Putting supply & exhaust ducting through ICF wall

[Happy Valley]

We need to put ducting through our ICF for the 125mm exhaust and supply ducting before we pour the concrete. 

 

I have two options for a pipe - one is has an internal diameter of 124mm being reported as a 125mm pipe but external dimension is 127mm. This is the type of thing we are looking at:

 

https://www.screwfix.com/p/manrose-125mm-round-ducting-1m/245gy

 

The other option is a 150mm internal diameter pipe which could just run the whole pipe through without joins but will leave a big gap around it which will need heavily insulating afterwards.

 

I don't have the items from the supplier yet as not needed at this stage so don't know the exact size of pipe that they supply.

 

Does anyone have any experience with this and recommendations as what size?

[MJNewton]

Whilst I don't have personal experience of your situation to draw upon I wouldn't consider anything but the 150mm outer duct option. It's only 12.5mm all the way round which seems ideal for the likes of expanding foam or similar, and of course gives you a bit of wriggle room for accommodating differences in nominal pipe sizes. 

Edited August 23, 2021 by MJNewton

[PeterW]

Use 160mm internal corrugated sewer pipe and foam in place and then foam the inlet and exhaust in place when you have it in your hand. Using 160mm corrugated is much stronger and will take the impact from the concrete pour. 

[Happy Valley]

Thanks - we have used smaller plastic pipes up to 80cm diameter as ducting for ASHP, plus flow and return pipes etc on the first pour with success. 

[Nick Laslett]

I’m using that exact 125mm pipe for my cooker extractor vent. The builders just cut a hole with a hand saw in the ICF and used expanding foam to fix the pipe. The walls how now been poured. To be honest I have not examined the pipe closely since the pour. I wanted to fit a larger pipe as a sleeve, put lacking @PeterW common sense I gave up on the idea. When I gave the issue some thought, I was reassured that very little concrete was impacting the pipe as it was at the very top of the wall. 

[Nickfromwales]

Is this supply and exhaust for an MVHR? If so, this is very small diameter duct for a whole of house ventilation system. 
What is going in, and what is it doing? 

[keith65]

I did mine the hard way and drilled the holes later as was not sure of finished position.

[Happy Valley]

1 hour ago, Nickfromwales said:

Is this supply and exhaust for an MVHR? If so, this is very small diameter duct for a whole of house ventilation system. 
What is going in, and what is it doing? 

 

Yes - all the designs I have show 125mm ducting for each. 

 

Likely to be Vent Axia Kinetic. 160 sq m property. Design has two flow and two exhaust on the ground floor and two exhaust and three flow on the first floor.

[Nickfromwales]

1 hour ago, Happy Valley said:

 

Yes - all the designs I have show 125mm ducting for each. 

 

Likely to be Vent Axia Kinetic. 160 sq m property. Design has two flow and two exhaust on the ground floor and two exhaust and three flow on the first floor.

Hmmmmm. 
Ive just done a Brink Sky 150 for a very small ( annex ) dwelling and the ducts to atmosphere and manifolds were in 160mm. 125mm is the size associated with a decent cooker hood.  

Not sure this will run very quietly. 

[MJNewton]

17 minutes ago, Nickfromwales said:

125mm is the size associated with a decent cooker hood.  

 

.. which tend to run at far higher air flow rates than MVHR systems given their intermittent operation so I wouldn't be too concerned about that (and I'd normally expect 150mm for high-flow hoods). 

 

For what it's worth our Titon 1.25 (feeding 6 supplies and 5 extracts) uses 125mm spigots and ducts and is practically inaudible. Only on boost do do you hear anything but that's just the expected air flow sound at the ceiling terminals and not due to the system/unit itself. 

Edited August 23, 2021 by MJNewton

[Nickfromwales]

Most of the audibility issues are when the system is boosting, but the boost causes the entire system to run at the higher rate so I’d heard in bedrooms for eg when a shower is being used elsewhere. 
A lot of the fan noise can be reduced by the fan not labouring against the absolute smallest ducts you can get away with. 
Less resistance vs same flow rate = quieter system. Some are more convoluted than others so results often vary. 

[Adam2]

I've just been doing this and used 150 duct through ICF with the cut out EPS as support for the inside of duct during the pour. Will just use this as the final external duct.

 

Check what external duct cowl your are using to be sure of one for 125 if that is your planned size.

 

If you use 150 I just got about 100m of the duct from an auction do will be selling loads cheap ?