Property Clinic: Should I invest in an aerothermal heating system?

Recently I had my gas meter inspected, and the engineer suggested my boiler was old and should be replaced. I have arranged a service, and as I scouted around for a new boiler, family and friends told me that I should be looking at an aerothermal heating system instead.

I am interested in this, but what are your views in relation to the payback value and economics of this outlay? I recently had an assessment for installation of PV solar panels for daytime electricity and hot water, and the payback period was 30 years!

So I want to be more environmentally conscious but not foolish with my funds as I near retirement. My house is a smallish former corporation terraced house in Dublin. I could give over space in a tiny bedroom to the internal equipment, and I have an outside patio and garden for the external equipment.

I plan to retire in five or 10 years and will be home more then, so a heating system that can be on for more hours of the day is very attractive.

What will €450,000 buy in India, France, Greece, the Netherlands and Westmeath?

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Fergus Merriman writes: This a great question that we should all have been asking ourselves for many years instead of being profligate with finite sources of energy we once thought were cheap and never ending.

Corporation houses were structurally very well built to last but like all landlords they thought the occupational comfort costs of heating and running such homes were the domain of the tenants. Therefore little consideration was made towards thermal efficiency during the design and insulation, if then available, was an expensive luxury the occupants didn’t need.

Therefore a ‘fabric first’ approach to reducing your energy needs should be your first consideration if you are to get a decent return on investing in new heating. This means insulating as much as possible the walls and attic, then improving windows and doors. There are grants available via the Sustainable Energy Authority of Ireland (SEAI) to help you with this. However, there will be some areas that cannot be addressed such as solid ground floors where the cost of change might be prohibitive in the short term.

Aerothermal heating systems are generally referred to as air source heat pumps (ASHP) where up to five units of energy can be taken from the air by a pump that uses only one unit of energy. Known as the co-efficient of performance this can be 500 per cent, as opposed to the best fossil fuel systems which might only reach 80 per cent efficiency. So already you can see a simple benefit and there are again grants available through SEAI who are keen to roll out such systems to save the country’s impending carbon penalties.

Complication arises trying to usefully distribute this energy for space heating and hot water needs because ASHP systems operate slowly with low grade energy that needs a large surface area over time to warm your home to a comfortable level and are generally best suited to underfloor heating. So perhaps it might make sense to replace your solid cold floor to give added benefit?

A second complication arises because in well-insulated and almost air tight homes some form of ventilation system becomes essential for health reasons. But of course air exchange also removes your costly energy as it’s replaced with outside fresh cold air.

In some of the retrofit and new homes I have designed I have specified double duct exhaust air heat pumps (DDEAHP’s) which combine the benefits of ASHP technology to save energy otherwise wasted in stale air by transferring heat into warm fresh air that permeates the home via small ducts. This maintains the home at the desired set temperature without the ‘boom/ bust’ cycle of traditional heating systems or the losses that simple ASHP systems suffer. These can be so efficient as to provide adequate volumes of hot water in a single unit without complicated controls.

Coupling DDEAHP systems with a battery backup PV system on a near south facing roof might collect sufficient energy to reduce heating costs to almost zero in certain instances. Again grants are available for PV systems through SEAI, but a lot will depend on the combination of reducing energy demand through fabric improvements and the efficiency of the system you eventually choose. A comprehensive investment strategy might result in a warm and bill free retirement for you but it’s something we should all think about and act on.

Your local building surveyor can assess the appropriate strategy for your home and might be your first port of call.

Fergus Merriman is a chartered building surveyor and member of the Society of Chartered Surveyors Ireland, scsi.ie