Smarter Homes: Ventilation

With good ventilation, your home will be drier, healthier and more comfortable.

Ventilation is about helping air to circulate in your home. It allows moisture and airborne pollutants to escape, and fresh, clean air to be drawn into your home. Well-designed ventilation will provide cooling in summer. In winter, it will let stale air out but keep warmth in.

Effective ventilation depends to a significant extent on the size, placement and type of windows, doors and other openings in your home. With good design, you can control the circulation of air, rather than having draughts.

With good design, you can use windows, vents and other openings for most ventilation – this will save on your energy costs.  However, you may need some mechanical (active) ventilation, for example, extractor fans to expel moist air from the kitchen, bathroom and laundry outside.

Does ventilation matter?

Yes. A 2005 BRANZ survey of the condition of New Zealand homes found that many were damp and poorly ventilated.

Most bathrooms relied only on windows for ventilation. Only half of kitchens vented moist air to the outside. And 40% of timber-framed homes had poor or seriously inadequate subfloor ventilation.

Poor ventilation allows moisture and airborne pollutants to build up inside your home. This can cause health problems such as asthma for you and other members of your household. Moisture can also make your home uncomfortable to live in and damage its structure.

When should you think about ventilation?

Planning a home or renovation

If you're building or renovating, ventilation should be considered early in the design process.

Good design should strike a balance between the need to introduce fresh, healthy air into your home and the need to maintain comfortable temperatures, so ventilation should be considered alongside passive heating and passive cooling options. If you consider heating without ventilation, you may end up with a home that's warm but not as healthy or comfortable to live in as it could be.

During and after construction

During the construction process and for a few weeks afterwards, you'll need to provide good ventilation to minimise your exposure to airborne pollutants such as formaldehyde from new building materials. See Unhealthy air for more.

In your existing home

Ventilation can be improved in an existing home without making significant alterations. Moving a door or window, or removing an internal wall might make a significant difference.

For ventilation to work as effectively as it should, your home should be well insulated. Then you can control your ventilation, rather than being draughty and cold.

Older homes tend to be less airtight than more modern homes. This can allow for some natural ventilation - but can also mean they're draughty and harder to heat. As a general rule of thumb, houses built before the 1960s will be very draughty, and houses built between the 1960s and 1980s will be quite draughty.  Modern construction, however, is much more airtight, meaning that problems with inadequate ventilation become more frequent.

Passive ventilation

How does it work?

Passive ventilation uses doors, windows, vents, louvres and other openings to bring fresh air into your home and let stale air out. The size and placement of these openings can be used to guide air into and through your home.

Where cooling is required, windows or other openings on upper levels can be opened to let warm air escape. In winter, well-designed passive ventilation refreshes the air in your home without creating draughts or letting out too much heat.

Passive ventilation can only work if air has clear, uninterrupted pathways through your home. You can maximise air flow by designing open plan areas or having high vents or other openings between rooms. In general, windows should be larger on one side of the home than the other in order to encourage air flow.

If your home is designed for passive ventilation, all you'll need to do is open and close windows, doors or other vents as needed to reduce the temperature and improve the quality of the air you're breathing.

To encourage cool air flow, you'll need larger windows opening to the breeze and smaller, higher windows on the walls on the opposite side of the house

Options

The appropriate ventilation options for your home will depend on the climate and microclimate of the area you live in, and what prevailing breezes there are. As a rule of thumb, the area of windows, doors and other vents that can be opened up to the outside should be at least 5% of the floor area for each living space - and more for high-use areas.

Some points to consider:

• Windows or other openings on opposite sides of your home will help draw air through.
• Opening windows on the south and east side are best for allowing cool breeze into your home from early in the day. Openings on the north and west sides, higher up, will keep the air moving.
• Vents or other openings in the roof or on upper floors will allow air to escape as heat rises.
• Built-in vents, louvres, slots and gaps in door or window framing can provide low-level ventilation over long periods without creating draughts or security risks.
• Different types of window can be used to guide air into your home - for example, side opening windows are better at catching breezes and pulling them into the house, than awning opening windows
• If your home is on more than one level, make sure there are opening windows and doors on each level. As hot air rises, high windows which can be left open on upper floors can be a good way of ventilating your house during summer.
• Fly screens and security stays installed on windows mean they can be left open at night, or when you’re out during the day, to help the house keep cool in summer
• Don’t forget to ensure cross-ventilation under your floor to get rid of dampness (see Moisture for more information)

See Glazing for more about window design.

