Analysis: as energy bills steeply rise, knowing how to retain heat in your home is becoming more critical than ever

As the weather begins to turn and energy bills steeply rise, knowing how to retain heat in your home is becoming more critical than ever. Let's look at what you can do cheaply and immediately, starting with your heating system. Make sure your boiler is working it’s hardest by getting it serviced annually to save 5% on your heating costs, and bleed your radiators if you feel cold spots. Move furniture away from heat sources and get thermal curtains which end short of your radiators.

Most radiator types dissipate heat in all directions, but installing radiator reflectors behind them will redirect much of heat back into the room. A thermal imaging camera can easily identify the lost heat from radiators in poorly insulated homes as shown under the upstairs windows in the left image below before insulation was installed.

Next, draught-proofing is one of the cheapest and most effective ways to save heat in a leaky home. Before you begin, make sure that your vents are clear to prevent condensation and mould. Exact figures on savings are case-specific, but blocking unused chimneys usually offers the greatest potential, followed by sealing around windows and doors which has less than a year payback period.

Other areas to check include the letterbox, skirting board, exposed floorboards, attic hatch and around pipes or other openings. Most of these can be fixed with some Googling followed by a trip to the hardware ofr DIY store. If you feel uncomfortable tackling this all yourself, you can employ a contractor relatively cheaply.

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From RTÉ Radio 1's Drivetime, a retrofitting Q&A with Ciarán Byrne from the SEAI

Deep retrofit can cost €75,000, making it unviable for middle Ireland. So, what should you invest in to effectively retain heat in your home without breaking the bank? Up to 30% of heat loss is through walls and a further 30% is through the roof. Floors, windows, doors and air infiltration makes up the remainder. Therefore, if you want the biggest impact on both your bills and your comfort, you should insulate your walls and attic and the Sustainable Energy Authority of Ireland (SEAI) offers grants for this work.

Cavity wall and ceiling insulation are the cheapest and least disruptive solutions, with the shortest payback period quoted as two to 12 years, depending on the source used. But be careful here: cavity-block (or hollow-block) walls are not the same as cavity walls. Filling small cavities in cavity-block walls is not recommended. The return is minimal at best since small pockets of still air have insulating properties similar to insulation and the thermal path through the concrete remains uninterrupted.

If you don't have cavity walls, your options are to insulate internally (also known as dry lining) or externally. Investment will be 10 to 14 times greater than cavity fill, but the grants are also higher. The most appropriate of the two largely depends on the details of your home and your own preferences. The SEAI provides a guide which includes questions to ask your installer.

Thermally speaking, external insulation is usually the best option if you can afford it. This approach minimises the risk of thermal bridges, those locations where heat can escape more easily. But this is not the only advantage. Retrofitters using SEAI grants are required to achieve a certain U-value regardless of the insulation method (U-value is a measure of steady-state heat flow through a thickness).

However, two walls with the same U-value can behave very differently in-use and walls rarely experience steady conditions. Weather changes, and the internal spaces heat up and cool down throughout the day, the week and the year. Because of this, the heat storage behaviour of the wall becomes important. In an uninsulated home, heat slowly passes through the walls to the outside. After the heating is turned off, the heat will continue to pass through the walls until both sides are similar temperatures.

If insulation is attached to the outside face of the wall, you will still initially lose a portion of heat to the walls when you turn the heating on. But now the heat is largely blocked from passing through and your walls have become a massive thermal storage unit.

When you turn off your heating, the air cools down until its temperature is lower than the walls. Once this happens, the heat stored in the walls will be partly returned to the room space. This has the effect of slowing the temperature changes in your home, which results in longer gaps between heating usage. Concrete, stone and brick have high thermal storage capacities, or thermal mass, compared to insulation.

For internal insulation, your heating system heats the air and does not get sucked into the walls, since the thermal mass is now hidden. This means that the air heats up very quickly. The air will maintain this temperature well after the heating is turned off so long as your home is otherwise highly efficient. However, if you live in an older house without other upgrades, your heat will quickly dissipate through the ventilation, windows, floors and roof, making the home drop down to less comfortable temperatures sooner.

Regardless of the insulation type you choose, research shows that you will feel an improvement in comfort and heat loss will reduce. In a study of nine lower to upper-middle income Irish homes, cavity insulation reduced heat loss through walls by up to 66%, and external insulation by up to 77% and everyone reported excellent comfort levels.

So when looking to retain your winter heat, start with the easy-wins. Then, if you can, invest in an insulation solution you can afford. How much of this translates to energy savings, depends on how much you value comfort versus cost.

The views expressed here are those of the author and do not represent or reflect the views of RTÉ

Dr Aimee Byrne is a Lecturer in Civil and Structural Engineering at TU Dublin whose research focuses on retrofit, building physics and sustainability

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