G3 required?

[sirocosm]

I am moving and the new house that has tank in the loft for a vented cylinder. I plan to change it to a thermal store, preferably unvented. Since I prefer things DIY, my understanding is that you do not require G3 certification for an unvented store if you use a plate exchanger, but you do if you use a tank with a DHW coil greater than 15 litres.

Is that correct?

 

[mrStat]

G3 does not apply to a hot water storage system of 15ltrs or less at mains pressure, so yes, a plate heat exchanger is generally well under 15ltrs. Although your terminology is slightly off as you I read your post as a “Unvented Thermal Store” - clarify the product you wish to install.

Please be aware, all cylinders need to be notified to building control

 

[sirocosm]

Thank you for your reply. I have not moved yet, but I am just trying to get plans together before I talk to the local building control at the new place, as I may have a small window of opportunity to do some renos before we move in.

Originally I was going to get something called a "hygienic storage Buffer tank": http://plumbingsupplies24.co.uk/hygienic-buffer-storage-tank-vertical/

But the DHW coil in the OEG is over the limit at 20 liters. It has 4.1 square meters surface area, and I don't want to go much lower than that, because I would like run the tank around 55C. I am not sure if there are any tanks with coils below the 15 liter mark that have that much area. The OEG has a corrugated stainless coil, and it is pretty wide (1-1/4" NPT), so a thinner but longer one should be possible.

By unvented thermal store I meant a store that runs at 1.5-2.0 bar, as opposed to a vented one with a tank on top. I am not sure of the correct term for that.