Background air leakage

Some features will provide low-level background movement of air between your home's interior and exterior. This is often called air infiltration, and can cause draughts and heat loss in winter. For example:

• timber joinery around windows and doors
• flues and chimneys
• recessed ceiling and light fittings
• extractor fan grills.

It is better to plan good ventilation together with a well-insulated house, than rely on leaks and draughts which you cannot control when you need to and won’t necessarily ventilate the right places.

Active ventilation

Active ventilation is ventilation provided mechanically - for example, by extractor fans, range hoods and whole house ventilation systems. These systems run on electricity - the bigger the system and the more components, the more power it will use.

A well-insulated, well-designed home may only need to use active ventilation for rooms where moisture is generated (bathroom, laundry and kitchen), while passive ventilation will be sufficient for maintaining air quality through the rest of your home.

Active ventilation may also be needed to get warm air into cooler, damper areas such as south-facing rooms - for example by heat transfer systems (see Tips for efficient home heating for more information).

Extractor fans/range hoods

Extractor fans quickly remove moist air from bathrooms, toilets and laundries. Range hoods do the same job for kitchens.

It's important to choose the right-sized fan for the job. A fan that's too small won't remove enough moist air to keep your home dry. A fan that's too large can create draughts. For a typical bathroom or toilet a ventilation rate of 25 litres per second should suffice. For more information see Table B1 in AS 166 part 2.

Extractor fans should be placed as close to the moisture source as possible. They must be vented to the outside or the moist air will end up in your roof space, damaging your insulation and roof supports (see Moisture for more).

Because extractor fans remove moist air but don't bring in fresh air to replace it, you'll need some other way of getting fresh air into the room. By placing air vents on the opposite side of the room from the extractor fan, or slightly opening doors or windows, you can encourage air flow.

Solar or electric-powered roof ventilation

These simple fan, duct and vent systems take hot air from the top of your home or roof space out through the roof.  Solar-powered systems are available that cost nothing to run.

Whole house ventilation systems

Whole house ventilation systems can be useful to bring in fresh air and combat condensation in modern airtight houses. There are two main types of whole house ventilation systems:

• Positive pressure / Roof cavity ventilation systems
• Balanced pressure / Heat recovery ventilation systems.

Positive pressure / Roof cavity ventilation systems

Positive pressure or roof cavity ventilation systems are the most common type available in New Zealand. They bring filtered air from the roof space into the house through a single, or multiple, ceiling vents. This forces the stale air to leak out through gaps, windows and doors. The performance of these systems depends on the sizing of the fans, the distribution of the ceiling vents throughout the house and how airtight your home is.

In an airtight house, pushing the filtered air into the house creates a positive pressure inside the house which causes inside air to move out.  However, in draughty houses, there are too many gaps and leakage points - the ventilation system will not be able to force the air into each room of the house.

The ventilation system will also not work properly if the roof space is not properly sealed from the inside of the house (for example, if you have downlights).  The stale indoor air will leak back into the roof and be pumped back into the house again.
Ventilation systems should bring fresh air into the house, but your roof space may be polluted by dust, mould and vermin. Most systems are fitted with filters - the quality of the air entering the house depends on the filter type and whether you regularly change or clean filters.

The Energy Efficiency and Conservation Authority (EECA) recommends that the home ventilation systems source their ‘fresh’ air from the outside, not from the roof space.

Balanced pressure / Heat recovery systems

Balanced pressure / Heat recovery ventilation systems are particularly suitable for homes in colder areas of the country, if they are already well heated and if they are reasonably airtight.

These systems have two fans: an intake fan which supplies fresh outdoor air into the house through several ceiling vents; and an exhaust fan which takes stale air from inside the house and discharges it to the outside. An air-to-air heat exchanger (usually in the roof space) transfers heat from the inside air to the incoming fresh air from outside. In this way, most of the heat is recovered.

Some products include additional features to utilise heat in the roof space when it is available on sunny winter days, or to avoid warming incoming fresh air in summer when it is hot.

