Opinions on Ducting for MHRV, please.

Zynks

I am retro-fitting a HRV system in my 1920s home. It has been extensively renovated and insulated and we are currently creating two new bedrooms in the attic.

We live in a noisy road, so we decided to introduce the heat recovery system to improve the air quality inside the house and reduce the need to open windows.

The ducting to a large extend will run in an insulated, but unheated part of the roof, and the supplier suggested these ducts saying that they don't need additional insulation, even if they are running inside unheated spaces.

I am quite unsettled with this because although it is double-layered, the claim that it will have minimal loss of heat sounds too optimistic.

Has anyone who has come across these ducts confirm that they don't need extra insulation?

Thanks in advance.

indie armada

Out of curiosity i have looked in the catalogs of three differ ant companies that sell the accessories for HRV systems, and they all show some sort of double insulated ducting in various sizes and diameters.
most of which is basic aluminum flexible duct, and one does a pvc duct with an outer aluminum layer.
none of the brands i've looked at show the type of duct pictured in the link.
Ventaxia do an insulated pvc also in 2mtr lenghts.

Andrew_Doran

Zynks wrote: »

Has anyone who has come across these ducts confirm that they don't need extra insulation?

Going by the picture it definitely needs extra insulation or the install will not reach near the claimed efficiency figures for the MVHR unit. Also, without insulation condensation forming within the pipes could cause problems.

You can buy glassfibre & foil insulation that you pull over the duct -- have a look in Lindab's catalogue. I would humbly suggest that and then heap cheapo glass fibre insulation over the lot wherever practical (this is what I did in my MVHR install).

Also, from hindsight, if practical I would locate the unit itself within the insulated envelope. If it's in an unheated space it may require additional insulation to meet the quoted efficiency figures, and it needs to be maintained (filters cleaning / changing every so often), which is a bugger if it's buried in the attic somewhere.

Good luck with your install.

indie armada wrote: »

Ventaxia do an insulated pvc also in 2mtr lenghts.

It may seem irrational but PVC is nasty stuff and given the option I wouldn't personally want to breathe through a PVC duct. PE duct as in the OP's link or ideally galvanised spiral steel for me.

Zynks

Andrew_Doran wrote: »

You can buy glassfibre & foil insulation that you pull over the duct -- have a look in Lindab's catalogue. I would humbly suggest that and then heap cheapo glass fibre insulation over the lot wherever practical (this is what I did in my MVHR install).

That is exactly was I was considering, and I am happy to hear this coming from someone who has gone through an installation. I will definitely go for the glass fibre wrapping.

Andrew_Doran wrote: »

Also, from hindsight, if practical I would locate the unit itself within the insulated envelope. If it's in an unheated space it may require additional insulation to meet the quoted efficiency figures, and it needs to be maintained (filters cleaning / changing every so often), which is a bugger if it's buried in the attic somewhere.

Good luck with your install.

The unit will be in the envelope, but not in a heated area, so the glass fibre should help compensate. The planned location is very accessible for servicing, but good point nonetheless.

Thanks for your good input!

Zynks

indie armada wrote: »

Out of curiosity i have looked in the catalogs of three differ ant companies that sell the accessories for HRV systems, and they all show some sort of double insulated ducting in various sizes and diameters.
most of which is basic aluminum flexible duct, and one does a pvc duct with an outer aluminum layer.
none of the brands i've looked at show the type of duct pictured in the link.
Ventaxia do an insulated pvc also in 2mtr lenghts.

Thanks for raising the issues. Material wise I am happy with this duct, it seems to have microbial resistance and by being semi-rigid it would be easier to spot issues such as accumulation of moist. Another advantage is that these ducts are thinner and you can run them in pairs into the intake or extraction vents, allowing for a less intrusive install.

Darbre18

I am currently installing a Mvhr system using this duct,Mine is is an unheated attic space,I kept my unit and manafolds in a central position to minimise long runs,also this should(depending on house layout)give you two main runs of ducting making insulating easier.
I'm grouping four/five ducts together and wrapping in 25mm rock wool foiled back and securing with foil tape,individual ducts running in between joists ill just cover with attic insulation.
Ill get up a few pics tomorrow.

Zynks

Hey, that's great, looking forward to the pics. Which unit did you go for?

Darbre18

Zynks wrote: »

Hey, that's great, looking forward to the pics. Which unit did you go for?

