Shall I install mvhr

[jpinthehouse]

Hi

Have read about mvhr, haven't included it in my current plans for new is it worth considering and what are the benefits.

Thanks John

[ProDave]

It all depends what you want from your house?

 

A lot of us here are aiming for very well insulated and very well sealed houses to make them energy efficient.

 

Once you get to a certain level of insulation, then the heat loss becomes more dominated by ventilation heat loss (you must ventilate the house somehow anyway) and that is where an mvhr unit really comes into its own to reduce ventilation heat loss and so improve energy efficiency.

 

It also improves air quality. Ventilation by natural means is so hit and miss and variable.

[Ian]

1 hour ago, jpinthehouse said:

Hi

Have read about mvhr, haven't included it in my current plans for new is it worth considering and what are the benefits.

Thanks John

If you are aiming for an airtightness value of less than 3 m3/hr/m2 (which isn't difficult) then the BCO will want you to install MVHR.

 

Natural ventilation is normally only acceptable as a solution when air tightness exceeds 3 m3/hr/m2

 

 

[RandAbuild]

For all the benefits you get from MVHR (filtered air, minimised heat losses, no noisy or problematic bathroom vents, trickle vents and droughts), I think it's a no brainer in a new build.

 

Ours cost us £2600 from BPC. It's easy to fit if you have easijoists and a suitable location for the box and ductwork.

[Redoctober]

I know this goes against popular opinion but we are looking to build a well insulated house but not seeking absolute airtightness. Time will tell as to whether or not we would need one due to the airtightness levels we record. It is accepted that anything under 4 would require one.

Our thinking is based on a few things. We like having windows open and an MHRV relies on electricity/energy, significant upfront cost investment and on going maintenance, which we are trying to avoid. It just seems a large investment and another thing to maintain, for an item that could only be in useful operation 6 months of the year.

Having said that, those with such a system will say it's the best thing they have installed.

Decisions decisions................

[ProDave]

A friend near here is building a new house. He originally went for the daft sounding idea of trickle vents in the windows and mechanical extraction from "wet" rooms permanently on (a centralised extraction unit)  Then he had an air tightness test done and it was too good. Building control told him he must have mechanical air input as well. He did look at adding a separate air intake system, I kept telling him the whole idea was bonkers (no heat recovery). In the end he has ripped it all out and installed mvhr, which is what I advised right at the start.

 

My mvhr unit was about £500 and ducting etc about £1000 you should comfortably get a system for £2K At it's lowers speed (which I am hoping is what I can use as the trickle ventilation rate) my unit uses about 30W of electricity.

 

Sure in summer, turn it off and open the windows.

[jack]

44 minutes ago, Redoctober said:

It just seems a large investment and another thing to maintain, for an item that could only be in useful operation 6 months of the year.

 

True, but during those 6 months of the year, you'll have fresher air in your house than you've ever experienced during winter, and will drastically reduce your heating costs.

 

Also, on very hot days, the MVHR keeps the air fresh while keeping some of the coolth in.

 

I'm one of those who wouldn't be without it now that I've lived with it.

[Jeremy Harris]

Work out how much you'd save by fitting MVHR.  Ours reduced the heating requirement by between 50% and 70%.  If you used the lower figure, then you could quickly work out the heating bill cost reduction.  For most houses an MVHR will probably pay for itself in around 5 to 8 years, I think. 

 

As above, the fresh air all year around is also a big bonus, as is the absence of noise from extractor fans.

[jpinthehouse]

Hi

Thanks for the replies,I will be using posi joists so that should make it easier, is it a diy fit ,may be I should put my plans on for some feedback and assistance with the mvhr

Thanks John

[ProDave]

Just now, jpinthehouse said:

Hi

Thanks for the replies,I will be using posi joists so that should make it easier, is it a diy fit ,may be I should put my plans on for some feedback and assistance with the mvhr

Thanks John

Definitely. It took me a weekend to install all the ducts.  For a DIY install it is probably best go go for a radial duct system such as that sold by BPC and others, rather than a branch system. This uses semi flexible duct pipes that easily wind their way through posi joists

 

[Gone West]

I have metal web joists and used a rigid plastic branch system. It's no problem as long as it's well thought out before fitting.