Heat Pumps

Background

The Selwyn District Council (SDC) is receiving an increasing number of noise complaints that relate to heat pump, and ducted heat pump systems. These systems are not considered during the building consent process as they are part of a self-certified electrical installation. With this in mind, we provide the following guidance information for designers, installers, builders and homeowners to help mitigate noise issues so all of our residents can enjoy their home environments without unreasonable noise.

Noise Rules

Section 16 of the Resource Management Act 1991 makes every occupier of land responsible for adopting the best practicable option to limit noise emissions from their property to a reasonable level.

The Selwyn District Plan sets out noise limits for different areas in the Selwyn district, the noise limits are based on the zone where a property is located. There are different allowable noise level limits depending on the time of day. These limits are used to identify a reasonable level for noise, including emissions from heating and ventilation systems. You can find out the zoning of a property and the relevant noise level limits by visiting the SDC District Plan or by contacting Council.

While the Selwyn District Plan should be used to precisely determine the reasonable level of noise for a particular zone, indicative noise limits for properties located in all residential zones are provided in the Table 1 below:

Table 1. Noise limits for different time periods in the SDC District Plan.

The Selwyn District Plan noise limits are measured in dBA (LAeq and LAmax) which is a sound pressure level with a frequency weighting that closely approximates the response of the human ear to sound. The LAeq level is a time averaged level, measured over a certain period of time. The LAmax is the maximum permitted noise level.

When responding to a heat pump noise complaint, Council Officers will measure the noise levels to determine if it is necessary to reduce noise emissions to ensure a reasonable level of noise is achieved. Noise will normally be measured at or within the boundary of the complainant’s property not on the same site as the noise source and is also measured in accordance with NZS 6801:2008 Acoustics - Measurement of Environmental Sound and assessed in accordance with NZS 6802:2008 Acoustics - Environmental Noise.

If a noise is found to breach the SDC District Plan noise limit rules, then Council will engage with the owner to mitigate the noise. It is the owner’s responsibility to mitigate the noise to a reasonable level. From time to time Council may need to use enforcement action in accordance with the Resource Management Act 1991.

Maintenance of heat pumps

Tonal type sounds or sounds with a narrow frequency range are common from rotating parts in units such as fans and motors. These noises can greatly increase if a heat pump system is not maintained regularly to replace worn bearings or limited life parts before they fail.

Loose screws in a metal casing are a common source of buzzing or rattling noises. When you have your heat pump system installed, ask the installer to provide you with an appropriate maintenance schedule.

Sound insulation methods

In urban areas there may not be enough space between properties for exterior heat pump units to be installed without causing noise problems. Noise may be directly transmitted to a neighbour’s house wall, or indirectly from reflection off the wall of the house being heated, or a combination of both.

Higher frequency sounds can be reduced by structures, but lower frequency sounds may penetrate structures unless they are reduced at the source. If you are unable to position the unit away from the vicinity of neighbouring property, especially near bedrooms, some degree of noise control may be necessary.

Conceptually, a soundproof enclosure should provide a noise reduction of at least 5 decibels. If it is well constructed, without gaps, and incorporating acoustic absorptive material a 10-20 decibel reduction may be achieved. Reductions of these magnitudes are generally enough to mitigate excessive noise so that there is compliance with the noise rules.

Selecting Heat Pumps

Manufacturers, installers and retailers have a community obligation to provide responsible advice and service to prevent noise nuisance. Ask the installer for advice on the most appropriate size of unit to install for the area to be heated. Select the pump that is most suitable to prevent excessive operation times or load on the unit. Choose a heat pump with a low sound power level. The exterior sound power level will be specified on the side of the unit and will give you an indication on how noisy the heat pump will be outside the dwelling. The higher the number the louder the heat pump unit noise will be. Note the sound power level is different from the sound pressure level.

Siting Heat Pumps

A reason for noise complaints from heat pumps is the inappropriate location of outside unit being, close to and facing neighbouring bedrooms and living areas. When installing a heat pump, considering the effects of noise on your neighbours and yourselves from the outside unit does help mitigate unreasonable noise levels.

Heat pumps should be located as far as possible from yours and your neighbour’s bedrooms, and where possible avoiding the fan facing directly towards the windows of a neighbouring dwelling, particularly habitable rooms and outdoor living areas.

Try to avoid mounting the pump on a wall and at a high level, as this can result in unimpeded transmission of noise to neighbouring properties. If possible, mount the heat pump at ground level and on a solid base, preferably a concrete pad or block. Use rubber pads between the unit and the base to eliminate vibration (Energy Efficiency Conservation Authority, 2009).

Ensure that where refrigeration lines pass through walls, they have adequate clearance and insulation. Vibration from within walls can magnify noise levels beyond acceptable levels. Make use of fences and walls between you and your neighbour’s home as these can help reduce the transmission of noise. If a nuisance eventuates, you may need to investigate other options such as acoustic barriers or acoustic treatment.

References

Energy Efficiency Conservation Authority (2009). Good Practise Guide: Heat Pump Installation.

For more information please contact the Council’s Compliance Team.