Because I've got old radiators, the return to my boiler when the heating
is running is pretty high. Which means that condensing boilers, which
like a return temperature below 55, wouldn't be running at peak. In
fact most of the time probably won't be condensing at all!

But it occurs to me that there's a nice cold fluid floating about in the
system - the incoming air. If the exhaust was used to preheat the
incoming air, the exhaust would be cooler and the pre-burn mixture
hotter - both Good Things. Power stations have been doing this for decades.

Anyone know of a domestic boiler manufacturer that uses this trick? Of
course, it would probably be a convenient side effect of a good long
balanced flue...

Andy

On Sun, 19 Apr 2009 20:41:06 +0100, Andy Champ wrote:

Because I've got old radiators, the return to my boiler when the heating
is running is pretty high. Which means that condensing boilers, which
like a return temperature below 55, wouldn't be running at peak. In
fact most of the time probably won't be condensing at all!

But it would still be more efficient than a standard-efficiency boiler.

Anyone know of a domestic boiler manufacturer that uses this trick? Of
course, it would probably be a convenient side effect of a good long
balanced flue...

Alpha and Baxi have adopted the z-something (forget the name) flue gas
heat exchanger that pre-heats DHW or a thermal store. But the value of the
return on money & materials is debatable.

--
John Stumbles -- http://yaph.co.uk

Who's *really* behind all these conspiracy theories?

In article ,
YAPH wrote:

Alpha and Baxi have adopted the z-something (forget the name) flue gas
heat exchanger that pre-heats DHW or a thermal store. But the value of the
return on money & materials is debatable.

Alpha call theirs the "gassaver" IIRC. We have one fitted and I was impressed
at just how much the incoming cold is preheated. Of course, it does nothing
to help when the heating is running though - just the hot water.

Seems these things sell for about 700 quid which seems ridiculous - no way
can it be worth anything like that. 700 quid gets you a lot of gas as well...

Darren

On Sun, 19 Apr 2009 21:31:26 +0000, dmc wrote:

Seems these things sell for about 700 quid which seems ridiculous - no
way can it be worth anything like that. 700 quid gets you a lot of gas
as well...

wot I said :-)

In article ,
YAPH wrote:
But the value of the
return on money & materials is debatable.

--
John Stumbles -- http://yaph.co.uk

You'll make some woman a fine husband, Dr Frankenstein

YAPH wrote:
On Sun, 19 Apr 2009 21:31:26 +0000, dmc wrote:

Seems these things sell for about 700 quid which seems ridiculous - no
way can it be worth anything like that. 700 quid gets you a lot of gas
as well...

wot I said :-)

In article ,
YAPH wrote:
But the value of the
return on money & materials is debatable.


I'm inclined to the same view on swapping the boiler for a condenser.

How much better *would* a condenser be, given too hot returns?
Certainly nowhere near the "book" figure.

The hot water isn't the issue - the tank's less than a year old, and
it's quite noticeable that the boiler no longer cycles when heating the
water. And the summer bills tend to point to heating being the lion's
share of the fuel.

Andy

On Mon, 20 Apr 2009 19:28:14 +0100, Andy Champ wrote:

I'm inclined to the same view on swapping the boiler for a condenser.

Indeed: unless you're heating a draughty, poorly insulated mansion which
you can't improve the efficiency of it's not worth while throwing out a
working standard-efficiency boiler and replacing it with a condensing one.
Not even for a 65% SEDBUK dinosaur.

If you have to replace the boiler anyway, for other reasons (e.g the
dinosaur is falling apart with corrosion) then the energy saving is a nice
bonus. However to then spend the price of a second boiler on a gizmo to
improve the fuel efficiency by a marginal amount makes singularly little
sense whatever the circumstances.


--
John Stumbles -- http://yaph.co.uk

This message has been rot13 encrypted twice for added security

"YAPH" wrote in message
...
On Sun, 19 Apr 2009 20:41:06 +0100, Andy Champ wrote:

Because I've got old radiators, the return to my boiler when the heating
is running is pretty high. Which means that condensing boilers, which
like a return temperature below 55, wouldn't be running at peak. In
fact most of the time probably won't be condensing at all!

But it would still be more efficient than a standard-efficiency boiler.

Anyone know of a domestic boiler manufacturer that uses this trick? Of
course, it would probably be a convenient side effect of a good long
balanced flue...

Alpha and Baxi have adopted the z-something (forget the name) flue gas
heat exchanger that pre-heats DHW or a thermal store. But the value of the
return on money & materials is debatable.

The Zenix is one of the few eco products available that does have short
return.

"dmc" wrote in message ...
In article ,
YAPH wrote:

Alpha and Baxi have adopted the z-something (forget the name) flue gas
heat exchanger that pre-heats DHW or a thermal store. But the value of the
return on money & materials is debatable.

