Whole House Ventilation

Why do we need ventilation?

 

Building regulations require a minimum rate of ventilation equivalent to one air change for the whole building every two hours.

 

General improvements in house construction, building regulations and much higher levels of insulation in modern dwellings mean that houses are becoming almost airtight. Consequently, the air inside becomes stale with a build up of moisture and smells. The moisture can result in condensation and mould, and a generally ‘stuffy’ atmosphere.

 

What types of ventilation are available?

 

1) Single room extractors

 

Traditionally, ventilation has been provided by individual extract fans fitted to bathrooms and other ‘wet’ rooms. These provide short term ventilation, usually very noisily. The extracted air is replaced by fresh air entering the house through trickle vents in the window frames. These are neither attractive nor particularly sensible (having spent a lot of money on a well insulated house with high specification double glazing, a hole is made in the window frame in order to create a draught!)

 

2) Central Extract Ventilation

 

As modern houses have more wet rooms, so it becomes more economical to replace several individual extractors with one Central extract ventilation unit. With a CEV unit, only one vent to the exterior is required (via wall grill or roof vent) in order to expel the stale air & only one electrical connection with the obvious savings in installation costs over individual extract fans.

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The extract unit is usually placed in the loft or a cupboard.

Using central extract ventilation, the replacement fresh air still enters the house through trickle vents. The fan runs continuously, allowing a gentle and imperceptible flow of air through the building. A CEV unit will have an override boost setting for the occasions when there are unpleasant smells or excessive moisture which need to be extracted. Whilst this is the minimum ventilation required by building regulations, it does mean that warm (stale) air is expelled from the building and is replaced cold fresh air, resulting in a loss of heat.

 

Poor ventilation allows:

 

  • a build up of humidity resulting in condensation
  • the growth of mould in damp areas
  • the accumulation of unpleasant smells
  • a build up of carbon dioxide and other noxious substances
  • conditions in which dust mites thrive

 

By removing the stagnant damp air from a building, central extract unit will prevent a ‘stuffy’ atmosphere and the problems associated with poor ventilation can be eliminated. Good ventilation is of great benefit to those who suffer from asthma & other respiratory complaints

 

3. Heat Recovery Ventilation

 

From the Building Regulations 1995 Part F, amended 2000

 

“Ventilation systems in buildings result in energy being used to heat fresh air taken in from outside and, in mechanical ventilation systems, to move air into, out of and/or around the building. Energy efficiency is dealt with under Part L of the building regulations but consideration should be given to mitigation of ventilation energy use, where applicable, by employing heat recovery devices, efficient types of fan motor and/or energy saving control devices in the ventilation system.”

 

The loss of heat can be avoided by using Heat Recovery Ventilation which works in the same manner as Central Extract Ventilation but additionally supplies fresh air from the exterior via a second fan instead of through trickle vents.

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The (warm) stale air from the wet rooms & the (cold) fresh air from the exterior both pass through a heat exchanger, in opposite directions & without mixing. The heat contained in the extract air is transferred to the incoming fresh air, which is introduced back into the living areas of the building. Heat Recovery Ventilation does not produce heat, but minimises the amount of heat which would otherwise be lost through ventilation, with degrees of efficiency varying between 70 - 97%. In doing so, it reduces the amount of heat that needs to be produced to keep a house warm.

Heat Recovery Ventilation systems are designed to run continuously, virtually silently, providing clean fresh air throughout the building. Normal operation is at a very low speed, allowing the gentle movement of air from dry rooms to wet rooms and then to the exterior. Heat recovery units have two or more speed settings so that larger quantities of air can be extracted as the need arises. Depending on which system is chosen, humidistats and timers can also be used to control the ventilation.

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Heat Recovery Ventilation offers the added bonus of filtering the incoming air so that there is less dust internally (and therefore less dusting to be done).

Pollen filters are available, which is a real boon to those who suffer from allergies, asthma and hay fever.

An HRV system can also be used to extract air from rooms which get uncomfortably warm ( garden or sun rooms, kitchens with range cookers, etc.) and redistribute the heat from this air, via the heat exchanger, to other rooms which are not so warm.

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