To ventilate effectively, these systems need gaps or vents in internal doors so that air can flow through all areas of the house between the intake and exhaust.

In winter, the heat exchanger transfers a portion of the heat in the warm exhaust air to the colder outdoor air, thus reducing the heat loss associated with the ventilation. To be effective, the house should be airtight so that almost all ventilation air passes through the heat exchanger, rather than being leaked out through draughts.
Heat recovery systems provide good fresh air ventilation but they are not a heating system.  However, they can recover between 67–95% of the heat from the inside air which means that the fresh air coming in will be warmer. This means you will need less heating to warm your home.

http://www.smarterhomes.org.nz/design/ventilation/

Energy Source Builder: Home Ventilation Options For Home Builders

In the old days, buildings were ventilated by the wind and other uncontrolled forms of air leakage. However, most people no longer accept the cold, drafty houses of the old days. Now, houses are expected to be cozy, draft free and energy efficient. A tight home is fine, as long as it comes with a controlled ventilation system. Modern building materials tend to make newly constructed homes much tighter than old ones. Plywood, housewrap, better windows, caulk and expanding foam are a few examples of common products that tighten a house. Research has shown that some builders inadvertently build houses much tighter than intended.

In any home, uncontrolled air leakage is a fickle ventilator. The only way to ensure adequate ventilation is to install some type of automatically controlled ventilation system. As you'll see, you have quite a few choices.

Ventilation Standards

Exhaust fans in the kitchen and bathrooms are standard equipment in new homes. They provide spot ventilation to expel moisture and odors from limited areas. With spot ventilation, people sense an obvious problem and then manually flip a switch to solve the problem.

The controlled ventilation described in this article is intended to maintain overall indoor air quality. It differs from spot ventilation in three ways. It affects the entire living space. It provides makeup air from outside. And, it's controlled automatically. It's called controlled ventilation to distinguish it from the more limited spot ventilation.

According to standards published by the American Society of Heating, Refrigeration and Air-conditioning Engineers (ASHRAE), houses should have a controlled ventilation rate of 15 cubic feet per minute (cfm) per person. So, a household of four would require 60 cfm. Some building codes and utility programs also use 0.35 air changes per hour (ach) as a ventilation target. (To quickly estimate the air flow in cfm needed to meet the 0.35 ach requirement, divide the floor area in square feet by 20.) Remember these ventilation targets are for controlled ventilation, not spot ventilation.

Basic Functions

Ventilation systems are more than exhaust fans. They serve three important functions:

• Expel stale air containing water vapor, carbon dioxide, airborne chemicals and other pollutants.
• Draw in outside air, which presumably contains fewer pollutants and less water vapor.
• Distribute the outside air throughout the house.
• Control system operation automatically.

The basic ventilation system has two elements. First, there's a fan to pull stale air out. Pickup points for stale air are generally in high moisture areas, such as the kitchen, utility and bathrooms. Second is the makeup air supply. Outside air is delivered around the house, with one supply point in each bedroom and at least one in the living area. The suction, also called negative pressure, created by the exhaust fan pulls air through the house from supply points to the pickup points. By properly locating the pickup and supply points, you make outside air travel through the entire house.

Equipment Options

The equipment that performs these four basic functions comes in all shapes, size and costs. Here are six sample systems:

• Surface-mounted Fan
• Remote-mounted In-line Fan
• Remote-mounted Multiport Fan
• Balanced Ventilator
• Air-to-Air Heat Exchanger
• Exhaust Air Heat Pump

Exhaust Only vs. Balanced

In simpler systems, the main component is an exhaust fan that places the building under a slight negative pressure. This draws outside air into the house through passive fresh air inlets. Because they are simpler, negative pressure systems are generally less expensive. Plus they help prevent water vapor from migrating into building cavities, such as walls and attics, where the vapor could condense and cause problems.

Unfortunately, fireplaces, wood stoves and gas-burning appliances were not designed to operate in a negative pressure environment. Under some conditions, even a slight negative pressure could cause flue gases, including carbon monoxide, to spill into the living space. You can either leave them out or install only sealed combustion appliances that draw air from outside.

