To vent or not to vent - that is the question...

[Dave876]

Hi All,

I am looking at replacing my existing hot water cylinder and considering the various options. I think I understand the options - but no idea on the best solution!

I currently have a Worcester Bosch Greenstar boiler (30CDi I think from memory) - just fitted last year - fully pumped, with open vented cylinder right above the boiler. The primary circuit is also open vented if that makes a difference.
The house will (eventually) be a 1 bath / 2 shower / 4 bed property.
Existing cylinder is too small (100L?) and takes an age to re-heat and has no immersion. Lots of renovations, so trying to do the major tasks first.

Option 1 - vented copper cylinder
Option 2 - vented stainless cylinder
Option 3 - unvented stainless cylinder.

Option 1 is fine - like for like - cheap fix. I have read some posts about which cylinder - all seem pretty much the same from what I gather so just need to check the re-heat times if possible.

Option 2 - tempted by the flashy look to be honest (sad aren't I?), plus the supposedly longer life.

Option 3 - Never dealt with these - I understand it would give mains pressure hot water and remove the need for the header tank. Currently there is a HUGE difference in pressure between cold mains and hot and there is no chance of raising the loft tank. Removal of loft tank is appealing as the loft is a nightmare. My concern would be - are there any risks with this approach?

So - can anyone tell me what they would suggest, and with the option which cylinders I should consider? I don't want to waste money per se - but would rather do the right thing and pay the extra. The budget got blown by the architect anyway...

Thanks,
David.

 

[Redhotferrari]

Unvented all the way would be my advice if you have the required flow and pressure rates. You wont regret it..............

Option 2 would prob work out cheaper than option 2 at the moment, I cna buy stainless cylinders cheaper than copper due to the high copper prices.

Good luck!

 

[gayzar]

I would recommend option 3 looking at a 210ltr tank if you have room to fit it. As stated before check your pressure and flow rates to ensure combatable.

Gaz

 

[Dave876]

Thanks both for the opinions - any recommendation on the cylinder and is it a DIY option?

I could get my Dad to give me a hand - but not sure his ticket to work on marine boilers back in the 60's is going to be much help!!

 

[Redhotferrari]

Unvented are DIY, you need an installer with the qualification to fit and maintain them.

 

[D_Hailsham]

Unvented are not DIY, you need an installer with the qualification to fit and maintain them.

There is a word missing!

 

[Dave876]

Hi All,

OK - So I cannot DIY the unvented option.

I know this appears to be a contentious issue, but what then is the deal with a thermal store? It's vented - so I can cover that, but the idea of having a bank of very hot water to heat up the mains water as it passes through seems a bit of a waste - don't you need to keep it constantly hot for the moment when someone turns on a tap?

I'm not immediately sold on the idea to be honest - but would like to know more - in particular I guess why there are some very strong opinions against it.

Thanks,
David.

 

[Muzz]

I diy installed a thermal store simply because it meant i could do it and it gave me mains pressure hot water. I also read up on pro's and cons and a lot of debate on here so I was initially nervous about my descision.

Once configured correctly mine works fine, it's a 170 litre tank which is supposed to be kep at 75c i think, i set mine to 70c. Our cold water in winter comes out the taps at about 5c and this tank gives enough heat for at least a 30 minute shower with a good flow rate, in summer i obviously get more as the cold water is warmer.

it's not a waste having a tank of hot sitting there as you would have to have a tank of hot for a vented or unvented too, but your tank does have to be 20 - 25 degrees hotter so it take more energy to heat up.

I did read some stuff about how thermal stores can extract more heat from the stored water as the cold does not mix with the hot in the tank. You don't get any turbulence from cold entering so you the hot water in the tank is not cooled prematurely. This was just stuff i read on the web which makes sense but have no real idea of the truth of it or not.

the other main thing is to make sure the thermal store is indirectly heated as i also read directly heated ones can be prone to filling up with sludge.

i would still consider the unvented again as my old house had one and it was great. i just did the thermal store as I couldn't find a good plumber/heating guy and wanted to do the project myself.

I should also point out I'm not an expert or thermal store fanboy, i just happened to have installed one myself and it sounds like your thinking about the same things i was a year or so ago. (i say that so the plumbing regulars don't give me a smackdown or think i'm that bigburner/watersystems guy, do a search and you'll see what i mean )

 

[RigidRaider]

Whatever you buy, consider spending a few squid extra and getting a cylinder with an extra coil for a solar panel to contribute some heat. Have a look at my post here: //www.diynot.com/forums/viewtopic.php?t=255833 You might want to install a panel at some time in the future.

I have just replaced our old small 20 y.o. cylinder with a new 160 litre job with two coils. Looking inside the old cylinder I was shocked at how small the coil was, just three or four turns, no wonder it took hours to heat up. The new one has a monster coil and half hour reheat.

I sold the old cylinder for £38 to a scrappie. If I had known, I would have removed the 200gms or so of foam and he wouldn't have deducted 2 kilos for it. I'd also have left the litre or so of water that was slopping around inside....

 

[Dave876]

Muzz - thanks for the info - it certainly sounds like we are coming from the same direction here!

I've read a bit more today and think I understand better - the cylinder is heated via a coil from the primary, and this in turn is heating the contents of the thermal store. The incoming mains (cold) runs through a seperate coil and is heated as it passes through - is that correct?

So yes - same as a regular cylinder (in terms of storing hot water). If this is open vented - does it get fed from the same header tank as the primary? Just not 'pumped'?

Why is there not a solution that has the cylinder full of primary heated water (open vented still) and just passing the incoming mains through a coil - so a regular cylinder in reverse?

Out of interest which thermal store did you go for and why that one?


RigidRaider - we have considered - and excluded - the possibility of solar. I think our position and the roof would preclude this as an option. Good tips on old cylinder though - I'll fix that before scrapping, and dump some wet sand inside for good measure.

 

[Muzz]

I've read a bit more today and think I understand better - the cylinder is heated via a coil from the primary, and this in turn is heating the contents of the thermal store. The incoming mains (cold) runs through a seperate coil and is heated as it passes through - is that correct?

That's how my one works

So yes - same as a regular cylinder (in terms of storing hot water). If this is open vented - does it get fed from the same header tank as the primary? Just not 'pumped'?

mine has it's own little feed and expansion tank, (i have a sealed heating system so don't have any other tanks anyway)

Why is there not a solution that has the cylinder full of primary heated water (open vented still) and just passing the incoming mains through a coil - so a regular cylinder in reverse?

i think you do get ones that do that, but in the same way your radiators can fill with sludge over time, your thermal store fills with sludge and you can't take that outside to hose out.

Out of interest which thermal store did you go for and why that one?

a gledhill torrent, just fitted my needs in regard to size and was the one i could find most information about.