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Living with MHVR


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In terms of living with it.  Almost nothing to do.  Just enjoy the fresh air and lack of condensation.  Ours has a manual boost to speed it up for showering or cooking so we just press a button. Some systems boost automatically based on humidity.

 

Routine servicing is simply inspect the filters and clean or replace as necessary.

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If your air tightness is less than 3ACH then in Scotland you have no option.

 

But great to live with, you put a toilet/ bathroom light on and silence, 3 month on I still still like it.

 

A well designed system is the best part silent and in the background.

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No boost here, no sensors or remote control panels. Just run it at a slightly higher speed to average out the overall effect of humidity. Took a few months to find the right number. Works fine. Now it never gets touched and we completely ignore it. 

 

I could hear it at night in bed so I built a DIY silencer which works a treat. 

 

Filters have to be changed which adds to the cost. Ours were €22 a pop so about €88/year. I changed to car pollen filters that fitted at €32/year.  Electricity about €30/year.  Realistically if you're using a heat pump or mains gas there's probably no payback on the cost of energy.

 

However. 

 

1.It means you can avoid holes in the wall or windows for ventilation. These leave you completely at the mercy of a the wind and will make your house drafty and need to be overheated to achieve the same level of comfort. You will need to have a bigger boiler and radiators also. 

 

2.Controlled filtered mechanical ventilation means your house's air is far cleaner. Less pathogens, less VOCs, less spores. A brilliant article here. https://passivehouseplus.ie/magazine/insight/natural-ventilation-does-it-work. This was a big pro for us with kids and me with hayfever. 

 

3. Humidity will be actively controlled. Less dust mites, less insects, less mould. This means not only less cleaning but also that the structure of the building will be protected. Far lower lightly hood of any decay of timbers etc. 

 

4. No traffic noise or whistling of wind through trickle vents. 

 

 

I'm sure there's more but its a big thumbs up from me IF  specified and installed correctly. 

 

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4 minutes ago, Thedreamer said:

 

Is that correct? I believe its just to have mechanical ventliation.

Nope.  A near neighbour had started installing basic whole house mechanical ventilation, had his air test done, better than 3, Building control told him he had to have full mvhr.

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Just now, Thedreamer said:

 

Not even MEV?

No, that is what he was installing.  Because he was so far through, he ended up with 2 separate mvhr systems for upstairs and downstairs to limit how much he had to strip back and re do.

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That is surprising as I could no reference to it being required under Scottish Building Regulations, just an example of a system that could be used?

3.14.11 Mechanical ventilation and systems

The design, installation and commissioning of a mechanical ventilation system should mean that it is capable of performing in a way that is not detrimental to the health of the occupants of the building and when necessary, is easily accessible for regular maintenance. Very few dwellings are air-conditioned but the use of continuously operated balanced supply and extract mechanical ventilation systems and of heat recovery units are becoming more popular as a result of the need to conserve energy and reduce greenhouse gas emissions. As building are constructed to lower infiltration rates, mechanical ventilation may be necessary to deliver the effective ventilation needed to provide a healthy living environment.

Simpler and more efficient systems are steadily being introduced that augment, complement and/or improve the natural ventilation of dwellings.Where infiltration rates of less than 5m3/h/m2@ 50 Pa are intended, such a system should be used. The following are examples of mechanical systems that will aid ventilation in a dwelling:

  • continuously operating balanced supply and extract mechanical ventilation systems. When combined with heat recovery these installations are known as Mechanical Ventilation and Heat Recovery (MVHR) systems. Installations should be in accordance with the guidance in BRE Digest 398. In hot weather windows can be opened to cool the dwelling while the system is not operating. Openable windows may also be needed for fire escape purposes

  • centralised mechanical extract ventilation (MEV) installed in accordance with the guidance in BRE Digest 398

  • where the infiltration rate is not less than 3m3/hr/m2 @ 50 Pa, decentralised mechanical extract ventilation units (dMEV), in rooms where there is likely to be high humidity such as kitchens, bathrooms and shower rooms. A dMEV should be designed, installed and commissioned to provide minimum continuous extraction rates in accordance with the following table:

 

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2 minutes ago, Thedreamer said:

 

  • where the infiltration rate is not less than 3m3/hr/m2 @ 50 Pa, decentralised mechanical extract ventilation units (dMEV), in rooms where there is likely to be high humidity such as kitchens, bathrooms and shower rooms. A dMEV should be designed, installed and commissioned to provide minimum continuous extraction rates in accordance with the following table:

 

 

Ooops. I see it there in the last bullet point. 

