Lots of quotes for Mvhr, help choosing which one please.

[Lincolnshire Ian]

Hi 

We have a new build timber frame house 200sqm with posi joists. We are going to install an MVHR system. 

We have received quotes for MVHR systems from BPC and ADM for five different units, but similar ducting etc.

The units they have suggested are:

* Vent-Axia Plus B

* Zehnder Q450

* Vent-Axia Sentinel Kinetic Plus 

* HRV4.25 Q Plus Eco

* Comfo Air Q350

 

The quotes are all within several hundred pounds, except the Vent-Axia Plus B which is much cheaper, the actual unit seems to be around half the price, or less, of the others. 

Does anyone have any experience of the Vent-Axia Plus B system (it's being suggested by BPC)? Is it worth paying the extra for one of the other systems?

What is your experience of BPC or ADM?

Thanks 

Edited February 16 by Lincolnshire Ian

[Bramco]

Can't say anything about the Vent-Axia but we have a Zehnder ComfoAir 350 and are very pleased with it.  We run it on it's lowest setting with automatic humidity sensing turned on which clears bathrooms quickly. Ours is a similar build but 250m2. Ours was installed by the builders contractor, so no experience with BPC or ADM.

 

I seem to remember a discussion about an issue with one MVHR unit, where the condensate was dripping from the base of the unit and was collecting on a side of the unit away from the drain. Might be worth searching for. Can't remember if it was a Vent Axia

 

EDIT - here it is -> 

 

Edited February 16 by Bramco

[Dreadnaught]

2 hours ago, Bramco said:

We run it on it's lowest setting

 

I have a Vigor W325 MVHR (was Brink), a very nicely built unit.

 

I run mine on its lowest speed setting too which is 50 m³/h and monitor CO₂ level.

 

What's the lowest speed setting on yours? I wish mine could go even lower.

[Bramco]

1 hour ago, Dreadnaught said:

What's the lowest speed setting on yours?

Not sure but on the setting we use it's about 170m3/h - which is fine for us - we have a lot of vaulted ceilings, so while it's 250m2, it's a lot more than normal in terms of volume.

[DownSouth]

11 hours ago, Bramco said:

Zehnder ComfoAir 350 and are very pleased with it.  We run it on it's lowest setting with automatic humidity sensing

@Bramco that’s the unit we are planning on getting. The website spec below talks about optional wall sensors for humidity and then later states there is an integral sensor. Do you need extra wall sensors fitted to measure the humidity?
 

https://www.bpcventilation.com/zehnder-q350

[Bramco]

We didn't have any additional sensors or switches installed. For us, running on the low speed setting with automatic humidity sensing turned on, on the unit works very well. Standing next to the unit, you can hear it change up a gear when it senses a high level of humidity.

 

If you are concerned you might need additional sensors and boost switches, you could always hide the wiring, so you could add them later.

 

Are you planning on opening widows in your bathrooms?  We have a couple with skylights, these clear very quickly. One en-suite has no opening windows, we should probably have had one in there. That one takes about 30 minutes for the steam to clear but we do have a massive Hansgrohe rain shower head in there.

Edited February 17 by Bramco

[DownSouth]

11 hours ago, Bramco said:

Are you planning on opening widows in your bathrooms

We have a window upstairs but not in the downstairs shower room so might need to add a sensor. Although it won’t be used that much…

[JohnMo]

46 minutes ago, DownSouth said:

We have a window upstairs but not in the downstairs shower room so might need to add a sensor. Although it won’t be used that much…

We have now been in the house with MVHR for a couple of years. We had manual over rides for boost and sensors in the MVHR unit. During winter humidity levels are so low, even after a shower boost is never needed.

 

Sensor for humidity is in the hall, humidity this afternoon was 39%, after boiling veg and potatoes for tea, humidity jumped up to 40% (1% difference), after an evening shower humidity up to 40.5%, 30 mins later back to 39%. Boost not used or didn't need to start.

 

MVHR flow rates are set lower than building regs

[JamesP]

We have Vent Axia Kinetic B Plus, all supplied by BPC. Fitted by myself.