I went for the Vent Axia sentinel kinetic plus,from talking to people and doin a bit of research it seems to be one of the better ones on the market,plus it has side spigots which suited me as I was restricted in height.
I should be finished insulating and have it up and running by the weekend.

Zynks

Thanks for that, that is a neat installation and very useful to me. It is looking like the Kinetic Plus for me also.

One thing that I am in doubt is when to use double ducting in a room. As it stands, I am rolling out a single duct to each room, except for the open plan kitchen where I will have a double one into the vent. There are two rooms where I wasn't sure whether to go single or double (a bathroom and a sitting room).

Darbre18

Zynks wrote: »

Thanks for that, that is a neat installation and very useful to me. It is looking like the Kinetic Plus for me also.

One thing that I am in doubt is when to use double ducting in a room. As it stands, I am rolling out a single duct to each room, except for the open plan kitchen where I will have a double one into the vent. There are two rooms where I wasn't sure whether to go single or double (a bathroom and a sitting room).

I got all double outlet plenum boxes incase I need to run a second pipe if I'm not getting the desired airflow when commissioning,and just blanking off the second outlet where it's not being used.
I ran two pipes to the open plan kitchen extract because you need to achive a minimum of 13l/s where toilets and utilities are only 8l/s.
I got mine up and running yesterday,just need to source a handheld anemometer for commissioning now,have no idea where to get one.
Yea im happy with the kinetic plus can't believe how quite the unit runs,some nice features too,I'm going to set it up so it boosts automatically when the shower is switched on.

sydthebeat

I would never ever specify flexible ducting for hrv systems. It impinges on air movement capacity and could can lead to problems with dirt and or condensate in the pipes.

If they have to be used to meet corners, they should be extended to capacity.

But it's always better to design the system so these are not needed

Zynks

Darbre18 wrote: »

I got all double outlet plenum boxes incase I need to run a second pipe if I'm not getting the desired airflow when commissioning,and just blanking off the second outlet where it's not being used.
I ran two pipes to the open plan kitchen extract because you need to achive a minimum of 13l/s where toilets and utilities are only 8l/s.

Same here with the plenum boxes. It is just that in some locations it may not be too easy to run a second duct if found to be necessary. I might run a second duct through the troublesome areas in case it becomes necessary, but leave it disconnected. Better safe than sorry, and it will probably cost me €20 in extra ducts.

Darbre18 wrote: »

I got mine up and running yesterday,just need to source a handheld anemometer for commissioning now,have no idea where to get one.

Will this do?

Darbre18 wrote: »

Yea im happy with the kinetic plus can't believe how quite the unit runs,some nice features too,I'm going to set it up so it boosts automatically when the shower is switched on.

Yes, that is a nice feature. I also like the summer bypass. Did your unit come with the wired control panel?

Zynks

sydthebeat wrote: »

I would never ever specify flexible ducting for hrv systems. It impinges on air movement capacity and could can lead to problems with dirt and or condensate in the pipes.

If they have to be used to meet corners, they should be extended to capacity.

But it's always better to design the system so these are not needed

Since the Lindab ones are semi-rigid, can I take it that you find these to be suitable? Sorry if I misunderstood your point.

Darbre18

sydthebeat wrote: »

I would never ever specify flexible ducting for hrv systems. It impinges on air movement capacity and could can lead to problems with dirt and or condensate in the pipes.

If they have to be used to meet corners, they should be extended to capacity.

But it's always better to design the system so these are not needed

I agree,but the discussion here is semi rigid ducting with a smooth internal wall,no different to rigid ducting.

Zynks wrote: »

Yes, that is a nice feature. I also like the summer bypass. Did your unit come with the wired control panel?

No it did not come with the control panel but I got it as an extra,bout €60 extra I think.
Have it running on summer bypass now,we were out all day and noticed how cool and fresh the house was when we got home opposed to being warm and stuffy.
Not sure if that anemometer would do the job,you might be able to make up some sort of a cardboard cone to fit over the valve,might give it a try for the sake of €20.
Get a few pics up when you have it going and if I can help with anything drop me a pm.

sydthebeat

Zynks wrote: »

Since the Lindab ones are semi-rigid, can I take it that you find these to be suitable? Sorry if I misunderstood your point.

My bad, I didn't realise this had a smooth inner face, all good

BarneyMc

sydthebeat wrote: »

My bad, I didn't realise this had a smooth inner face, all good

Does this mean if HRV ducting has a smooth inner surface it doesn't matter if it's flexible, rigid or semi-rigid?