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Ventilation in your home - guide

Ventilation in your home - guide
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Ventilation systems for the home - your guide

 

To keep a house warm you need to block up any gaps and keep out draughts. We’ve known that for hundreds of years.

A house left like this stays in good order, provided that there are no animals inside. Dogs and cats are bad enough, but it’s homo sapiens I have in mind. Not only do animals breathe, but when they do so they exhale water vapour. Worse still we increase humidity further by cooking and taking hot showers. Aagh!

Water vapour condenses on cooler surfaces where it provides a rich micro-environment for fungi and all manner of invertebrates that start living off it. Eventually these organisms start consuming the very fabric of the building itself: dry rot, wet rot, woodworm, carpet moths and mildew all thrive in unventilated space.

 

For the last half-century we’ve ‘solved’ that problem by installing bathroom and kitchen fans. They suck warm humid air from the house and expel it outside, along with all the heat energy which we paid to have in our house over the previous few hours.

 

 

In bedrooms and living spaces we’ve installed windows with trickle vents above them. These re-introduce the small draughts which have carefully been eliminated elsewhere. There is an alternative.

We can expel the air but extract much of the heat from it when we do so. That’s the basic idea behind Mechanical Ventilation with Heat Recovery (MVHR).

 

At the heart of an MVHR unit is a heat-exchanger comprising a series of thin plates where heat is passed to incoming fresh air without the two air-streams actually mixing.

Small MVHR units are now available sub-£300 for use in just 2 or 3 rooms of a house. Here’s the HR100 from Vent Axia:

 

It has 5 ports:

  • fresh-air input from outside
  • warmed fresh air to living area(s)
  • stale/humid air from bathroom & kitchen
  • stale-air to outside after heat has been extracted
  • 19mm condensate drain to outside

Here’s one I fitted in a garden-office about 6 years ago. This is positioned above a doorway to the en-suite toilet area. It is therefore the “bottom opening” version so that the heat-exchanger element can be removed from below and cleaned out once a year:

 

 

The Vent Axia HR100 has standard 100mm diameter connections. I used a combination of rigid and flexible pipes to squeeze everything into the small space above a suspended ceiling.

Houses with MVHR units can operate on a lower setting than the usual 15-litres/sec air extraction rate because they work continuously. See Building Regulations Part-F for information.

 

Whole-house ventilation:

A whole-house installation is more common, using a larger heat-exchanger to feed fresh air into all the living spaces.

 

You will need to decide whether to connect the cooker-hood to a whole-house system. My preference is to keep it separate, thereby not allowing oils and fat to enter the ducting where fluff could stick to it.

The heat-exchanger unit for a “whole-house” installation would typically cost around £1100-£1600 depending on the quality of the fan motors and the exchanger plates.

 

Vent Axia Integra (left) and Blauberg KOMFORT EC D5B-180 (right)

 

 I’ve added an additional radiator within my unit with water fed from the same thermal store outlet that supplies my underfloor heating.

 

 

The 150x150mm mini radiator is normally used by PC gamers for their water-cooled processor chips and graphics cards. I screwed it inside the heat-exchanger case immediately before the outlet supplying fresh air to the house. The input/output ports take ½-inch flexible hose which run through a couple of rubber grommets in the side-wall of the enclosure.

The main cost of a whole-house ventilation system is the running of the pipes themselves. Without taking up floorboards to work out how the pipes might be inserted it’s not really possible to give a price estimate.

Beware that many firms leave the pipe-runs to be installed by the most junior member of the team. That means he/she may not appreciate the need for:

  • sufficiently air-tight seals between joints
  • rigid (not flexible) pipe where possible to maintain pressure
  • adequate insulation around all pipes, especially at bends
  • the use of round pipe rather than rectangular to reduce noise
  • no pipe joins within 4 pipe-diameters of an outlet vent
  • not sawing through the odd joist(!) to reach a tricky location

 

And that’s why I’ve installed everything myself so I know it’s optimal!

 

 

The ducting components themselves are cheap and readily available online from suppliers such as TLC Direct and BES. Most of my installation uses 100mm rigid pipe which I’ve encased in aluminiumised bubble-wrap (400mm wide strip).

 

Thermawrap by YBS

I hope this is helpful in letting you know your options for home ventilation! 


13 replies

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@nealmurphy @hydrosam and anyone else… Have the aliens returned ? I have the red exclamation and the flashing cloud back on my passive system box. Once again it’s very hot in the loft of course, is that just a coincidence ?

Nothing out of the ordinary on my system, just the usual 7 green lights, 1 yellow light and a red fuse switch light. Certainly won’t need to buy any more Christmas lights this year!

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If only there was some sort of device which could be used to extract heat from those Passiv communication boxes and put somewhere else, like a great big tank of water :thinking:

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Well I too am a mere DIY’er… but I did insulate the whole loft!

 

This is called Warm Roof Construction. To implement it properly, the entire rafter must be within the warmed envelope of the house. So I removed all the roof slates, laid an additional 50mm of PIR board on the outside of the rafters, then counter-battened vertically and fitted slates back onto new horizontal battens.

Having read that, I’m pretty certain you won’t be copying my strategy!

Yes, you’re correct that the most difficult part of the installation is working right down in the eaves to ensure that the insulation seals down to the wall-plate. It’s easier if you employ a teenager :wink:

As you have gable-ends, you could arrange the input/outlet pipes to go through there, sealing the outside using a grill with a fly-screen. Domus is the main UK manufacturer. Here’s one of theirs available from BES.

