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Author Topic: MHRV in listed property - Vent advice  (Read 1778 times)
Pile-o-stone
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« on: May 04, 2020, 08:53:47 AM »

I've just purchased a Vent Axia Hugh Flow Heat Recovery Unit and will be installing it in a couple of months once I've finished some other work. I live in a listed building (former mill) that was built in the 1700s and the MHRV will be placed in the loft and vented through the house's east facing gable end. Unfortunately this end of the house is very much on display so I need to make sure I don't fall foul of the listed building officer, plus I want to keep the house as attractive looking as possible. A shower room is currently vented thru the gable end via a small grey plastic vent, which I'll be using for the supply vent. I'll then make another hole in the wall 2m away to site the exhaust vent.

The spiggots on top of the MHRV are 180mm diameter, so I guess I'll be fitting 180mm diameter pipework and vent.

I've so far looked at cast iron vents but I was concerned that they might allow water ingress in the supply vent as this end of the house is quite exposed. I therefore wondered about fitting a bull-nosed vent (pic attached) which I will paint black.


My questions are therefore:

1. Will the bullnosed vent look awful (even if painted black)?
2. Do I need a 180mm vent and pipework to supply the 180mm spiggots?
3. Do I need to worry about rain coming in?
4. Anyone with vent suggestions?
5. The gable end of the house is above a lean to extension so I can't easily access it. I've be using a cherry picker to fit the vents. I therefore can't fit a fly screen if they need cleaning. Do I need to fit one?

Thanks in advance for any and all suggestions!

NB: The attached pictures show the gable end, the existing small plastic shower vent and the bull nosed vent I'm pondering.

 





« Last Edit: May 04, 2020, 09:02:01 AM by Pile-o-stone » Logged

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pantsmachine
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« Reply #1 on: May 04, 2020, 09:11:09 AM »

I have these vents for passive cross airflow in our cabin, used them for about 10 years, zero water ingress in any conditions. If you decide to go stainless buy high quality ItalIan rather than chinese as they don't use best grades off s/s. They might call it 316 but it's not.

My one's have built in fly screen.

You won't even notice them when they are up. The bigger you go on the outlet the less you have to worry about back pressure on the fan and system efficiency.


« Last Edit: May 04, 2020, 09:27:36 AM by pantsmachine » Logged

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Countrypaul
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« Reply #2 on: May 04, 2020, 10:22:26 AM »

I have the same bull nosed vents complete with built in fly screen for our MVHR system. The house is in a conservation area but not listed so we had no restrictions on the appearance.

The Unit has 180mm fitttings, but after discussion with the suppliers they said 150mm pipework and vents would be more than adequate as long as the pipework was not that long. Our pipe work is about 5m long and changes from 150 round to 90x220 rectangular and back aagain to get through various restrictions (it is fitted between the open web joists but has to cross at least 2). The section of pipe to the vent slopes slightly up from the vent to ensure any condensation can run out, with the pipes well insulated thoughout the length.

Talk to your suppliers/manufacturers about what size ducting is required for your installation, and even if the vent can be smaller than the pipework. The listed building officer may even have other suggestions that may be helpfull.

The vent pipe for the soil pipe on our house exists via special roof tile fitting so cannot be seen be looking at the roof unless you know exactly where to look and what to look for, even then most people cannot see it. Unfortunately whilst it works well for our tiled roof, your looks to use stone tiles and therefore may not be an option. This is similar to what we have: https://www.tudorrooftiles.co.uk/ventilation.html the MVHR system is on the ground floor and we could not use this approach for that.
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TT
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« Reply #3 on: May 04, 2020, 04:55:48 PM »



https://www.justfans.co.uk/diecast-external-oultlet-ulma-p-572.html

looks not too bad, I'm sure it could be sprayed to match external ironmongery/rainwatergoods.
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Pile-o-stone
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« Reply #4 on: May 11, 2020, 02:26:21 PM »

Thanks all for responding. Good to know about the fly screens and water ingress. I'll speak to the MHRV supplier to see what they say - I'd rather fit 150mm than 180mm if possible. I know it's not a such difference but every little bit matters when you're trying to keep off the LBO's radar!
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marshman
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« Reply #5 on: May 11, 2020, 07:44:22 PM »

Thanks all for responding. Good to know about the fly screens and water ingress. I'll speak to the MHRV supplier to see what they say - I'd rather fit 150mm than 180mm if possible. I know it's not a such difference but every little bit matters when you're trying to keep off the LBO's radar!

150mm diameter is 30% smaller area than 180mm diameter!!  Having said that my MHRV system works fine with a 150mm main Inlet duct - house is approx 240 m sq.

I would recommed a flyscreen / filter at some stage before the heat exchanger, doesn't have to be in the cowl but could be a filter box closer to the main unit. In my experience they do catch a surprising amount of flying debris - but then we get plagues of mosquitoes and other fly insects all year round - darn't leave a window open at night!

Roger
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sam_cat
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« Reply #6 on: May 12, 2020, 08:49:41 AM »

Basic wide mesh screen on the outside vent to stop big stuff/birds. Internally use a filterbox:
https://www.ebay.co.uk/itm/Filter-Box-Verz-stahlblech-Filte-G3-100-125-150-160-200-250-315-355-400-450/143378542597

Then on your regular service you can pop the lid and give it a quick vaccum around/replace filter if feeling super keen.

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