Unvented hot water cylinders - pros n cons?
Discussion
We are having some building work done at the moment with a new shower room and the builder suggested changing our current set up (cold tank above gravity fed HW cylinder) for an unvented indirect cylinder. I like the idea to get some HW pressure without using a pump.
Has anyone got any recommendations, thing to watch for? Will the additional pressure expose/create leaks? It is a system gas boiler, so should be easy enough to fit, but at what £ cost for typical installation?
Has anyone got any recommendations, thing to watch for? Will the additional pressure expose/create leaks? It is a system gas boiler, so should be easy enough to fit, but at what £ cost for typical installation?
went for a Heatrae Sadia in 2005 on a 2000 build home.
before that 3 showers with no pumps so was looking at 3 x stuart turners with all the mess.
obviously 2005 was a different time price wise. looked ridiculously cheap looking at what I paid for the kit and then the installation.
nearly 20 years later and never regretted it.
the house is fronted by a water softener so I was concerned at first but no issues.
only breakdown was a cartridge for one of the external valves (the one that increases pressure to 3 bar).
I knew how to empty the system so was able to do that myself.
before that 3 showers with no pumps so was looking at 3 x stuart turners with all the mess.
obviously 2005 was a different time price wise. looked ridiculously cheap looking at what I paid for the kit and then the installation.
nearly 20 years later and never regretted it.
the house is fronted by a water softener so I was concerned at first but no issues.
only breakdown was a cartridge for one of the external valves (the one that increases pressure to 3 bar).
I knew how to empty the system so was able to do that myself.
Greenmantle said:
went for a Heatrae Sadia in 2005 on a 2000 build home.
Hmmm... mine is a Victorian (1890) terrace with some of the original lead pipes in some areas. We are replacing as much lead as possible during the works but they maybe some remaining. I expect it will be able to handle 2 bar pressure as the incoming mains is higher than that.gmaz said:
Hmmm... mine is a Victorian (1890) terrace with some of the original lead pipes in some areas. We are replacing as much lead as possible during the works but they maybe some remaining. I expect it will be able to handle 2 bar pressure as the incoming mains is higher than that.
If you can drain down you can pressure check the piping with a dry pressure test gauge & a footpump.Make sure the installer is G3 certified to carry out the job. Location of the cylinder also needs to be taken into account due to the D2 discharge pipe. If using copper its need to be to spec and discharge to a safe place, if using plastic your soil pipes need to be to spec.
I know this because our new build didn't meet these building regs, the 22mm copper pipe was too long including bends and 28mm should of been used. In the end half the floor was pulled up to use a plastic pipe terminating into a soil stack.
I know this because our new build didn't meet these building regs, the 22mm copper pipe was too long including bends and 28mm should of been used. In the end half the floor was pulled up to use a plastic pipe terminating into a soil stack.
Does anyone know why there doesn't seem to be much love for having a thermal store and a plate hex for the hot water?
It does get away from the need to store pressurised hot water and its relief issues.
I am looking at changing from our gravity fed hot water tank at present.
A thermal store seems to mean that you could also be running the heating from the store that may be heated either by a boiler or 'spare' electrical input from solar.
It does get away from the need to store pressurised hot water and its relief issues.
I am looking at changing from our gravity fed hot water tank at present.
A thermal store seems to mean that you could also be running the heating from the store that may be heated either by a boiler or 'spare' electrical input from solar.
For me at least, I looked at thermal stores, but was put off by the sheer size required. They're also a bit niche & therefore hard to find someone to install and maintain. An unvented cylinder in contrast is common as muck.
I'm also unsure how well a thermal store will function with the lower flow temperatures achieved by a heat pump. I'm sure other far more knowledgeable folk will know more though.
I'm also unsure how well a thermal store will function with the lower flow temperatures achieved by a heat pump. I'm sure other far more knowledgeable folk will know more though.
Considering one at the moment. Had 2 "heat geeks" firms around to quote. Eye watering prices (5k+) but includes new boiler, but no heat loss calcs done just a finger in the air as to boiler and tank sizing. They are supposed to know their stuff, heat geeks, but one didn't even do the flow test properly and spec'd his recommended system with a disclaimer that the flow probably is too low. One spec'd 200l the other 250l. Honestly I don't know why i get "pros" out.
Oh and neither had any concern with pressurising the existing vented pipework but neither, when asked, were planning to do a dry test either. Just deal with leaks as they happen.
Oh and neither had any concern with pressurising the existing vented pipework but neither, when asked, were planning to do a dry test either. Just deal with leaks as they happen.
bmwmike said:
Considering one at the moment. Had 2 "heat geeks" firms around to quote. Eye watering prices (5k+) but includes new boiler, but no heat loss calcs done just a finger in the air as to boiler and tank sizing. They are supposed to know their stuff, heat geeks, but one didn't even do the flow test properly and spec'd his recommended system with a disclaimer that the flow probably is too low. One spec'd 200l the other 250l. Honestly I don't know why i get "pros" out.
