Appliances
Ventilation systems
Introduction
Does your house suffer from "crying windows"? A ventilation system could help.
If your home suffers from streaming windows, mouldy curtains and a damp unhealthy feeling, you need to improve your ventilation. We tell you how to stop the sources of moisture, and we check out ventilation systems.
Note: this report does not contain test results or brand-specific recommendations, but we do compare the price and features of 60 ventilation systems currently on the market.
Types of system
There are three main types of ventilation systems.
Forced-air ventilation systems
These blow dry air into your house from the roof space above the ceiling. They work best where there is a decent amount of space in the roof. The roof space must also be dry and reasonably warm on sunny winter days.
Note: Strictly speaking, roof space air does not comply with the building code requirements. Good filtration is essential.
Most forced-air systems make a big thing of the ability to recover heat from the roof space. This is often possible - but not all the time. There won't be much warm air up there on frosty nights. To cope with this, most systems automatically slow or even stop the airflow when the roof space temperature falls below certain levels. That means your ventilation slows down or even stops, unless there is a heater fitted.
Heat-exchanger ventilation systems
These extract warm damp air from living spaces, remove the heat using a heat exchanger, transfer this heat to cold dry air from outside, then pump it back into the house. These can work even where there is no roof space, for example in an apartment.
These heat-exchanger systems have two advantages. They run all the time, regardless of air temperature in the roof. And they fully meet the building code's requirements for ventilation with outside air. But a properly designed heat-exchanger system for your house can be quite expensive.
Solar-powered ventilation systems
These use the sun to heat up panels, which are mounted on the roof or an outside wall. These panels then warm the incoming air, with solar cells being used to power the fan. So there are no running costs with solar-powered ventilation, and you get fresh outside air that's nicely warmed up. There's also an optional cooling kit for summer ventilation.
But solar power depends on getting adequate sun, and won't suit some locations. You'll also still need additional heating in the house at night - and on very cold wet days.
We've found only one solar-power model suitable for a typical-sized New Zealand house, and it's quite expensive.
"Heat recovery" units
There is quite a lot of confusion over so called "heat recovery" systems. The most effective type of "heat recovery" unit is the heat-exchanger system, which extracts warm damp air from living spaces and passes this through a heat exchanger to heat up dry air which the system brings in from outside. Inline heaters are not required.
This type of system conforms to the heat recovery definitions of the American Society of Heating, Refrigeration and Air-Conditioning engineers (ASHRAE). Local ventilation standards are based on ASHRAE standards.
Another type of "heat recovery" unit, sold by HRV, claims to recover heat from the roof space. In our opinion, this is a forced-air system. The HRV unit can undoubtedly extract warm air from the roof space on sunny days (like a forced-air system does). But HRV also offers the option of inline heaters "for reduction of relative humidity", which means that the unit doesn't operate on true heat-exchanger principles.
Which system is best?
The best system for you depends on the design of your house, its floor area, the location, how much sun the house gets, the type of roof ... even the local climate.
So before you install any system, do some homework. We've outlined how the different designs work, and some of their pro's and cons which should let you decide if your house is suitable for any of the different types of system available. Consider what you want to achieve against the types of system on offer - and also consider any extra features you might need, to meet your particular requirements.
For best results, a system should be designed specifically for your house and your needs. But this can be quite costly, especially if you choose a fully automated system with multiple outlets or other options.
We recommend getting quotes from several installers who are familiar with your local climate.
Checklist
Here's what to consider before you buy a ventilation system.
Capacity
To meet building code minimum requirements for ventilation, the system needs sufficient fan capacity to move the whole volume of air in your house every three hours. All makers listed in our table offer units that can meet this requirement, offering a range of models to match house sizes. If you have higher than usual ceilings or an unusually complicated house design, you may need a larger unit, and/or more outlets.
Extra outlets
Forced-air systems can be installed with one centrally located outlet, designed to push the damp air outwards, and out via windows and doors - or they can be installed with outlets in several rooms, especially those with severe condensation problems. Larger houses will ventilate better with several outlets rather than one large one.
