Is it now cheaper to heat a tank with electricity?

[Neutrino]

My tariff is Flexible Octopus. With the price cap I pay:
• Gas 7.34 p/kWh
• Electricity 29.232 p/kWh
Electricity costs about 4 times more than gas. Considering that a condensing boiler has an efficiency of about 90% it costs about 3.6 times more to heat with electricity than with gas.
Switching from gas to electricity reduces CO2 emissions from your boiler but increases demand on the grid. Until there is enough renewable energy, this additional demand is met by fossil fuel generation. The best combined cycle gas turbine (CCGT) generators have an efficiency of around 50%. Until such time as there is a surplus of renewable electricity, switching from gas heating to electric resistance heating will almost double CO2 emissions.
https://www.gridwatch.templar.co.uk/
I estimate that it takes 8.72kWh to heat my tank of 150 litres from 10°C to 60°C (ΔT 50K). The cost is:
• Electricity £2.55
• Gas about £0.71
In summer add about £0.07 to the gas cost for heating the 4 litres of water in the boiler and 10 litres of water in the 32m of 22mm pipe between the boiler and hot water tank. This is hot in any case if the heating is on.
It will take about almost 3 hours to heat the water with a 3kW immersion heater and about 30 minutes with an 18 kW boiler.
The calculation is here:
Specific heat of water : 4184 J/kgK
Hot water cylinder capacity: 150 kg
Temperature increase from 10 to 60°C: 50 K
Heat required: 31,380,000 J
Conversion: 3,600,000 J/kWh
Heat required: 8.72 kWh
Electricity price: 0.29232 £/kWh
Cost to heat water using electricity: £2.55

Gas price: 0.073 £/kWh
Assumed boiler efficiency: 90%
Cost to heat water using gas: £0.71

[richlist]

But you won't be heating your domestic hot water tank from cold every day, surely you draw hot water, its replenished by cold water and the immersion heater heats it to the 60 deg thermostat setting.

My domestic hot water is heated by solar panels. The tank is set at 60 deg. The solar panels continuously keep the water hot throughout the day. Yesterday it took 1.85kWh of energy to maintain my domestic hot water temp at 60 deg. Presumably if it wasn't heated by solar and I'd need the immersion heater instead......it would have used 1.85kwh.

[DrFfybes]

We have 7p per unit electricity 00.30 to 04.30am. Rest of the day it's around 40p. Gas is now 11.5p which is around 3x what it was a few weeks ago until the contract ended. I expect another increase in gas price in October and again in January. The electric price is fixed for a year. Will have to think about whether electric or gas is the best way to heat a tank of hot water in summer when the heating isn't running.

On the other hand, in winter when the gas heating is already running, it's probably more effective then to use the gas heating for water heating too.

If you can heay the water on 7p electric, then that is the way to go.

Using the gas when the heating is on sounds fine, but in our system what it does is simply divert the hot water from the boiler to the cyl from the rads, so the house cools down.

Paul

[BullDog]

We have 7p per unit electricity 00.30 to 04.30am. Rest of the day it's around 40p. Gas is now 11.5p which is around 3x what it was a few weeks ago until the contract ended. I expect another increase in gas price in October and again in January. The electric price is fixed for a year. Will have to think about whether electric or gas is the best way to heat a tank of hot water in summer when the heating isn't running.

On the other hand, in winter when the gas heating is already running, it's probably more effective then to use the gas heating for water heating too.

If you can heay the water on 7p electric, then that is the way to go.

Using the gas when the heating is on sounds fine, but in our system what it does is simply divert the hot water from the boiler to the cyl from the rads, so the house cools down.

Paul

Thanks. It's a typical Y plan heating system with a three way diverter valve. Nothing exotic. Makes zero difference here if I heat the house only or heat the house and the water cylinder. All things being equal, it sounds to me like your boiler is of marginal heat output if heating water cools the house.

