Compare running costs of unvented system to combi

[Ron]

Would it cost more to run central heating with an unvented hot water
cylinder and system boiler or a combi boiler with no HWC?

R.

[CB]

In my opinion yes. All other things being equal there will be some heat
lost from the hot water cylinder which in summer will be wasted.

This will not be the case with the combi. Unless the "non combi" boiler
is more efficient as a pure heat source (unlikely - but possible I don't
know the details of boiler design) it must cost more to run.

However pure running cost is not the only consideration for a heating
and hot water system.

--
CB

[RJH]

On 19/01/2015 13:15, CB wrote:
> On 19/01/2015 12:40, Ron wrote:
>> Would it cost more to run central heating with an unvented hot water
>> cylinder and system boiler or a combi boiler with no HWC?
>>
>> R.
> In my opinion yes. All other things being equal there will be some heat
> lost from the hot water cylinder which in summer will be wasted.
>

I think the 'all other things equal' would need to be qualified. For
example, I've got a dishwasher and an electric shower, so need very
little hot water from the boiler. And not everyone needs (or wants) a
room heated by the cylinder.

--
Cheers, Rob

[Andrew Gabriel]

In article <m9j0h4$rsf$1...@dont-email.me>,

Yep, and things like number of people in the house, how predictable
their occupancy is, etc.

If you have a very predictable load, say, 3 showers every morning,
you can ensure the cylinder is heated up ready. OTOH, if the load
is very unpredictable, away half the week but different days, only
one person, etc, then you will end up wasting some of the hot water
and/or maybe not having it when you want it.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

[CB]

So you are confirming that (for you) a combi is cheaper than un-vented
HWC. I am struggling to come up with a scenario where the HWT may be
CHEAPER than a combi (but I can think of many scenarios when it may be
more convenient).

--
CB

[Dave Plowman (News)]

In article <m9j334$66j$1...@dont-email.me>,

CB <ne...@salis.co.uk> wrote:
> So you are confirming that (for you) a combi is cheaper than un-vented
> HWC. I am struggling to come up with a scenario where the HWT may be
> CHEAPER than a combi (but I can think of many scenarios when it may be
> more convenient).

You'd need to take into account repairs and replacements too. Combis tend
to be less reliable and shorter lived than a system boiler. Although
cheaper to install from scratch.

--
*We have enough youth, how about a fountain of Smart?

Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.

[Broadback]

Or if, as happens here, you get fairly frequent power cuts then a combi
is a PITA. Also on the odd occasion you have a boiler problem you
immediately lose hot water. If someone is in the bathroom having a
shower then another person runs the hot water tap the showering person
will get an unpleasant surprise, all these things are avoided with the
none combi system you are considering. I moved over to a combi when I
moved here 15 years ago, gave me extra room as the cylinder had been
located in the bathroom. However it has many disadvantages.

[Dave Liquorice]

On Mon, 19 Jan 2015 13:46:32 +0000 (UTC), Andrew Gabriel wrote:

> If you have a very predictable load, say, 3 showers every morning,
> you can ensure the cylinder is heated up ready. OTOH, if the load
> is very unpredictable, away half the week but different days, only
> one person, etc, then you will end up wasting some of the hot water
> and/or maybe not having it when you want it.

Maybe but when the time switch on the CH/HW (open vented cylinder)
failed I took a while fixing it, then noticed that the gas bill had
dropped so didn't bother until I moved out. The cylinder would only
take 20 mins to reheat and would stay hot enough for washing hands
and dishes for the best part of 48 hours. Running the system under
"on demand" rather than a time switch certainly saved money.

--
Cheers
Dave.

[Andrew Gabriel]

In article <nyyfbegfubjuvyypb...@srv1.howhill.co.uk>,

Yes, of course, but the idea of waiting 20 mins before you can have
a shower will not be acceptable to many people. When you've finished,
there's still hot water left which might get wasted if you aren't
around to shower for a few more days. If you only heat a cylinder
on demand, then a combi is probably cheaper to run for you (and
more convenient, being instant).

[Dennis@home]

On 19/01/2015 12:40, Ron wrote:

The CH will cost about the same.
The hot water may cost a bit more than with the combi depending on how
efficient it is at heating the water at the desired flow rate vs the
heat loss from the hot water tank. A well insulated tank may cost about
2p a day in heat loss, a poor one >25p a day.

[RJH]

On 19/01/2015 14:08, CB wrote:

Well, yes, especially with the cost of installation.

I accept of course that the HWT system has a number of advantages, and I
could well be persuaded on the grounds of, say, reliability.