 

Or use a pantile-vent unit which replaces one of your existing tiles. Here’s one sold by Mammoth Roofing Supplies at just under £30.

 

Vents like the two I’ve just described are usually made with a spigot at the back to allow direct connection to plastic ventilation pipes. You just need to check which pipe format it offers.

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You can have a variable valve within the ‘cupboard’

air-supply-valve 100mm

To completely seal it, just screw it up.

If you’re unsure, just invite one of the Professional Installers back. They’ve shown themselves adept at screwing things up :hugging:

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Venting the entire loft is certainly an option. But from where would you be able to draw on sufficient volume of cold air on a hot day like this?

If you built a ‘cupboard’ around the heat pump area alone, then you require very much less cold air.

I have practical experience of installing my own whole-house ventilation system (with heat recovery in winter).

Look at the bottom two photos in the Tutorial on Ventilating your home. It shows attic-runs of rigid 100mm pipe which I’ve insulated using aluminium bubble-wrap.

That just happens to be the right diameter for a computer fan of course. Remember that you get a steadier air-flow if you suck rather than blow.

You can buy all the ducting, bends, adaptors and grills here at BES.

 

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@Transparent sounds good, I think they’re on the same lines ref controlling the fan, the loft is big so they were going to check out the outlet size/fan speed to suit, with the intention of ventilating the whole loft. However, if I build an insulated enclosure around the heat pump I’d want cool air drawn in when loft temp is say >30 deg C, but not have cold air coming in during winter. They were talking about an open grille for air input just above the pump, but I’d want it to close off in cold conditions, (as I’d want to keep the heat in within the enclosure).

 

 

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@juliamc coincidence or confirmation of the issue… Did you get any feedback last time about the operating range of the heat pump components in the loft?

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Ventilation of an attic:

 

The following conversation has been moved here from the Smart Home Treehouse area.

The posts from Julia describe a situation encountered during the Zero Carbon Heating Trial in July 2021. Her Air-source Heat pump (ASHP) control unit has been installed in an attic. This is getting very hot during daytimes, with possible malfunctioning of the electronics and/or the sensors.

 

@nealmurphy @hydrosam and anyone else… Have the aliens returned ? I have the red exclamation and the flashing cloud back on my passive system box. Once again it’s very hot in the loft of course, is that just a coincidence ?

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To move this forward @juliamc - can we have some clarity from you on the option of installing a ‘cupboard’ around the attic-based equipment:

Are you intending to have inflow and outflow ducting to this cupboard?

Or by some quirk of thermodynamics were you going to attempt dumping the excess heat from the ‘cupboard’ back into the main attic space?

Looking for advice !! I suppose I’ve been thinking “what if I had a ‘warm loft’?” it wouldn’t get to the high temperatures that it does now. However, I’m only a mere diy-er and not prepared to insulate the whole loft between the rafters etc, having done the loft floor between the joists, so I thought could I insulate just the area around the heat pump unit. Much more manageable.

You can just see the outdoor unit at the chimney end of the house.

I feel that I only need to deal with the first three rafters-worth! That would be less than a metre deep, to the gable end wall. Not planning to go all the way to the eaves, but drop a wall of insulation down this structure that the heating pipes have been attached to:

Any thoughts? Would I be wasting my time? Should I just get the whole caboodle down to the sitting room below?

 

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Venting the entire loft is certainly an option. But from where would you be able to draw on sufficient volume of cold air on a hot day like this?

If you built a ‘cupboard’ around the heat pump area alone, then you require very much less cold air.

 

@Transparent Agreed, but any air at all would be welcome ! Btw I’m not going down the soffit vent route as the soffits are asbestos.

I’m struggling to imagine how I could close (and possibly insulate) the air inlet within the ‘cupboard’ for winter?

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Your electrician is on the right track @juliamc 

You could use a 100mm 12v as normally found in desktop PC cases. Then drive it from a small solar-panel. That way it will only operate in sunny/hot conditions.

If you want to be a bit more sophisticated about it, use a 12v computer fan with a 3-wire connection so that its speed can be regulated. Then buy a £2 speed control module from China with an integral temp-sensor on the end of a wire.

This version comes from RQG Official Store on AliExpress and it’s temp-sensor is embedded in a metal connector with an M5 bolt-hole through it.

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No @hydrosam now it’s up there I don’t think anyone’s particularly concerned :rolling_eyes:  I also have the LAN adapter up there (not running yet) which has operating range up to 35 deg C. I’m thinking all I can do is insulate the area around the heat pump to keep the heat out in summer and in in winter. I have some 70mm Celotex offcuts which could go between the rafters, then make up a wall of something to enclose the sides. My electrician has suggested I have an air inlet to draw cool air in with an extractor fan at the opposite end of the loft…  but I don’t want cold air coming through in the winter. I need one of you self builders here to suggest how to go about it !

If I can’t regulate the temperature in the loft to suit the heat pump the alternative is to have the whole thing moved into the sitting room and hidden behind a cupboard. 

Userlevel 7
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To move this forward @juliamc - can we have some clarity from you on the option of installing a ‘cupboard’ around the attic-based equipment:

Are you intending to have inflow and outflow ducting to this cupboard?

Or by some quirk of thermodynamics were you going to attempt dumping the excess heat from the ‘cupboard’ back into the main attic space?

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