[DrFfybes]

Using the gas when the heating is on sounds fine, but in our system what it does is simply divert the hot water from the boiler to the cyl from the rads, so the house cools down.

Paul

Thanks. It's a typical Y plan heating system with a three way diverter valve. Nothing exotic. Makes zero difference here if I heat the house only or heat the house and the water cylinder. All things being equal, it sounds to me like your boiler is of marginal heat output if heating water cools the house.

Similar system - 28mm to the 3 way valve from the boiler, but our valve is next to the tank and connected by 45cm or so of 22mm pipes, the lounge rad is along 10m of 22mm under the landing and then a 3m drop of 8mm microbore, so the water takes the easiest route We actually down spec'd the ne boiler slightly to 28kW from 30, partly due to availability but the old 30kW one was cycling all the time as the limiting factor was getting the hot water to the rads, not getting it hot in the first place. Perhaps we need a secondary pump?

Consequently our HW comes on for 20-30 min before the heating does so at least the rest of the system is hot when the heating kicks in.

[BullDog]

Using the gas when the heating is on sounds fine, but in our system what it does is simply divert the hot water from the boiler to the cyl from the rads, so the house cools down.

Paul

Thanks. It's a typical Y plan heating system with a three way diverter valve. Nothing exotic. Makes zero difference here if I heat the house only or heat the house and the water cylinder. All things being equal, it sounds to me like your boiler is of marginal heat output if heating water cools the house.

Similar system - 28mm to the 3 way valve from the boiler, but our valve is next to the tank and connected by 45cm or so of 22mm pipes, the lounge rad is along 10m of 22mm under the landing and then a 3m drop of 8mm microbore, so the water takes the easiest route We actually down spec'd the ne boiler slightly to 28kW from 30, partly due to availability but the old 30kW one was cycling all the time as the limiting factor was getting the hot water to the rads, not getting it hot in the first place. Perhaps we need a secondary pump?

Consequently our HW comes on for 20-30 min before the heating does so at least the rest of the system is hot when the heating kicks in.

Or if there's a convenient gate valve on the water to the cylinder heating coil, use it to increase the resistance across the cylinder to balance better between the heating and water cylinder circuits. Close it half a turn at a time until the circuits balance.

[DrFfybes]

Having lagged our tank a month or so ago, I've been measuring flow temps, heating times, costs etc.

I have found that having the hot water from the boiler for 20 min from 7am is not quite enough to keep us going.

However I have found it uses about 5kWh/day of gas,[...]

Running the 3kW immersion heater for 30 min whilst I do brekky (so 1.5 kWh, worked out as about 3 times as long as we spend in the shower which would typically be 9kW 'heat on demand') has a similar effect, OK for a couple of showers but that's about it.

Paul

Richlist in viewtopic.php?p=526308#p526308 says 2kWh/day for his hot water.

Having upped our boiler timings we're using 8kWh/day of gas.

So approx 4 x the amount required, jut depends on the cost of your units. It also suggests the claimed efficiency of the new boiler might be optimistic

Paul

[richlist]

Having lagged our tank a month or so ago, I've been measuring flow temps, heating times, costs etc.

I have found that having the hot water from the boiler for 20 min from 7am is not quite enough to keep us going.

However I have found it uses about 5kWh/day of gas, which currently costs 7p/kWh, up from our previous 2.8p (both plus VAT), so about 35p.

Running the 3kW immersion heater for 30 min whilst I do brekky (so 1.5 kWh, worked out as about 3 times as long as we spend in the shower which would typically be 9kW 'heat on demand') has a similar effect, OK for a couple of showers but that's about it. Electricity is now 26.5p up from 16.7p/kWh, so costs us 40p.

So, given a 250% increase in gas compared to a mere 150% increase on our electric, it is now pretty marginal which is cheaper for us, gas probably still has a slight edge.

However using the gas is a lot simpler, as that has a timer and I don't have to remember to set the cooker timer to remind me to go upstairs to turn the immersion heater off.

