Type of ducting for MHRV

bikerboy_ie

Is there any advantage in using galvanised steel ducting as opposed to PVC ducting for use in a MHRV system?

sas

The Passive House Institute recommend the use of rigid steel ducting only.

That's good enough for me and it is what I will be using.

YourAverageJoe

Metal ducting better for fire resistance
Metal ducting a good bit more expensive
I have seen galvanised sheeting rust over a long period of time which combined with the price made me choose pvc ducting.

Just make sure whatever you choose it is rigid so that it can be cleaned, although no one seems to have figured out how to clean the ducts yet anyway, as far as i know.

CJhaughey

+1 Spiral wrap Galvanised ducting, sized for flow.
Using flex tubing will greatly reduce the airflow inside the duct due to turbulence.

gman2k

YourAverageJoe wrote: »

I have seen galvanised sheeting rust over a long period of time which combined with the price made me choose pvc ducting.

You won't see MHRV galv ducting corroding.

newbie4

sas wrote: »

The Passive House Institute recommend the use of rigid steel ducting only.

That's good enough for me and it is what I will be using.

Be careful, just because some one recommends something, it dosent mean its the best.
No one recommends something for the good of their health,

sas

newbie4 wrote: »

No one recommends something for the good of their health,

I'll disagree with that. There are people\organizations that will recommend something based on their experiences. The PHI are system independent. I asked them which of the ducting options I should be using and they recommend the spiral metal ducting. I am building a home to meet their standard, so their opinion is definitive in my case.

From here on is my opinion. The reason the other types have arisen is to make installation easier, not to improve the end result. Certain options were then added to allow ducting to be run in narrower spaces e.g. those pvc rectangular sections. I have never seen these recommended as being better than the round sections in terms of system performance.

Whenever I've noticed ducting systems in commerical environments, it's always spiral metal ducting.

The reason most people choose the non metal spiral options is because they are cheaper.

I also have concerns about the use of pvc in my air supply system.

Carlow52

newbie4 wrote: »

Be careful, just because some one recommends something, it dosent mean its the best.
No one recommends something for the good of their health,

Whats the point in making such disparaging comments in a thread that is a year old?

PHI is an internationally recognized entity in this space and all they are doing is recommending standards of material and workmanship. Its up to the market to offer products that meet these standards and the end consumer to decide whats best for them.

For the benefit of other readers who are interested in the issues here I add the following comments

Metal ducting is preferred if only from a fire propagation perspective within a building.

The MHRV units should have a fire damper fitted but if not or if it fails the prospect of a pvc ducting system catching fire, leading to deadly fumes being circulated silently around a house does not bear thinking about.

The spiral metal is used because it has smooth internal finish which reduces pressure/flow losses across the system.

The pvc ducting may be more suitable in a demand controlled ventilation system with no heat recovery.


Pressure loss calculations and much else can be done here
http://www.engineeringtoolbox.com/

Poor Uncle Tom

newbie4 wrote: »

Be careful, just because some one recommends something, it dosent mean its the best.
No one recommends something for the good of their health,

Did you resurrect this thread just to impart that jewel of wisdom? or do you have something constructive to add? like maybe an opinion of which you think is better, metal or PVC and why?

If you have a business interest in either metal or PVC ducting, now would be a good time to declare it.

newbie4

Poor Uncle Tom wrote: »

Did you resurrect this thread just to impart that jewel of wisdom? or do you have something constructive to add? like maybe an opinion of which you think is better, metal or PVC and why?

If you have a business interest in either metal or PVC ducting, now would be a good time to declare it.

yes I am in the hrv buisness
I am not here to promote myself or to gain buisness. (in PM form or otherwise) I am here to learn, to debate and to add my opinion.
I have seen where some organisations use there recomendations. Generally there is a fee top be paid to become registered. Or there is some fee to be certified

In relation to fire proofing point. In a domestic situation if a fire were to stat,by the time the fire would have burnt through your plasterboard to start burning pvc ducting do you think that the smoke alarm should have kicked in, and if you wired in your hrv unit to your smoke alarm it should cut the power to it.
Pvc is exceptionally smooth
Sections that are rectanhular are not nessacirly bad they just make instalation a bit easyier, and help avoid "boxing" out sections. Not all houses were designed with Hrv in mind
PVC conducts less heat
PVC does not degrade
PVC has been used in many aplications for years look aroun your house
I am not saying one product is better than the other I have not put one product down over the the other, Its just from experience,
I have seen my competitors reccomended over me, they have used less efficient machines, that used more power, not SAP listed. Reason they were recomended, cnsultant and installer in same network group. Henc why i say becareful what is recommended. Make a decision on the independant test carried out, Let figures speak for themselves

newbie4

Carlow52 wrote: »

Whats the point in making such disparaging comments in a thread that is a year old?

PHI is an internationally recognized entity in this space and all they are doing is recommending standards of material and workmanship. Its up to the market to offer products that meet these standards and the end consumer to decide whats best for them.

For the benefit of other readers who are interested in the issues here I add the following comments

Metal ducting is preferred if only from a fire propagation perspective within a building.

The MHRV units should have a fire damper fitted but if not or if it fails the prospect of a pvc ducting system catching fire, leading to deadly fumes being circulated silently around a house does not bear thinking about.

The spiral metal is used because it has smooth internal finish which reduces pressure/flow losses across the system.

The pvc ducting may be more suitable in a demand controlled ventilation system with no heat recovery.


