Every journey starts with a first step . . .

[iansr]

So this is me taking my first steps on the DIY MVHR journey.  I was prompted to think this was feasible after talking to David Hilton at the recent Home Building/Renovation show in Harrogate.   So one of the first questions I need to address is whether I should go with a pro design or try designing it myself?    I’ve already had one pro design quote from a company called ADM who happen to be based in West Yorkshire where we live.  David Hilton has a company himself that provides such a service and I’ll get a quote from him too.  However, I would like to do a deep dive into this myself and so I was wondering whether anyone could point me to a comprehensive “how to” guide ?

 

Any other comments / thoughts will be gratefully received.  FYI we are radically altering a dormer bungalow including extending outwards and upwards.  It will be 250 m2 when finished.

[JohnMo]

BPC Ventilation do a guide.  Building regs will state flow rates you need to achieve.

 

Ducting, metal or plastic stiff duct will need silencers between room to eliminate cross talk.  Semi flex, connect via a plenum chamber and eliminate the cross talk.  Don't go with flexible tube as the pressure loss is huge, so fan run at higher speed to compensate, making system use more electricity and make more noise.

 

Passivhaus institute has some good reading material.

 

The basic things I thought about, keep ducts short as possible, buy a bigger unit than you think you can get away with, as fan speed for a given output will be lower. Shop around.  Read as much unbiased info as possible.

[Iceverge]

Good Guide here. 

 

https://www.paulheatrecovery.co.uk/mvhr-guide/ 

 

My pointers in no particular order. 

 

1. Locate MVHR unit within heated envelope or build a dedicated insulated enclosure if this is impractical. 

2. Don't be afraid to mix and match suppliers of ducts, units etc.   

3. Locate Inlet and Exhaust terminals on an exterior wall but not by a bedroom window (noise).

4. Place room vents over a window opposite the room door.  (avoids obstruction by furniture and is unlikely to cause a draft on a bed/chair) 

5. A radial semi rigid ducting works well, ease of install, minimal cross talk, cheapish. 

6. Don't forget about a condensate drain. 

7. Locate the unit where you can service the filters. 

8. Consider the noise of the MVHR unit. Suspend it by wires or rubber mounts in the attic. Bolt it to a solid wall or sit on a concrete floor to reduce vibrations. Leave plenty of space for rigid silencers (or DIY them).

9. Forget about meaningful cooling or heating form MVHR. It is really only a ventilation system. 

10. Don't get carried away with smart controls/remote switches. We just set ours to 35% and rarely touch it. 

11. A higher capacity MVHR unit will run quieter. 

12. Don't be afraid to DIY the design. It's not rocket science.

13. Don't use floppy ducting anywhere. Semi rigid is fine. 

14. Insulate the Exhaust and Intake ducts for condensation. 

 

 

 

 

[iansr]

Thank you guys.  Interesting comments about ducting as I had read a comment somewhere that flexible ducting is way easier to install.  However there are clearly other factors based on the above comments.

[JohnMo]

Also worth considering are Coanda effect outlet nozzle, these throw the air several metres, so across a room, clinging to ceiling.  This gives more flexibility for outlet positions

[JohnMo]

Semi flexible is quite flexible. BRE do some design guidance notes also.  

 

Flexible duct is supposed to be pulled tight, but I wouldn't waste my time or money, to do it correctly is hard, so in a lot of cases, it's just installed badly.

 

As said mix and match manufacturers, you don't need smart control, humidity control can be hit or miss as our humidity fluctuates greatly across seasons.  Simple boost switch in wet rooms and kitchen.

 

 

[MJNewton]

14 minutes ago, JohnMo said:

humidity control can be hit or miss as our humidity fluctuates greatly across seasons.  Simple boost switch in wet rooms and kitchen.

 

Rate-of-rise humidity detection addresses that, but I didn't spot any off-the-shelf solution to had to roll my own so I accept it might be undesirable for many. It does work perfectly though and, to my knowledge, has never suffered a false positive or negative.... It also doesn't rely on my family pressing boost buttons which they could but wouldn't in practice! 

Edited November 12, 2021 by MJNewton

[iansr]

Some good info on that PaulHeatRecovery site.  It’s a good example of implicit selling and its pretty effective in that regard.  I suspect they are at the top end of the price range though . . . .

[Iceverge]

I have no idea. Maybe get a quote if they're in your area. We DIY'd ours. 

 

MVHR is lightly to be disappointing if it is installed by cowboys so, like everything else, cost should only be part of the equation. 

[JohnMo]

I bought a few bits from them, where the prices were ok and prior to that got a full installation cost, hence going DIY.

[iansr]

I’ve already decided on DIY installation.  I need to decide whether to design it myself or outsource that aspect.