Boiler continious, timed or Immersion Heater?

rachelandgromit

I have had a new Viessman boiler fitted, opting to keep the water tank in my airing cupboard and not to go on a combi. Everything is on one level (bungalow) and the tank is close to the boiler (I only mention this as from reading previous threads I think this is important). Now obviously at the moment I have no heating on. Now which do you think is more economical for water (there are only two of us and we both work f/t).

1 Putting the immersion heater on just in the evening for showers
2 Using the boiler set to 'continious hot water' so it's on all the time
3 Setting the timer so the hot water just comes on for an hour or so

I can't seem to get an answer, my parents think the immersion heater is best, the plumber who did my boiler said he has the water on all the time, and I would have thought the timer is more economical! I don't pay a standing charge for my gas/electricity with the tarrif I am on with Southern Electric at the moment. I think this is was as the house was empty for sometime and I've only recently moved in so my unit price is higher as I've not been paying a standing charge and I don't know whether to change this tarrif?

alleycat`

Number 1 is going to be the most expensive.
Electric costs more to use than Gas per KWh and that is just how it is.

2 is going to cost slightly more than 3.
2 is slightly more practical than 3 in as much as the tank is reheated after use (rather than waiting for a timer to kick in).
2 Allows more flexibility in terms of if your day isn't what you expected and then have to heat a tank up that is "half used".
2 isn't always on in real terms (as the tank thermostat will make the boiler turn off / on as the heat is lost / gained).

For what it is worth i use option 3 and have the boiler run up twice a day for 40 minutes to heat the tank up but i also have an electric shower so the hot water tank is mostly for washing up and my little ones bath.

The most logical thing to do is:-
Take a meter reading, try option 3 and see how you get on with it.
Then a week or two later follow the same and try option 2.

Whatever you find works best for you is the way forward :-)

The immersion really should be for if you have a boiler / gas outage.

my 2 cents.

essexman77

Another option is having it on over night and economy 7 but like the other poster electricity is more expensive than gas

jalexa

rachelandgromit wrote: »

I have had a new Viessman boiler fitted, opting to keep the water tank in my airing cupboard and not to go on a combi.

Now which do you think is more economical for water (there are only two of us and we both work f/t).

The answer to the question depends mostly on how well insulated the hot water cylinder is.

*If* well insulated it doesn't take long for the boiler to get it fully heated. Also during the heating season any cylinder "losses" contribute to the house heating.

Even if you have the boiler hot water "on" continuously it will only actually run when the cylinder requires topping-up. Probably less than an hour a day. I would go for a combination of 2 & 3, just setting the timer to stop any heating in the middle of the night.

1 is easily the least economical.

grahamc2003

1 Putting the immersion heater on just in the evening for showers
2 Using the boiler set to 'continious hot water' so it's on all the time
3 Setting the timer so the hot water just comes on for an hour or so

You can certainly say that 2 will be more expensive than 3, so dismiss 2.

Just because gas is 1/3rd the price of electricity doesn't automatically make 3 cheaper than 1. The gas boiler will be operating well away from it's ideal efficiency, since it's designed (presumably), to heat both the water and a few radiators.(i.e. it works best when dumping 8 or 9 or more kw of heating from the circulating water, rather than when it's dumping 2 or 3kw).

I'd experiment - a week of heating with gas (measure carefully both the gas and electricity usage for that week), then a week with the immersion (measure carefully the electricity consumption, and assume gas is zero). You'll have to choose a couple of weeks when the electricity usage (other than the immewrsion) is similar, but you should be able to work out the costs of both methods from that data. If you do, please post the results! - this question has always interested me since I assume heating just water with a big boiler is very inefficient).

M271

I use a combination of 2 and 3. Timed on and off during the working week and on continuous at weekends when the amount and times of using hot water is more unpredictable.
On the rare occasion during the week when more hotwater will be required, I just use the one hour button on my controls to ensure there is enough hotwater available.

Cardew

There is no question that '3' will be the cheapest option.

However, provided you have a modern well lagged HW tank, the differences between having the heating timed or continuous is not that great.

Modern tanks are tested to a British Standard and typically will lose 2kWh to 3kWh in a 24 hour period with the water at 65C.

Given that there will still be losses from the tank even when timed, the difference might be, say 1kWh to 2kWh a day - 4p to 8p??

Also it must be bourne in mind that the heat loss is not really 'lost' as it warms the fabric of the house - which is why most HW tanks are in the airing cupboard.

Pincher

Remember you want to condense as much as possible.

Let's assume you set the hot water cylinder thermostat to 63 degrees, to kill all known bugs dead. If you set your boiler timer to continuous for Hot Water, the thermostat will trigger the boiler when the cylinder drops to say 60 degrees. The boiler fires, and the cylinder goes back to 63 degrees.

How hot does the boiler flow have to be to heat 60 degree water to 63 degrees? In such a scenario, HOW HOT is the returning water from the cylinder to the boiler? Is it going to condense anything: NO!

If you heat the cylinder from cold, lots of condensing happens, which stops as the returning water invitably get close to 50 degrees.

So, what temperature do you set your cylinder thermostat to?

What happens if you set it to 40 degrees? Lots of condensation, but bugs might multiply.

jalexa

Pincher wrote: »

Remember you want to condense as much as possible.

Shhhhhhh. This is the condensing boiler secret economics achilles heal, or "Prezzanomics". As you point out there is also a theoretical health implication.

We were all supposed to go for a combi.

Prezza's department failed to ensure that domestic system condensing boilers (which we were *required* to install) had separate heating and DHW flow and returns. We were conned, though is it a "con" if you know?

Pincher

One of these days, I expect them to legislate wives and girl friends into Band A (Charlize Theron) , B, C, D, E, F and G (Kathy Burke), and you get a scrappage scheme voucher, to help you get a better wife.

System

OP :-
You have not mentioned if the hot water tank is a modern well insulated type.

You have not mentioned if it is a pumped indirect heating tank.

You have not mentioned if the Hot Water and Central Heating flow is controlled via valves to enable selection of :

• CH only
• HW only
• CH and HW together

You have not mentioned if the tank has a thermostat which switches off the gas boiler (and pump where appropriate) when the water temperature in the tank reaches the set level.

If you have all of the above, then it is almost certain that using the timed option for the gas boiler will be the cheapest. Especially for you as you are out at work, so you should only heat the water when you need it.

If you have it timed to switch on the HW twice a day for example, then you may find you only need it on for an hour or so at a time just to top up the water temp. Use a little trial and error to work out the time it needs to come on and switch off just before leaving for work and getting home from work.