Heat-exchanger systems operate across the whole house, and usually have at least two outlets and two inlets inside the house. The inlets are typically located in warmer areas, and the outlets in cooler areas. Be guided by your installer on the location and number you need.
Controls
When set up correctly for your house, the controls should need little adjustment. That's the ideal arrangement - set and forget. With forced air systems, it's handy to be able to do some basic things from a control panel in the house, like switch the system off in summer. But, otherwise, it's easier to let the system do the work.
Some of the more expensive forced-air models let you check temperatures in the roof and the house, and make your own adjustments to temperature cut-out settings or adjust the air flow. Others will automatically change airflow as required, and even switch to summer cooling or switch on heat transfer systems at pre-set temperatures.
Regardless of this, a basic system can provide ventilation just as effectively as one with complicated control options.
Extra features
You'll need to consider these if you're buying a forced-air system - although they're often standard on higher specification (more expensive) models. Heat-exchanger systems make some features like heaters and heat transfer unnecessary.
Most of the optional inline heaters for forced-air systems are small, just designed to take the chill off the air, But some makers offer larger units that can substitute for some of your normal heating. If you're thinking of a forced-air system and you want to maintain good ventilation during the colder months, we think additional heating is essential - but this will increase your running costs.
A heat-transfer feature allows the fan to take warm air from one part of the house (near a wood burner, for example) and move it to a colder part of the house.
Whether you need summer cooling depends on the design of your house, and on the local climate. In forced-air systems, extra ducts are added so that fresh air is drawn from outside (rather than warm air from the roof space). Look for a model with an automatic or remotely controlled changeover feature - or you may have to send someone up into the roof space to alter the settings.
If effective summer cooling is really important to you, air conditioning is better than a ventilation system - although heat-exchanger systems work well in conjunction with air conditioning.
A shower boost is offered only on heat exchanger systems, and uses sensors on the hot water pipes to detect when the shower is running and switch the fan to high speed to extract the extra steamy air.
Filters
Forced-air systems need good filters, as they draw on roof space air that can contain fibreglass from batts, dust, debris from bird nests, and other pollutants. Most of these systems come with EU4 or G4 grade filters, which can remove 80 to 95 percent of particles down to 10 microns. Some makers of forced-air system offer finer filters as standard, others offer this as an option.
If you know your roof space is very dusty or dirty, finer filters will prevent more of that dust from getting into your house. Heat-exchanger systems draw in outside air. So they don't usually need filters, unless there's pollen or severe air pollution.
If you want to keep costs down by changing or cleaning your own filter, check how easy this is. Some makers won't sell you a filter; they only provide a filter-replacement service. Some filters are washable - but wash them carefully by hand, and replace them if they get torn or damaged. Driveaire says its filters can be washed up to six times. Electrostatic filters require regular washing in special solutions.
Warranties
If there's some doubt whether a forced-air system will work in your house, make sure you get a money-back warranty. Look for a "three winter months" warranty, (not offered on most DIY systems) so you can evaluate the system's performance in more extreme conditions. Warranties are in addition to your usual protections (repair, refund, or replacement) under the Consumer Guarantees Act.
DIY
This is possible for both forced-air and heat-exchanger systems - provided you're reasonably handy. (Heat-exchanger systems are more complex, but they come with comprehensive instructions.) You'll still have to use an electrician to make the connections to the mains or to fit a 3-pin outlet, which adds to the cost.
DIY's also the cheapest option - Bunning's offer the Comfortmaster kit for as little as $600. It's a basic one-outlet forced-air system. Weiss and Smartvent are available through hardware stores like Mitre 10 and Placemakers, but you may have to ask your store to order one.
Some of the other makers of forced air units will supply systems for DIY, but they don't usually offer a winter performance warranty if you install it yourself. And, if you have to get an electrician to wire the unit up, the cost savings are minimal.
DIY kits are also available for Solar Venti solar systems, as well as Cleanaire and Vent Axia heat-exchanger systems. Usually you have to supply your own ducts and vents for DIY heat exchanger models.