Alpha call theirs the "gassaver" IIRC. We have one fitted and I was
impressed
at just how much the incoming cold is preheated. Of course, it does
nothing
to help when the heating is running though - just the hot water.

Seems these things sell for about 700 quid which seems ridiculous - no way
can it be worth anything like that. 700 quid gets you a lot of gas as
well...

When using a thermal store/heat bank, it can heat the stored water in the
cylinder at all times the burner is on. The stored water may be used for
DHW and CH. Well worth doing.

"YAPH" wrote in message
...
On Mon, 20 Apr 2009 19:28:14 +0100, Andy Champ wrote:

I'm inclined to the same view on swapping the boiler for a condenser.

Indeed: unless you're heating a draughty, poorly insulated mansion which
you can't improve the efficiency of it's not worth while throwing out a
working standard-efficiency boiler and replacing it with a condensing one.
Not even for a 65% SEDBUK dinosaur.

What figures do you have on this?

If you have to replace the boiler anyway, for other reasons (e.g the
dinosaur is falling apart with corrosion) then the energy saving is a nice
bonus. However to then spend the price of a second boiler on a gizmo to
improve the fuel efficiency by a marginal amount makes singularly little
sense whatever the circumstances.

You need to do some figures. Going from 60% to 92% saves a hell of a lot of
expensive gas.

"Andy Champ" wrote in message
...
Because I've got old radiators, the return to my boiler when the heating
is running is pretty high. Which means that condensing boilers, which
like a return temperature below 55, wouldn't be running at peak. In fact
most of the time probably won't be condensing at all!

A good condenser lowers the burner to achieve a low return temperature. 90%
of run time a boiler is on part load - full output not required.

But it occurs to me that there's a nice cold fluid floating about in the
system - the incoming air. If the exhaust was used to preheat the
incoming air, the exhaust would be cooler and the pre-burn mixture
hotter - both Good Things. Power stations have been doing this for
decades.

Some boilers may have long concentric flues - efficiency is lifted when
these are used.

Anyone know of a domestic boiler manufacturer that uses this trick? Of
course, it would probably be a convenient side effect of a good long
balanced flue...

On Tue, 21 Apr 2009 00:15:15 +0100, Doctor Drivel wrote:

What figures do you have on this?

65% and 90% SEDBUK efficiencies, circa £2K for a boiler replacement and
take your choice of interest rates and gas prices averaged over the next
few years.. The rest is O-level maths.

You need to do some figures. Going from 60% to 92% saves a hell of a
lot of expensive gas.

Where do you get 60% and 92%?

But in any case you've got to compare your 'hell of a lot' with the other
hell of a lot of expensive boiler replacement.

--
John Stumbles -- http://yaph.co.uk

Fundamentalist agnostic

"YAPH" wrote in message
...
On Tue, 21 Apr 2009 00:15:15 +0100, Doctor Drivel wrote:

What figures do you have on this?

65% and 90% SEDBUK efficiencies, circa £2K for a boiler replacement and
take your choice of interest rates and gas prices averaged over the next
few years.. The rest is O-level maths.

You need to do some figures. Going from 60% to 92% saves a hell of a
lot of expensive gas.

Where do you get 60% and 92%?

But in any case you've got to compare your 'hell of a lot' with the other
hell of a lot of expensive boiler replacement.

approx £1,500 per ann. gas bill on 60% efficiency. That saves approx £500 a
year. £2K to replace a boiler to 92% efficiency and the payback is 4
years - on current gas prices. As the gas prices go up over the next 3
years the payback shortens. Sounds good to me and you have a new boiler
with maybe a 3 to 5 years guarantee. After the payback period you have a
cheaper to run boiler, a selling point if selling the house, and maybe lots
of space released.

The Zenix heat recovery top box is one of the few eco additions that really
does do what they say. Solar panels can have a payback of 10 years, while
these top boxes can take 3, especially if coupled to a thermal store when
heat is recovered when the burner is on at all times, not just when DHW is
called.

"Doctor Drivel" wrote in message
...

"YAPH" wrote in message
...
On Sun, 19 Apr 2009 20:41:06 +0100, Andy Champ wrote:

Because I've got old radiators, the return to my boiler when the heating
is running is pretty high. Which means that condensing boilers, which
like a return temperature below 55, wouldn't be running at peak. In
fact most of the time probably won't be condensing at all!

But it would still be more efficient than a standard-efficiency boiler.

Anyone know of a domestic boiler manufacturer that uses this trick? Of
course, it would probably be a convenient side effect of a good long
balanced flue...

Alpha and Baxi have adopted the z-something (forget the name) flue gas
heat exchanger that pre-heats DHW or a thermal store. But the value of
the
return on money & materials is debatable.

The Zenix is one of the few eco products available that does have short
return.

Ravenheat use it too.