Other systems strive for a balanced flow by using two fans: one for exhaust and another for fresh air. In theory, backdrafting shouldn't be an issue. However, experience with forced-air heating systems shows that balanced air flow can be difficult to achieve. Detailed duct design and careful installation are needed. Once installed the system must be adjusted. Even then the carefully balanced air flow can be thrown off by someone closing a door between a supply and a pickup.

Heat Recovery or Not

Controlled ventilation systems collect the outgoing air into a single duct so it's possible to capture heat from that air with a heat-recovery ventilator (HRV). The most common type of HRV is an air-to-air heat exchanger. It transfers heat from the outgoing air stream to the incoming one. In these systems, air flow is balanced. Another type of HRV is an exhaust air heat pump. Commonly used in Sweden, it transfers heat from the outgoing air into the domestic water tank. The compressor is about the size of a window air conditioner.

High Quality Fans

Controlled ventilation systems operate many hours every day. Some never turn off. You want a durable, high-quality fan intended for continuous operation. Most high-quality fans use permanent split capacitor motors. Because this fan will run thousands of hours per year, look for a fan motor with low electrical consumption.

Noise prevents many people from operating fans. Surface-mounted fans should have a noise rating of 2.0 sones or less. A few manufacturers make fans with noise ratings less than 1.0 sone. Low sone ratings are less important for remote-mounted fans. However, you should use sound absorbing fan mounting and duct connections to prevent sound transmission into living areas.

Control Options

Here are a few control options that would work with most types of ventilation systems:

• Twenty-four hour timers allow the occupants to set certain times for ventilation. Set the timer to run the fan at least eight hours per day.
• Twist timers, also called interval timers, allow occupants to engage the fan whenever it's needed. Twist timers can be set up to 60 minutes and are generally located in bathrooms, utility rooms or kitchens.
• Speed controllers allow the fan to operate at low speed for background ventilation with a manual high-speed boost.
• Indoor air quality sensors activate a fan when they detect carbon monoxide, formaldehyde or other pollutants. This is an option in a couple of the more sophisticated controls.
• Dehumidistats engage the fan on rising humidity. They work well when relative humidity accurately indicates the need for ventilation. By setting the dial at 40, you are telling the dehumidistat to operate the fan whenever the humidity is 40 percent or higher. Unfortunately, relative humidity isn't always a reliable indicator. Climates with low humidity might never reach 40 percent, so the fan would never turn on. In wet climates the fan might never turn off. Dehumidistats aren't used as much as they once were because of this problem.
• Continuous operation simplifies the controls, but you should at least install an on/off switch. It's a good idea to locate the switch out of the way to reduce the chance that someone will accidentally flip it off.

People generally aren't reliable ventilation controllers, so you shouldn't count on a manual switch as the primary ventilation control. An automatic control is essential. However, people should have the option to activate ventilation when it's needed. So, most systems require at least two controls wired together. For example, a single 24-hour timer can control background ventilation while twist timers allow manual control.

Furnace Integration

It's tempting to combine a controlled ventilation system with existing forced-air heating and cooling ductwork. However, running the furnace blower causes three problems.

First, virtually all duct systems in new and existing homes have significant air leakage. Second, homes with forced air systems frequently have air pressure differences around the house that increase building air leakage. Third, typical furnace blowers are turned by large, inefficient motors. Running the typical single-speed blower an additional eight hours per day could easily burn more than 2,000 kWh per year. Some new air handlers reduce energy use with multispeed controls or more efficient motors.

Before using heating and cooling ducts for fresh-air distribution, these issues need to be resolved.

Occupant Information

Controlled ventilation systems are new to most home buyers. It's your job to educate the occupants.

• Label all components, including the fan, controls and ducts.
• Write a brief description of the system that explains the principles of operation, control strategy and maintenance. Attach product literature for the components used.
• Show the occupants the location of each component and how to operate the system.

Good information is essential because even the best ventilation system needs to be operated and maintained properly.

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Surface-mounted Fan

The simplest controlled ventilation system uses a quiet, high-quality surface-mounted fan. Fresh air enters through passive vents located in window sashes or outside walls. Surface-mounted fans provide good ventilation for smaller areas. Large houses may need more than one.

