Positioning Heat Sink Radiator on a Gravity Fed System

[Jon Russell]

Hi - I am putting in a new multifuel boiler stove (max 9.6kw to water), connected up to my vented thermal store, which I am looking to do on 100% gravity. The pipework runs 2m vertically from the stove, 2x45 degree bends, then a 7m horizontal run (with a very slight incline), another 2x45 degree bends, then finally a further vertical run of about 1m up to the thermal store, with an overflow up into a copper F&E tank in the loft.

As I see it, I've got three options for heat-sink on the gravity circuit;

1. Position the heat sink radiator about half way along the horizontal run (as shown in diagram). I don't know whether this would have any problems though as I've only ever seen a heat sink radiator spurring off a vertical section of a gravity system..

2. Position a heat sink radiator above the thermal store in the loft, so that it can take a feed from the vertical pipework in a more 'traditional' design. The problem with this is the heat would be 'lost' to the house and I presume I'd also need to raise the F&E tank to above the radiator!

3. Not bother putting in a heat-sink radiator and rely on the thermal store (500L) to take everything the stove can throw at it.

Can anyone offer any words of wisdom?

 

[Jon Russell]

Please note: This post is to seek advice on what my options are - so that I am prepared and I know what to ask for when I get this work done by a professional fitter.

 

[Chalked]

As drawn is ok.

 

[Best]

A professional fitter will know you need a heat leak radiator and where best to position and how to pipe it if they know about solid fuel systems.
Should be no need to ask them for it, but if they don't know then try another more experienced person.
I disagree with the way you show it on your drawing connected. Air which should normally simply go up the vent pipe - some will continually go into radiator. Auto vent on radiator not needed. Tee off on flow can be taken off with branch horizontal.
Pipes to radiator can also be done other ways, as it will circulate, but I won't elaborate. If the main primaries are done correctly there will always be circulation and therefore will draw the heat through rad, unless rad has bad pipe design.
Never put a heat leak rad in an attic as just a waste of fuel

 

[Jon Russell]

Thanks for your reply Best, but the problem is, as a home-owner, knowing whether to take the advice of the "professional fitter"...

For instance, the option 2 (heat leak in the loft) - the option you are saying never to do - was actually the ONLY option presented by the fitter that I got in to quote already. It sounded suspect to me, which is why I've researched myself and come up with my own alternatives. This is someone who is HETAS registered and was actually recommended by the stove manufacturer. What am I supposed to do? Which "professional fitter" am I meant to trust?

So you're saying in principal the design is fine, but could be improved by branching horizontal to the radiator to avoid the need for the autovent?

 

[Best]

Yes, I am saying your basic drawing is near enough correct, but needs someone to view it all. The tee off vertically is something I would never do. I have been doing solid fuel pipework and link ups many times in the past and used to it.
The HETAS registered are just legally qualified, but might not always know how to do the work. So you just have to try and find one of them who knows how to design the pipework and install it properly. Good luck with that because I don't see much really good plumbing.
The primary pipes need to be 28mm and the vent 22mm or more. Manufacturer of stove instructions must be adhered to. Air vent at correct size to room also needed.

 

[Best]

A heat leak radiator with the flow (preferably from top connection of radiator) taken from a tee from the vertical primary flow and dropping down to rad is also fine. Return connection doesn't need to rise to rad.
Sounds just a lazy fix to fit rad in attic. The HETAS registered guy who said the heat leak rad had to go into the attic should be queried on how he would pipe it and why the heat loss has to be wasted to the attic? To pipe the rad to the attic off the primaries, going by your drawing would mean the thermal store hot water would transfer its heat to the heat leak rad when the stove fire dies down or is not lit, leaving you with little or no warm water.
Edit -( That is if pipes are taken from primaries at, or above thermal store)

 

[Jon Russell]

Thanks. That's really helpful. Confirmed my fears about the guy that quoted and has given me some ammunition for the next person that I get to quote!

 

[Best]

Thanks. That's really helpful. Confirmed my fears about the guy that quoted and has given me some ammunition for the next person that I get to quote!

You are right to be careful who you get.
Try not to show you have much knowledge until the plumber tells you how he would pipe it. You don't want to put all your cards on the table. If the next plumber has some other ideas, post them on here for advice from any on here