I have an oil-fired boiler for heating the house. The hot water
output goes to conventional radiators, plus a radiant floor system.
The odd thing, to me, about this system is that the boiler output,
besides branching off to the radiators and the radiant floor system,
loops back directly into the cold-water return. This loop-back takes
place immediately above the boiler, so the distance that some of the
output hot water takes is only about 8 feets before it returns to the
boiler via the cool-water return pipe. Thus the "cold-water" return
pipe is just a hot as the hot-water pipe leaving the boiler (i.e., you
can't touch it with your bare hands). There is a shut-off valve which
can break this loop. I have asked some plumbers and some say that
that is an efficiency issue, needed to prevent the boiler from having
to heat up the fully heat-released return water; i.e., since the
return water is hot, the boiler doesn't have to work as hard. This
sounds true but nuts to me (and to some other plumbers), since much of
the water is bypassing heating the house and is just cycling directly
(and to me, pointlessly) back into the boiler.

Can anyone clarify if this makes sense (to have this immediate
feedback), or can I safely eliminate this loop by using the shutoff
valve?

On 3 Feb, 18:44, wrote:
I have an oil-fired boiler for heating the house. *The hot water
output goes to conventional radiators, plus a radiant floor system.
The odd thing, to me, about this system is that the boiler output,
besides branching off to the radiators and the radiant floor system,
loops back directly into the cold-water return. *This loop-back takes
place immediately above the boiler, so the distance that some of the
output hot water takes is only about 8 feets before it returns to the
boiler via the cool-water return pipe. *Thus the "cold-water" return
pipe is just a hot as the hot-water pipe leaving the boiler (i.e., you
can't touch it with your bare hands). *There is a shut-off valve which
can break this loop. *I have asked some plumbers and some say that
that is an efficiency issue, needed to prevent the boiler from having
to heat up the fully heat-released return water; i.e., since the
return water is hot, the boiler doesn't have to work as hard. *This
sounds true but nuts to me (and to some other plumbers), since much of
the water is bypassing heating the house and is just cycling directly
(and to me, pointlessly) back into the boiler.

Can anyone clarify if this makes sense (to have this immediate
feedback), or can I safely eliminate this loop by using the shutoff
valve?

take a look at bypass circuits, especially in conjunction with TRVs on
the radiators and zone control valves

On Tue, 3 Feb 2009 10:44:34 -0800 (PST) someone who may be
wrote this:-

I have an oil-fired boiler for heating the house. The hot water
output goes to conventional radiators, plus a radiant floor system.
The odd thing, to me, about this system is that the boiler output,
besides branching off to the radiators and the radiant floor system,
loops back directly into the cold-water return. This loop-back takes
place immediately above the boiler, so the distance that some of the
output hot water takes is only about 8 feets before it returns to the
boiler via the cool-water return pipe.

Two likely reasons for this pipe. Thermostatic valves have already
been mentioned. Do you have any?

Secondly, the pipe is raising the return water temperature in order
to minimise corrosion of the boiler. Thermostatic valves can be
fitted to the pipe to minimise heat losses.





--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Tue, 03 Feb 2009 19:54:53 +0000, David Hansen wrote:

On Tue, 3 Feb 2009 10:44:34 -0800 (PST) someone who may be
wrote this:-

I have an oil-fired boiler for heating the house. The hot water output
goes to conventional radiators, plus a radiant floor system. The odd
thing, to me, about this system is that the boiler output, besides
branching off to the radiators and the radiant floor system, loops back
directly into the cold-water return. This loop-back takes place
immediately above the boiler, so the distance that some of the output
hot water takes is only about 8 feets before it returns to the boiler
via the cool-water return pipe.

Two likely reasons for this pipe. Thermostatic valves have already been
mentioned. Do you have any?

Secondly, the pipe is raising the return water temperature in order to
minimise corrosion of the boiler. Thermostatic valves can be fitted to
the pipe to minimise heat losses.

I would suspect all those are true. Probably the valve shouldn't be all
the way open, though - it should make a high resistance path compared to
the main heating loop, otherwise you probably won't get much hot going
round that way..