As things stand the combi seems to do the job *for me* just fine.

--
Cheers, Rob

[harryagain]

"Ron" <r...@flymail.fm> wrote in message
news:wX6vw.195160$Wk7....@fx28.am4...

> Would it cost more to run central heating with an unvented hot water
> cylinder and system boiler or a combi boiler with no HWC?
>
> R.

The issue is not vented v unvented, that is neither here nor there.
Any system with a stored water vessel will have standing losses (ie constant
heat loss from the heat store)
This is negated if you generate water as required with a combi boiler.
However they cost more and are less reliable.

A new installation is cheaper to install with a combi boiler, which is the
main reason there are so many about.
However, it's debatable whether it's a good idea to rip out an existing
vented sytem and put in an unvented combi.

However if you install a some sort of solar collector, (either thermal or
PV ) you get free hot water for part of the year. But you need the heat
store.

There are further savings if you have local hot water generators (eg
undersink heaters either small storage or instantaneous.).

The big debate with hot water storage vessels in Summer is "Is it cheaper to
turn on the CH or use an immersion heater?"

[Dave Liquorice]

On Tue, 20 Jan 2015 09:18:19 -0000, harryagain wrote:

> The big debate with hot water storage vessels in Summer is "Is it
> cheaper to turn on the CH or use an immersion heater?"

Why would one turn on the CH to heat the HW? Something very wrong
with the control system if you have to do that.

Costs? Gas 5p/unit 80% effcient = 6.25p lecky is 10p/unit or more...

--
Cheers
Dave.

[Dave Liquorice]

On Mon, 19 Jan 2015 16:57:51 +0000 (UTC), Andrew Gabriel wrote:

>> Maybe but when the time switch on the CH/HW (open vented cylinder)
>> failed I took a while fixing it, then noticed that the gas bill
had
>> dropped so didn't bother until I moved out. The cylinder would
only
>> take 20 mins to reheat and would stay hot enough for washing hands
>> and dishes for the best part of 48 hours. Running the system under
>> "on demand" rather than a time switch certainly saved money.
>
> Yes, of course, but the idea of waiting 20 mins before you can have
> a shower will not be acceptable to many people.

Some people must have a very poor abilty to think/plan ahead... Bear
in mind that 20 mins was to 60 C plus from 20 ish. It would be hot
enough for a shower in not much over 10 minutes. Get up, turn on HW,
make coffee. have a slurp, 10 mins gone easy.

> When you've finished, there's still hot water left which might get
> wasted if you aren't around to shower for a few more days.

No other washing? Be that just hands or the dishes?

> If you only heat a cylinder on demand, then a combi is probably cheaper
> to run for you (and more convenient, being instant).

I reckon it would be quite close with a well insulated tank and
normal HW use for hands dishes etc.

--
Cheers
Dave.

[Dave Plowman (News)]

In article <m9l6fs$mkt$2...@dont-email.me>,

harryagain <harry...@btinternet.com> wrote:
> The big debate with hot water storage vessels in Summer is "Is it
> cheaper to turn on the CH or use an immersion heater?"

It's only a debate by those incapable of looking up the comparable costs
of their gas and electricity per kilowatt.hr. And, of course, doing the
sums given the boiler efficiency and any heat loss in the pipework between
it and the cylinder.

Other thing is it's a good idea to have the boiler in occasional use
throughout the warm times of the year to prevent the pump and valves etc
seizing up.

--
*Why is it that doctors call what they do "practice"?

[harryagain]

"Dave Liquorice" <allsortsn...@howhill.com> wrote in message
news:nyyfbegfubjuvyypb...@srv1.howhill.co.uk...

The debate is about heating a boiler, water and pipework (plus losses from
pipework) up from cold to get a bit of hot water as compared with just
heating the water in the HW store with the immersion heater.

If the boiler is already running for heating the house then obviously it's
cheaper to use it.
But in Summer the economics are questionable.

[Dave Plowman (News)]

In article <m9m02h$tj2$2...@dont-email.me>,

harryagain <harry...@btinternet.com> wrote:

> "Dave Liquorice" <allsortsn...@howhill.com> wrote in message
> news:nyyfbegfubjuvyypb...@srv1.howhill.co.uk...
> > On Tue, 20 Jan 2015 09:18:19 -0000, harryagain wrote:
> >
> >> The big debate with hot water storage vessels in Summer is "Is it
> >> cheaper to turn on the CH or use an immersion heater?"
> >
> > Why would one turn on the CH to heat the HW? Something very wrong
> > with the control system if you have to do that.
> >
> > Costs? Gas 5p/unit 80% effcient = 6.25p lecky is 10p/unit or more...

