How to calculate cost to fill hot water cylinder using Gas Conventional Boiler - confused!

Gerry1

Lfc1969 said:

lohr500 said:

Something else to consider when comparing gas vs electricity is the length and/or position of the immersion heater element.

If only a short element has been fitted, it won't heat the full tank of water, wheres the heating coil from the gas boiler is likely to cover the full height of the hot water tank. Energy consumption comparisons may not therefore be comparable.

Good point. The immersion element goes into the middle of the tank, a little above half way. It’s an 11” element so not one of the 27” ones that goes in at the top.

No idea about the heating coil.

There's almost certainly another immersion heater hidden away at the the bottom of the tank.

The idea is that you can get a full tank of HW at the cheap overnight E7 rate, with the ability to top up with half a tank at the expensive day rate if you run out.

Leaving one or both switched on accidentally is a classic cause of high electricity bills.

The hot water from the boiler heats the tank via a large coil in the tank.  The flow enters at the bottom and leaves at the top so you get a full tank of hot water.

FreeBear

Lfc1969 said: I guess the last question may be very specific to our set up so I’m really looking for some information on the first question about how much gas the Worcester would use to just heat water.

It really depends on whether you have a thermostat on the side of the tank and what temperature it is set to. The size of the tank will also affect the amount of gas used.

If you are one of these people that have the tank stat set to 60°C or higher, turn it down to 50-55°C. You will save gas, and if you are worried about legionella, the bacteria will still be killed off (just takes a little longer).

markin

Gerry1 said:

Lfc1969 said:

lohr500 said:

Something else to consider when comparing gas vs electricity is the length and/or position of the immersion heater element.

If only a short element has been fitted, it won't heat the full tank of water, wheres the heating coil from the gas boiler is likely to cover the full height of the hot water tank. Energy consumption comparisons may not therefore be comparable.

Good point. The immersion element goes into the middle of the tank, a little above half way. It’s an 11” element so not one of the 27” ones that goes in at the top.

No idea about the heating coil.

There's almost certainly another immersion heater hidden away at the the bottom of the tank.

The idea is that you can get a full tank of HW at the cheap overnight E7 rate, with the ability to top up with half a tank at the expensive day rate if you run out.

Leaving one or both switched on accidentally is a classic cause of high electricity bills.

The hot water from the boiler heats the tank via a large coil in the tank.  The flow enters at the bottom and leaves at the top so you get a full tank of hot water.

Houses with Gas boilers usually only have 1 element as back up, if it has one at all.


If you aren't running out of hot water often then the Gas for 1hr will be cheaper than 2hrs of electric.

The diverter valve is to save money, without it you would always be heating hot water when you only need heating, Or always heating over summer when you only need hot water.

Lfc1969

markin said:

Gerry1 said:

Lfc1969 said:

Houses with Gas boilers usually only have 1 element as back up, if it has one at all.


If you aren't running out of hot water often then the Gas for 1hr will be cheaper than 2hrs of electric.

The diverter valve is to save money, without it you would always be heating hot water when you only need heating, Or always heating over summer when you only need hot water.

Yes we definitely only have one element,

I guess the question is, is one hour using the Worcester 40 CDI cheaper than 45p? Because two hours of cheap overnight electric is only 45p. (3KW element would be approx 22p per hour at cheap 7.5p KWh Octopus rate)

markin

Manual says ''Min. rated heat output net 80/60°C  9.4 kwh''

But i suspect the actual burn time is only 30-40min cycling on and off after a 20min warm up.

RavingMad

We have a 15kwh boiler which currently heats up the water twice a day, 30 mins each time but usually only fires up for 20 mins.

I have Hugo app and it tells me I use between 4 and 7kwh each day 

QrizB

Lfc1969 said:

I guess the question is, is one hour using the Worcester 40 CDI cheaper than 45p? Because two hours of cheap overnight electric is only 45p. (3KW element would be approx 22p per hour at cheap 7.5p KWh Octopus rate)

You're asking the wrong question.

6kWh of electricity is enough to heat 100 litres of water from 20C to 70C and will cost you 45p.

To do the same using gas, burned in your boiler, would use between 7kWh and 8kWh of gas. At 7p/kWh that's 49p to 56p.

But - we don't know how much water your immersion heater will heat, or how much water your boiler will heat. We think that the coil for the boiler is lower in the tank than the immersion heater, so the immersion will heat a smaller volume of water.

markin

The gas heating stat on the water tank would normally be set at 60c, and immersion heaters are often left at 75-80c, so from cold it would probably be about even.

If its an un-vented system you could lower the gas heating stat on the tank to 50c or 45c and heat 30min twice a day so the is less heat loss, Heat to 60c once a week as a  

Legionnaires cycle.

But you would need data to see if its saving money or not.

Netexporter

I can say one thing for sure; having hot water permanently available is an expensive hobby, even if you have a foam lagged cylinder. The reason I did my measurement, quoted upthread, was because at the time, probably 10 years ago, I realised it was costing about £60 per quarter in the summer months, when there was no heating load. As well as working out how much it cost to heat a cylinder of water, I also timed it. I then worked out that I could heat enough water for a shower, with a bit left over for hand washing, in 6 minutes. My quarterly summer cost fell to well under a tenner.

If I wanted a bath, rather than a shower, or more hot water for other reasons, I adjusted the burn time to suit.

debitcardmayhem

When taking readings for you gas meter look at the meter, not the IHD.