Could water be convecting from the hot water tank?

[MikePP]

I have a sealed heating system with a Flowmaster Titan Plastech tank in the garage. The hot water pipe exiting from the top of the tank is hot to touch all the way up until it enters the house even when hot water is not being drawn. The pipe has a horizontal dog-leg before it is routed vertically. There is insulation in the garage but I assume that this will stop once the pipe enters the house. Water from the tank is pretty tepid after about 3pm (when it's hot in the morning and unused in the day). Do you think I might be loosing a lot of heat in the pipework from convection? If so, is there a way to reduce this effect - a check valve maybe?

 

[SimonG]

Do you have any pictures of the set up?

 

[steadyon]

If you have a secondary circulation system to reduce the time between opening a hot tap and hot water coming out of it, this could cause the symptoms you have. See if there is a circulation pump, probably near the hot water cylinder. If so then:

a. This may be on a timer which you could re-set to more suitable operating hours.
b. It is even more important that all pipework, whether in the garage or the house, is properly insulated.

 

[MikePP]

Looking around, there's just a single circulator pump and it is off until the boiler kicks in. I've attached a photo of the top of the tank (and removed the insulation that's usually wrapped around the tap).

 

[townfanjon]

Your tank is an unvented cylinder , the hot pipe is conected to all your hot water draw offs , it will always be hot .

 

[Ric2013]

Your tank is an unvented cylinder , the hot pipe is conected to all your hot water draw offs , it will always be hot .

OP states it remains hot even when water is not being drawn. I assume he means it remains hot even when water has not been drawn for over an hour?

 

[SimonG]

Would like to see a bigger picture of the whole cylinder and ancillary pipework.

 

[townfanjon]

OP states it remains hot even when water is not being drawn. I assume he means it remains hot even when water has not been drawn for over an hour?

There has to be a certain amount of thermal transfer , and we dont know the size and temp of the cylinder .

 

[MikePP]

Great to get so many replies so quickly. I wondered - should it always be hot? I guess what I'm trying to understand is why the pipe is good and hot all the way up to the garage roof (1.5m...2m maybe) even if no hot water is being used, the heating is turned off and no other pump is running. I'm assuming that it is possible for hot water to continuously rise up under convection if there's nothing to stop it leaving the tank. Is that possible? I did wonder if it might be a hot water leak, but there's no sign of that. So I'm wondering if a hot exit pipe is normal (when no water is being drawn) and whether there is anything that can be done to reduce the heat loss (other than insulation since I can't get at the pipe once it's inside the house).

 

[Ric2013]

There has to be a certain amount of thermal transfer , and we dont know the size and temp of the cylinder .

True, but if the pipe is actually hot and not just warmer than the cold room, this seems unusual, given that the OP looks to have the usual 450mm horizontal run.
OP: how long is that horizontal run? I had a similar problem when I bought my own house. Didn't want to move the vertical pipe or the cylinder at the time, so made the horizontal section longer by replacing it with one with two bends in the horizontal plane and... it worked. But we also need to see the other pipes attached to that cylinder to comment further.

 

[Chuck]

Do you think I might be loosing a lot of heat in the pipework from convection?

Convection driving hot water around the secondary loop through a stationary pump? Doesn't seem likely to me.

My guess is that you have a hot-water leak somewhere. Don't draw any water and monitor the water meter. Wait for an hour after drawing any hot water and trace the hot pipe. It will be warm up to the leak and cooler after it.

You could rule out convection-driven circulation around the secondary loop by putting an isolation valve (if there isn't one already present) in the return just before it gets back to the cylinder.
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There has to be a certain amount of thermal transfer , and we dont know the size and temp of the cylinder .

True, but the OP told us that the hold time of the cylinder was less than 12 hours, which is shorter IMO than can be accounted for by heat loss by conduction in the absence of flow.

 

[SimonG]

True, but the OP told us that the hold time of the cylinder was less than 12 hours, which is shorter IMO than can be accounted for by heat loss by conduction in the absence of flow.

Dependant upon how much of the water in the cylinder has been heated.

Also, might have missed it, but no mention from op with regard to secondary return.

 

[Best]

Hot draw off pipe from unvented cylinders should always be dropped downwards before ever rising so to completely prevent hot water rising into the colder water in the rest of pipe run

 

[Ric2013]

Hot draw off pipe from unvented cylinders should always be dropped downwards before ever rising so to completely prevent hot water rising into the colder water in the rest of pipe run

Makes sense really when you think about it.

 

[Best]

Makes sense really when you think about it.

Yes it seems so obvious, but I rarely see other plumbers doing it properly.
Only requires the hot draw off to be dropped a little to prevent hot water rising.
Same exactly with the pumped circuits on some boilers.
Doesn't matter if pipes are insulated, the hot water will continually slowly rise out of cylinder

 

[Chuck]

Also, might have missed it, but no mention from op with regard to secondary return.

They mentioned a circulator pump in post #5, which I interpreted referring to a secondary loop. I was probably mistaken.

 

[MikePP]

Hi there - to try and address all the questions above... Tank is 210L and water is set to 55deg. Yes, the horizontal pipe section is bang-on 45cm. Some more pipework pics are attached. Thanks for all the feedback BTW - lots of food for thought - and I hadn't considered the possibility of checking for leaks using the water meter. Another thing I might try is shutting off the tap at the top of the tank (with everything turned off) and seeing what the water temp is like in the afternoon. It's possible that the losses are not as much as I think they are. If it's not a leak, then perhaps I need to consider a bend or drop in the pipe where the horizontal section is currently. But - yeah - I can also see the point that this is perhaps what the 45cm section is there for already.

 

[SimonG]

They mentioned a circulator pump in post #5, which I interpreted referring to a secondary loop. I was probably mistaken.

Could have been me, didn't have my glasses on