Pluming question for those in the know - vented cylinder

[Damon]

Hi everyone, no doubt you'll all be getting bored with my questions soon

I am soon to be installing a hot water system into the house we are in the process of buying. What I'll be doing is essentially moving around and adapting the current system albeit with all new pipework and cold water storage tank. The current setup includes a hot water cylinder which takes up half of the kitchen (i'm not exaggerating, it has its own plasterboard room)! + a bathroom that is a part of the 60's extension to the rear of the property. We are going to be changing the current bathroom to a pantry/ storage room and fit a bathroom to one of the upstairs bedrooms.

The setup is an vented cylinder with a cold water tank heated indirectly by an oil boiler. The water pressure isn't great enough for a unvented cylinder and to be honest I'd rather have a system that I can personally work on and maintain without calling out a "specialist" every year for a checkup.

The main question I have is that I would like to keep the hot water cylinder down on the ground floor. My understanding is that this wouldn't be a problem as it is only the cold water head that needs to be kept as large as possible. The hot water cylinder will be next to the oil boiler for simplicity and space reasons.

The second question I have is that we have a beautiful 200ltr freestanding roll top to fit in the bathroom. The bath's cold will be mains fed whilst hot water is from the cylinder. I'm going to buy a new cold water tank anyway so I know exactly when it was fitted and how old it is. Would a 150L tank be sufficient for this? I'm not 100% sure on the size of the hot water cylinder at present but it's not a small one!

Finally, (thank god I hear you say) We plan to fit a gravity fed shower with it's cold supplied from the cold water tank via 22mm pipes. Would the proposed 150L cold water tank be big enough for this purpose or should I just fit a biggun/ piggyback a couple of them just to be safe?

Below is an image of the setup I plan to use. Can anyone in the know confirm this would be ok or give me a slap? I haven't included any of the heating circuit into the diagram other than an expansion vessel to show it's a sealed pressurised system.

I really appreciate the help - This forum has already been an invaluable source of information and advice.

 

[MikeG]

...............Changed my mind............

 

[Feltwell]

First off - big caveat - I'm not a plumber! However I had a not dissimilar vented setup here that I've worked on many times, so here goes......

The setup is an vented cylinder with a cold water tank heated indirectly by an oil boiler. The water pressure isn't great enough for a unvented cylinder and to be honest I'd rather have a system that I can personally work on and maintain without calling out a "specialist" every year for a checkup.

Fair enough, the system you describe is pretty simple and easy to work on, but it's still a good idea to get the boiler properly serviced each year - carbon monoxide from a faulty coal-fired boiler killed my sister-in-law's father. It's not that expensive to get a service.

The main question I have is that I would like to keep the hot water cylinder down on the ground floor. My understanding is that this wouldn't be a problem as it is only the cold water head that needs to be kept as large as possible.

Correct - it makes no difference where the hot water cylinder is so long as it is far enough below the cold water tank that feeds it. It's the head from the cold tank to the highest hot water tap that matters. When we moved into this house, which is over 3 storeys, we had a hot water tank on the 1st floor and a cold water tank sat on the floor of the 2nd floor. A sink in a 2nd floor bedroom had a mains fed cold tap but could not have a hot tap as the tap would have been above the level of the cold tank.

I've moved the cold tank above the 2nd floor ceiling, up at the very top of our roof space. The hot tank is still well below it on the 1st floor. The hot water now feeds a tap on the 2nd floor sink with no problem. Not a huge flow but perfectly adequate, there's about 10' of head giving the pressure.

The second question I have is that we have a beautiful 200ltr freestanding roll top to fit in the bathroom. The bath's cold will be mains fed whilst hot water is from the cylinder. I'm going to buy a new cold water tank anyway so I know exactly when it was fitted and how old it is. Would a 150L tank be sufficient for this? I'm not 100% sure on the size of the hot water cylinder at present but it's not a small one!

