Attic water tank setup

nav60

I have two 50 gallons attic tanks in tandem. I am planning to get them replaced as they are very old. Two questions.

1. What is the pros and cons of having 2x50 gallons vs one 100 gallon tank ? I have a so-called semi sealed heating system. Basically filling loop is connected to one attic tank via a Non Return valve. I do no think that is the reason to have 2x50 setup tho.
2. Any recommendation on coffin tank Kingspan, Carbery ?

10-10-20

The dual tank setup is simply there as they fit through the attic trap door. You can go larger if you can fit it alright, but the support structure under the tank(s) should also be reviewed so that it's up to the requirements of the new tank!

Wearb

Very bad idea to have your heating connected to it. Get it completely separated when doing the work. The heating will only need a very small tank.

10-10-20

If the heating doesn't require a tank (if it's not running a back-boiler, etc) then have a plumber fit it out to be a sealed system. It might only take an expansion vessel, refill loop and a gauge to do so.

blackbox

If you have a 2 tank system, you should have the ballcock in one and the outlet from the other so that the water doesn't get stagnant in either tank.

nav60

Thank you all for reply.

As I understood having 2x50 or 100 tank is only depends on the access. Probably one tank is simpler setup as there is no need to fit a link. From structural support point of view, I guess should be same, two tanks are connected in a way that they look like a big, long tank.

I agree, this semi sealed system was just a sneaky shortcut to remove F&E tank as new system boiler has expansion vessel internally and that is enough for gravity pressure. I would like to have a quick test with sealed system first, I am not sure what is the status of central heating piping, there is chance I get leak somewhere. So before committing to upgrade to sealed system, I will pressurise system with main water and wait for couple of weeks to see if pressure drops or not.

youtheman

https://www.boards.ie/discussion/comment/123115207#Comment_123115207

Just one word of caution. My house was built in 1990. Was an open vented CH system. I eventually went for a condensing boiler that was designed for a sealed system. But the plumber was cautious about pressuring up all the plumbing and the risk of a leak. So I have a semi sealed system; the overflow to the header tank was removed (there is an expansion vessel and relief valve to handle pressure fluctuations), the supply from the tank hand a NRV fitted. The operating pressure is 0 bar, and I presume the low pressure switch is inhibited. Works fine. So this is one reason for keeping the header tank.

Wearb

It should get above zero, even on a semi sealed system. Perhaps non return valve is not working.