Recently built 3-storey home and looking into MVHR systems

[Jde00]

Hi,

I live in a recently built 3-storey home, this house is fairly well insulated (floors could perhaps improve as we have vinyl on concrete slab downstairs) and has a air tightness score of  5.8 m³/h.m²

The windows are equipped with the usual trickle vents. The utility room and 3 bathrooms are equiped with timed extractor fans which are quite noisy and not very useful. We have an open plan kitchen/siting area and the hob extractor fan doesn't seem to cope well with smells as the entire sitting area usually smells of food and stale air.

 

as I said the house is well insulated with good air tightness values. We have ASHP for central heating and hot water and really love the system.

 

I hear a lot of people talk about MVHR systems, and I quite like the idea of having fresh air renovating in the property. I do have some questions.

My main objective would be to renovate air in the house, I'm not necessarily looking to improve energy efficiency as it's already quite good.

Can this be retrofit into a fairly decent new build? How would it be installed? If hte unit goes in the 1st floor I can see how the ducts could easily go into the ground floor ceiling and throughout the first floor, but we have our master bedroom and en-suite bathroom on the second floor so not sure how the ducts would go up there. Is the system less efficient if we keep a window ajar during the night? that's how we currently keep fresh air in the bedroom, but perhaps with a MHVR system we won't have to?

Are the systems noisy? 

I understand the system would take air from the wet areas (kitchen and toilets) filter, heat exchange into fresh air from outside, and distribute that air to the rooms. But would the system distribute fresh air into the kitchen area as well?

 

I'm in Cambridge.. any recommendations who I can ask? 

[ProDave]

A full mvhr system has a central heat exchanger unit and from there it needs to supply fresh air in to all living rooms and bedrooms and extract stale air from kitchens, utility rooms, bathrooms and toilets.

 

Your biggest challenge is going to be retro fitting this into a new build, where almost certainly you will have chipboard panel floors which are not exactly easy to take up.

 

Your best hoe will be can you find a route for all the downstairs vent positions to get up into the loft, perhaps up via a cupboard or wardrobe for instance to minimise the amount of floors to take up.

 

Is it a house that you built?  If not then you won't even know much of the construction and what you might find in your way.

[Bitpipe]

While your airtightness is not bad (BR is 10?), it's too high for the heat recovery effectiveness of MVHR to be effective - 2 is normally the target. A passive house is 0.6 or less. I may have got my units mixed here as I am more familiar with ACH so ready to be corrected !

 

As @ProDave says, the biggest consideration will be the disruption of the retro fit.

 

Even in a new build house, pulling the duct to every room through web joists is not a trivial task and you may well find obstructions from other services.

 

The MVHR unit is ideally centrally located (but not essential) and needs insulated large bore (150mm) feeds to outside for air intake and extract, then manifolds for the internal supply/extract which feed individual runs of 75mm flexi duct to the room terminals. These are usually ceiling mounted, with a design that encourages airflow across rooms. Visualise the extracts in the bathrooms and kitchen pulling damp air out and the supply vents in bed / living rooms providing fresh replacement. Doors need 7600mm2 area at base to allow airflow between rooms.

 

The efficiency comes from the transfer of the heat of extracted air warming the incoming air so you don't need to heat it again from scratch - unlike the cold air that comes in from your trickle vents.

 

Extraction normally runs at 30% of fan speed and 50% for boost - triggered manually (switch) or via humidity sensors or electrically via bathroom lights / prox detectors or the hob extractor circuit (you may want to switch that to re-circulation).

 

The system is balanced to provide equivalent incoming air, although the more airtight your house is, the less you can prevent cold air just being pulled in through the fabric or trickle vents. 

 

If specified and installed well, the system is fairly silent at the vents with boost being a bit more noticeable. Some add silencers to further attenuate noise. The unit itself should not generate much noise, depends what it is sitting on and if its isolated to any degree.

 

 

[Mr Punter]

The setup you have at the moment relies on trickle vents to provide fresh air.

 

You may be best making sure the trickle vents are left open and changing the extract fans for ones that are quieter and more efficient.

 

For the kitchen, if it would not be too focal you could look at an externally mounted unit or change for a better / quieter one and make sure the exhaust hole is 150mm diameter.

[MikeGrahamT21]

Taken from the Paul website:

 

MVHR Systems provide controlled ventilation with slow but constant air movements. In contrast, natural ventilation through background ventilators (trickle vents) is a form of uncontrolled ventilation, which fluctuates with wind speeds, temperatures, internal obstructions, such as the opening or closure of internal doors, trickle vents, blinds and curtains. Therefore, it is recommended to install such systems only in properties with relatively good air tightness. We recommend an airtightness of at least 5 m3/(m2*h) at the pressure test (q50), ideally below 3 m3/(m2*h). Air tightness targets should always be set for new built and refurbishment properties.

E.g. in a refurbishment project where windows are exchanged and other measures to increase the insulation and air tightness are being undertaken, MVHR system can definitely be a beneficial addition in the aim to increase the energy efficiency and avoid black mould infestation and the proliferation of house dust mites.

