Ventilation is key for a healthy, efficient and comfortable home – keeping moisture, dampness and mould at bay – especially now that we've settled into our new homes to hibernate over winter.
Ventilation is key for a healthy, efficient and comfortable home – keeping moisture, dampness and mould at bay – especially now that we’ve settled into our new homes to hibernate over winter.
The pioneer of modernist architecture – Le Corbusier – famously said: “A house is a machine for living in.” This machine can now be drier, healthier, more comfortable and therefore more efficient than ever before, by adding three interrelated factors: insulation, heating and ventilation.
Ventilation is often missed from the equation and yet the more airtight and warmer a home becomes, the more critical good airflow is. Simply put, an effective ventilation system will remove moisture, odours and airborne pollutants, replacing ‘bad’ air with drier, fresher air from outside or from the roof.
While heat loss is inevitable it is offset by the fact that it takes less energy to heat dry air than damp air. If done correctly this will ultimately keep heating bills down. Adequate ventilation without excessive droughts is key, so too is a relative humidity of 20-70 per cent. Ideally that means the equivalent of 0.4-0.6 air changes per hour in a new home and 0.5-0.7 in an existing structure.
Considering home heating without ventilation may result in a warm home that does not ‘breath’ well, and is therefore not as healthy, efficient or comfortable as it could be. However, there’s no such thing as a ‘silver bullet’. As Eion Scott, Eco Design Advisor at the Auckland Council, points out: “For every house and every household there is an individual solution.”
The design, layout, choice of building materials and airtightness of a house are just one set of variables. Then there are location and aspect, local weather patterns and temperatures. The occupant’s lifestyle also plays a role. And of course there is the inevitable bottom line.
“We do an in-home assessment so we can observe any issues and have a face-to-face discussion to find out the needs and habits of the homeowner,” says Eion. “Then we can make an informed recommendation.”
A passive ventilation system can be as easy as opening windows. At the very least plan for each room to have windows that can be opened, preferably in more than one wall to allow free cross-ventilation. They should have security stays so they can be safely left open when the house is unoccupied.
A properly designed system using tilt-and-turn windows or trickle vents (commonly used in Europe) will provide a controllable level of ventilation and will eliminate condensation. The former can be left open in a secure ventilation position or fully opened like a casement window.
Trickle vents can be retrofitted to existing windows. As they rely on natural pressure differences around the building, they are better suited to buildings that have a reasonable exposure to wind.
Active or mechanical ventilation can mean anything from heat transfer systems to dehumidifiers, and all require electricity to run.
There are balanced pressure heat recovery ventilation systems as well as positive pressure heat transfer systems (which utilise the roof cavity). Basically, both systems circulate air continuously through the home via a network of ceiling vents, reducing condensation, purging odours and creating a ‘warmer’ home through the supply of dry air. Neither system is an actual heater.
A balanced pressure heat recovery unit has a supply fan, an exhaust fan and a heat exchange core. It draws fresh ‘dry’ air from the outside and exhausts damp air from the home. Around 95 per cent of the heat from the damp air is used to heat the incoming fresh air. These systems are best suited to colder climates, are especially effective in airtight homes and require no roof space.
DVS – the only BRANZ appraised positive pressure system – states that their heat exchange option “negates the need for any extractors in wet areas in the home.” Using a fan (and filter to remove pollutants) they draw air from the cavity above the ceiling and force moisture out through the walls and joinery.
While the EECA recommends that the air supply of home ventilation systems are the cheapest to run and most common in New Zealand. They are very effective for retrofits of older homes, although they are not as suitable for South Island winter conditions and less effective on overcast days with little solar warmth to heat the cavity. Solar assisted systems can both warm the incoming air and power the fans through external solar cells.
Another option is a heat transfer system, which essentially draws the heat from one room and redistributes it through a ventilation system to colder areas of the house. It works best with a heat source like a wood burner and can be installed by a ventilation supplier or bought as a do-it-yourself kit.
Whatever your choice of continuous ventilation, in winter it needs to work in tandem with effective heating. If budget is a factor DVS recommends sorting insulation first, before purchasing one of their systems. They say properties where condensation, mould and musty odours are not an issue; money is probably best spent on a heat pump. Again it’s a home-by-home scenario. Don’t be sold on cost alone and use a consultant who knows the area.
Heat pumps are one of the most economical, energy efficient and quiet ways to heat (and dry) a home. For every 1kW of energy used they produce up to 4kW of heat. Check a heat pump’s energy rating efficiency and be aware that some pumps may not perform at a temperatures below 3°C. Look for the H2 (2°C) rating.
Heat pumps can be mounted on the floor, wall or ceiling. For a total luxury package a multi-room ducted option will forever remedy any ‘cold rooms’. In air conditioning mode, heat pumps effectively dehumidify the air to cool it down. Little but design separates the trusted brands. Fujitsu are recognized for their self-cleaning filters and quietness. They offer a warranty of six years if fitted by an accredited installer.
Finally, the trusty dehumidifier is an easy to use, short-term answer to excessive moisture issues. A heater and a dehumidifier working together will heat a cold and damp room more quickly and cost-effectively than a heater alone.
This article featured on page 90 of Issue 003 of New Zealand Renovate Magazine. New Zealand's first and only magazine solely dedicated to home renovations.
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