We're having a loft conversion, with an en-suite shower room. We're looking at showers and getting confused. The plumber is not particularly helping, so I thought I'd throw it out to the empeg brain trust.

Our existing bathroom has a mixer shower. The house has a combi boiler.

We've ruled out a power shower because you can't use them with combi boilers apparently. Is this true?

Similarly, we can't really use another mixer shower, because the combi won't be able to provide enough hot water if both showers are running.

This leads us to look at electric showers. My understanding is that they're only connected to mains-pressure cold water, which doesn't go anywhere near the combi boiler. Is this correct?

Given this, our plumber's assertion that we won't be able to use the mixer and the combi at the same time seems a little odd, given that the mains water pressure seems to be plenty high.

I'm confused. Can we use an electric shower or not? Can we use it at the same time as the mixer shower?

Another question: I saw a recommendation (in Which? magazine, I believe) that recommended thermostatic controls. These, theoretically, deal with a drop in the water pressure and maintain the temperature, so that you don't get alternately frozen and boiled when someone runs the cold tap in the kitchen. However, given that the electric shower runs from a single, cold, feed, what's the point?

And, while I'm here, does anyone have any shower recommendations?

Things are different, to say the least, over here, even in rural areas that don't have their own gas supply to run a boiler and pull their own water from a well. But at the end of the day, heating water is heating water.

Ignoring everything else for the moment, you mention a capacity issue which sound like it's boiler-specific, not pressure-related. In that case I'd start first by replacing the boiler if it's feasible, with a more powerful unit. I'd think once that's done you'd be able to install whatever plumbing you'd like to get you both hot and cold supplies at your shower.

This is the kind of boiler that fires up only when water is flowing through it right? AKA, "on-demand water heater" or "tankless water heater" here in NA, such as those produced by Bosch, Takagi, etc.

BTW, in a very quick search I've found power showers (a pressurized shower system) that works with both your hot and cold supply. But it's suitable only for a low-pressure supply.

The municipal water supply pressure around these parts is relatively high. When I lived on a rural property with our own supply we had a large pressure tank to serve the entire house, so every plumbing fixture in the place, including showers were quite standard affairs. It seems like picking fixtures is a lot more complicated in the UK.

I don't have a whole lot to offer, but, wow, plumbing culture in the UK sure is different from the US.

I assume "mixer shower" is one where it takes cold and hot water supplies and mixes them together to achieve the proper temperature. So, a standard shower in the US.

I had to look up "combi boiler". This appears to be a tankless water heater that also provides hot water for radiators (or other water-based house heating systems).

You use both of the terms "power shower" and "electric shower". It seems that an "electric shower" is a shower head that has a builtin heating unit. Do you mean "power shower" to be the same thing, or is it one that has a pressurizing system?

I don't see any reason that an electric shower would have any dependency on the water heater at all; it completely bypasses it. The only thing I can think of is that both of them would be large electricity consumers and maybe your service doesn't have the capacity to run them both at the same time.

I have a feeling you misspoke here: "we won't be able to use the mixer and the combi at the same time". Did you mean the mixer and the electric shower? If so, again, I don't see why not, other than power consumption. Have you asked your plumber why?

As to the thermostatic controls, if you're referring to the electric shower, if the pressure drops and you don't have a thermostatic control, that means that there would be less water flowing through the system, but the same amount of heat being generated, which would cause temperature fluctuations. I don't have experience with these systems, so I don't know how significant they would be. As for mixer showers, they have had passive pressure matching technology for decades now. Thermostatic controls are only useful if you specifically want to set a particular temperature, rather than fiddle with the mix.

I believe it's all got to do with flow, and thus the diametre of your pipes. I believe with 'power shower', you mean one of those 'raindance showers'? If yes, then it's like so that those kind of showers require pipes with larger diametres than come standard in houses (in Belgium this is 16mm, a raindance shower needs at least 22 mm), otherwise the flow is too limited and you'll never have a good shower experience.

An electric shower should work, since as you say it's only connected to the cold water pipe and completely bypasses the boiler. But again, here also applies: if your pipes are not wide enough, the flow is too limited, hence and electric shower also wouldn't work (well). Also take into account that, if the piping in your house is more than 10 years old, the inner diametre of a pipe becomes even smaller because the water continously adds layers of calcium to it (unless you've installed a water softener of course, which I would highly recommend!).

It is true. The difference between an "electric shower" and a "power shower" is that the former has a heater but no pump, and the latter has a pump but no heater. If you have a combi boiler, your hot water system is mains pressurised, and you're not allowed to pump the mains because that's unfair to other consumers. (A power shower pumps water from the hot water tank of a conventional boiler system, which is not mains pressurised.)


Yes.


All electric showers have thermostatic controls. Many power showers do. The new thing is (passive, mechanical) thermostatic controls for mixer showers.


I don't see why not.


If you're doing that, you probably want thermostatic controls on the mixer. The mains pressure will drop a little when the electric shower comes on, and it might affect hot and cold pressure differently.

Peter

To add to what Peter has already said, you may also find that if you are using the electric shower and someone starts to use your existing mains fed shower that the drop in pressure will knock out the heater on the electric shower for a time. This is to prevent the heating element from over heating the water (which is now flowing slower through the element) and burning you.

If your water pressure is good you may be ok, but if you think about it you will be taking quite a lot of water with both showers running at the same time.

Your plumber is right about having 2 mixer mains fed showers in the same system, especially off a combo boiler. I have 2 in our house (fed from a tank actually) and if you use both showers at the same time only the one on the middle floor gets the hot water, the ensuite goes cold as the pressure is released through the path of least resistance. I was told this would happen when it was plumbed in, the solution is not to use the 2 showers at the same time.

Cheers

Cris

I'm thankful we can run 2 showers, a washing machine and a dishwasher all at the same time off municipal supply pressure. Of course since we have a tank-based water heater, the hot water will run out if those showers go long.

I'm actually planning to replace the tank, as like in all newer construction here is a rental (what a scam). Instead of replacing it with another (but better) tank, I may just install a Bosch tankless system, with enough capacity to heat two showers.

Peter can't really help you , BUT if your plumber can't help either then change plumbers. He should be able to advise on the basic mechanics of what you can and can't do.

I have nothing to add except if you get an electric shower, I highly recommend the Mira Sport Max 10.8Kw. Its on par with a mixer. You do need 10mm cabling though.

!!

Two 10-minute showers per day (one for me, one for SWMBO) would nearly double my electric bill, from $183 per year to $319 per year. And yes, we have discovered through pleasant experience that sharing a shower does NOT save any hot water, since the time spent uhhh... showering increases dramatically.

If I hadn't already taken steps to minimize my electrical billing, that heater could easily end up more than tripling my annual electricity cost because of the punitive rates applied to high usage here.

BTW, I consider those punitive rates to be a Good Thing (tm) in the interests of conservation. My across-the-street neighbors have a large swimming pool, heated with passive solar (black pipes collecting sun on their roof) but with all the pumps and filters, etc, plus being a large house where they are careless with lighting, their electric bills run more than 15x mine. They are perpetually on the DAC (Domestic Alta Consuma) rate so in addition to their using a great many more kWh than I do, their rate per kWh is nearly four times mine (2.52 pesos per kWh vs. my rate of .71).

There may well be more economical methods of heating shower water, depending on where you live and what your various utility rates are.

tanstaafl.