Overall happy with BPC, I probably would not spend any more on a MVHR system than necessary as simple bit of kit.

It runs at 30% unless auto sensor from bathrooms kick in.

Think you need a manual boost switch in a WC, our BC was very picky about it being signed off by an"expert".

Do check volume as well as sqm as our unit was undersized

[Tom Heywood]

I understand the key is in the ducting design, not the MVHR unit, you need a low pressure ducting system and need to ensure the MVHR designers is running acoustic tests to make sure its inaudible. Then putting a good unit on it will result in a high performing system. Zehnder Q units have humidity sensors built in so I'd argue additional ones aren't required in a domestic setting 

[Mike]

On 16/02/2025 at 07:41, Lincolnshire Ian said:

Is it worth paying the extra for one of the other systems?

Yes if it performs well in the Passivhaus database, which lists models that have been independently tested to more accurate standards than those required in the UK and those used by manufacturers: https://database.passivehouse.com/en/components/list/ventilation_small. Vent-Axia do have 3 models in the database, but the Plus B isn't one of them.

 

BTW, the 'Efficiency Ratio' (which takes into account electricity used as well as heat recovered) is the key figure for comparison. For example, the near-identical Zehnder ComfoAir 200 & 225 models both have a heat recovery rate of 92%, but the 225 has more efficient fans so has a higher Efficiency Ratio (0.69, rather than 0.67).

[Nickfromwales]

On 16/02/2025 at 13:05, Dreadnaught said:

 

I have a Vigor W325 MVHR (was Brink), a very nicely built unit.

 

I run mine on its lowest speed setting too which is 50 m³/h and monitor CO₂ level.

 

What's the lowest speed setting on yours? I wish mine could go even lower.

I believe you can dial in to the (Brink) units, engineer level programming maybe, to reduce the lowest setting. I can check next time I speak with CVC, prob early next week as they're designing a system for me atm for another clients build 👍

[Nickfromwales]

On 19/02/2025 at 22:22, Tom Heywood said:

I understand the key is in the ducting design, not the MVHR unit, you need a low pressure ducting system and need to ensure the MVHR designers is running acoustic tests to make sure its inaudible. Then putting a good unit on it will result in a high performing system. Zehnder Q units have humidity sensors built in so I'd argue additional ones aren't required in a domestic setting 

But also the efficiency of the unit in terms of % of heat recovery. Some cheap units have very optimistic numbers.

 

@Lincolnshire Ian

FWIW, I have been using / installing Brink units (Flair+325 and 400 mostly) and these have done very well in both sound and heat recovery statistics. Never had issues with shutdown during extremely cold weather either, unlike another manufacturers unit (thread linked to above) which is "giving jip".

 

I go to CVC Systems in Oxford for all my units / design / supply & fit whenever I'm too busy, and never missed a beat; in over 6 years of promoting and installing MVHR for self build clientele. 

[Dreadnaught]

20 minutes ago, Nickfromwales said:

believe you can dial in to the (Brink) units, engineer level programming maybe, to reduce the lowest setting. I can check next time I speak with CVC, prob early next week

 

Oh, please do!

[tuftythesquirrel]

On 17/02/2025 at 21:05, JamesP said:

our BC was very picky about it being signed off by an"expert".

Hi,

I've read Approved Document F and can't see where any reference is made to "an expert" or a "competent person".

Appendix C provides a checklist for the commissioning engineer but there doesn't seem to suggest a competent person is mandatory.

I was going to self cert. 

A lot of people seem to be 'DIY'ing  the flow settings using the Buildhub anemometer, which made me think about how do you fill in the "Date of last UKAS calibration" column in the checklist, when using this. Has it been calibrated?

 

Edited February 23 by tuftythesquirrel

[tuftythesquirrel]

On 19/02/2025 at 22:22, Tom Heywood said:

I understand the key is in the ducting design, not the MVHR unit, you need a low pressure ducting system and need to ensure the MVHR designers is running acoustic tests to make sure its inaudible

Agreed for the first bit, but how are the acoustic tests carried out? You will only ever find this out when you turn yours on and every installation is unique.

[JamesP]

40 minutes ago, tuftythesquirrel said:

Hi,

I've read Approved Document F and can't see where any reference is made to "an expert" or a "competent person".