Oh and neither had any concern with pressurising the existing vented pipework but neither, when asked, were planning to do a dry test either. Just deal with leaks as they happen.
A dry test would need to be done with the system empty I would have thought and no plumber is going to waste time draining it all down, fitting a gauge and coming back a few days later to check it only for you to get someone else to do it!Oh and neither had any concern with pressurising the existing vented pipework but neither, when asked, were planning to do a dry test either. Just deal with leaks as they happen.
Hi
We looked at getting an unvented cylinder when we upgraded our old gravity fed system and shower pumps, but in the end went for large combi boiler and upgraded the water supply pipe to the street.
Immediately before moving into our current house we rented for six months due to the fun that is the house buying process, and that had an unvented cylinder - which was great aside from the ability of my early teenage children to empty the cylinder of hot water a couple of mornings a week! The recharge didn't take that long, but it persuaded me to get a large combi instead which has been great - decent showers and a simple setup. It's entirely possible that the experience in the rental was due to a poor or undersized setup and my experience isn't typical!
We looked at getting an unvented cylinder when we upgraded our old gravity fed system and shower pumps, but in the end went for large combi boiler and upgraded the water supply pipe to the street.
Immediately before moving into our current house we rented for six months due to the fun that is the house buying process, and that had an unvented cylinder - which was great aside from the ability of my early teenage children to empty the cylinder of hot water a couple of mornings a week! The recharge didn't take that long, but it persuaded me to get a large combi instead which has been great - decent showers and a simple setup. It's entirely possible that the experience in the rental was due to a poor or undersized setup and my experience isn't typical!
londonpob said:
Hi
... and that had an unvented cylinder - which was great aside from the ability of my early teenage children to empty the cylinder of hot water a couple of mornings a week!
Was the boiler running to reheat the water while they were using it? With a decent size boiler the water it should reheat pretty well as fast as you're using it for a shower.... and that had an unvented cylinder - which was great aside from the ability of my early teenage children to empty the cylinder of hot water a couple of mornings a week!
It's not the very cheapest way of using them but for maximum convenience the HW should just be left on. They rarely cycle if water isn't used - ours is off overnight and doesn't re-fire in the morning until water is used as the cylinder stays hot enough.
Sheepshanks said:
Was the boiler running to reheat the water while they were using it? With a decent size boiler the water it should reheat pretty well as fast as you're using it for a shower.
It's not the very cheapest way of using them but for maximum convenience the HW should just be left on. They rarely cycle if water isn't used - ours is off overnight and doesn't re-fire in the morning until water is used as the cylinder stays hot enough.
I don't think so - it would get close to completely cold when emptied and then recover over the next 20 to 30 mins. Sounds like a solution might have been a simple setting away! It's not the very cheapest way of using them but for maximum convenience the HW should just be left on. They rarely cycle if water isn't used - ours is off overnight and doesn't re-fire in the morning until water is used as the cylinder stays hot enough.
I went from a combi to one of these and love it, have 3 kids and 2 separate showers, get great pressure and have not yet run out of hot water ever.
The cupboard it's in is warmer so must have some thermal loss but that's offset by drying kids clothes in there rather than the tumble dryer.
The cupboard it's in is warmer so must have some thermal loss but that's offset by drying kids clothes in there rather than the tumble dryer.
jonwm said:
I went from a combi to one of these and love it, have 3 kids and 2 separate showers, get great pressure and have not yet run out of hot water ever.
The cupboard it's in is warmer so must have some thermal loss but that's offset by drying kids clothes in there rather than the tumble dryer.
Of course I appreciate the benefits of a non-vented cylinder for a larger property, but it's not always the answer.....an adequately sized combi boiler and pipework will be more than able to run 2 showers of good flow rate simultaneously.....we have a 38kW Vaillant combi and that will do the above comfortably with good pressure and flow, without any need for a separate storage cylinder etc.....The cupboard it's in is warmer so must have some thermal loss but that's offset by drying kids clothes in there rather than the tumble dryer.
un1eash said:
Old and new house with thermal store and now unvented only uses 18kw boilers so there will be savings in running costs.
I had friends in smaller properties with combis always asking how come I paid so little in Gas.
Sorry, but it won't be down to the Combi Vs unvented cylinder alone.I had friends in smaller properties with combis always asking how come I paid so little in Gas.
A combi only heats the water it delivers and there are no standing losses, hence a decent specification combi, sized and set up correctly will be more efficient than a traditional boiler with cylinder, regardless of the maximum output of the primary heating source.
Furthermore, (assuming set up correctly), modern boilers will modulate boiler output down to suit the target flow temperature (heating or DHW) and as such run at a minimal output as required, so the boiler rating is, to a degree irrelevant. (e.g. my 38kW boiler will turn down to c.6.5kW, smaller output boilers can turn down much further)
Edited by MattyD803 on Wednesday 8th November 09:40
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