Finding the chase and cutting to it

Last week, we looked at the cash return on replacement windows, which, on the face of it looked marginal at best. But of course, we have made other investments over the past twelve years.

Easy steps, let’s look at the LED lighting.

About a year, just in saved electricity. Initial cost was about £350 for the whole house, and the kitchen lights alone (£250) paid for themselves in three months.

What about the solar panels?

Our panels cost circa £6,000. With the SEG and FIT, and the money they have saved us in terms of not having to buy electricity, they paid off in about 5 years.

The tado heat controls.

Like the lights, a chunky cost, incurred back in 2014 and 2015, over six months, but around £750 for our eight smart radiator valves and five thermostats, and one hub. The radiator valves were the initial step and proved themselves, so expanded the system to the whole house.

These allowed us to go from using c. 17MWh in gas a year to c. 14MWh in gas a year, just when gas prices trebled. So, two-three years to pay off.

Can the same be said for the heat pump?

From Number crunching part 2 we can see the power used to heat our house has gone from 13,270.888 kWh to 3,966.20 kWh – we’re going to pretend we have bought this electricity, just to keep the numbers simple.

At today’s prices, gas is £0.0603, so the gas would have cost £800 and a standing charge of £0.35 per day, so annually that’s £928.

The electricity has already had its standing charge paid for because we need the fridge power, lights to come on when it is dark and to be able to cook our food – we only pay that charge once. We’re not using gas for anything but heat and hot water.

So, at £0.2527 per unit, our heating has cost £1,002.26 – if we’d paid for it all. But we didn’t, during the summer, a good 750 kWh was used straight off our solar cells or batteries. So let’s run that again, giving £812.73. Which is cheaper than the gas per annum by £115.27, so in hundred years, or so it pays off. Our boiler was dying anyway – a new boiler would have cost £7,000 (it’s a big house, it needs a big powerful heat pump or boiler, many houses do not need as much capacity) – so should we say the difference is what we’re paying off? In which case, 43 years!

I suspect we’ve spent more than we needed to, as we punched big holes in to our house to do the renovations back in the tail end of November 2025. I’ve also learnt a great deal about how to balance what we’re generating against what we’re using.

Of course, without the smart radiator valves and thermostats, it would have been a different story. Without the fabric of the house being well insulated, it would not have come in as quickly either.

I’m cheating a little, because we already had the solar cells – we were about 35% self-powered last year for everything, including our car. We don’t have to pay twice for the standing charge.

Buying our new windows should help accelerate that period.

But I think that is a good way to look at the total cost and pay back period. This wasn’t a big bang but a series of smaller steps.