Should I remove an installed MVHR?

[mico1411]

Hi, we've just bought a house that has a very old MVHR installed which needs the main unit replacing and the ducts cleaned and balanced.

 

We are not planning on having an airtight house and will keep windows open during warmer months. We cannot decide if the benefits of running an MVHR in a non-airtight house warrant the cost to upgrade/service.

 

We cannot find anyone in the local area (North East) that can assess our installation and make recommendations so would be grateful for your opinions.

 

The installation is very old, the main unit is branded "Flow Engineering" and I've attached some photos. I can hear the fans are working but I cannot feel any air movement through the vents. 

There is galvanised metal ducting to every room and it extracts from kitchen, utility and bathrooms. The unit is mounted in the loft and there is no loft insulation at all. 

 

Is it worth upgrading and servicing the MVHR system or would it make more sense to install an MEV with the existing extraction ducting and remove the rest of the ducting in favour of loft insulation?

[mike2016]

Is it an airtight house? When was it built? 

I'd buy some moisture/humidity sensors and measure levels through the winter. You could have moisture build up and monitoring this will be key to keeping a healthy house - kitchen, showers, drying clothes, dryer, sleeping areas where we breath out a lot of moisture all need to move somewhere, outside preferably! 

Did they close/block/remove the passive air ducts through the walls or are there just trickle window vents? The MEV will depend on how it draws air in. You could end up pulling air in unforseen ways which can lead to new issues. Plus you're drawing in cold air, no heat recovery. Great in winter!! I put a positive air pressure unit into the loft and the frost protection melted the frost on the inside of the roof felt in the attic and caused a LOT of attic moisture on me last year - put in an upstairs MVHR instead for 3K. 

If you can get the metal ducts cleaned so they can be reused, then a replacement MVHR might be an option but baseline your house now with a sensor or two like Sensorpush & gateway from Amazon or something like that. 

You can get a blower door test to measure ait tightness but that and a new MVHR will lead to more cost so if that's not your immediate goal, open windows in the summer sounds fine but it's the rest of the time you need to watch out and plan for......

 

Looks like someone was thinking well ahead of their time....!

[mico1411]

Thanks for your reply mike2016.

 

The house was built in 1986. It was built for an architect's family so I think the system could be that old - very much ahead of its time!

 

You're probably right, I need to spend more time assessing humidity levels etc before making a decision. There are tickle window vents on every window. I'm guessing the house could potentially be quite airtight but I've never tested it and I can't see us relying on MVHR for ventilation - windows and doors will be left open!

 

How do people generally clean the ducts in a residential  installation? Does it involve getting in a specialist cleaning company that typically services commercial ducting or can you do it yourself?

 

[Temp]

Our house isn't airtight but we still love our MVHR. 

[MJNewton]

1 hour ago, Temp said:

Our house isn't airtight but we still love our MVHR. 

 

Same here. I'd suggest replacing the unit and making the most of the existing installation. 

[Olf]

6 hours ago, mico1411 said:

There is galvanised metal ducting to every room and it extracts from kitchen, utility and bathrooms

And for that reason alone you should keep it: the house may not be airtight, bit that means the draughts happen likely not where you want them. MVHR lets you suck the humid air where you do want. And then you get some of the effort put in heating that air it back.

 

6 hours ago, mico1411 said:

will keep windows open during warmer months

Makes sense, especially with uninsulated ducts in the attic: this will act as a preheater on sunny days.

 

Loft insulation is always a good idea, and will help with MVHR ducting.

 

Considering the age of the unit I don't expect high effciency, I'd get some modern unit off ebay for few 100s and interface it with the existing ducting.

[ProDave]

+1 to replace with a current unit, adapting the ducting as necessary.

 

The loft not currently being insulated is a bit of a bonus. You can insulate the loft ensuring ALL the ducting is enclosed within the insulation, e.g loft roll insulation simply going OVER all the ducting.  Box in an enclosure for the new mvhr unit and take the insulation over that.

 

Add external inlet and outlet vents with those also enclosed by the insulation.

[mike2016]

19 hours ago, mico1411 said:

How do people generally clean the ducts in a residential  installation? Does it involve getting in a specialist cleaning company that typically services commercial ducting or can you do it yourself?

Not sure - would get a quote from a few companies and see what it costs. Expect to have to do the same with mine in a few years. At least it's an infrequent expense and you need to factor that into the cost to re-commission. If you get a new MVHR they might offer that as part of the package?  

[Iceverge]

You may have a perfectly well functioning system.

 

Have you lived with MVHR before?The air flow volumes are very low. You shouldn’t feel a breeze unless your face is literally beside the vents. 

 

Have you checked/changed the filters?

 

 

[mico1411]

Thanks everyone for the comments, plenty to think about.

 

Iceverge - the unit is very old, it has a metal grease filter that's built into the case but no removeable filters.  A new unit is needed but just working out if we can justify the more expensive MVHR or just go for a cheaper MEV to extract only. We've not had an MVHR before.