Not sure to be honest. How big is the house? My thinking though would be that a 200ltr bath shouldn't have 200ltr of water in it, as there's a human volume to allow for - unless that's already accounted for in the 200 ltrs! The hot water cylinder size needed will depend on likely usage - if you've got your monster bath, plus a power shower elsewhere in the house and a washing machine that has a hot fill, and they may all be used at once, you'll need a monster tank! In my house (5 beds, 5 people) the only real usage for hot water is the bath plus a bit for washing up and the sinks. The showers are electric and the washing machine and dishwasher are cold feed only. A 50 gallon cold water tank has never given us any problems but also our hot water cylinder is not massive. If you've space then I'd stick a minimum 50 gallon cold water tank in personally, don't forget if you've space (and a strong enough structure to support it) adding a 2nd tank is fairly easy if you find you get problems with your monster bath emptying the hot water cylinder faster than the cold tank can refill it.

Finally, (thank god I hear you say) We plan to fit a gravity fed shower with it's cold supplied from the cold water tank via 22mm pipes. Would the proposed 150L cold water tank be big enough for this purpose or should I just fit a biggun/ piggyback a couple of them just to be safe?

Just a straight gravity fed shower (no pump), and you're not likely to be filling the bath at the same time? 150L is about 40 gallons, sounds enough to me. Again a 2nd tank will be easy enough to add if need be, if you've got the space. Why 150ltr by the way? All the cold tanks I've seen are still imperial, usually 25 or 50 gallons. Is an electric shower an option for you with your water pressure? We find, with a family, having the showers independent of the hot water tank is a definite advantage, no squabbling over who used all the hot water! Electric showers have improved a lot - get a high enough rated one and you do get a decent shower, not the pathetic trickle some of the older ones gave!

Below is an image of the setup I plan to use. Can anyone in the know confirm this would be ok or give me a slap? I haven't included any of the heating circuit into the diagram other than an expansion vessel to show it's a sealed pressurised system.

If your aim is to keep it simple, why bother with a pressurised heating system? If you've space for small 4 gallon feed & expansion tank in the loft then an open vented system is far simpler to my mind, certainly easier to diagnose and fix problems in the future. Someone else's take on this here:-

http://www.miketheboilerman.com/openorsealed.htm

As for your diagram - I can't see an obvious problem, it's more or less what I've got, except in my case the boiler is gas and the shower is electric and fed from the rising main.

Hope that is of some use, not a 100% answer I realise! Cylinder / tank sizing always seems to prompt an "it depends" type of answer.

 

[Feltwell]

Forgot to say - watch the vertical distance between your cold water tank and the shower head - I *think* it has to be at least 3', but even at that you're not going to get much water pressure on hot or cold.

If it's a problem then it's either an electric shower off the rising main as I suggested above, or fit a shower pump.

 

[Damon]

Thank you ever so much for your input. It's really appreciated and more than helpful advice.

First things first don't worry the oil boiler will gets an annual inspection. It's just the water side i'd like to maintain myself.

There are only two of us in the house and it's a small 3 bedroom cottage so the floor space isn't massive at all. I've changed my mind after doing a bit of thinking/ research (thanks to your advice also) and an electric shower plumbed in directly to the mains cold water would make much more sense. I think a 40 gallon CWT would probably then be more suited as it's not supplying a shower too. Are there any advantages to a smaller CWT other than to save space?

The current central heating is already in place and a pressurised system. It's a fairly modern setup so it doesn't warrant replacing.

Thanks again for your help with this. It's really nice to know there are such friendly folks on here

 

[Feltwell]

No problem. Enough folks on here have helped me! Sometimes it's good just to bounce ideas around and get a different perspective.

Are there any advantages to a smaller CWT other than to save space?

Not really, they're a bit cheaper of course but not much. Not as heavy on your ceiling joists. Easier to get through the loft hatch (although the "coffin" type tanks are easy to get through at any size, and spread their weight across more joists - worth considering.)

If your cold water tank is just going to supply the hot tank only, I agree a 40 gallon should do it. Just to be on the safe side, if you can install it in such a way that you can put a second tank alongside at a later date if you find you have problems, then you're well covered.

 

[Penners]

Not as heavy on your ceiling joists.

I agree with everything that Feltwell has said, and I'm glad that he added this point. Do remember that water is heavy stuff- 1kg per litre. So make sure that your ceiling joists can support the load and, as you have and Feltwell have mentioned - if you plan to have greatly increased cold water storage, do it by doubling up on your tanks, with the second tank resting on different joists from the first.

If you're going for an electric shower, it will probably be fine on mains pressure but it's worth checking its spec. and your mains water pressure. Remember that you'll need a high amperage supply cable and fuse ( or mini-breaker) - spec. will depend on the wattage of your shower.