MHRV info

Wavehopper

Hi all,
First time post, building a new two-storey house with cavity block and taking steps to have as air-tight as possible, e.g. wrapping hollow-core, taping windows, membranes at roof level, air-tight stoves, etc. Therefore, I plan to install MHRV system and have looked at several suppliers.

Most of the units are very similar from the ones I've looked at, some slight differences in fan power & efficiency from SAP Appendex Q. However, the one thing that frustrates me is the different opinions on ducting, every supplier I talk to has a different take;
- one recommends steel ducting (much better fire resistance) but another says it will be noisy. It also makes system expensive and won't be insulated either
- one recommends rigid ducting but another says it will be noisy, will be a fire hazzard and will result in fire spreading from room to room and will gather dust/dirt due to static. This also won't be insulated but was told to throw atic insulation over it
- one recommends flexible ducting (noise proof, much better fire resistance, anti-bacterial, comes insulated) but another says it will be less efficient due to flexible nature of duct.

One supplier installs all 3 types of ducting but recommends the flexible (insulated non-woven, anti-bacterial, better thermal efficiency) ducting and states that the new flexible ducting is much better now than what was previously available. Was also told it won't be any different in terms of fan speed, unit efficiency than rigid.

The potential for noise and fire spread with rigid PVC has alarmed me so I'm leaning towards this flex ducting.

Just wondering if anyone has rigid PVC installed, if they could let me know if they have any issues with noise through inlet valves. It will drive me mad if I can hear air travelling through pipes or valves in bedrooms for example.....but maybe this is just scaremongering. If you want to mention suppliers you have used, please PM.

Thanks a lot.

gizmo555

I have a system with rigid PVC ducting and while not entirely silent, the sound it makes is completely unnoticeable except late at night when the house is otherwise completely quiet, then you notice a very low background hum. It certainly doesn't disturb me or my sleep! If you're really concerned, ask your prospective supplier to show you a running installation and judge for yourself.

On the question of fire protection, based on advice I found in this forum I specified fire damping vents on all ducts, which automatically spring shut in the event of fire. The supplier's standard specification was intumescent collars behind the vents, which expand with heat and close off the ducting. However, I was concerned these might be too slow acting - the vents I got added about 10% to the system price but are worth it in terms of peace of mind! In fairness to suppliers, this is an area which is I understand not yet covered by the building regulations, so it's left entirely up to them (and you as the client!).

The notion of not insulating ductwork, at least where it passes outside the insulated envelope of the house, say, into attic space, is plain daft.

JuniorB

+1 to all Gizmo said.
Ours should be turned on in next couple of days ... rigid PVC ducting ... call over for a listen !!

Wavehopper

Thanks for the info Gizmo, especially around the fire damping vents.
Bit worried about the background hum that can be heard in bedroom but maybe its something I could used to. I'll also give my supplier a shout on this.

Many thanks for the kind offer Junior to call to see the system working, I might just take you up on that offer.

william

We have the rigid PVC installed on an MEV system. Set up on various lines is typically as follows:

- Fan leading to:
- Short length of foil flex duct, leading to:
- Rigid PVC round ducting 125mm, leading to:
- Rigid PVC Elbow bend (turning right or left), leading to:
- Rigid PVC round ducting 125mm, leading to:
- Rigid PVC Elbow bend (turning downwards), leading to:
- Short length of foil flex duct, leading to:
- Ceiling Fitting/Vent

And yes, there is noise. It is not air noise though, it is the noise from the fan which travels inside the ducting and enters the rooms at the ceiling fixtures/grills. It can be heard from our bedrooms at night.

Up in the attic, the fan is virtually silent and there is no noise coming from the ducting. The fan is acoustically insulated externally so obviously the noise is moving along within the system internally.

I'm currently looking at solutions for this. One possibility may be to install something like this in the ducting - http://www.efoam.ie/Sacoustic.php

Would welcome an ideas others may have.....

henryporter

As a much cheaper (to install and run) alternative check out Demand Control Ventilation - companies such as Aereco provide the necessary window vents etc. I'm an architect who has specified MHRV systems in the past and tbh I'm not convinced about the quality of installation or equipment.

imitation

Wavehopper wrote: »

Hi all,
First time post, building a new two-storey house with cavity block and taking steps to have as air-tight as possible, e.g. wrapping hollow-core, taping windows, membranes at roof level, air-tight stoves, etc. Therefore, I plan to install MHRV system and have looked at several suppliers.

