A quick online search will find lots of questions and debate about the merits of different types of Home Ventilation Systems. There are various systems but the two main types in New Zealand are … Positive pressure or roof cavity ventilation (PPVS) and balanced pressure heat recovery ventilation (BPVS). All home ventilation systems use fans to move air into your house and should provide adequate ventilation without the need to open doors and windows. A well ventilated home is warmer, drier and healthier. The fresh air introduced will reduce weeping windows, combat mould and mildew and make the air in the home easier (and cheaper) to heat during cold weather. In the summer the house stays fresh without the need to keep windows open.
It should be understood that ventilation systems are not heaters. Some offer ‘add-on’ heating but generally these are not efficient or economical. There are three elements to a warm, dry, healthy home. Adequate insulation, adequate ventilation and adequate heating when required. Experts maintain that each of these elements should be addressed separately with products that are efficient at the task for which they are designed.
Positive pressure or roof cavity ventilation systems are the most popular type available. They force filtered air from your roof space into the house through ceiling vents. They generally draw fresh air from the roof space. Contrary to common perception, this roof space is not a dusty area contaminated by rodents and insulation material. This air is constantly changing, is fresh and ideal for home ventilation. A quick look in your ceiling will show the air is not full of dust or other contaminants and the amount of dust that has collected on rafters etc over a long period is very small. All positive pressure systems have at least G4 filtration to eliminate any material that is unwanted in the home. This makes them far more effective at keeping contaminants out than opening doors and windows and logically, better air than that which is blowing around outside.
Positive Pressure systems are also the least expensive to purchase and the cheapest to operate. Prices start at under $1,500 for a system suitable for a typical home and are around $1 per month to run. The Unovent system is also able to be installed DIY as it’s a 12v system (or an electrician can install it in half a day). A PPVS is the best system for older (unsealed) homes.
The Balanced pressure heat recovery systems are arguably more suitable for homes in colder areas of the country, if they’re already well heated and reasonably airtight. However they are expensive and also arguably offer no more advantage than a PPVS if the insulation/heating is already installed.
These systems have two fans for two separate air streams. One fan supplies fresh outdoor air into the house through ceiling vents. The exhaust fan extracts an equal volume of air from inside the house and discharges it outside while some of the heat from the exhaust air is transferred to the incoming air in a heat exchange unit, usually in the roof cavity. They operate best in the winter and there is no advantage over the PPVS systems in summer.
Purchase and installation costs are higher as are the running costs. They are more popular in countries that have very cold (snow) winters. It is important to have a fully sealed house if these systems are used.
Both systems are available with fully automated controls and both improve the ambiance of the home. They are most noticeable during winter when windows are weeping but in fact are doing very good work during the warmer summer months when moisture is higher in the air as it is warmer.