[Jde00]

The thing is that we think the passive trickle vents is not the best option for an ASHP system that relies on slow flow temp. Whenever we open the vents we get draught and it feels cold, as a consequence the ASHP kicks more often than really needed.

 

This a house built by a small developer, it wasn't self-built.

Edited February 22, 2021 by Jde00

[MJNewton]

I retrofitted MVHR into a 3-storey 2007 developer-built house and whilst it was doable it was hard work as I didn't want any visible boxing in! I was lucky in that the house uses I-joists which happen to all run the right way (I had to go through one but that wasn't too difficult), the top floor has a dressing room and walk-in wardrobes so was easy to run pipes from the loft-mounted unit down into the lower floors, and I was extending the ground floor so ripped the ceilings out to make ducting (and everything else) easier. We've now removed the extractor fans, foamed up the trickle vents and haven't looked back - it's superb and would highly recommend it if you're prepared for the sleepless nights planning ducting routes.

Edited February 22, 2021 by MJNewton

[Jde00]

Ha! I have no idea what I-joists are. I can ask the builder but doubt they'll even reply.

 

I think assuming we can fit the main unit where our water tank is, most rooms are easily accesible. Not all though.

This utility closet is in the first floor, within a couple of meters of two bedrooms and family bathroom. Right over the kitchen. Master bedroom and en-suite right above. We have a walk in wardrobe too.

 

The hardest pleace to reach in my opinion is the living room.

 

I suppose I could try to insert a camera through one of the spotlights and see what the ceiling looks like in terms of joists

Edited February 22, 2021 by Jde00

[MJNewton]

6 minutes ago, Jde00 said:

Ha! I have no idea what I-joists are.

 

They're just engineered joists made from timber with an OSB web between them (left pic below). Due to their inherent strength they can span longer distances than conventional joists and you can knock huge holes in them if required (bracing can be required in some circumstances). If they're pozi joists (right hand picture) then you really are laughing!

 

 

Quote

I can ask the builder but doubt they'll even reply.

 

I wouldn't bother. If it'll be a DIY job then you'll soon learn exactly how your house is built - indeed you'll end up knowing more than the builders!

Edited February 22, 2021 by MJNewton

[Jde00]

there's no way I'm doing myself

I have a good builder who's the husband of a colleague and he doesn't know it yet but I have him in mind for a long list of jobs in the house

 

Going back to one of my original questions. I assume that since you have continuous air flow, you don't need to open any windows but if you were to open one, can you pause the system to avoid wasting energy? We are bit peculiar and do like sleeping with the window open.. Crazy European things...

[MJNewton]

7 minutes ago, Jde00 said:

I have him in mind for a long list of jobs in the house

 

Okay that's good, as retrofitting MVHR really is a long list of jobs! 

 

Quote

Going back to one of my original questions. I assume that since you have continuous air flow, you don't need to open any windows but if you were to open one, can you pause the system to avoid wasting energy? We are bit peculiar and do like sleeping with the window open.. Crazy European things...

 

We open our windows far less than we used to, but it's perfectly fine to do so. Whilst you can have all manner of controls you can still keep it running 24/7 anyway as there are still benefits to be had even when the windows are open eg more thorough ventilation, dust/pollen collection, slight cooling/freshening effect in hot weather etc. Running costs are minimal - we're drawing 15W in continuous background rate which works out at around £20/yr when used 24/7/365.

Edited February 22, 2021 by MJNewton

[Jde00]

and I just noticed I should have posted this in the MVHR forum

[Russell griffiths]

Whats your budget to do this, I would think the disruption and making good of areas cut out to install it could seriously effect your view on putting it in. 

@MJNewton how much do you think you spent on the system and the making good afterwards. 

[MJNewton]

3 hours ago, Russell griffiths said:

Whats your budget to do this, I would think the disruption and making good of areas cut out to install it could seriously effect your view on putting it in. 

@MJNewton how much do you think you spent on the system and the making good afterwards. 

 

Good question. The kit is the easiest to answer as I've everything in a spreadsheet - £1440 for everything down to the last screw (well, almost).

 

Labour though and consequential costs is virtually impossible though. I did all the work myself and dread to think how many hours I put into it - whether that be real work or planning (procrastinating). I can't even give a ballpark figure... 50 hours? 100 hours? I really don't know. The consequential costs is tough one too as I took a ceiling down for our new 'family room' and replaced a stud wall to hide some ducting. These required new boards and then skimming (plasterer did the skimming) but I was pretty much doing this anyway so it didn't really add to the bill.

 

But, yeah, I love the system and would definitely fit one again. Would I pay someone else to retrofit one? Probably not in all honesty as the costs could spiral and would a builder spend six hours routing a single awkward duct like this idiot...?

Edited February 22, 2021 by MJNewton

[Iceverge]

I think your airtightness levels are too low and with your house already being built built it's a non starter. 

 

Read up on decentralised MVHR but decentralised DCV (demand controlled ventilation ) is probably the best you can do in terms of performance and price.