• Noise Rating: 2.0 sones or less
• Locations: central hallway or bathroom
• Air Flow Capacity: 80-400 cfm
• Heat Recovery: none
• House Pressure: negative
• Makeup Air: passive inlets
• Multispeed Operation: no
• Equipment Cost: $100 - 150
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Remote-mounted In-line Fan

Remote-mounted fans can pick up stale air from a single point. Or, they can be attached to a branched duct system with picks ups in two or three locations. This makes them a good choice for large houses. If properly rated, the fan could be attached to a range hood.

• Noise Rating: not applicable
• Locations: basement, attic or crawlspace
• Air Flow Capacity: 80-400 cfm
• Heat Recovery: none
• House Pressure: negative
• Makeup Air: passive inlets
• Multispeed Operation: optional
• Equipment Cost: $150 - 250
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Remote-mounted Multiport Fan

Large houses and several multifamily units can be ventilated by a single multiport fan. Some units can accept a duct from the range hood. Most operate at two or more speeds. Several manufacturers sell complete kits with all the ducts and accessories. These may cost a bit more, but the kits simplify installation.

• Noise Rating: not applicable
• Locations: basement, attic or crawlspace
• Air Flow Capacity: 100-400 cfm
• Heat Recovery: none
• House Pressure: negative
• Makeup Air: passive inlets
• Multispeed Operation: optional
• Equipment Cost: $200 - 700
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Balanced Ventilator

If you want balanced operation, without the extra expense of heat recovery, these would be a good choice. Only one or two manufacturers make balanced ventilators without heat recovery.

• Noise Rating: not applicable
• Locations: basement, attic or crawlspace
• Air Flow Capacity: 100-400 cfm
• Heat Recovery: none
• House Pressure: balanced
• Makeup Air: ducted
• Multispeed Operation: optional
• Equipment Cost: $400 - 800
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Air-to-Air Heat Exchanger

This type of heat-recovery ventilator provides balanced air flow and recovers up to 85 percent of the heat from outgoing air. By warming the incoming air, AAHXs provide greater comfort in cold climates than other types of ventilation systems. Units can be sized for any home and small commercial buildings.

• Noise Rating: not applicable
• Locations: basement, inside utility or any tempered space
• Air Flow Capacity: 150-1200 cfm
• Heat Recovery: 60 - 85% recovery efficiency
• House Pressure: balanced
• Makeup Air: ducted
• Multispeed Operation: standard on many units
• Equipment Cost: $800 - 2,000
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Exhaust Air Heat Pump

By employing a heat pump unit about the size of a window air conditioner, an exhaust air heat pump (EAHP) offers exceptional heat recovery efficiency. It can also provide most of the hot water needed by an average family. While the exhaust fan is controlled by timers, heat recovery engages only when hot water is needed. That means ventilation sometimes occurs without heat recovery. The operating characteristics of an EAHP lead to greater air flow than required for a typical small house.

• Noise Level: similar to refrigerator
• Locations: basement, inside utility or any tempered space
• Air Flow Capacity: 100-200 cfm
• Heat Recovery: 200 - 300% efficiency
• House Pressure: negative
• Makeup Air: passive inlets
• Multispeed Operation: no
• Equipment Cost: $1,000 - 3,000 

http://oikos.com/esb/39/VentOpt.html

Home ventilation systems

Home ventilation systems use fans to move air into your house and can provide continuous ventilation regardless of the weather and without the need to open doors and windows. Ventilation systems are not, however, an effective way to heat your home, or fix moisture or dampness problems.

Is a home ventilation system right for you?

A well designed and installed home ventilation system can offer you the convenience of good ventilation by delivering required air replacement continuously and independently of weather conditions.
Ventilation systems are not the only way to ventilate. Opening your doors and windows regularly is a simple and effective way to ventilate most homes.
Note that a home ventilation system is not a good solution for fixing cold and dampness problems in homes. If you are trying to make your existing home warmer, your money will be better spent on insulation and installing an effective heating system. If dampness is your main concern, then address the source of the moisture problem first, before looking at ventilation systems. (see related pages below)
Be aware that the performance of ventilation systems can vary widely depending on a range of factors - the type of system and how well it is installed, your type of house and the climate.
Ask your supplier for independent test performance reports for the system they are proposing. You should also get a ‘no questions asked' guarantee of performance that includes removal of the system if it doesn't work and repair of all damage to your home - e.g. holes in ceilings should be fixed to prevent undue air leakage.

