We hope soonish to have one shower upstairs and one shower downstairs.
To do both from stored water and get a reasonable shower we would need a shower pump upstairs. Gravity should be O.K. downstairs with a header tank in the roof.
Alternatively we could have a mains pressure stored water system, or just a simple direct hot water combi. With a direct hot water combi there is unlikely to be the water pressure to work two showers adequately and it would also require a lot of power in the boiler to supply enough hot water. Others have had one shower off the combi, and the second one an electric shower (although that doesn't solve the water pressure issue).
So has anyone gone with a hot water cylinder and loft header tank heated off a combi for the downstairs shower, plus direct hot water from the combi for the upstairs shower? Variation would be both showers (and the bath) off stored hot water and a pump, but all other hot taps directly off the combi.
In many ways this seems to negate most of the benefits from changing to a combi - no tank in the loft, no hot water cylinder, no useless heat loss from stored water in the summer. However it does give you good hot water pressure to two showers, and also leaves the door open to future additions to the stored hot water system such as a back boiler from a stove and solar water heating from the roof.
However we will probably just go with a combi and not use both showers at one :-)
Our first house had a gravity shower on the first floor and the cylinder and header tank in the loft. So probably only about six or seven feed of head for the shower (header tank was fixed some distance off the loft floor on a stage). The valve and head in question were designed for low pressure and worked well enough in some senses. It produced adequate warm water, but no sensation of pressure etc. So its doable with just gravity, although a pump would help.
For both these the starting point needs to be assessment of the incoming cold main here. There are two relevant factors to consider: Static pressure, and flow rate (or dynamic pressure if you prefer).
Static pressure is usually not an issue. If you have more than a couple of bar then that will be adequate. The more critical issue is flow rate. i.e. can the main deliver a volume of water fast enough to meet your concurrent demands?
A test with a bucket and a stopwatch on the best tap in the house would be a good start. Generally if you have 10 lpm or less, then any mains fed system will dissapoint. 15 lpm is marginal but workable IME. 20 is more than adequate is many cases, and 25 - 30 is really good.
Pressure is unlikely to be the limitation - you will notice a drop in shower "sensation" when both are running together, but delivery of water will still far exceed what an electric shower can muster. However you will need enough flow rate to satisfy two showers, and that will mean at least 12 lpm at a minimum, but 15 ish being a more realistic figure. To get that heated fast enough from a straight through combi will mean one of 35kW or better.
When I converted the loft on the previous place, I had to lose the tanks in the loft, and went with a 35kW combi. The mains flow was "adequate" but nothing special at about 17 lpm. One shower in use at a time was excellent. Both at once was actually ok, although you were aware that there was a reduction in flow rate with both going. The boiler however could just about cope, if there were no other demands on it. (one shower and washing machine or dishwasher filling was noticeable but tolerable, two showers and any other hot water user would mean two tepid showers!)
It probably would in the sense that even the most powerful electric shower will not usually muster more than 4.5 lpm. Add that to the 6 - 8 lpm typical of a mixer shower, and you are still within the capabilities of most water mains and pretty much any combi - even an wheezing old
24kW one.
Its a workable solution. There is the limitation that the combi can only run heating OR hot water in most cases, so using the upstairs shower will proclude reheating the cylinder. This is not an issue if its big enough to meet all your days demands from storage, but may be a problem if you are relying on reheating a small cylinder on the fly to keep up with demand.
Yup. Or unvented stored hot water, and everything from that.
As with all these things you need to balance your requirements, circumstances, and costs to arrive at a solution that works for you. Arguments along the lines of "Solution x is better because..." usually omit relevant detail to make the round peg fit the square hole!
A heatbank/thermal store would be yet another option. Big tank of water heated from whatever source is handy, but then used indirectly to heat incoming mains water. Needs good mains flow rate, but gets round the problems of power limitations of the combi, no need for routine servicing and maintenance on the protection systems on an unvented cylinder.
Another option... ;-) (although depending on the number of people in the house, not always as easy to enforce)
I'd have stored hot water *and* a booster pump for *both* showers - and just use the "instant" water from the combi for kitchen sink and wash-basins.
In my main home, I've got two pumped showers - admittedly both upstairs
- and they work fine. In my holiday flat. I've got an un-vented hot water system which feeds the shower directly. The shower is ok - but nothing like as good as as the pumped showers here. I wouldn't want to try to run two showers at the same time from it.
[OK, you could pipe everything in 22mm to try to increase the flow - but you're still limited by the rate at which the mains can supply water.]
fwiw a drain heat exchanger on the 2 showers would reduce their hw demands, enabling less hw storage volume, lower power boiler and lower hw flow rate, as well as reducing run costs.
I sure this has been covered before but the energy that can be recovered from waste water is pretty minimal in domestic situations compared to the cost of recovering it, even if you DIY it. Shower water in particular gives up a lot of its energy to the air and shower tray before it goes down the drain.
I've done it in a house where a builder had installed a combi in error, beside a 300 litre mains pressure water heater. The cylinder is wired as a heating zone on an s-plan plus system, with a suitable timeswitch/controller.
A gravity system is adequate for everything, but the shower pressure is deemed inadequate by some. A combi supplying one shower would be my choice. Pumps do what they're meant to, but are still very noisy.
Not exactly. I have a combi boiler that heats a stored hot water tank. The header for the HWC is in the attic (2nd floor). I have a shower on the ground floor and one on the first floor. Both wonderfully decent pressure and heat at the same time. None of this ridiculous /either/ hot water /or/ a decent water stream.
(The HWC is actually in the cellar, but that makes no difference (it's the header tank that does) other than giving a bit of heating to the cellar. It used to be in the first floor bathroom.)
I don't see why your upstairs shower pressure is inadeqate. You've said the header is in the loft, that should be enough pressure for a first-floor shower, unless you've got lots of kinks and contrictions in the piping. My header tank is about four feet off the floor in the attic, so about six feet or so above the first floor shower head.
It /may/ be better the other way round. It depends on where the boiler/tank is relative to the draw offs, both in length of pipe, and head.
I've toyed with (when system boiler replacement is nigh) of combi to downstairs util and kitchen and tank still feeding bathroom upstairs, or the other way round. Pipe runs are in favour of the first, and pressure in favour of the second.
I may end up with a heatbank (and system boiler) for both. or either of the above combi solutions.
I've done it in a house where a builder had installed a combi in error, beside a 300 litre mains pressure water heater. The cylinder is wired as a heating zone on an s-plan plus system, with a suitable timeswitch/controller.
You put in zone valves? Was the combi suitable for hot water in the cold inlet? If so.... The unvented cylinder could be heated directly by the combis water section set to 60C DHW. Have a bronze pump on the cold inlet switched by the cylinder stat. The CH off the CH flow and return. Simple! And reheat the cylinder zippo as it is direct and puts 60C at the top of the cylinder.
Even heating the cylinder via its coil from the CH section of the combi, as per a normal system boiler, one shower can be off the combi if two in the house. Then one does not interfere with the other.
That's a proper dribble solution... theoretically possible, but fraught with potential gotchas, and added complexity for marginal gain... Not had one of those for ages, just like old times ;-)
A better solution, and ok if the mains supply can keep up. You might be better off just using a bigger cylinder in the first place so that it can cope with water for two showers.
If the system is main pressure then all depends on then mains supply. Cylinder size is irrelevant as all goes down one mains pipe. A bigger cylinder means more expense...and space.
Combis are about the same price as system boilers yet few ever think of using a combi and the water section for one shower. The cylinder can have summer/winter stats so that only half is heated in summer saving money in heating - if showers are only used in summer.
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