Posted 31 August 2022
Hot Water - Gas usage = 0.7kWh or 10p per hour just to keep hot water hot when potentially not need, could you save this as well?
This might we be useful to others, hence posting. This will vary given different boiler/hot water setups, but I had my hot water set to come on twice a day:04:30-8:00 - I shower in the mornings
15:00-20:00 - My wife showers and Son has a bath in the evening
I have not changed these timings since I stopped working in London, when I used to shower at 5am, now typically 7am.
Looking at my smart meter/EDF energy hub, I noticed that typically each morning (4:30am) the boiler kicks in and heats the hot water, using 2.1kWh or at current rates 31p
Then each hour to keep this water hot, uses 0.7kWh or 10p each hour
After showering we use another 2.1kWh to heat the water again 31p
During the day we use very little hot water, pretty much only wash hands, etc. as our appliances (dishwasher) use cold water and heat it by electric.
At 15:00 when I forgot to turn off the hot water whilst away we used another 1.44kWh, which implies the water had lost most of the temperature between 08:00-15:00 and needs re-heating. Therefore my re-heat costs = 2 hour keep warm cost, for those keeping the hot water hot all day.
Where i am going with this is it costs me, with my setup, 10p per hour to keep water hot, when I have no requirements for that hot water.
Hence I have significantly reduced the hot water "ON" timeframes. in theory changing the hot water ON time from 04:30am to 06:30am should save 1.4kWh of gas or 20p per day, see first graph/picture.
The second picture shows when I forgot to turn off the hot water whilst we were away. So no hot water was used this day yet between 20:00 and 04:30 the hot water tank lost temperature and required 2.1kWh (31p) to heat is back up, then 0.7kWh (10p) per hour to keep it hot. Then 08:00-15:00 lost temperature and required 1.44kWh (21p) to heat it back up, and 0.7kWh per hour after that. Total usage cost that day = 85p, when I used no hot water.
I appreciate I'm talking pence, but with prices only going up, reducing non-required usage might help others and add up to pounds per week.
Community Updates
34 Comments
sorted byI can’t understand why you would need to have it on 9 hours a day in the first place just for 2 showers and a bath. (edited)
1) Your single biggest saving will come from using an efficient gas boiler or heat pump. Viessmann 200-W are the most efficient combi/ system boilers money can buy - they can modulate down to 2kW and provide 98% efficiency at full modulation. Vaillant AroTherm are the best heat pumps available but they're not cheap.
2) Your next biggest saving will come from setting your hot water temperature to 52 degrees (with a weekly legionella cycle at 60 degrees).
3) Switch off the "pre-heat" hot water feature combi boilers to save 10%. For cylinders, schedule your hot water showers/ baths during the morning or evenings (but not both) and have the boiler run only for a couple hours during this time to recharge your cylinder
4) Insulate the cylinder and the piping going into and coming out of your hot water cylinder if you have one. This can save 15% on HW bills.
For heating this winter:
5) Set your boiler flow temperature to 50 degrees
6) Invest in radiator reflectors and loft insulation. Block off any air leaks with tape if you cannot invest in triple glazing.
7) If you have single fin (thin radiators), now is the time to replace them with the largest possible T22 double panel double fin radiators. The heating output is greatly increased while allowing for the reduced flow temperature to save £ (edited)
ive got a boiler and hot water cylinder and just trying to get the best combination of temp on both to ensure we get good hot water but efficiently. hot water is heated between 4am and 6am and now because of school, 2pm to 3pm.
I did previously lower the temp of the boiler but found the water heated in the boiler wasnt getting as hot as people liked and so had to up the temp
I also have a conventional heating system with a hot water cylinder and have done similar with the heating time periods. A boiler is at it's most "wasteful" when it has to heat up from cold (ambient). Therefore, in the summer months I have my system set to heat hot water for just two 45 minute periods each day - first thing in the morning and late in the afternoon. I have also upgraded the insulation of the cylinder which has reduced the heat loss from the cylinder to around 0.5 degrees C per hour. This provides two of us with more than sufficient water hot during the day for our needs - typically two+ showers per day.
In the winter I now ensure that the hot water and central heating periods either immediately follow or overlap with each other - to again minimise the number of 'cold starts' of the boiler.
A few years ago when I was working we used to consume 30,000 kW per year in gas - 4 of us living in 4 bed detached house. By installing more insulation and investigating/understanding the system, now just 2 of us have reduced the usage to 8-9000kW in each of the past few years.
Awaiting delivery of a MyEnergi Eddi to use excess solar to power the immersion. I can also just run for an hour at 3.30am off the grid on the 7.5p off peak tariff. This should take most, if not all the load off the gas water timer, if it does then i will just turn off the timer for water on the boiler.
Had a problem with ours not staying hot recently, discovered the boiler wasn't turning the circulating pump off taking the heat away from the cylinder when the boiler was cold, which was caused by welded relay contacts on the control board. Apparently the early versions of the high efficiency Grunfos Alpha 2 pump I fitted a few years ago has a high inrush current, which can cause this.
If you've got an old fashioned induction motor based central heating pump, you can probably save quite a bit of electricity upgrading it. My old pump was 100 watts continuously when the boiler was on, the new a maximum of 60 watt due to the electronic motor, but also saves more power by its smart electronics adjusting the output power as tvrs open and close, so can use as little as 5 watts.
Also discovered (when I broke it) that the 20 year old plastic components in the Drayton cylinder thermostat had been sticking, making the water temperature go too high and wasting gas. (edited)
I have a pressurized 210ltr tank which pretty much stays warm the entire day. I am thinking about doing away with the evening 30min top up altogether and seeing how we get on.
We do have two Mira digital showers which can control the flow rate. We have them on the lowest flow setting (its pressurized so very good pressure on mains) and 36c temp so I don't imagine we use too much hot out of that 210ltr tank.