Pressure loss calculations and much else can be done here
http://www.engineeringtoolbox.com/

I am new to boards so didnt realise the date of the thread
Have I broken some rule

sas

newbie4 wrote: »

there is a fee top be paid to become registered. Or there is some fee to be certified

I assume you're refering to the PHI and you also don't appear to know too much about them so here's some of what I know about them.

You don't register with them. You can get a product certified by them and yes there is a charge for this but it isn't substantial I'm told (by a certified product owner).

You are not required to use any PHI certified systems in order to obtain certification, it does make it easier however.

The PHI were very keen for me to not import systems and to use whatever was available locally. The point being that the concept won't gain a foothold in any area where commonly available materials\products aren't available.

They have no registered ducting systems. They were very definitive however about what they believe to be the best.

sas

newbie4 wrote: »

PVC conducts less heat

Unless you are using a post heater for your supply air, the guidance again from the PHI is that you don't need to insulate pipes inside the body of the house. Hence I don't think this is particularly relevant.

Plus if you are using a post heater, you are advised against using pvc ducting I'm told.

newbie4 wrote: »

PVC does not degrade

I've seen enough pvc windows to make me doubt this.

newbie4 wrote: »

PVC has been used in many aplications for years look aroun your house

Asbestos was commonly used in buildings too for years.

newbie4

sas wrote: »

Unless you are using a post heater for your supply air, the guidance again from the PHI is that you don't need to insulate pipes inside the body of the house. Hence I don't think this is particularly relevant.

Plus if you are using a post heater, you are advised against using pvc ducting I'm told.



I've seen enough pvc windows to make me doubt this.

Also PVC water tank
Pvc waste pipe
Light can make pvc degrade but the new types have resolved this, but ducting is not in open sunlight




Asbestos was commonly used in buildings too for years.

what has asbestos got to do with anything

PHI alow you to use non registered products but they penalise the products that are not registered
NOT every one builds PHI standard

sas

newbie4 wrote: »

what has asbestos got to do with anything

PHI alow you to use non registered products but they penalise the products that are not registered
NOT every one builds PHI standard

You made the point that PVC is a commonly used material which by insinuation makes it safe. I pointed out a material that was previously commonly used and believed to be safe which it turned out not to be.

The DEAP software also penalises systems that aren't tested by certain specific bodies. If you provide the phi with the necessary data they will make an informed judgement on the efficiency they will allow for a Hrv. If you don't they subtract something in the region of 8% from the efficiency and if it is still above a certain threshold, you are free to use it.

Agreed, not everyone builds to the phi standard. It is in my opinion what the aim should be and any guidance they issue would be wise to considered.

gman2k

newbie4 wrote: »

Pvc is exceptionally smooth
Sections that are rectanhular are not nessacirly bad they just make instalation a bit easyier, and help avoid "boxing" out sections. Not all houses were designed with Hrv in mind
PVC conducts less heat
PVC does not degrade
PVC has been used in many aplications for years look aroun your house
I am not saying one product is better than the other I have not put one product down over the the other, Its just from experience,

1. Pvc is exceptionally smooth
What does 'exceptionally' mean here? spiral galv is smooth also - do you have airflow figures for one over the other? And the impact of same on overall efficiency.
2. Not all houses were designed with Hrv in mind.
I've rarely seen a building whether resi or comm that was designed with mech services in mind properly!
3. PVC conducts less heat
All ducting should be insulated regardless, mandatory in unheated spaces such as attics, where most MHRVs are placed.
4. PVC does not degrade
Nor does galv spiral. Both will be in enclosed spaces away from sunlight.
5. PVC has been used in many aplications for years look aroun your house.
So have metal products.
6. I am not saying one product is better than the other
Well, you are trying to say that.

BTW, have you started manufacturing your uPVC ducting systems yet?

creedp

gman2k wrote: »

1. Pvc is exceptionally smooth
What does 'exceptionally' mean here? spiral galv is smooth also - do you have airflow figures for one over the other? And the impact of same on overall efficiency.
2. Not all houses were designed with Hrv in mind.
I've rarely seen a building whether resi or comm that was designed with mech services in mind properly!
3. PVC conducts less heat
All ducting should be insulated regardless, mandatory in unheated spaces such as attics, where most MHRVs are placed.
4. PVC does not degrade
Nor does galv spiral. Both will be in enclosed spaces away from sunlight.
5. PVC has been used in many aplications for years look aroun your house.
So have metal products.
6. I am not saying one product is better than the other
Well, you are trying to say that.

BTW, have you started manufacturing your uPVC ducting systems yet?

What is this thread trying to achieve/prove/argue? Is is that that galv spiral is better than pvc for ducting? Or is is that both can be used for the purpose? Just because PHI require spiral galv does not necessarily mean that pvc is not fit for purpose? The same could apply for the MVHR units and many other aspects of house builds as PHI requires very high std for certification, but that does not mean if you dont religiously follow PHI stds you necessarily have a low std of house build. I think the reactions to newbie's comments are pretty dogmatic as I interpreted them as saying that just because PHI require spiral galv thhis does not mean that pvc should be considered by non PHI builds which is something I completely subscribe to.

newbie4

Not yet its only an idea, It may never take off, the reason is what is on my other post
I have not slated Metal unlike other who have.
But I have not seen a reason to pick one over the other
Have you
If I can get a seintific reason why one is better than the other

Asbestos is a completely diffrent argument not comparable, different generation, different science.

I thinki will leave it at that