> The debate is about heating a boiler, water and pipework (plus losses
> from pipework) up from cold to get a bit of hot water as compared with
> just heating the water in the HW store with the immersion heater.

I doubt many would be happy with 'a bit of hot water' given most
households will use pretty well the same amount regardless of season. So
you'd let either the boiler or the immersion heat the full tank - same as
usual.

> If the boiler is already running for heating the house then obviously
> it's cheaper to use it. But in Summer the economics are questionable.

Don't agree they are. You'd need enormous losses in the pipework to the
cylinder. Modern boilers contain very little water and heat quickly.

--
*We have enough youth, how about a fountain of Smart?

[Dennis@home]

You are paying ~60% too much for your gas.

[Dennis@home]

No. The debate is whether the solar panel will heat the water up before
the CH boiler cuts in.
Gas is cheaper than electricity even in summer.

[Dennis@home]

You would think that an expert like harry would have insulation on the
circuits anyway. Mine has 35 mm of foam around all the primary circuit
and quite a lot of the heating.

[Dave Liquorice]

On Tue, 20 Jan 2015 20:36:59 +0000, Dennis@home wrote:

>> Costs? Gas 5p/unit 80% effcient = 6.25p lecky is 10p/unit or
more...
>
> You are paying ~60% too much for your gas.

I don't pay anything for gas, at least not by the unit.

You can get gas at 2p/unit? Anyway cheaper makes the gap between gas
and lecky even bigger.

--
Cheers
Dave.

[Dennis@home]

3p.

[harryagain]

"Dennis@home" <den...@nowhere.invalid> wrote in message
news:54bebd80$0$11669$b1db1813$fc1c...@news.astraweb.com...

You forget shit-fer-brains that my house needs no central heating system at
all.
When I need hot water it is all by electricity and heated within 300mm of
the point of use.
The electricity is mostly from the PV system.

[harryagain]

"Dennis@home" <den...@nowhere.invalid> wrote in message

news:54bebce7$0$11669$b1db1813$fc1c...@news.astraweb.com...

The OP never mentions solar panels SFB.
Gas hot water systems are less efficient than electricity. only the cheaper
price of gas makes them viable.

[Dennis@home]

They also generate less CO2, there are no transmission loses and the
thermal efficiency is higher.
Its only the tax on others that makes solar panels viable.

How much wood have you burnt in the last week? Using lots to get the RHI
payment up?

[Dave Liquorice]

On Wed, 21 Jan 2015 09:35:55 +0000, Dennis@home wrote:

>> Gas hot water systems are less efficient than electricity. only
the
>> cheaper price of gas makes them viable.
>
> They also generate less CO2, there are no transmission loses and the
> thermal efficiency is higher.

CCGT is pretty effcient, you still have transmission loses though. Is
a condensing combi running in condensing mode when only heating HW?

> Its only the tax on others that makes solar panels viable.

What "tax on others" for Solar Thermal? Only stand alone HW only
systems or hybrid systems where the other heat source is a biomass
boiler are eligable. "Biomass boiler" does not include a log burning
stove with boiler.

Solar Thermal that is part of a hybrid system with an oil boiler are
*not* eligable for RHI payments. Mains gas rules you out of RHI right
at the beginging.

RHI comes from central government not from a levy on everyones
electricty bill like the FIT payments.

> How much wood have you burnt in the last week? Using lots to get the RHI
> payment up?

AIUI Harry has a log burning stove, not sure if it also has a boiler.
Not that it matters log burners aren't eligable for RHI payments.

--
Cheers
Dave.

[harryagain]

"Dave Liquorice" <allsortsn...@howhill.com> wrote in message
news:nyyfbegfubjuvyypb...@srv1.howhill.co.uk...

I have a log burning stove, no RHI payments.
The fuel is free.
Some, I grow my own by coppicing.
The rest I gather oportunistically.
I have a saw in the back of the car.
It's a rural area, so lots of windfall timber.
I am also in a canal society, we cut down lots of trees as part of opening
up a derelict canal.
I have an estimated five year supply stashed away.

In very cold weather I run the stove for a couple of hours in the evening,
warms the whole house.
Approx 1m3 of wood does me for a heating season. Less if it's mild.

