You don't need to be an 'investor' to invest in Singletrack: 6 days left: 95% of target - Find out more
We have a closed (?) central heating system with a large hot water tank by the boiler. My understanding is that hot water is heated by the boiler and stored in tank. Two adults and one soap-dodging eleven year old in house, usual appliances running cold water washes etc.
Question is, is it cheaper to heat water continuously and assume boiler is just topping up heat or only have boiler running once or twice per day for a couple of hours to service two morning showers?
How well insulated is the tank?
Does appear to have any external insulation but was new four years ago so think it’s lined with insulation
*Doesn’t
I would assume heat on demand so you don't have piping hot water say there for hours cooling off and being topped up.
Our HW comes on 1st thing before we have morning showers, which we then consume. It then reheats a bit so we have water for washing up etc, but we don't really care how warm that is.
If we want hot water at a random time, we just hit Boost, only takes 20 mins to heat up.
Can't answer your question, but we have ours on for an hour on a morning and an hour for tea time.
Electric shower, washing machine off the cold, so hot water is only really for washing up (2-3 times a day as at home) and hand washing.
It's marginal cost wise to leave it on 24hr or timed, you'll use the same amount of hot water either way and if it's 4 years old it'll be well insulated so won't lose much at all. Just set it to whatever fits your lifestyle most appropriately.
It will be well-insulated then. In which case it can hold water at a good temperature probably for up to 24 hours. If you run it first thing for your showers, it will bring the water back up to temperature at that point for all your other needs that day.
https://www.cse.org.uk/advice/advice-and-support/energy-mythbuster
Thanks guys! Think I’ll try on/ off for a while and se if we notice any difference!
A boiler heating up a cold tank will run more efficiently than heating up a warm tank. Also, the required temps to heat the water are higher than are optimal for your radiators.
If your boiler allows you to set different boiler temperature for hot water and for heating, then set the hw to come on when the ch is off and it will work better and you'll save money.
In which case it can hold water at a good temperature probably for up to 24 hours.
Just FYI we have a 200L megaflo tank in our other place that's heated only by the PV panels. It currently loses 10c (64c down to 54c) in 21hrs.
The cylinder cupboard is currently 13c (house is unheated ATM) so in a heated property the temperature drop would be slightly less.
If I had to pay for it, it would cost 89p to reheat back to 64c (2.45kWh)
At home we just heat the hot water in the evening for about 1.5hrs. That covers baths/showers and morning showers.
If your boiler allows you to set different boiler temperature for hot water and for heating, then set the hw to come on when the ch is off and it will work better and you’ll save money.
Is that a thing that exists? I'd really like that but our boiler temp is set by a physical control on the front. It seems like such a simple and easy win for efficiency if I could set the boiler to 65-70 for HW but 40-50 for rads.
But then wouldn't you have to run the boiler a separate times for heating and hot water - thus using more gas?
Why would that use more gas? If the hot water in my tank is already up to temperature (which is would be most of the time if I run HW whenever my CH is on) then it makes no difference to anything. But if I can turn my boiler down to 40-50 when I am only running CH, I can run at a lower load (more efficient) and lower return temp (extra more efficient for condensing boilers).
Other question: if I do have HW and CH on and my cylinder is up to temperature, am I guaranteeing that the return to the boiler will always be hot because of water running through the tank and not losing heat before returning to the boiler? Or will the HW circuit shut if the tank's thermostat tells it to? Do I need to make sure the tank's thermostat is lower than the boiler temp to ensure this happens?
Sorry for the hijack. Maybe I need a chat with a plumber.
Or will the HW circuit shut if the tank’s thermostat tells it to?
If you have a motorised valve on the HW circuit I would have thought that the tank thermostat will tell it to shut once the tank is up to temp.
Ok that's encouraging, I might test that. Still, it feels like some logic like "if the HW valve is shut then only run the boiler at 50 degrees" would be dead useful
if I do have HW and CH on and my cylinder is up to temperature, am I guaranteeing that the return to the boiler will always be hot because of water running through the tank and not losing heat before returning to the boiler? Or will the HW circuit shut if the tank’s thermostat tells it to?
The thermostat on the tank should shut off the HW when it's up to temp.
Do I need to make sure the tank’s thermostat is lower than the boiler temp to ensure this happens?
Yes. There's a heat geek article on how hot your HW really needs to be. The recommended 65C kills Legionella instantly, but a few hours at much lower temps is also enough.
Still, it feels like some logic like “if the HW valve is shut then only run the boiler at 50 degrees” would be dead useful
Yeah I think that is called 'priority hot water' setting, see if your boiler has it. Mine doesn't, but I think I can mod it pretty easily...