Finding the chase and cutting to it

I wanted to follow up on Walking in the shadows, which looked at the using passive cooling methods for coping with the Heat Dome, which affected Africa and Europe in the last week of May 2026.

After all, we hear the same advice every year, but life gets in the way. We get home from work, exhausted, and think, “I’m buying a fan or air-con unit,” as we find ourselves stuck in the fiery furnace of our own living rooms. Indeed, that was the very advice I was giving this time last week.

I thought I would share exactly what we did, and when we did it, and whether it actually worked. So, here is a measured look at our strategy, tracked through the detailed data provided by our Tado smart radiator and room thermostats.

The strategy.

As I mentioned in the blog, we set up to test the thermal resilience of our building and window infrastructure by following the advice of keeping windows shut and curtains closed. We were not alone in this, talking our usual evening postprandial, many of our neighbours were doing the same thing, many south, east, and west facing windows were shuttered against the sun.

But did it work?

Basically, yes, but we did manage it.

First post on this subject was the 22^nd May, today is the 30^th May. Let’s track our bedroom over that period (why this room? Well I don’t know about you, but when hot weather happens, you need a place you can be cool where you sleep).

So, not looking too bad. The curtains are blocking the heat. You can see on the 23^rd, we cooled the room by opening our windows after sunset. Having had French windows fitted, we opened them and the en-suite velux window wide open, which created a through draft. I shut the door to the landing and left the room to it. You can see when we went closed them too, at 10pm ish.

You can see this impact on Sunday, that sharp drop, again just post sunset.

The Monday, with people back on the road, our weather forecast may have said 29°C, but the thermometer for the Viessman reported 31°C! Same pattern and by the time we went to bed, the room was a comfortable 22°C.

Now, we have not used a fan to help.

Tuesday 26^th May, and the first outside forecast of over 30°C.

You can see I was late in opening the windows, but if anything that helped as the air was cooler.

We forgot and opened the draws on the 27^th May, so despite a cooler forecast, we were in a similar position until the magic time when the windows were flung open and the cool air can come in.

Again on the 28^th.

Only this time, I didn’t open the windows like I did on Friday.

The pattern was repeated in all our south facing rooms. Many have not required windows being opened and if they have, we were reasonably disciplined about ensuring it was post sun-down.

Isn’t it easier just to plug in a fan and forget about it? Or buy air-con?

The short answer is yes. But shall we examine those options.

If you buy a fan, and plug it in, moving hot air around with a motor, which is generating heat, is not going to work long term. You need to ventilate. Should we have used a fan at the same time? Interesting question, but actually, we didn’t need to and our “summer fan” is still in the loft.

Air-con is really efficient, but again needs to be vented and maintained. When I ask people about when they last changed their filters and topped up the fluid, I generally get met by a blank stare.

I have to say, if we’d had “heat and air” in the house for our air pump, so we could get it to cool during hot weather…

But we don’t.

Actually, talking of the heat pump…

I did completely switch off the heating circuit, and the heat exchanger has pretty much coped without needs to run the fan at all. Our hot water has used:

Day	Electricity (kWh)	Heat generated (kWh)
23/05/2026	1.25	6.51
24/05/2026	1.55	7.05
25/05/2026	2.44	11.9
26/05/2026	1.25	6.58
27/05/2026	1.4	5.93
28/05/2026	2.3	11.6
29/05/2026	1.54	6.63
30/05/2026	1.85	9.85
Total	13.58	66.05

Which gives us a SPF of 66.05 / 13.58 = 4.89. Which is not as good as we get for doing the heating circuit, in the spring, when we need to heat, the SPF is typically above 6!

Still, it is better than we get for the solar diverter.

What about the days when it was above 1.6 kWh? These are days when we’ve done many loads of washing or had a bath and the water went from its usual 58°C to 33°C. It is allowed to use a bit more in those circumstances. I also did a hygiene programme on Thursday.

Solar generation-wise, we have done really well since the 23rd. We have had a day where we have been up over 99% self-powered. Even charging the car by 60%. Because we used passive cooling, our power consumption a day was typically 10kWh for a house that is 244m², that’s 4.1kWh per 100m² which is passive house territory.

Global warming not an issue for you then?

This is not good for the UK and our flora and fauna. Being human, we can use tools to adapt, but this is not yet past the point where people can’t make a real difference.

This is happening everywhere, to people who don’t have the luxury of well insulated houses and free electricity to power fans and air-con. Even if we had heat and air, it’s a shock to walk out of rooms chilled to 18°C when it’s 35°C outside. Who wants that?