Most of the units are very similar from the ones I've looked at, some slight differences in fan power & efficiency from SAP Appendex Q. However, the one thing that frustrates me is the different opinions on ducting, every supplier I talk to has a different take;
- one recommends steel ducting (much better fire resistance) but another says it will be noisy. It also makes system expensive and won't be insulated either
- one recommends rigid ducting but another says it will be noisy, will be a fire hazzard and will result in fire spreading from room to room and will gather dust/dirt due to static. This also won't be insulated but was told to throw atic insulation over it
- one recommends flexible ducting (noise proof, much better fire resistance, anti-bacterial, comes insulated) but another says it will be less efficient due to flexible nature of duct.

One supplier installs all 3 types of ducting but recommends the flexible (insulated non-woven, anti-bacterial, better thermal efficiency) ducting and states that the new flexible ducting is much better now than what was previously available. Was also told it won't be any different in terms of fan speed, unit efficiency than rigid.

The potential for noise and fire spread with rigid PVC has alarmed me so I'm leaning towards this flex ducting.

Just wondering if anyone has rigid PVC installed, if they could let me know if they have any issues with noise through inlet valves. It will drive me mad if I can hear air travelling through pipes or valves in bedrooms for example.....but maybe this is just scaremongering. If you want to mention suppliers you have used, please PM.

Thanks a lot.

SAP appendix Q actually recommends rigid ducting in there own installation check-list for efficiency.

http://www.sap-appendixq.org.uk/documents/MEV_Installation_Guide_Final.pdf

Wavehopper

Thanks for your replies on this thread.

I went for round rigid ducting after (150mm downstairs, 125mm upstairs)
Haven't decided on the fire collars that collapse the vent if there is a fire, I think they are an additional €500.
My ducting is being installed at the moment.

Bit worried William that you can here noise from the unit travelling down the rigid ducting. Could you PM me if you manage to get this sorted in any way if you don't mind.

william

Wavehopper wrote: »

Bit worried William that you can here noise from the unit travelling down the rigid ducting. Could you PM me if you manage to get this sorted in any way if you don't mind.

I put the foam into the ducts but the noise is as bad as ever.

Will now be replacing PVC ducting with about 6 ft of insulated flex ducting (starting from fan). If that doesn't work, then I will just decommission the duct line in the toilet nearest the bedrooms. Will keep the bathroom/shower/kitchen area one going obviously.

I am very surprised that I didn't pick up the noise issue until now - very little has been written on it - most literature and discussion is about mould prevention within ducts and also pressure drops within flex ducts. Nothing about noise......

The biggest relief I have is that I didn't go for whole house MHRV - can't see how the same issue of noise travelling down the ducts and into the bedrooms could be avoided - noise in bedroom is alot worse that noise in bathroom.

morning delight

henryporter wrote: »

As a much cheaper (to install and run) alternative check out Demand Control Ventilation - companies such as Aereco provide the necessary window vents etc. I'm an architect who has specified MHRV systems in the past and tbh I'm not convinced about the quality of installation or equipment.

It certainly seems a very interesting alternative, especially in a retrofit scenario. Have you feedback from homeowners who have this DCV installed? Are they happy with it?

gears

william wrote: »

We have the rigid PVC installed on an MEV system. Set up on various lines is typically as follows:

- Fan leading to:
- Short length of foil flex duct, leading to:
- Rigid PVC round ducting 125mm, leading to:
- Rigid PVC Elbow bend (turning right or left), leading to:
- Rigid PVC round ducting 125mm, leading to:
- Rigid PVC Elbow bend (turning downwards), leading to:
- Short length of foil flex duct, leading to:
- Ceiling Fitting/Vent

And yes, there is noise. It is not air noise though, it is the noise from the fan which travels inside the ducting and enters the rooms at the ceiling fixtures/grills. It can be heard from our bedrooms at night.

Up in the attic, the fan is virtually silent and there is no noise coming from the ducting. The fan is acoustically insulated externally so obviously the noise is moving along within the system internally.

I'm currently looking at solutions for this. One possibility may be to install something like this in the ducting - http://www.efoam.ie/Sacoustic.php

Would welcome an ideas others may have.....

Instead of using the mat you showed I remember seeing a unit from Canada which was suspended from the ceiling using heavy duty rubber straps so no vibration from the unit could travel any where.