MVHR system in new build

[dpmiller]

^yep

[Rishard]

There certainly is plenty to think about. I may have been foolish to think the suppliers ‘free’ design service would be enough to produce the plan! Hearing others experience on here, the system is relatively diy, however it may be worth starting this process earlier than planned. I allowed for a reasonable space for plant and have flexibility within internal walls to make alterations if more space is needed. Maybe I should post up a floor plan to hear opinions on system location ect. (Possibly on a new thread?)

Edited March 14, 2022 by Rishard

[JohnMo]

Based on that figure, the fans specified as intermittent are fine.

 

But with a polystyrene ICF build you may be a lot more air tight and could end up with mould, poor air quality etc.

 

As a minimum I would get dMEV installed, these fans will fit into the existing/planned holes in the wall, match the windows you may have already been installed/ordered, with trickle vents and give you the least hassle.  Best of all they are silent.  The way dMEV works, the fans run at a low speed continuously, extracting air from the wet rooms.  Air is drawn in through tickle vents in dry room windows.  The air cross flows through the house/under doors etc. and out through the wet room fans.  Think you are aiming for 0.3 ACH through the ventilation system.

[Conor]

15 hours ago, TerryE said:

 

Conor,  You've got your commission order out of sequence.  MHVR should have been just be about the first thing to commission after 2nd fit as soon as you have a temporary electricity supply up.   Pretty much everyone here on the forum (at least those that have sized and commissioned their MVHR systems correctly) agree that you live in a house that always smells fresh and  that never have problems with damp or condensation.   The tickle vents and four holes will be a PITA to seal properly once your MVHR is commissioned.

 

The MVHR system was one of the things that Jan and I did ourselves.  The sizing calcs are straightforward as is a star manifold installation, though to do need to properly calibrate and commission the system.  If done properly, the B Insp will accept a self-certified commissioning report.  It performs really well.

 

We've not finished yet. Boarding, joinery and second fixes still to do in the basement and two bathrooms. We're in a bit too early but had to get out of the rental!

[Happy Valley]

Designed plans for the MHVR unit have changed in reality with our ICF build. Initially we had the manifolds in the plant room on the ground floor but we have fitted them in the loft as there are way more ducts to the 1st floor than the ground. It's a warm roof. The unit is still within the plant room but moved slightly because of the manifold change. Luckily we have enough room in there to do this. There is a cupboard above the plant room which means we can hide all the pipework from the loft to the unit well and again allowed for variations in locations of the manifolds and unit. 

 

Our original design came off our plans emailed to a company with no one visiting the build. As already alluded to it is advisable to have some degree of flexibility if possible to move things around.

[PeterW]

23 minutes ago, Rishard said:

I may have been foolish to think the suppliers ‘free’ design service would be enough to produce the plan!

The issue is those free services make a lot of assumptions. The good ones take this into account and also understand all your systems and services, the others sometimes forget to tell you that you need “x ducts of 75mm through the floor” which is something if you have beam and block you need to know about at design time not installation !

 

As @Nickfromwales and @Happy Valleypoint out - plant space is premium in a build and it is surprising how little gets planned in to start with. If you search MVHR installation on the forum you’ll find plenty of examples of people having to be creative in siting units to take into consideration space that hasn’t been planned at design time. 

[Rishard]

17 hours ago, JohnMo said:

Easy to work out read building regs for your region.  In Scotland it's basically 0.5 ACH.  So calculate the internal volume, divide by 2.  That's the basic normal flow, add 25% for boost.

 

Choose a unit that flows your boost figure at about 70% or lower it's rated capacity.

 

Extract in wet rooms and kitchen, supply everywhere else.  

 

As Dave say semi rigid is easy to install, just plan ahead.

 

 

 

Are all your ceilings vaulted? Did you go for a warm roof design with insulation over your rafters or are you blowing in insulation? 

[JohnMo]

All vaulted, except a small part of hall.

 

Spray foam insulation between and under rafters.

[deuce22]

On 14/03/2022 at 08:31, JohnMo said:

Based on that figure, the fans specified as intermittent are fine.

 

But with a polystyrene ICF build you may be a lot more air tight and could end up with mould, poor air quality etc.

 

As a minimum I would get dMEV installed, these fans will fit into the existing/planned holes in the wall, match the windows you may have already been installed/ordered, with trickle vents and give you the least hassle.  Best of all they are silent.  The way dMEV works, the fans run at a low speed continuously, extracting air from the wet rooms.  Air is drawn in through tickle vents in dry room windows.  The air cross flows through the house/under doors etc. and out through the wet room fans.  Think you are aiming for 0.3 ACH through the ventilation system.

So, I'm guessing these were out prior to MVHR systems and they don't work, nowhere near as good?

 

Do they only need fitting in bathrooms and is there a benefit to add them to other rooms?

 

I'm assuming that these are what has been specified by the SAPS company. Why would they not specify a MVHR system, considering it's an ICF property?

[JohnMo]

What are you referring to "these"?

 

dMEV fans go in the following rooms.

 

Utility, bathroom, shower room, en-suites, kitchen, anywhere where moisture is generated.  The combination of all the fans must give an air change of 0.3 an hour.  So calculate the internal volume of the house, divide by 0.3,this will give you are target M3/HR flow rate.

 

Read building regs related to ventilation that will tell you exactly what is needed, for flow rates in each room, but base any discussion on an airtightness of less than 5.

 

 

[deuce22]

Thanks JohnMo