Roof terminals either side of ridge

[LinearPancakes]

We're in the process of, for better or worse, self-designing our MVHR system and currently looking at the terminals to outside.

 

I understand that it's best to keep extract & supply on the same elevation to avoid pressure imbalances caused by the weather. However it would work well for us if we can put the terminals either side of the ridge, a bit like in the image on the Ubbink website here: https://www.ubbink.com/int/products/ventilation/terminals-and-seals/roof-terminals/ventus-roof-terminal-200-180-pitched-roof/#specifications

 

They'd be 1.5m apart, to plan, and they'd be pretty close to the top of the ridge anyway (maybe the top of the vents 30cm or so below the ridge), so I'm wondering if this is going to be that imbalanced in practise? The roof would likely shelter one of the vents from prevailing wind a bit more than the other.

 

Thanks!

 

 

[Iceverge]

 

 

It's almost guaranteed have a vastly different external pressures with any kind of wind as seen above. 

 

It might be a nightmare to balance. 

[LinearPancakes]

Wow, many thanks @Iceverge, great that there's some data available on this. What was the source?

 

Disappointing that the manufacturer chose to showcase their product being used in a bad practise installation. I saw another promotional material the other day where the terminals were around the corner of the house from each other.

 

It gets me thinking about what is optimal here. Probably the same type of terminal is also important. Different types of terminal, in additional to having different air resistance generally (which I expect you could balance out), might be more susceptible to wind than the other, e.g. something like this might also be hard to balance: https://www.ventilationland.co.uk/product/15660/thermoduct-flat-horizontal-roof-terminal-diameter-180-for-sloping-roof.html

[Iceverge]

Wind flow over the low-rise building models with gabled roofs having different pitch angles - ScienceDirect

 

I didn't look too much into it. It's just a pretty picture that represents the wind flow differences at both sides of a roof apex. 

 

Do you have any more details of your install? Plans etc. The more info you provide the more lightly someone will recognise and already have a solution to your problem. 

 

We used one of these. Paul make something similar. 

 

[JohnMo]

I am using a combined grille on the gable end, seems to be working well.  Less stuff going through the roof.

 

https://www.paulheatrecovery.co.uk/product-category/mvhr-ducting/terminals-external/

[Simplysimon]

4 hours ago, Iceverge said:

Wind flow over the low-rise building models with gabled roofs having different pitch angles - ScienceDirect

last time i went down the science direct rabbit hole i ended up reading about 6 pane glazing units and the max no. teeth for a saw blade, hours of fun

 

[Nickfromwales]

4 hours ago, LinearPancakes said:

 

It gets me thinking about what is optimal here.

There is the money statement. Optimal. 
Too many folk looking to put a crown on an unicorn imho, and things will work, life will go on, just not at the 100th percentile.

It’s perfectly acceptable and with merit to strive for the 100th, but at what cost? And I mean that literally.

 

Installers will give you practical advice based on results, manufacturers will offer 2 free unicorns with each system purchased, and you, without divine intervention, are supposed to decide what / which is best.

 

So;

The best place to be, is, on this impartial forum, where the good, bad and ugly are aired and those who have installed and have experience provide their “watrs ’n ’all” feedback. 
 

A lot harp on about their opinions about vents on opposing elevations, but not many recount where they both reside on the same adverse elevation…..but it was fine. 
 

Pinch of salt time  

[Iceverge]

 

 

4 hours ago, JohnMo said:

Less stuff going through the roof.

 

 

Amen brother!

 

We have literally zero penetrations throughout ours and it's still too much IMO! 

[Roundtuit]

As @Nickfromwales says, it may not be optimal on paper, but realistically, I struggle to believe it makes a significant difference in most cases.  We have the exhaust on the south pitch and intake on the north pitch, mainly to fit around solar panels without using loads of ducting and compromising internal roof space. 

 

I balanced the system without a problem, but accept that I have no idea which way the wind, if any, was blowing at the time.  The system has continued to do it's job with no noticeable difference in performance over the last few years, regardless of weather, which is fine for me!

 

[LinearPancakes]

Many thanks for the feedback. That's why I find myself keeping coming back here, such a melting pot of knowledge that has been put into practise.

 

I'd seen the combi grilles. They'd be a good option, but the gable wall available is at the front of the [brick] house and would stand out a lot. I'm currently leaning to using the gable wall using more low profile separate intake/exhaust. Any thoughts on this arrangement for the unit & terminals? Our loft is a cold loft, so will be insulating all the things. Airtightness layer underneath the joists.

 

I was originally trying to keep the duct runs to the terminals going upwards, to minimise condensation draining from the terminal. But seeing that others have them going down to the terminals as well, I wondered if it would be that much of a problem in practise. Running them this way allows them to be roughly 3m apart, and sheltered under the eaves to reduce rain/wind.

 

Rytons look to have nice brick sized terminals, with a range of grilles for low resistance, that could be colour matched. I'll have to call them and see if they can do one with a 160mm dia round duct on the back to avoid limiting airflow. (MVHR unit has 160mm internal dia)

Edited October 2, 2022 by LinearPancakes