On Tue, 3 Feb 2009 10:44:34 -0800 (PST),
wrote:

I have an oil-fired boiler for heating the house. The hot water
output goes to conventional radiators, plus a radiant floor system.
The odd thing, to me, about this system is that the boiler output,
besides branching off to the radiators and the radiant floor system,
loops back directly into the cold-water return. This loop-back takes
place immediately above the boiler, so the distance that some of the
output hot water takes is only about 8 feets before it returns to the
boiler via the cool-water return pipe. Thus the "cold-water" return
pipe is just a hot as the hot-water pipe leaving the boiler (i.e., you
can't touch it with your bare hands). There is a shut-off valve which
can break this loop. I have asked some plumbers and some say that
that is an efficiency issue, needed to prevent the boiler from having
to heat up the fully heat-released return water; i.e., since the
return water is hot, the boiler doesn't have to work as hard. This
sounds true but nuts to me (and to some other plumbers), since much of
the water is bypassing heating the house and is just cycling directly
(and to me, pointlessly) back into the boiler.

Can anyone clarify if this makes sense (to have this immediate
feedback), or can I safely eliminate this loop by using the shutoff
valve?


This is a bypass to prevent the pump from working against to higher
resistance if all of the radiators are shut off or restricted by TRVs.
If I remember correctly it should be set to allow about 10% of the
maximum flow rate through it. The shut off valve is used as a
restrictor to provide this flow and should not be closed..

Our old pump had an adjustable bypass buit into it, and some
installations have one radiator, such as the bathroom, permantley
locked at a setting to provide this.

Harry

On Feb 4, 10:19*am, Harry Parkes wrote:
On Tue, 3 Feb 2009 10:44:34 -0800 (PST),
wrote:





I have an oil-fired boiler for heating the house. *The hot water
output goes to conventional radiators, plus a radiant floor system.
The odd thing, to me, about this system is that the boiler output,
besides branching off to the radiators and the radiant floor system,
loops back directly into the cold-water return. *This loop-back takes
place immediately above the boiler, so the distance that some of the
output hot water takes is only about 8 feets before it returns to the
boiler via the cool-water return pipe. *Thus the "cold-water" return
pipe is just a hot as the hot-water pipe leaving the boiler (i.e., you
can't touch it with your bare hands). *There is a shut-off valve which
can break this loop. *I have asked some plumbers and some say that
that is an efficiency issue, needed to prevent the boiler from having
to heat up the fully heat-released return water; i.e., since the
return water is hot, the boiler doesn't have to work as hard. *This
sounds true but nuts to me (and to some other plumbers), since much of
the water is bypassing heating the house and is just cycling directly
(and to me, pointlessly) back into the boiler.

Can anyone clarify if this makes sense (to have this immediate
feedback), or can I safely eliminate this loop by using the shutoff
valve?

This is a bypass to prevent the pump from working against to higher
resistance if all of the radiators are shut off or restricted by TRVs.


I don't believe it is for the flow resistence; most CH pumnps are
designed to handle zero flow consitions. AIUI it's a tempertaure
issue: If TRVs all switch to off then (without this loop) there
would be no flow at all and the boiler "flow temperature" sensor would
not detect the rising temperature of the water in the heat exchanger
which could then lead to overheating.

Such a loop, with a tap in it set to 'trickle' is used so that there
is a small flow even if all the TRVs are off. Thus the flow temp
sensor detects the high flow temp and turns off the heat properly.


Robert

On Wed, 4 Feb 2009 04:33:18 -0800 (PST) someone who may be RobertL
wrote this:-

Such a loop, with a tap in it set to 'trickle'

It should be set so that the manufacturer's specified minimum flow
rate through the boiler is maintained under all conditions.

We still haven't heard whether there are any TRVs in the heating
system.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

"David Hansen" wrote in message
...
On Tue, 3 Feb 2009 10:44:34 -0800 (PST) someone who may be
wrote this:-

I have an oil-fired boiler for heating the house. The hot water
output goes to conventional radiators, plus a radiant floor system.
The odd thing, to me, about this system is that the boiler output,
besides branching off to the radiators and the radiant floor system,
loops back directly into the cold-water return. This loop-back takes
place immediately above the boiler, so the distance that some of the
output hot water takes is only about 8 feets before it returns to the
boiler via the cool-water return pipe.

Two likely reasons for this pipe. Thermostatic valves have already
been mentioned. Do you have any?

Secondly, the pipe is raising the return water temperature in order
to minimise corrosion of the boiler. Thermostatic valves can be
fitted to the pipe to minimise heat losses.

Correct. To prevent condensation inside the boiler by raising the return
temp. With having low temp UFH on and rads off, the return temp will be too
low for the boiler and condensation will occur inside the boiler rotting it.

It should have a blending valve on the boiler return keeping the return temp
just above dew-point.

As it stands it probably just needs the gate valve cracked open.