On Apr 19, 8:41*pm, Andy Champ wrote:
Because I've got old radiators, the return to my boiler when the heating
is running is pretty high. *Which means that condensing boilers, which
like a return temperature below 55, wouldn't be running at peak. *In
fact most of the time probably won't be condensing at all!


You could try altering the way the radiators are fed. Rads usually
seem to be connected across the bottom with internal conection used to
spread the heat within the radiator. AIUI if you feed in at the top
and out at the bottom (diagonal opposite) you will get a lower return
temperature for the same heat output (but lower flow rate).


Robert

RobertL wrote:

You could try altering the way the radiators are fed. Rads usually
seem to be connected across the bottom with internal conection used to
spread the heat within the radiator. AIUI if you feed in at the top
and out at the bottom (diagonal opposite) you will get a lower return
temperature for the same heat output (but lower flow rate).

When the heating is running they're hot all over.

When it starts up they do seem to heat top down. I don't know whether
this is internal piping or just convection.

Andy

"RobertL" wrote in message
...
On Apr 19, 8:41 pm, Andy Champ wrote:
Because I've got old radiators, the return to my boiler when the heating
is running is pretty high. Which means that condensing boilers, which
like a return temperature below 55, wouldn't be running at peak. In
fact most of the time probably won't be condensing at all!


You could try altering the way the radiators are fed. Rads usually
seem to be connected across the bottom with internal conection used to
spread the heat within the radiator. AIUI if you feed in at the top
and out at the bottom (diagonal opposite) you will get a lower return
temperature for the same heat output (but lower flow rate).


He has a system designed for 80C flow and 70C return. Using a top-rated
condensing boiler - a Broag with weather compensation - the return
temperature can be lowered.

In article ,
RobertL writes:
You could try altering the way the radiators are fed. Rads usually
seem to be connected across the bottom with internal conection used to
spread the heat within the radiator. AIUI if you feed in at the top
and out at the bottom (diagonal opposite) you will get a lower return
temperature for the same heat output (but lower flow rate).

It won't make any difference. When bottom fed, the hot rises to
the top in the first couple of channels, and then it's like a top
fed radiator. It's important the return is from the bottom, but
the flow can be either.

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

Andrew Gabriel coughed up some electrons that declared:

It won't make any difference. When bottom fed, the hot rises to
the top in the first couple of channels, and then it's like a top
fed radiator. It's important the return is from the bottom, but
the flow can be either.


I wonder - how much difference would it actually make if the flow was at the
bottom and the return from the diagonally opposite top?[1] If you have
drops from ceiling to all your rads, as I will have, it would help clear
the air from the system.

I suppose it partly comes down to how fast is the water flow through the
rad - if it's fast enough to beat convection, perhaps it won't make much
difference...

Stupid thought for the day ;-

Cheers

Tim

On Apr 22, 1:25*am, Tim S wrote:
Andrew Gabriel coughed up some electrons that declared:

It won't make any difference. When bottom fed, the hot rises to
the top in the first couple of channels, and then it's like a top
fed radiator. It's important the return is from the bottom, but
the flow can be either.

I take your point, but I suspect that if flow and return are both at
the bottom there will be a significant flow of hot straight across the
bottom of the rad which will not be there if it is diagonally fed. I
do agree completely that return from the bottom is essential.


I wonder - how much difference would it actually make if the flow was at the
bottom and the return from the diagonally opposite top?[1] If you have
drops from ceiling to all your rads, as I will have, it would help clear
the air from the system.


That would not be good at all. The hot would convect to the top and
you'd draw it striaght off up the return pipe. Much of the rad would
remain cold. Robert

"RobertL" wrote in message
...
On Apr 22, 1:25 am, Tim S wrote:
Andrew Gabriel coughed up some electrons that declared:

It won't make any difference. When bottom fed, the hot rises to
the top in the first couple of channels, and then it's like a top
fed radiator. It's important the return is from the bottom, but
the flow can be either.

-I take your point, but I suspect that if flow and return are both at
-the bottom there will be a significant flow of hot straight across the
-bottom of the rad which will not be there if it is diagonally fed. I
-do agree completely that return from the bottom is essential.

Mine are all bottom in and bottom out and there is no significant flow
straight across - you can feel it as it heats up, unless, perhaps, the pump
speed is set too high. The flow does exactly as AG describes. Top in, bottom
out is worse as there is a dead area at the bottom end below the flow
connection.

I have had both and bottom in bottom out is better for heat and better for
less sludge collection.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)


I wonder - how much difference would it actually make if the flow was at
the
bottom and the return from the diagonally opposite top?[1] If you have
drops from ceiling to all your rads, as I will have, it would help clear
the air from the system.


That would not be good at all. The hot would convect to the top and
you'd draw it striaght off up the return pipe. Much of the rad would
remain cold. Robert