Are Vented and Unvented Water Heaters the Same?

[DIYWell]

Ok, don't explode into flames please. This is genuine curiosity and a distillation from crap I've read in other threads and forums and we all know that everything on the internet is true. And I'm only thinking of the sub 15l non G3 ticket electric heaters with a cold outlet close by.

What I know: Vented need open outlet taps to let any pressure build up drip out of the tap safely. Unvented need a PRV, check valve and expansion vessel and use standard taps.

Question: If the venting part of the equation is driven by thermal expansion that has to go somewhere safely, could a vented water heater be plumbed in with a PRV, check valve and expansion vessel to allow it to use standard taps?

I.e. are the water heaters the same but the vented/unvented just refers to how the pressure is relieved?

I'm hoping I can get a sensible answer from someone in the know without having my knackers toasted by someone too keyboard happy. My Plan B would be buying a couple of used ones from fleebay and a hacksaw and playing spot the difference.

 

[jeff the gasman]

Answer is NO.
If you seal an unvented it will burst, guaranteed.
There are some sealed ones that do not require a safety group, they expand back into the main.
http://www.airconcentre.co.uk/redri...&network=pla&gclid=CNDLme3ymcsCFawy0wodOt8M8w

 

[muggles]

And I'm only thinking of the sub 15l non G3 ticket electric heaters with a cold outlet close by.

No such thing any more - the sub-15l exemption was removed a couple of years ago

And no, vented and unvented are very much not the same thing. Unvented heaters are under constant mains pressure, whereas vented heaters sit at virtually zero pressure with a valve on the inlet side to drive the stored water out as required. If you try to seal a vented heater it'll most likely burst

 

[DIYWell]

There are some sealed ones that do not require a safety group, they expand back into the main.
http://www.airconcentre.co.uk/redri...&network=pla&gclid=CNDLme3ymcsCFawy0wodOt8M8w

Ok. That's witchcraft. How on earth does that work??

 

[DIYWell]

And I'm only thinking of the sub 15l non G3 ticket electric heaters with a cold outlet close by.

No such thing any more - the sub-15l exemption was removed a couple of years ago

I had no idea. Anyway, I'm in Scotland and we have different building regs

And no, vented and unvented are very much not the same thing. Unvented heaters are under constant mains pressure, whereas vented heaters sit at virtually zero pressure with a valve on the inlet side to drive the stored water out as required. If you try to seal a vented heater it'll most likely burst

Thanks. Yes, that makes sense to me now I read it.

 

[DIYWell]

There are some sealed ones that do not require a safety group, they expand back into the main.
http://www.airconcentre.co.uk/redri...&network=pla&gclid=CNDLme3ymcsCFawy0wodOt8M8w

Ok. That's witchcraft. How on earth does that work??

Well I had a look at the Redring site, and the blurb is unclear. "The EW has been designed to provide stored hot water from a mains pressurised water supply, where there's no requirement for a temperature/pressure relief device, making installation simple." which sounds good excpet it also says it comes with a "6bar expansion relief valve" and the brochure says "EW supplied as unit only. Safety protection devices will be required relevant to the installation." so really the EW is a standard unvented heater.

 

[jeff the gasman]

Take it or leave it.
You asked for advice. I gave it.!

 

[DIYWell]

Take it or leave it.
You asked for advice. I gave it.!

Yep, and thank you for taking the time to reply. I had hoped that the product you mentioned was something different, but now I've looked, it's the same as all the rest of the unvented heaters but if I hadn't looked, I'd have been none the wiser lol

 

[jeff the gasman]

A small expansion vessel and pressure reducing valve Is all you need in extreme situations.

 

[Madrab]

Interesting, looking at the manual for that heater, it seems that the EW does need a relief valve, it's just not integrated into the heater itself. So it seems they are advertising it incorrectly. Expansion can be dealt with through adequate length of the pipework but seems it still needs a PRV.

http://www.fastlec-pdf.com/product_pdfs/ew_mw_handbook.pdf