I have two questions. We have a ground-source heat pump located in a small room on the ground floor of our two-storey house. It is very noisy, especially at night. The company that installed it has offered no real solution. The unit should have been installed on noise-absorbing pads but this was not done. Would you have any reasonable solution? The house is four years old.

Another issue is blooms of mould we have noticed this winter in some of the rooms upstairs. The house is warm but temperature is lower upstairs 16°-20°. The house has filled cavity walls and the attic floor is well insulated. Any suggestions about what could be causing this?

Heat pumps are a great way to heat a home, because they obtain about three to four times’ their energy output from the environment, helping to reduce climate change. Your ground-source unit should not produce a much greater volume of noise than a traditional wall-hung gas boiler or similar domestic appliance, and many hundreds of thousands of units are installed trouble-free.

Air-source heat pumps have a fan to obtain energy from the air, which can be much colder than the ground. These are less efficient and can be noisy, so are usually fitted outside.

Installing your type of heat pump in a small space such as a utility room is normal, because you also gain inside the house the energy the unit itself creates. If the room is too small, however, the low level of noise produced can reverberate and amplify through small gaps into adjacent rooms.

Certainly the unit should be fitted on acoustic mounts – good-quality units have pads pre-fitted inside the cabinet to avoid any potential problems. Check that the cover panels are all snugly fitted and that any internal noise baffles are intact. Any small gaps where pipes pass out should be sealed with an acoustic grommet or caulk.

Ensure that the unit’s settings are not asking for too steep a temperature curve, because high demand can drive the compressor harder than needed, creating excessive noise. If it also produces hot water, set back the demand temperature to about 45° or turn it off to observe the noise difference. Another difficulty may be low compressor gas or system pressure, so get the unit checked and serviced by the agent.

Generally these units should have a long trouble-free life but require annual maintenance. If the supplier/installer won’t assist you to resolve issues then you may have to resort to legal action as a last resort. Once you have advised the company you should assemble all documentation and take legal advice.

Lack of ventilation

Regarding your second query, the most common cause of mould is lack of ventilation. In warm conditions with high vapour levels, mould forms where cold spots – often caused by poor standards of construction – create an uninsulated “cold bridge”, allowing condensation to form, on which mould can thrive.

Warm air rises and carries with it moisture from cooking, bathing and even just breathing. Increasing ventilation will help disperse that warm, moist air but will take with it the energy you have put into it, so consider a heat-recovery ventilation system which will help maintain healthy air quality and reduce the amount of energy you might otherwise waste to the environment.

There may also be hidden causes to your problem and because the presence of mould indicates potentially unhealthy air quality you should take advice from your local building surveyor on how the problem might best be resolved.

Fergus Merriman is a chartered building surveyor and a member of the Society of Chartered Surveyors Ireland