Types of home ventilation systems

There are two types of home ventilation systems commonly available in New Zealand:

• Positive pressure roof cavity ventilation systems
• Balanced pressure heat recovery ventilation systems

Positive pressure/roof cavity heat transfer ventilation systems

Positive pressure/roof cavity ventilation systems are the most common type available in New Zealand. They force filtered air from the roof space into the house through a single, or multiple, ceiling vents. This pushes air inside the house out through gaps around doors and windows and other leakage areas.
How well these systems are able to ventilate the whole house depends on:

• the performance of the fans
• distribution of the ceiling vents throughout the house and;
• the building air tightness.

In draughty houses the ventilation system will struggle to force the air into each room of the house. If the roof cavity is not properly sealed from the inside of the house (for example if you have older recessed downlights) the system can short-circuit, i.e. indoor air will migrate into the roof cavity and be pumped back into the house again.
Roof spaces are often polluted with dust, mould and vermin. To keep the air supply clean, positive pressure/roof cavity ventilation systems are usually fitted with filters. The quality of the air entering the house is highly dependent on the filter type and how often it is cleaned. As suppliers have yet to prove that home ventilation system filters are effective at reducing these contaminants to safe levels, EECA recommends that the supply air of home ventilation systems be sourced from the outside, not from the roof cavity.
The New Zealand Building Code requires homes to have means of ventilation with outdoor air to maintain air purity. Ventilation systems that draw air from the roof space and not directly from outside do not comply with ventilation standard NZS4303:1990 "Ventilation for acceptable indoor air quality" and cannot be used to comply with the Building Code Acceptable Solution for ventilation.
Research recommends that you should not install this type of system for heating purposes
University of Otago research shows that the heat available from moving roof space air into your home (as the most common type of ventilation system does) does not provide significant benefits compared with what you need to properly heat a home in winter.
The research also found that pumping air from the roof space into the living area would often push internal temperatures away from the desired level, rather than toward it.
In summer, roof cavities quickly become excessively hot, and systems that pump roof space air into your house without a summer bypass will have to be turned off for extended periods in order to avoid overheating your house.

Balanced pressure heat recovery ventilation systems

Balanced pressure heat recovery ventilation systems are particularly suitable for homes in colder areas of the country, if they are already well heated and if they are reasonably airtight.
These systems have two fans for two separate air streams. One fan supplies fresh outdoor air into the house through several ceiling vents, while the exhaust fan extracts an equal volume of air from inside the house and discharges it to the outside. Some of the heat from the exhaust air is transferred to the incoming air in a heat exchange unit, usually located in the roof cavity.
Some products include additional features to utilise heat in the roof cavity when it is available on sunny winter days, or to avoid the incoming supply air being warmed up by the exhaust air during summer nights to assist with cooling.
To ventilate effectively, the air must be able to flow freely between the supply and exhaust vents inside the house, requiring gaps around or vents in internal doors. Care is also required to ensure that a ‘short circuit' route is not created between the supply and exhaust vents which would result in areas of the house being bypassed by the system.
In winter, the heat exchanger transfers a portion of the heat in the warm exhaust air to the cold supply air, thus reducing the heat loss associated with the ventilation. The overall effectiveness of the heat exchanger depends on two factors:

• having an airtight house, to ensure that uncontrolled ventilation losses are minimised so that almost all ventilation air passes through the heat exchanger
• having a temperature difference between the inside and outside air. The larger the difference the better the heat exchanger will work. In many areas of New Zealand the temperature difference will not be enough for the heat exchanger to make much difference.

Optional electrical heating unit add-ons

Some ventilation system suppliers offer the option of an electrical heating unit add-on, to provide some pre-heating of air coming from the roof cavity when it is cold. These are known as electric in-line duct heaters.
Most electric in-line duct heaters don't have sufficient capacity to meet a home's heating needs.
Like any other type of electrical heaters (except heat pumps), electrical in-line duct heaters are a relatively expensive and inefficient way to heat a home, particularly if you already have a more effective heater (like heat pump, wood or wood pellet burner, or flued gas heater).
Electric in-line duct heaters lose some heat through the ducts, so it's actually more efficient to use a heater directly in the room you want to heat.

http://www.energywise.govt.nz/your-home/ventilation/systems