Appendix C provides a checklist for the commissioning engineer but there doesn't seem to suggest a competent person is mandatory.

I was going to self cert. 

A lot of people seem to be 'DIY'ing  the flow settings using the Buildhub anemometer, which made me think about how do you fill in the "Date of last UKAS calibration" column in the checklist, when using this. Has it been calibrated?

 

Most self builders on the forum had no issues with their BCO and MVHR. 

 

My BCO rejected my first self certifying report as the Anemometer had no proof of being calibrated, (used the Buildhub anemometer) I  hired this : https://www.inlec.com/testo-417-vane-anemometer-with-flow-hoods so hopefully will now accept my report.

 

Just looked through past emails and found this reply from the BC. 

I have checked the ventilation commissioning paperwork and this needs to be undertaken in accordance with the below paragraphs from Approved Document F.

 Air flow rate testing and commissioning of ventilation systems4.42 The Regulations require:• mechanical ventilation systems to be commissioned (where they can be tested and adjusted) to provide adequate ventilation and a commissioning notice to be given to the BCB;• air flow rates for mechanical ventilation systems in new dwellings to be measured and a notice to be given to the BCB.4.43 For dwellings, the procedures approved by the Secretary of State for measurement of air flow rates and for commissioning of mechanical ventilation systems are in Sections 2 and 3 of the Domestic ventilation compliance guide. Section 5 of the guide contains air flow measurement test and commissioning sheets which should be completed by the person responsible for commissioning.

 

 

[JohnMo]

On 21/02/2025 at 20:42, Nickfromwales said:

believe you can dial in to the (Brink) units, engineer level programming maybe, to reduce the lowest setting.

That's what I like about the titon units, super easy to adjust, normal rate adjustment by individual flow and return potentiometers, same for boost. Setback just falls midway between current normal setting and min acceptable flow.

 

Had a look at Titon frost strategy for cold weather without input heater. As it senses heat exchanger frosting is likely to occur, it starts to slow the supply fan down, once temp is outside frost zone it starts to slowly increase fan speed. So over a prolonged cold period supply fan will cycle speed up and down slightly.

On 19/02/2025 at 22:22, Tom Heywood said:

understand the key is in the ducting design, not the MVHR unit, you need a low pressure ducting system and need to ensure the MVHR designers is running acoustic tests to make sure its inaudible

Only part of the story 

You need a low pressure drop over the system, to get fan speed as low as possible. But the MVHR also needs to be generally quiet also.  But you also need the supply or extract terminal to be open as far as possible to reduced localised noise generation. But also have system balanced. That is part of commissioning, you can model noise as much as like, but poor commissioning will lead to a noisy system.

[Weebles]

We have a BPC supplied Vent Axia Kinetic High Flow. Installed by us to an BPC design. And commissioned by us using the BuildHub anemometer (no questions asked from BCO). Very pleased with its performance. 
 

Bearings in one fan just failed though (see separate post today) but hopefully we are on the way to fixing it ourselves. It is just over 5 years since we switched it on. Have cleaned it annually and regularly changed the filters. Also worth noting the the outside intake got incredibly gummed up with “cack” (it’s near trees) so we are more diligent on checking that now. Had to buy a replacement Airflow hood as the rubber seal had perished. Now trying to source a spare seal as the supplier doesn’t sell the rubber seal on its own.  

[JamesP]

@Weebles

Do you know the sqm your Vent Axia High Flow was designed to accommodate?

Worth checking the external cowl annually.

Edited February 23 by JamesP

[Weebles]

34 minutes ago, JamesP said:

@Weebles

Do you know the sqm your Vent Axia High Flow was designed to accommodate?

Worth checking the external cowl annually.

Sorry, I don’t know what the original design was for in terms of sqm. I looked back over the quote but it doesn’t specify.

And, yes, you are right to say that checking the cowl annually is a good idea. I didn’t realise that and discovered it was gunked up because it had got rather hot in the plant room as I guess everything was struggling a bit……

[JamesP]

@Weebles

If possible the sqm of your home and possibly the volume as well, thank you.