Is your house an 'energy black hole'? Here's how to fix it

Before energy expert Paul Testa has even set foot in my house, he’s labelled it an “energy black hole”. The sash windows (all 23 of them) are the killer, he says, eyeing the bay window by the front door; not only are the casements in poor condition but the single glazing is conducting as much as 30 per cent of our heat straight out of the house.

Then there’s the roof, which isn’t properly insulated, and the single-skin walls. The list goes on and on. But Paul, an architect (hemarchitects.co.uk) whose own family home is now so fuel-efficient that his energy bills are set to total just £1,488 in the current energy crisis, isn’t, thankfully, about to suggest I fix all these issues straight away. Retrofitting a Victorian family house like mine to optimum efficiency would cost in the region of £500,000.

The aim of his energy audit is to find realistic, affordable ways to bring down my heating bill, set to be a scary £5,500 this year, as well as my electricity and hot-water usage, which – worst-case scenario – could bring my total energy expenditure to over £8,000.

Most new UK houses, according to the Passivhaus Trust, have a heating demand of 90 to 120 kw/m2.a; his fully retrofitted 1970s house stands at around 25, whereas mine pushes 200. “It’s all about lessening the demand on the system,” he explains. “If you carried out a full retrofit, including new windows, a heat pump, solar panels, ventilation system and insulation you’d slash your bills to around £1,375, but if you reduce heat loss even marginally you’ll be better off. I always recommend doing any cheap repair or retrofit to ensure your house performs better.”

We begin the audit in the kitchen, with some good news – the new extension that we finally moved into last month will actually save us money. By replacing the back of the house with modern walls and glazing, we have cut out a large percentage of heat loss.

The new appliances are also less demanding on the system, as is the underfloor heating, while the boiling water tap, which seemed like such an extravagance at the time, is also making us a small saving: running a kettle costs around 12.5p per day, compared with just 3p for a Qooker boiling water tap. I can further reduce demand on the system, Paul says, by running my new appliances on eco mode and turning down the underfloor heating (although the room still needs to feel comfortable). “Microwaves are the most efficient way of cooking, so steaming vegetables in the microwave will help, and if you do use the hob, make one-pot meals,” he adds.

There’s more good news in the laundry room, where Paul, much to my surprise, is as excited about the new cast-iron overhead clothes dryer as I am. A simple clothes dryer can save hundreds of pounds on energy, he says, as tumble dryers currently cost £2 to £3 per load. With four children and their endless games kit, our tumble dryer works hard; by leaving it only for emergencies I could save as much as £1,000 per year. My relatively new washing machine, with an A grade energy rating, will further keep costs down – so long as I use it as infrequently as possible and always on eco settings.

Paul is keen to point out, however, that upgrading appliances that work perfectly well for more energy efficient alternatives is not the answer this winter. He doesn’t even recommend I buy a new boiler (or heat pump) as my eight-year-old combi boiler is still (just) within its efficient lifespan. Far more immediate savings will be made, he says, by investing in the fabric of the house: walls, windows, floors, roof. We’ve reached the playroom, where cold air is gushing in through leaks in the sash window and warm air is floating up the chimney.

Ideally, I’d replace every window in the house with a triple-glazed mock sash at a cost of around £100,000, saving £800 per year. Yet a far more cost-effective way of shaving £300 off energy bills is to restore my window brushes, seal up leaks with silicon and invest in a chimney sock, £10 on Amazon. “Air leakage accounts for about 10 per cent of heat loss in a house; making these changes will halve it,” Paul says. “Sticking insulating film to the windows will make an even bigger difference. Thin, old glass conducts heat straight out of the house. Even if your casements are a bit tired, it can be worth replacing the glass, although glass is expensive at the moment.”

The family bathroom has been recently renovated with a UPVC sash window in the shower, which I like a lot more when Paul tells me it is the most energy efficient (as well as affordable) type of window money can buy. The new aerated shower head will also help us to use less hot water. “Always wash hands in cold water and consider screwing a flow restrictor on to your taps, which give the same aerated spray as the shower head, making the water feel warmer – and take showers, not baths, wherever possible,” he explains.

I must also, immediately, reduce the operating temperature of my combi boiler, he continues, as it’s not running as efficiently as possible, increasing household gas bills and emitting more carbon. “Reducing the ‘flow temperature’ half a degree to below 50 degrees can instantly save £200 to £500, depending on what your flow rate is and how low you can drop it,” he says. Our old radiators will help matters, he says, as they’re large enough to give off sufficient heat at the lower flow temperature. “You’ll soon know if you’ve dropped too low and your radiators are too small because you’ll feel cold.” To find out how to lower flow temperature, Paul recommends reading this article on the Heating Hub; theheatinghub.co.uk/articles/turn-down-the-boiler-flow-temperature.

Giving radiators some TLC is another easy way of saving £100 per year. Our piecemeal network of old and new radiators will be more efficient if we bleed them to release trapped air and allow hot water to fill the whole radiator and then retrofit thermostatic valves, enabling us to regulate the amount of steam entering a radiator by sensing the surrounding air temperature. Where the radiators are on external walls I should fit reflective blankets behind them (around £30 for a pack of three), Paul adds.

As our loft is mostly converted into a bedroom, there’s little we can do to insulate it properly without taking down the ceiling. We can, however, save money by insulating the eaves either side of it using mineral wool rolls bought from any DIY store. “You can get rolls with perforations to make it easy to split it between joists and then add additional layers on top. Go for a minimum of 300mm, more if possible,” he advises. As we use the eaves for storage, he suggests installing decking to ensure we can insulate the floor, too. “Roof losses are probably 15 to 20 per cent of a typical poorly insulated house, so good levels of insulation will reduce this dramatically, saving you £500-£700 a year,” Paul says.

Another way to boost the insulation of our house, Paul explains as we make our way downstairs, is to insulate the floors, which account for about 15 per cent of the heat loss. Insulating even one floor of my house could save more than £500 per year, yet the outlay is high: £300/m2 including new floor finishes, either by pulling up floors, or spraying foam beneath the floorboards (q-bot.co).

Unfortunately I don’t have a cellar, but if I did I’d be able to insulate the ground floor myself using mineral wool as above. My only other option is to pull up any carpets and pay a company to insulate beneath the floorboards using spray foam delivered by small robots that drive under the floor.

As Paul leaves, I tentatively ask which of his retrofitted energy-saving measures has been the most effective in his house. “My triple-glazed windows,” he replies. “Not only do they save us money but they never have condensation on the inside, ever; my daughters sit on the windowsills to read, even in the depths of winter.” While he has no plans to upgrade his boiler for a heat pump until it genuinely needs replacing, he recommends air source for anyone upgrading this winter; they’re 380 per cent efficient, compared with 80 to 90 per cent for a new gas boiler, and even in the current crisis the payback is eight to 10 years.

His next investment, however, is solar panels; they’re being installed in March at a cost of £8,000 (including scaffolding), which he believes will pay back in five years. “They directly power the immersion heater and surplus electricity is stored in batteries for later use,” he says. “They’re one of the quickest ways to start making big savings.”

With the waiting list for solar panels now stretching into next summer, however, my best way to save money this winter is to embrace the DIY fixes he’s mentioned. “You also need to invest in a draught-excluding snake,” Paul says, noticing the gap beneath the front door as he leaves. I add one to my shopping list, along with a Dryrobe. A heavily insulated dressing gown is what we’ll all be needing this winter.

Paul Testa is a director of HEM architects and retrofitting expert for the Homebuilding & Renovating Show, next in Farnborough, January 14-15 2023: farnborough.homebuildingshow.co.uk