Clearing the air on home ventilation

May 5, 2020

Clearing the air on home ventilation

by | May 5, 2020 | Maintenance

Not only do we live in a cold climate for half the year but many of our homes are damp. Managing the eight litres of moisture created by the average New Zealand family daily is about having the right balance of insulation, heating and ventilation in place.

Damp homes are unhealthy homes. Ventilation, whether by a system or by doors and windows, is necessary to remove the moisture created in our everyday activities like cooking, cleaning and washing and to maintain a healthy air quality. The problem escalates in winter when we spend more time indoors and open windows less – we actually make it worse by doing our best to trap heat in.

Ventilation is as much about protecting the property as it is its occupants. Water damage from leaks, cold, dampness and musty smells can be horrific – it can devalue property and cause good tenants to move out.

Renovation and maintenance expert Mark Trafford of Maintain To Profit is also a property investor and advocates for providing healthy homes for tenants, but the key he says it to do it smartly to keep a fair market return.

“Condensation is a huge killer of properties internally – it starts with the walls and ceilings, particularly if they’re poorly insulated and then it rots the carpet eventually, it just smells awful,” Mark says.

Small things can help a lot, like security latches to encourage tenants to keep windows open.

“It’s really not an expensive thing to put a window latch on and if it keeps tenants happy and safe, then great.”

Mark sees a lot of damp properties in his work along with the best and worst of tenants and landlords. If you provide a house in good condition to tenants and they aren’t ventilating it then give them a 14-day notice to force them to do it. On the other hand, a landlord who doesn’t uphold their responsibilities in providing a sound place, could end up in the Tenancy Tribunal with the tenant saying the house is unhealthy.

Sorting the source
Before fixing a mould or dampness problem, it is important to determine its source. In many cases it can be relatively cheap and easy to identify and fix the problem.

EECA’s residential general manager Robert Linterman says protecting against mould growth for wet areas comes first.
“It’s having good extraction systems in the wet area in the home – bathroom.

Look for leaks in wall and roof claddings, flashing and near showers and baths.

Regular property inspections, whether by you or a property manager, are very important too. Mould needs to be wiped clean as it appears, so keep an eye out during inspections and ask tenants to clean it. Ask tenants if they are opening windows. Symptoms of excess moisture and dampness include musty smells, mouldy clothing or shoes in wardrobes, mould forming behind wall hangings, rotting wood and stains on ceilings and walls. Condensation isn’t always a sign of dampness if it only happens occasionally during winter.

Know your property well and be clear on whether it’s a dry house or is likely to have problems. Know what areas don’t get a lot of light and be proactive about potential problems.

A dehumidifier helps with controlling moisture and providing your tenant with one is a cheap option. It’s a portable box that basically sucks the moisture out of the air, but doesn’t dry the house and is not fixing the problem. They can be expensive to run, need to be emptied by tenants, can be noisy and must be run constantly.

Heat transfer kit
Ideally your rental property has a dry heat source like a wood or pellet fire or heat pump. If this source isn’t able to heat the whole house properly then a heat transfer kit system is a cheap and efficient way to spread the heat around. Kits can be bought at stores like Mitre 10 and Bunnings and you can DIY install. There is a vent in one room, sucking up heat with a fan and pumping the warmer air into other parts of the house.

Home ventilation systems
An automatic ventilation system is a much more effective way of reducing condensation than a dehumidifier and is very convenient. There are two types of systems – positive pressure and balanced pressure.

Many factors including house design, air tightness and floor area will influence which system suits the house best, along with the type of roof and how much sun it gets.

Positive pressure ventilation systems are the most common type available in New Zealand. They basically take air from the celling cavity, filter it to remove dust, pollen and other contaminates and then fan this clean air through ceiling vents into the house. Air inside the house is pushed out through natural gaps and air leaks in houses especially around doors, and windows, creating air flow. The quality of the incoming air depends on the filter type and how often it is cleaned or replaced (usually every two years). These systems don’t generate heat and shouldn’t be regarded as a heating system, but they should make heating a house easier. Positive pressure system can extract warm air from the roof space when it’s available, but usually warmth is most needed on cold winter days when the roof space is also very cold. Positive pressure system suits older houses with wooden joinery more than modern houses with sealed aluminium joinery – unless windows are opened or additional vents fitted.

Balanced pressure or heat transfer systems are the other type, these work best in more airtight, modern homes that are already well heated. There are two fans for two separate air streams- one supplying outdoor air into the house and the other extracting air and venting it externally. Features can be added to assist with heating and cooling, with the likes of heat recovery units that extract warm damp air from living spaces and pass it thorough a heat-exchanger to heat air which the system brings in from outside.

A range of factors including the type of system, how well it is installed, your house type and the climate can impact performance so do your homework when choosing a ventilation system. Get quotes from several installers who are familiar with your area and ask about guarantees and independent test reports.

EECA’s website has useful information for landlords around ventilation systems, along with information on heating and insulation. A government grant scheme for insulation is still running with a new one set to start in a few months. Visit for more information.

Tips to control moisture
• Kitchen, bathroom and laundry are the areas where ventilation is most important. Fit externally vented extractor fans in each room. Fans must vent to the outside and not just recalculate damp air, or vent it to your celling space. Clean fans regularly to maintain performances.
• Ask tenants to open windows and doors as often as possible.
• Check for dampness under the house. Look for any mould or mildew – take some dirt and rub it firmly on your hand. Check for drainage, guttering, downpipes or plumbing problems. Uncover any vents that may have become blocked by plants or soil. Get vents installed if there aren’t any. Put a vapour barrier down (like thick polythene sheeting) on the ground. It keeps the moisture in the ground and stops the air under the floor from getting damp. Check the joints, ensuring a tight fit around piles. Check that drainage systems are diverting water away.
• Fix any leaks in the roof or around windows. Look for leaks in walls, roof claddings and flashings. Also check for leaks in plumbing services, especially around showers and baths.
• Look for mould during inspections, check for signs in hidden areas also, like wardrobes, under carpets and behind curtains and furniture. If you find any mould, then ask tenants to remove it.

Free Healthy Home Assessments
Approved energywise provider Greenstar is offering free healthy home assessments to help investors find out where they can improve with warmth and dryness of their properties. Greenstar is able to offer insulation subsidies up to $1,300 on the cost of underfloor and celling insulation on houses built before January 2000. In addition, Greenstar is currently offering Healthy Home packages with discounts of up to $500 each on both heat pumps and ventilation. You can get an on-the-spot quote, and Greenstar will organise the subsidy for you. Easy payment options include topping up your mortgage (many of the main banks are waving loan fees for insulation costs) or Aucklanders can add the cost onto Auckland Council Rates and pay as little as $7/week.

For more information to arrange for you Free Home Insulation Assessment please call 0800RUNWARM(789-276) or visit

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