Heat loss from tank vent pipe

[AndyB]

Hi

Today I have been tinkering and adding insulation to my vented tank. All the pipes to and from are well lagged but I notice that the vent pipe is quite warm, looking at my graph I am loosing about 20°C in 12 Hours, measured at the top of the tank, this seems to be very high.

Can anybody give me some pointers please

Andy

[dhaslam]

Does the top of tank outlet go sideways and if so how far?

[AndyB]

Thanks for the reply
the vent pipe goes straight up and the  hot water immediately goes 90° for about 40cm.

[clivejo]

Is the pipe not insulated/lagged?

[dhaslam]

On my cylinder the outlet pipe is horizontal as far as the wall where it joins the  vertical vent pipe and other outlets.   The horizontal pipe temperature is  just a degree or two above room temperature at the point where it joins the vent pipe.       

In plumbing books cylinders are usually  drawn with a vertical expansion pipe and  horizontal  hot water outlet so it may be a regulation.   

[Philip R]

Sounds like you have got one pipe circulation on your outlet/ vent pipe.

On leaving the cylinder, hot pipe should go horizontal ( slight upward gradient to vent gases) to corner of airing cupboard of at least radius of cylinder plus a few inches, recomended at least 12 inches before joining hot distribution vertical pipe.

Do you live in bungalow or is cylunder upstairs with water flow going down to floor level for distribution. An upward journey via the attic may be somewhat lossy.

PhilipR

[GavinA]

could it be that you've got some thermosyphoning going on within the pipe itself?

[AndyB]

We do live in a bungalow and the pipework seems to be how PhilipR suggests, I will have to take a closer look and some measurements I feel and report back.

Andy

[Richard Owen]

The test shouldn't be that hard.

Just insulate the pipe and see what happens.