This chart shows our gas consumption by month and year since we moved here in August 2015 (the first full month shown is September 2015), Along the way several changes are marked which might be thought to influence gas consumption, although with natural variation month-to-month and year-by-year the effect of those changes isn’t dramatically obvious.
What is of course obvious is the dramatic difference in gas consumption between summer and winter as gas is our main means of space heating, and there’s no need for space heating in summer. Most homes would exhibit such a pattern. Ours is probably a bit more marked than many because of our water heating. Many homes with gas will use the gas for both space and water heating, but for us the gas water heating is the back-up not the primary water heating system. Our home is set up to divert surplus solar electricity from the PV panels to water heating during the day. Only in the evening is gas water heating enabled and then it does no heating if the water is up to temperature. The gas water heating thermostat is also set a few degrees colder than the immersion heater, so gas is separated from electric water heating by both time and temperature to prioritise electricity.
Previously I had just disabled the boiler in summer, but occasional dull days would leave my wife complaining about lack of hot water. The new arrangement with the boiler operating later and with a lower temperature set-point has avoided that and is robust as long as your hot water cylinder is big enough for your daily needs so you only need to fill it once with hot water which is then stored available for use until the next day.
Over time 3 changes are called out which should reduce gas consumption further:
- In December 2015 we replaced the boiler, hot water cylinder and controls. The previous boiler had demonstrated that it was incapable of heating the whole home as we went into our first winter so a replacement was rapidly arranged. The new boiler is considerably more efficient which should reduce gas consumption for a given heat output, but it now heats the whole house, so that might counteract the improved efficiency.
- In late 2016 we upgraded the loft insulation from 100 to 270 mm which should be worth £73 in gas per year according to our EPC. February, March and April 2017 do seem to show some benefit compared to 2016, but then there also variation in the weather year-to-year.
- In May 2017 we started adding smart heating controls which has gradually expanded over the following months. The overall concept here is that most rooms now have smart radiator valves which are both thermostatic and contain their own schedule. The schedules allow rooms to be heated for fewer hours: for example lounge not heated on weekday mornings, playroom not heated after children’s bedtime etc.
Just starting on this journey. Added some EveThermo’s a few weeks ago and just working on your boiler really trick now. Disappointing to see the lack of impact on your charts but I guess there is so much year on year variation it may only show with time.
Do you think the PV energy into heating your water is better than considering direct solar water heating?
We had solar thermal panels (as well as PV) on our prior house – indeed the solar thermal were fitted first by some years. They provided effective hot water generation in the summer. I wouldn’t however describe them as ‘direct’ since the hot water in the panels formed a closed circuit through heat exchange coils in the hot water cylinder, much like the hot water generated by a gas boiler circulates through heat exchange coils in the hot water cylinder.
My rationale to NOT go down the same route here was a combination of the investment cost for solar thermal in the thousands versus a few hundred for the ImmerSUN (which for me was included with my PV system), and the fact that I was regularly chased to get the solar thermal system serviced. Each service visit negated any cost saving from gas reduction in that year. I reckon that the water heating from PV saves me only £30-£40 annually based on electricity diverted because Gas is relatively cheap.
My EPC suggests solar water heating typically saves £47 per year for a house of this size at a cost of £4-6,000. We only have 3 people at home, so I can easily accept that £47 (rather than £30-40) could be typical for a house like this with more occupants and/or who bathed more (we mostly shower).