Combi Vs Conventional Boiler with a tank

macman

Soniclord wrote: »

That's exactly my level of thinking, the whole how could it not be more expensive with a conventional boiler Glad you agree with me on that point.

No offence to any other info I've used but I'm just using what I think is common sense.

I did notice in one of the houses we looked in it had a fairly small tank as well so wouldn't hold enough water to run a full bath :cool: or so it seemed by the size of it. And that wouldn't be good.

I did ask the agency if they'd ask the landlord if he would consider replacing it, but they came back to me and said no landlord in their right mind would consider replacing an energy efficient boiler considering the cost would be in excess of £1200..

Energy efficient? Not sure what planet he was on!

Wonder if they'd replace it if I said I'd pay for the combi? Hmmmm

Not sure what the cost would be to fit it though!

You might save (very optimistically) 10% of your hot water bill by using a combi? So maybe a total annual saving of 10% of one third of your gas bill. Assuming £900 a year bill, that's around £30 a year saving. So based on a (very low) replacement cost of £1200, it will take 40 years to break even on the combi (which will probably last about 10 years).
Seems to me that your LL is indeed in his right mind-especially as he would not benefit.
What the property does appear to need is a larger hot water tank.

Cardew

Soniclord wrote: »

Perhaps but in my experience (I've never used a conventional boiler, so it's limited) I prefer combis anyway, I can say that based on the fact I'd rather have hot water instantly than have to rely on heating it up first lol.

I suggest then you read WHICH on boiler efficiencies or there are some highly technical reports on boilers that discuss combi v conventional boiler.

With a Hot Water Tank you do have Hot water 'instantly' - often much quicker than from a combi.

The problem with a combi is you don't get Hot water 'instantly' as it takes some time( a few seconds) to heat up the water and a few seconds more for it reach the tap - running off cold water first. Some combis alleviate this issue by having a small tank inside the combi that is kept full of hot water.

There really is no point in stating your experience or not with combis/conventional boilers because the conditions cannot be replicated. I have a combi and a conventional boiler/HW Tank in my property and the HW tank wins hands down for convenience, but I wouldn't know which was cheaper)

This is why organisations carry out tests on our behalf and they state that it is perfectly possible for a combi to be more expensive at providing DHW.

In any case as Macman pointed out the difference either way is minimal. With a combi you are usually 'running off' lots of water before hot reaches tap, and if you are metered for water, that can add up to over a period of time.

Soniclord

Cardew wrote: »

The problem with a combi is you don't get Hot water 'instantly' as it takes some time( a few seconds) to heat up the water and a few seconds more for it reach the tap - running off cold water first.

Maybe not instantly (does a few seconds really matter..) but you also don't have to wait for a conventional boiler to heat the water first, I know which I prefer.

Cardew wrote: »

There really is no point in stating your experience or not with combis/conventional boilers because the conditions cannot be replicated. I have a combi and a conventional boiler/HW Tank in my property and the HW tank wins hands down for convenience, but I wouldn't know which was cheaper)

With respect there is a point! My experience tells me that I get hot water from a combi within seconds (in my mind that's instant enough) it matters not that I can't replicate the conditions. In my opinion by using common sense which would cost more, I believe a combi is far cheaper as you only get hot water on demand, no waiting for it to heat up (well apart from the few seconds you have to wait) which is much less than any conventional boiler IMO.

Cardew wrote: »

This is why organisations carry out tests on our behalf and they state that it is perfectly possible for a combi to be more expensive at providing DHW.

With respect they can run all the tests they like, I'll still make my own mind up. No offence intended.

Cardew wrote: »

In any case as Macman pointed out the difference either way is minimal. With a combi you are usually 'running off' lots of water before hot reaches tap, and if you are metered for water, that can add up to over a period of time.

Well not 'lots' of water as it's only a few seconds till it gets hot but I see your point. And if people are metered for water then running a combi off for a few seconds would still be cheaper than waiting for a tank to fill with hot water surely..

I'm pretty certain waiting to heat a tank full of water/waiting for said tank to fill up DOES use more water than running a tap for a few seconds through a combi boiler. Common sense does dictate that!

Again no offence intended.

macman

You don't have to wait for hot water with a conventional system unless you have run the tank dry. It's otherwise controlled by a timer or programmer so that the hot water is available when you need it.
And modern tanks have very little heat loss.
You may well prefer a combi, which is fine, but your preference is not based on any factual evidence that it's cheaper-because it isn't.

Baker89

macman wrote: »

Your preference is not based on any factual evidence that it's cheaper-because it isn't.

Well no it's not based on factual evidence as I've not compiled any factual evidence, though I dare say there is plenty out there. That said I do appreciate all the posts and information.

