MVHR inlet and outlet combined external vent

[tanneja]

I have obviously read a fair few posts on MVHR dos and don'ts on this forum, one of the critical pieces of advice being the 3m separation of inlet and outlet vent.

 

I was surprised when going into the Paul Heat Recovery online shop for external grills, that their range comprises mainly of combination external vents as seen here: https://www.paulheatrecovery.co.uk/product-category/mvhr-ducting/terminals-external/

 

It is really surprising to me that these would be the online choice offered on their site.  I appreciate vents can be obtained from any number of places online, but it has be rethinking, as one of these vent types would make my installation far simpler.  I plan to call them tomorrow to discus what negatives there are to situating the vents in this way, but presumably it is a bad idea?  Perhaps these are a product for where an end user simply has no choice but the penetrations to be in the same location, and there is an accepted level of airflow contamination based on the wind etc.

Edited January 27, 2021 by tanneja

[Savage87]

I would say this is bad idea, this is my personal opinion, I would only use this as a last resort. I have my ones 3m apart and I would have placed them even further apart if it would have been easy to do so.

[Iceverge]

We have one from Proair in Galway. No issues so far although it's not the prettiest of contraptions. 

 

https://www.proair.ie/wp-content/uploads/2017/10/1305-proair-fex-terminal-brochure.pdf

 

I have my suspicions that you could probably put regular the terminals right next to each other but intakes and inlet staggered by a few cm and it'd be fine anyway. I intend to take off the cover and test out the theory some day if I get a chance. 

 

One of the greatest advantages is that you can have a minimum run of inlet and exhaust ducts inside the heated envelope. Here is a snap of ours from the inside during installiation. The two ducts on the RHS are for the external terminal. I reckon there's less than 1m of ducting run here in total. 

 

[tanneja]

1 hour ago, Iceverge said:

We have one from Proair in Galway. No issues so far although it's not the prettiest of contraptions. 

 

https://www.proair.ie/wp-content/uploads/2017/10/1305-proair-fex-terminal-brochure.pdf

 

I have my suspicions that you could probably put regular the terminals right next to each other but intakes and inlet staggered by a few cm and it'd be fine anyway. I intend to take off the cover and test out the theory some day if I get a chance. 

 

One of the greatest advantages is that you can have a minimum run of inlet and exhaust ducts inside the heated envelope. Here is a snap of ours from the inside during installiation. The two ducts on the RHS are for the external terminal. I reckon there's less than 1m of ducting run here in total. 

 

Those silencers look quite short.  I am space constrained and so effective short flexible silencers have been on my wish list.  Probably subjective, but do you think they do a good job for you, and if so, what are they please?  Are they the perforated on the inside as other attenuators would be?

 

I'm not sure how you would really ever know whether  cross contamination was happening, perhaps only with some CO2 monitoring?

 

Speaking with PAUL today, they said the exhaust air speed is forced at least 1m away from the unit before it would slow enough to be capable to coming back to the intake for any kind of contamination, so in effect there is zero cross contamination.

[Iceverge]

They were 150mm diameter acoustic silencers from BPC ventilation, 500mm long. I would recommend them for build quality and ease of installation but I can't comment on their efficacy as to sound attenuation, they seem to be working. Yes perforated inside as best I remember. They're pretty cheap also. 

 

https://www.bpcventilation.com/quiet-vent-semi-flexible-silencer-range

 

5 hours ago, tanneja said:

I'm not sure how you would really ever know whether  cross contamination was happening, perhaps only with some CO2 monitoring?

 

I'm yet to see any evidence of it ever happening so as of yet I'm unconvinced it's anything more than a theoretical issue. If I was to build again I'd consider not bothering with a specialised terminal. 

 

One thing that I took some trouble over was fashioning the insulated ducting to run from the MVHR to the exterior. As you can see I taped the joints with airtightness tape to back up the internal seals. If you put your hands against these joins you can feel it's colder than the rest. I'm going to wrap more insulation over it when the builder is finished filling the holes in the plasterboard. I'd hate to see ducting being left insulated. It'd be a huge heat sink in a well insulated house.