Someone "in another place" was asking about electric combi boilers

I have no experience of such beasts, does anyone have any positive
recommendations ?

.... and no, he's not interested in alternative recommendations, just
what to go for in an electric combi



--
geoff

On 20 Oct, 22:31, geoff wrote:
Someone "in *another place" was asking about electric combi boilers

I have no experience of such beasts, does anyone have any positive
recommendations ?

... and no, he's not interested in alternative recommendations, just
what to go for in an electric combi

I wouldn't fancy one. My gas combi, which gives adequate but not
outstanding performance, is rated at 27kw. At 230v that's 117 amps.
Please ensure he doesn't run it off a spur from the ring main via a
three-way multi socket.

Cheers!

Martin

In an earlier contribution to this discussion,
ronald wrote:

"Martin Pentreath" wrote in message
...
On 20 Oct, 22:31, geoff wrote:
Someone "in another place" was asking about electric combi boilers

I have no experience of such beasts, does anyone have any positive
recommendations ?

... and no, he's not interested in alternative recommendations, just
what to go for in an electric combi

I wouldn't fancy one. My gas combi, which gives adequate but not
outstanding performance, is rated at 27kw. At 230v that's 117 amps.
Please ensure he doesn't run it off a spur from the ring main via a
three-way multi socket.

Cheers!

Martin

http://www.thermaflowheating.co.uk/index.htm


Maximum 12kW - that's going to provide a fast-filling bath NOT!
--
Cheers,
Roger
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"Roger Mills" wrote in message
...
In an earlier contribution to this discussion,
ronald wrote:

"Martin Pentreath" wrote in message
...
On 20 Oct, 22:31, geoff wrote:
Someone "in another place" was asking about electric combi boilers

I have no experience of such beasts, does anyone have any positive
recommendations ?

... and no, he's not interested in alternative recommendations, just
what to go for in an electric combi

I wouldn't fancy one. My gas combi, which gives adequate but not
outstanding performance, is rated at 27kw. At 230v that's 117 amps.
Please ensure he doesn't run it off a spur from the ring main via a
three-way multi socket.

Cheers!

Martin

http://www.thermaflowheating.co.uk/index.htm


Maximum 12kW - that's going to provide a fast-filling bath NOT!

It's a thermal store. It will fill it fast and instantly heat the incoming
cold water.

If mains gas is available in the street, oddly enough, use that :-)

Taking 15,000kW total heating cost for heating.

E7 cost...
- Energy = 5p / unit
- Maintenance = zero
- Depreciation = £100/yr or 10000/15000kW = 0.7p / unit
- Effective Cost = 5.7p / unit

Gas cost...
- Energy = 5p / unit
- Maintenance = £100/yr or 10000p/15000kW = 0.7p / unit
- Depreciation = £300/yr or 30000p/15000kW = 2.1p / unit
- Effective Cost = 7.8p / unit

Depreciation is the 10yr replacement of boiler, powerflush, odd
radiator, TRV, improved programmer and such odds n sods.

Notes :-)
1 - If the heating is 30,000kW per year figures change.
2 - If you need peak elec boost, cost is 2.5x HIGHER.



For electric boilers...
#1 Insulation must be very high
a) recent house b) Cavity & Loft insulation and chimney's trickle
vented.

#2 Thermal store is required
The bigger the better to best use cheap rate electricity, with
75-100mm rockwool insulation "sock" rather than the miserable 25-50mm
expanding-foam-in-place stuff.

#3 Electricity rate must be E7 or E10
E7 requires a gargantuan thermal store, E10 can reduce it a little.

#4 You hit the limits of the supply cable.
7hrs at 9kW = 63kWhr... that is not actually a lot.
10hrs at 12kW = 120kWhr... that is pretty reasonable.

Realise the volume of thermal store you need after the house is
initially heated overnight, it's really enormous - 1000L or 1500L. The
figures do not work well, you end up needing peak or E10 because you
just don't have a liquid sodium thermal store handy at B&Q.

Hence they are favoured for well insulated flats, anything else gets
tough - you need 3-phase E7.

The solution would be a 9kW heat-pump (£1k), plus thermal store, plus
backup E7 "brick" storage heaters for the coldest days. That will
become quite a common solution in about 10yrs, CO2 heat pumps whilst
nutty price now (3.7k vs 1k) will eventually drop in price, it is just
a dual-stage DC compressor - hardly rocket science just lack of
economy of scale and screw the early adopters as usual.

As to actual install - make sure the terminals are tight, because
quite a few burn-out the PCBs if they are not.

Some idiot-installs have a) not used a thermal store b) not used a
suitable E7 E10 rate - in either case the result is horrific as you
can imagine.

Roger Mills
wibbled on Wednesday 21 October 2009 14:38

http://www.thermaflowheating.co.uk/index.htm


Maximum 12kW - that's going to provide a fast-filling bath NOT!

It's like a gas combi, only more crap ;-

Though, I would like a bit of background violin accompaniment now... Until
my heating system is done (ha) I will be living off a 9kW multipoint
heater[1]. Time to fill bath about 20-30 minutes...

[1] Because it's cheap (to buy), simple quick bodge and I can recoup some of
the capital on ebay later...

--
Tim Watts

This space intentionally left blank...

Correction...

#4 You hit the limits of the supply cable.
7hrs at 9kW = 63kW... that is not actually a lot.
10hrs at 12kW = 120kW... that is pretty reasonable.

On the face of it, it seems fine.

The reality is the problem of thermal store sizing.
Which translates into using on-peak, economics go AWOL.

If it is for a 1-bed flat, they will work fine.
For anything bigger, you balance heat store size/number against on-
peak electricity usage.

In message , geoff
writes

Someone "in another place" was asking about electric combi boilers

I have no experience of such beasts, does anyone have any positive
recommendations ?

... and no, he's not interested in alternative recommendations, just
what to go for in an electric combi

Well, thanks for the contributio0ns, but nobody actually answered the
question, did they

maybe an omen for him

--
geoff