MVHR install help

[Eric]

Hello all,

 

This is my first post on this forum.

I have read a lot of posts but can’t find the info that I am looking for. I am installing a vent axia MVHR system & I’m unsure how fussy I need to be with the air in & out pipe work.

So the questions I have are,

 

Can you just go straight out the wall from the unit with the pipe or should you have the pipe lower to reduce the chance of rain water entering the unit through the pipe?

Should I just floor mount it instead, use the existing extract hose for the bathroom fan, then make another hole for inlet? Probably easier I think.

Can I put the drain to the SVP? 
Am I just overthinking it & crack on?
Any help/ideas will be appreciated, I don’t want to core holes to find it’s unsuitable etc.

 

Regards,

Eric

 

 

[Stones]

Hello @Eric welcome to the forum. 

 

Is this a retrofit or a build just being finished off? You could either take the intake and outlet pipes our through the gable end or through the roof (you get vent terminals for both). Ideally you need at least 2m separation between the two.   To save having to core through a finished wall you could take out the intake and outlet via the soffit (overhang of the roof truss outside). Both should be on the same elevation, up here on the leeward side from the prevailing wind direction.

 

You could use the existing bathroom vent wall penetration of big enough, as you won't need the bathroom extractor assuming you have / are fitting an extract vent in the bathroom, so only one additional to core.

 

Yes you could use the SVP for the drain but you DO need a trap between the MVHR and the SVP to prevent smells coming back.

[Eric]

Thanks @Stones 

 

Its a retrofit on a bungalow. I was planning to take the in & out pipes through the gable wall that the unit is on, the question was is it ok to go straight out the wall or should I drop the pipe down before going out the wall to try & minimise rain water entering the unit etc.

Yes, I will use a trap.

The bathroom extractor fan will be getting removed so I would like to use the existing hole for it so I only have to core 1 more hole. So it might be easier to floor mount the unit.

 

Regards,

Eric

[jamieled]

I too have recently installed a vent axia unit. The instructions told me to ensure a slight fall from the unit to the inlet/outlet cowls on the outer walls.

I assume to stop rainwater ingress and allow condensation to move away from the unit.

[Eric]

Thanks @jamieled

 

Yes, it could be a neat install if I just went straight out the gable wall but I think it will be better to drop the pipe down before going out the wall.

 

Regards,

Eric 

[JFDIY]

As long as the fall is to or from the unit you should be fine, it's when you create a U-bend that it will cause an issue.

 

My ducts come from above the unit (similar vent-axia), the instructions don't preclude it, but I do have well shielded terminations to the outside.

 

Looks like you're putting it in an unheated space so make sure all the ducts get well lagged to prevent condensation forming on or in them.

 

You can use a waterless trap or at least 75mm or cover on a wet trap if memory serves.

 

 

 

 

 

[Eric]

Ok, so I have fitted the unit, & all the pipe work etc. 
I have run the system to test it & there seems to be very little extract flow, inlet is fine at 30% & 50% etc. The extract doesn’t feel like it gets any better with boost etc.

There is plenty of flow from the exhaust side. All pipe work is correct & tight.

I have opened the inlet valves around 3 turns open.

The summer bypass doesn’t activate & it doesn’t seem to detect humidity.

Any ideas or suggestions?

Edited April 23, 2020 by Eric

[JFDIY]

You can't 'feel' negative pressure/flow as easily as the supply.

 

Are you feeling it at the port on the MVHR unit or at the end of a duct run?

 

Once you cover an extract duct the flow drops to zero and it certainly doesn't feel as though anything us happening compared to an inlet where there is a rush if air pushing behind it.

 

There are also separate settings for the extract compared to inlet, so you may get have to check the values also are at 30% and 50% as a starting point to match inlets.

 

[Eric]

@JFDIY it feels fine at the port on the unit, just way less at the extract valves. I will have an anemometer next week so I should be able to see what it is actually doing. Just seemed very little on the extract.