Paul

Dare I suggest you try to change habits. Do you need to shower every day, do you do particularly dirty jobs ? Like others we have gym membership and use the facilities there and others have shower facilities at their work places. Perhaps in the current energy crisis, gym membership will be seen as the golden ticket that can pay for itself. In the coming months thinking out of the box is going to be required quite often.

[Mike4]

Richlist in viewtopic.php?p=526308#p526308 says 2kWh/day for his hot water.

Just to mention, the above is not that all that helpful. Richlist might use no hot water at all and this 2kWh per day might be the heat lost from his or her less-than-perfectly-insulated hot water cylinder. A perfectly viable possibility.

On the other hand, and if Richlist happens to have one of those elusive perfectly insulated cylinders, the 'rule of thumb' that 1 kWh of electricity will heat approx 30 litres of water through 30 degrees C tells us they actually consume 60 litres of hot water per day at 50c.

(Assuming incoming water at 20c, as it probably would be in summer. In winter it's a different story with incoming mains at say 5c.)

The reality will be somewhere in the middle but for a family of say five, each having a 5 minute, 10-litre-per-minute shower a day will be consuming 5.5kWh in electricity, assuming a hot:cold ratio water mix of 2:1, just for the showers and never mind washing machine, washing up, and all other sundry hot water use. The energy needed to heat the hot water actually used in a family household usually dwarfs the standing heat losses from a modern well insulated hot water cylinder.

[DrFfybes]

Dare I suggest you try to change habits. Do you need to shower every day, do you do particularly dirty jobs ? Like others we have gym membership and use the facilities there and others have shower facilities at their work places. Perhaps in the current energy crisis, gym membership will be seen as the golden ticket that can pay for itself. In the coming months thinking out of the box is going to be required quite often.

It wasn't an exercise in saving money, as much as an exercise to see how little we needed to heat the water, and which was cheaper.

I hadn't thought of joining a gym to save money, but then again our nearest is a Bannatynes, so at £45/month that is a lot of showers each. An 8 miles round trip to the nearest cheap one to have a shower doesn't really appeal (plus the diesel alone would cost more than heating our water, even without the gym membership.

Besides, we are retired, semi rural, have an outdoor fitness centre about 100 yards away, and hacen't gotten around to using that yet Generally I'm too busy lazing around cutting hedges, mowing lawns, digging holes, maintaining fences, or cutting/mixing concrete

[pje16]

Besides, we are retired, semi rural, have an outdoor fitness centre about 100 yards away, and hacen't gotten around to using that yet Generally I'm too busy lazing around cutting hedges, mowing lawns, digging holes, maintaining fences, or cutting/mixing concrete

That sounds like enough to keep you fit
When I go to my brother's for a week or so, to help to do similar things, I tend to lose several pounds in weight

[UncleEbenezer]

Dare I suggest you try to change habits.

Always worth trying once he's found an indicator of excessive waste.

Do you need to shower every day, do you do particularly dirty jobs ?

But I'd be looking for the kind of change that isn't detrimental to lifestyle. I don't need to shower every day, but I choose to because I feel much better for it.

Like others we have gym membership and use the facilities there and others have shower facilities at their work places. Perhaps in the current energy crisis, gym membership will be seen as the golden ticket that can pay for itself. In the coming months thinking out of the box is going to be required quite often.

So the gym has energy costs like everyone else, plus all its other costs (staff, premises, equipment, profit, whatever). Yeah, right, several quid for a session there vs a few pence for that shower at home. Besides, don't all gyms inflict relentless torture on you from a hammering sound system?

When I moved here I thought the showers at a local pool could be an emergency backup if mine failed. Then came lockdown, and some cold showers when the boiler conked out in that cold snap between xmas 2020 and new year 2021.

[richlist]

Well I'm not suggesting any of it is compulsory but if you want to save energy bills then you probably need to use less energy. Using someone else's shower might contribute to that saving.