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3 hours ago, Si3 said:

I am thinking about installing MVHR in our new build. I am just wondering is it worth the cost of, and what is it like to live with? 

 

I've lived with it in a highly insulated and airtight house for about 6 years, and there's no way I'd ever voluntarily live in a house without it in the future.

 

It costs a bit to buy and run, and you need to replace filters periodically, but I think it's a small price to pay for consistently fresh air all year around.

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3 hours ago, MJNewton said:

Quite simply: yes, and easy! 

 

Ours was a retrofit so a lot more work, so putting it in a new build would be so much easier and so much easier to achieve the benefits. A no brainer I'd say. 

+1 on both worth it and that its harder to do later.

 

We have 100m2 floor area and our MVHR runs at 17 Watts normal and 25 Watts on boost, so it would cost us £40-45 a year to run but we have PV so even less.....  That's 45 pence per year per m2 flooring.

 

 

 

 

Edited by Marvin
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3 hours ago, Iceverge said:

3. Humidity will be actively controlled. Less dust mites, less insects, less mould. This means not only less cleaning but also that the structure of the building will be protected. Far lower lightly hood of any decay of timbers etc. 

 

 

There was a period on BuildHub when the excessively dry atmosphere caused by MVHRs was a recurring point of discussion. Has this problem gone away? I recall some fit special MVHR units that transfer moisture back into the feed air supply to maintain a health higher humidity level.

 

The notion that an MVHR combats damp, rotting timbers and mould is a bit fanciful in a new build.

 

I will be fitting one but in the interests of giving the OP a balanced view let's not get carried away with group-think.

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13 hours ago, Si3 said:

what is it like to live with? 

Hi @Si3

 

It's different than before we had one. No trickle vents. An almost unobservable flow of fresh air. Sometimes noise travels down the rigid ducts.The boost function clears the air. Never hear the MVHR at normal speed.

 

Air temprature outside this morning 1.7C.  Fresh air temprature entering living room after heat recovery, 15C. Definetly keeps the place warmer in the winter. 

 

Sometimes feels dryer but we only have 100m2 floor and the humidity from showering seems to compensate even though we have automatic humidity sensors that boost the MVHR.

 

Cooking can be a challenge if you don't boost the system enough when cooking as the smells can linger.  

 

Even in the summer we now leave the MVHR on to avoid any problems with the pipes.  Usually look at the filters once or twice a year. 

 

It has been a tricky process because we retro fitted the the system and had to super insulate the ducts in the exposed loft.

 

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Good luck

 

M

 

 

 

 

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Related to this is the real benefit of an air tight house with mvhr and no trickle ventilators. You can open one door or window, even on a windy day, and virtually no wind enters or leaves through that open door, and none of the internal doors blow shut.

 

Our previous house, open the front door on a windy day and the kitchen door blew shut as the wind passing through exited the cooker hood vent and the cat flap.

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21 minutes ago, Si3 said:

Advice here is brilliant, thanks all. With regards to the noise is one of those things you only notice after it’s installed, and the. Just blends into the background?

Ah!  Sound down pipes from other rooms! Rearly hear it but live in a quiet area.

 

No. Not for us. Wife says no noise unless on boost and then only a low hum with ours far far quieter than the fridge Freezer!! Toothbrush charging makes more noise! 

 

HOWEVER we followed the installation instructions to the letter. Our unit is 2 meters from the bedrooms above the ceiling. Wife is noise sensitive!

Edited by Marvin
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