Property

My gas boiler is old and expensive to run. Should I upgrade or change to solar?

Property Clinic: Expert advice from chartered building surveyor Fergus Merriman

Regardless of its quality, any older gas boiler is likely to be much less efficient than a new model

Tue Jan 12 2021 - 06:00

I have a gas boiler heating our home and providing hot water since the house was built, in 1988. I have not had any problems with it until recently, when an engineer diagnosed a couple of problems that render it liable to give up any day.

Because of its age, I am informed that spare parts are available and a new boiler is recommended as soon as possible for peace of mind. Gas bills for the four months in the depths of winter would be €220 every two months at peak, and between €150 and €180 during the rest of the year. When on holidays it might drop to about €120.

During my discussion with the engineer, I asked about solar panels. His view was that thermodynamic solar panels are very efficient and that one panel would ultimately provide all the hot water required for a year in a house with four adults.

This made me think, subsequently, that if a thermodynamic solar panel is heating water, then a gas boiler would not be required to do so, and hence the output of a new gas boiler in circumstances where a solar panel exists would be significantly less than if the boiler was providing heat for radiators and water.

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My question, then, is: what output would be required for a heat-only boiler for a four-bedroom, 1,700sq ft house with 10 radiators, taking it that between four and six radiators would be the maximum number in use at any time, and where a thermodynamic solar panel is providing hot water?

Is this a time to consider the abandonment of a gas boiler system altogether and switch to thermodynamic solar panels for both water and heat? I presume that the cost of installation is the key factor here.

Any advice would be appreciated.

It’s probable that even a good quality gas boiler that is 32 years old is near the end of its useful life and will be much less efficient than a new boiler. There are also safety issues to consider, so before it breaks down completely it may be prudent to replace it, ensuring of course that your plumber is a competent gas-registered installer.

The investment case for thermodynamic solar collectors in Ireland is marginal at best, with some pundits indicating that the return on investment may in fact never be achieved if your hot water demands are not able to maximise the “free” energy. This is because you are emptying the tank after sunset – which is mostly the case for working families – and you will need the reheat to be recovered by traditional means during the night to be ready for the morning.

The case for solar thermal for space heating is even less tangible. The basic physics tells us that the energy gained from the sun is limited to the orientation and extent of your collector array, and that this must be calculated over a year to ascertain what energy might be available. Of course, less energy is available during the winter, which is when you will have maximum demand for heating.

The overall energy efficiency of your home will be a major factor when assessing the feasibility for a combined heating and hot water array so it’s not surprising that although it might sound attractive to avail of free energy, there are virtually no satisfactory domestic installations in Ireland. Even large solar thermal arrays such as that at the ecovillage in Cloughjordan could not supply demand in the depths of winter when short cloudy days can’t supply enough solar energy.

If you are keen to escape the penalties of fossil fuels, there are a number of investment options you might consider. Starting with a fabric-first approach, you should examine where energy is being lost and upgrade insulation, windows, doors, and airtightness. When these are at optimal levels, you will have a better idea of the type of heating and hot water system which best fits your situation. However, I doubt that solar thermal will be your best solution.

For a similar investment, a photovoltaic (PV) array may be better value. Coupled with a battery backup, a small hot water-only heat pump could supply you with low-cost, maintenance-free hot water. Any spare energy produced will be used on the house side of the meter, reducing your electricity bills. In the event we get a renewable energy domestic feed-in tariff, which would pay for excess energy feeding back to the grid, then PV panels will be the most sensible solution.

Refer to your BER rating and the assessor’s report for initial guidance, then refer to the Sustainable Energy Authority of Ireland (SEAI) to research what grant assistance might be available to you. Your local building surveyor can advise on what building upgrades might be appropriate too.

[ scsi.ie ]

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