[Dennis@home]

On 21/01/2015 10:17, Dave Liquorice wrote:
> On Wed, 21 Jan 2015 09:35:55 +0000, Dennis@home wrote:
>
>>> Gas hot water systems are less efficient than electricity. only
> the
>>> cheaper price of gas makes them viable.
>>
>> They also generate less CO2, there are no transmission loses and the
>> thermal efficiency is higher.
>
> CCGT is pretty effcient, you still have transmission loses though. Is
> a condensing combi running in condensing mode when only heating HW?
>
>> Its only the tax on others that makes solar panels viable.
>
> What "tax on others" for Solar Thermal? Only stand alone HW only
> systems or hybrid systems where the other heat source is a biomass
> boiler are eligable. "Biomass boiler" does not include a log burning
> stove with boiler.

Both solar PV and thermal only makr finacial sense with the subsidises.

>
> Solar Thermal that is part of a hybrid system with an oil boiler are
> *not* eligable for RHI payments. Mains gas rules you out of RHI right
> at the beginging.

No it doesn't, not for water heating.
You can get 19.6p per unit.

>
> RHI comes from central government not from a levy on everyones
> electricty bill like the FIT payments.

Its a tax.

>
>> How much wood have you burnt in the last week? Using lots to get the RHI
>> payment up?
>
> AIUI Harry has a log burning stove, not sure if it also has a boiler.
> Not that it matters log burners aren't eligable for RHI payments.
>

Wood pellet burners are eligible so harry has probably got one of these
and leaves the windows open so it doesn't get too hot while maximising
the readings on the heat meters.

[Dave Liquorice]

On Wed, 21 Jan 2015 19:35:22 +0000, Dennis@home wrote:

>> What "tax on others" for Solar Thermal? Only stand alone HW only
>> systems or hybrid systems where the other heat source is a biomass
>> boiler are eligable. "Biomass boiler" does not include a log
burning
>> stove with boiler.
>
> Both solar PV and thermal only makr finacial sense with the subsidises.

Solar PV I'd agree, Solar Thermal not, though it depends on how soon
you expect to break even. It's not a short term retern...

>> Solar Thermal that is part of a hybrid system with an oil boiler
are
>> *not* eligable for RHI payments. Mains gas rules you out of RHI
right

>> at the beginning.

>
> No it doesn't, not for water heating.

I pretty damn sure that mains gas used to rule you out of all of the
RHI but briefly reading around Ofgem and Energy Savings Trust that
appears to have disappeared.

In the Ofgem Guidance document it states very clearly, several times,
that Solar Thermal is for domestic hot water only to be eligable for
RHI.

> You can get 19.6p per unit.

Provided the Solar Thermal is only heating domestic hot water.
Connect to a thermal store and you can't get the RHI. I don't
understand the reasoning behind that, it's heat FFS. We burn about
200 l less oil over the summer (May - Oct) since the thermal store
and solar thermal went in. Are they saying that that saving is in
lieu of the RHI? If we'd installed the Solar Thermal as "stand alone"
DHW with the same oil boiler as back up we'd get the RHI *and* the
saving on oil. There was not even a whisper back then that this
restriction was about, I don't think it was mentioned in the
consultation either. It just appeared when they launched the domestic
scheme.

Now they are fiddling with the scheme rules and the documentation
seems to be written by people who don't understand what they are
writing about or are not writing what they think they are.

I might give the EST or Ofgem a call, one or the other sent an email
a while back saying I haven't applied yet. I haven't applied because
I don't think our hybrid solar thermal/oil/log burner to thermal
store feeding HW and CH is elgiable. Mind you I'm still not sure it's
worth jumping through the hoops of getting an EPC and Green Deal
assessment for just £1000 spread seven years.

--
Cheers
Dave.

[harryagain]

"Dennis@home" <den...@nowhere.invalid> wrote in message

news:54bfff7b$0$11135$b1db1813$926e...@news.astraweb.com...

You have a nasty mind.
I don't have a wood pellet burner.
The economics make no sense and the eco-benefit is doubtful.

[RJH]

The 2p loss sounds incredibly low. Do you have a make/model in mind that
could keep water that warm?

--
Cheers, Rob

[Fredxxx]

On 19/01/2015 12:40, Ron wrote:
> Would it cost more to run central heating with an unvented hot water
> cylinder and system boiler or a combi boiler with no HWC?

This may assist:

http://energy-surprises.blogspot.co.uk/2012/10/combi-boiler-versus-hot-water-tank.html

[RJH]

Including standing charge? Net unit charges are pretty meaningless.

--
Cheers, Rob

[Dennis@home]

But that would depend on how much you use and ofgen wants the bills to
separate the network costs from the fuel costs.

[Dennis@home]

Anything with 100mm of foam should manage that. Its almost a kw hour.