I live in a Victorian house, so it loses heat like crazy. There are some rooms which stay nice and cool in the summer, but they’re also cold in the winter.

And I have the data which tells me that we average 32kWh of gas a day, over the whole year. Over the summer it’s about 6-8kWh/day, and that’s about four months – June-September, our base load of hot water. April, May, and October are 2-3 times that. November-March are 45-75kWh/day. During those peak months, like last January, some days were over 100kWh.

Our electricity is a fairly reliable average of 6.5kWh/day, all year round. Ideally, the gas boiler won’t be replaced like for like, but I’ve no idea what could deliver upwards of 75kWh of heat cost effectively. Finding a way to do 7-8kWh/day (broadly: some other way of heating the water) would represent about a fifth of our heat load, so that’d be a start.

In the mean time, the problem I want to fix is: heating the wrong rooms at the wrong time.

Our toddler’s room has three outside walls, and a sash window, and cools quickly.  But it doesn’t make sense to try and pump heat into it all day, only to heat it up for her nap, and again overnight.

Our dining room is used for the two main meals, so probably only needs four hours of heating a day.

I have tried to manage these sorts of adjustments manually, but I get it mostly wrong.

We have a Tado app based heating control, which has improved things a lot from the original dumb thermostat in the unheated hallway, but it’s not granular enough. Tado do smart thermostatic radiator valves (TRVs) but they’re not cheap, and I’m not sure if they do what’s needed. And I’d be locked in.

I’m going to investigate Radbot and OpenTRV.

• https://www.radbot.com/
• https://vestemi.com/
• There’s a short talk about it from November 2020 by their CTO.
• https://github.com/opentrv/