

[Nickfromwales]

2 minutes ago, JohnMo said:

A normal heat exchanger the air and moisture simply cannot mix, they are two flow paths, the heat exchanger is just a heat exchanger.

 

Enthalpy heat exchanger are different but should only allow humidity cross over between the two streams.

 

So would suspect an internal leak within the unit 

“Stinks” of a manufacturing defect.

 

Unit needs a forensic strip down and rebuild, and to actually see / examine every joint and junction.

 

Probably something very simple, there’s not much to go wrong with these things. 

[Jolo]

Thank you @JohnMo and @Nickfromwales for your fast and clear replies, much appreciated 👍

 

It's good to know that I'm not losing it!

 

The unit was manufactured earlier this year, and it's only been installed and running for a couple of months, so I'm hoping there'll be a quick resolution.

[Nickfromwales]

1 hour ago, Jolo said:

Thank you @JohnMo and @Nickfromwales for your fast and clear replies, much appreciated 👍

 

It's good to know that I'm not losing it!

 

The unit was manufactured earlier this year, and it's only been installed and running for a couple of months, so I'm hoping there'll be a quick resolution.

Keep us posted please!

[Temp]

Perhaps check that all vents are moving air in the right direction. eh that the bedroom vent is an incoming not an extract by mistake? 

[ProDave]

Did they check the unit was actually connected correctly?  When I installed my unit I found the terms used to describe the ports confusing.  Could it be something like the supply vents supplying air to the rooms is mistakenly connected to the exhaust air port that should be exiting the house?

 

I would have expected Brink to have checked this on their visit but perhaps they "assumed" it must be connected correctly?

[Russdl]

4 hours ago, ProDave said:

When I installed my unit I found the terms used to describe the ports confusing

Likewise. 

[Jolo]

Everything is definitely connected properly, I've checked it all about a thousand times, and the bloke from Brink checked it too. I've not gotten around to boxing in any of the ducting yet, so it's really easy to see what goes where, and follow it to its destination.

 

We've also tested the issue by disconnecting the house ducting from the unit entirely, and just putting two single internal ducts on the top -- one on the extract port, one on the supply -- to prove that the problem exists purely within the unit, so it can't be due to anything wrong inside the house.

 

Incidentally, I've also tested by sniffing at the exhaust duct, and the smells do also come through there, so it's definitely mixing air streams inside the unit. (If I'd somehow mixed up the exhaust and supply ports, the smells should only come through one of the "blow" holes, not both!)

 

I'm hoping to hear back from either Brink or the supplier in the coming days, I think they're planning to do a smoke test. I'll keep this thread updated!

[Iceverge]

Strange. Do you have a trunk and branch system or a radial? 

[Jolo]

On 03/11/2025 at 11:08, Iceverge said:

Strange. Do you have a trunk and branch system or a radial? 

Oops, I missed your reply somehow! It's a radial system. Small house, really simple, the ducting is mostly still visible so it's all been checked a dozen times.

 

We've even tested it with just an elbow and a metre or two of ducting on the extract and supply ports, and the problem still exists, so it's definitely not a problem with the internal ducting.

[Jolo]

Update... there is no update!

 

I'm a bit disappointed with Brink and the supplier, to be honest. I don't get any progress unless I push for it, and there seems to be no answers forthcoming. The latest "news" is that it's been passed to the R&D department to figure out what might be causing the issue. 

 

One question for those with experience of such systems -- should the MVHR system help regulate the moisture inside the house?

 

I ask because we've had really high moisture levels indoors, like 80 - 90% RH sometimes, which is surprising to me. Windows covered in condensation in the morning, even though we're running the unit at around 0.45ach.

 

We're not doing anything weird like hour-long showers or running a commercial kitchen! I've taken to opening the window vents, which helps a lot with the humidity but of course defeats the purpose of the whole MVHR system!

[JohnMo]

With enthalpy heat exchanger it should be at a steady 50% humidity.

 

So are you sure it's plumbed correctly - i.e. all extracts to extract manifold and to correct nozzle on MVHR?

 

Go around each terminal 2 sheets of toilet roll. Extracts should hold up the toilet roll, supplies will not. Confirm every one is correct and report back.

[torre]

You mentioned a smoke test earlier, has this been done? It sounds the obvious next step.

[Mike]

6 hours ago, Jolo said:

should the MVHR system help regulate the moisture inside the house? I ask because we've had really high moisture levels indoors, like 80 - 90% RH sometimes, which is surprising to me

As mentioned in another thread, text from a PassivHaus MVHR certificate says that 'In case the unit’s moisture recovery rate is larger than 60 % its airflow rate must be controlled based on the indoor air humidity, in order to prevent temporarily elevated humidity levels.'

 

So yes, it seems that there is a potential for excess humidity in some circumstances so, to avoid problems, the unit needs to automatically switch to boot mode if humidity gets too high. If it's not doing that, I guess that there are at least 3 possibilities:

• it could be there's a control problem;
• maybe it requires (an additional / replacement) humidity sensor(s);
• maybe some of the exhaust air is finding its way back into the supply.

 

6 hours ago, torre said:

You mentioned a smoke test earlier, has this been done? It sounds the obvious next step.

+1