But me saying "it's cheaper" and you saying "it isn't" is you saying a combi isn't cheaper than a conventional boiler. Is this based on your personal experience or actual facts compiled by many others experiences using both whom you've asked?

Because I'd bet pound to a penny that any decent combi boiler uses far less energy than a conventional boiler. I could be wrong but I don't think I am. After doing a little more research, many threads on here back that up as well.

But everyone is entitled to their own opinion which is why I clearly stated IMO combis are cheaper to run, you blatantly put that they aren't cheaper. But whatever.

yonk

You can buy a house with a conventional boiler and change it...but it's very expensive and only worth doing if the current boiler is at the end of it's life.

You are worrying for nothing. You would adjust quickly. Just be grateful you haven't rented a house with Economy 7 water heating, where once it has been used, that's that until the next night.

As for asking the landlord to change the boiler, how would you feel about being asked to spend £2k to change say your car because you would save a small amount a week in petrol and even that would be debatable? That's the same analogy.

macman

The only way that a combi could be cheaper to run is if a) it heated water more efficiently (which it doesn't-the burner and heat exchanger mechanism is not that different), or b) if the stored hot water lost enough heat to make it wasteful (which it doesn't-and any 'lost' heat heats the house anyway).
If conventional boilers used 'far' more energy than combi's, then the government would have banned them for new installs long ago, just as they banned non-condensing boilers.

Mister_G

One point I would like to make is that in hard water areas combi boilers are more prone to furring up. I have experience of that and that is why I now have a conventional boiler.

Conventional boilers also appear to be of a simpler design and are less prone to going wrong.

This is just my own personal experience.

Cardew

Soniclord wrote: »

I'm pretty certain waiting to heat a tank full of water/waiting for said tank to fill up DOES use more water than running a tap for a few seconds through a combi boiler. Common sense does dictate that!

You are basing your 'common sense theory' on a circumstance that doesn't exist. I don't know of anyone who 'waits to fill a tank full of water'.

My tank always has hot water ready for use and I get it far quicker than a combi.

As explained several times, a modern HW tank loses very little heat - even if filled with water at 65C, and the heat that is 'lost' from the tank(3p to 4p a day) isn't really lost as it warms the house - which is why most NW tanks are in an airing cupboard.

This is on a recent thread:

Report on the Effcicency of Boilers in Situ - Not What the Maufacturers Say.

http://www.google.co.uk/url?sa=t&rct...UJd30g&cad=rja

I do not know if this has been posted, but if not here are the effceincy results for 60 boilers in peoples actual homes.

Some myth busters in here.

So you think your combi is 95%,(efficient) well in actual usage it could be as low as 17%.

Think that you hae a well insulated tank and that is good, then think again - depends on how much water you draw but could be lower than combis.

Also there are lots of nice gas usage charts for people that have the CH coming on at set times during the day and people that leave the CH on from dawn to dusk.

Christmas come early for the boiler boffins on here.

Note that this is a Government report and these are 60 tests of boilers in people's homes.

It is important to note that with DHW the pattern of drawing off water has a large effect on water heating efficiency - a combi being particularly poor if drawing off small amounts(i.e. hand washing)

8.4 Comparing the annual efficiency of regular boilers with DHW storage,
with combination boilers.

The average of the measured annual efficiencies of the regular boilers in the trials
was nearly 3% better than the combination boilers, 85.3% as opposed to 82.5%. The
difference is thought to be due to the lower efficiency of condensing boilers when
operating in DHW mode (about 73%). When tank and primary pipework losses
associated with regular boilers are included a more valid comparison of regular and

combination boiler annual efficiency may be 80.3% compared with 82.5%.

spinningsheep

What you should consider soniclord, is how many times a day does your boiler fire up to provide you with instant hot water? I mean ALL of them, every time you turn on a hot tap. All those small bursts of heating add up. You should only need to heat a very well insulated hot water cylinder for about 1 hour twice a day, MAX, you can experiement, you may even find that it needs less than that if the heat is held well from the previous timed period. It's very doubtful you will notice any difference at all. Just add an extra hot water jacket to the cylinder if you're in doubt, can be purchased very cheaply. As you say it's a rented house so you are very limited as to what you can do other than reduce the amount of time the water is heated for and insulate the tank as much as you can. When we had a conventional water tank and an old non condensing boiler (which yours will be if it was installed since 2006, easy to check, is there a white plastic pipe that comes out of the boiler and discharges into the drain outside or a sink trap? Do you get a noticeable "plume" of steam from the the flue when it is running, even on a warmer day?) we used to keep the water off as much as possible in summer and boil kettles for the dishes etc, as we have electric showers anyway.