Hello! I'm rennovating a house that I intend to rent out. Essentially I have two bathrooms, each of which is going to have a bath with shower over. I want to be able to run both showers at once (as there will be six people in the house), and my plumber thinks the only way to do this is with electric showers. Does anyone know if there's a way to run two showers (with thermostatic mixer valves) at the same time off the one combi boiler I'll be putting in, or is my plumber right?
It is extrremely doubtful that a cheapo combi will have suffuicuinet power to heat two showers going flat out simultaneously.
Combis I have expereinced struiggle to geat evben one, but then, I am not a fan of combis
The solution is eiher a much bigger combi to cope with peak demands, or a heat bank - which is basically a fancy name for a sort of hot water tank- or a mains pressure boiler and pressurised hot water tank.
Cost and avaiable space will decide which is your best option.
What I tink is teh worts of all possible worlds ins a normal un pressurised system with hot water cylinder and elkectric pumps to get teh pressure.
I costed out various alternatives in my build, and space not being a problem,. decided on mains pressure boiler and hot water tank. Even that struggles with teh whole family here for holidays etc. I like a huge hot bath, and that takes about 50% of a tank.
I susp[ect a BIG combi might have been cheaper, but even then two shower max seems to be the order of the day.
I had little space for boilers but a lot for a water tank...so there ya go.
There is another advantage of fitting an electric shower in this scenario... as you have no immersion heater, consider what happens if your combi breaks down: your 6 tenants are without any form of central heating or (more importantly) hot water. You'll be frantically trying to get an emergency plumber to fix it; and what happens if he can't get the parts for a couple of days? Answer - you'll be footing the bill for alternative accomodation for your tenants.
Having an electric shower, completely independent of the combi, gives you a bit of flexibility at least if the worst happens: at least the tenants can still wash!
He is wrong. Divide and rule. Try two combi's. one doing one shower, one doing the other. Combine the outlets for the baths to fill them quickly, using non-return valves and a shock arrestor on the bath side on the non-return valves.
Have one combi do upstairs heating and one do downstairs. Simple and cheap and effective. Have each combi have its own gas supply right back to the gas meter.
Check the mains water pressure and flow. Replace the mains stop c*ck with a full-bore stop c*ck irrespective, and have dedicated 22mm cold supplies to the combi's from the stop c*ck. Take the cold supply for each shower off the combi supply just before the combi. Any pressure fluctuations on that line will be equal on both cold and hot at the shower.
Combi's are cheap.
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Hi Ellen, We successfully run two showers at the same time from one combi. It's an oil-fired Trianco unit. Basically the flow rate reduces when both showers are in use, but they are still perfectly usable.
As one of the other posters said, even when used like this the flow is still comparable or better than many electric showers I've used.
One of the showers has a thermostatic mixer (the kids use this one), while the other has a manual temperature/flow control. If you're using the thermostatic one the only thing you notice is that the flow slows down a bit. When using the non-thermostatic one you need to turn it a bit hotter than normal to compensate. They're both in use most mornings as eneryone tries to get freshened up and out of the house at the same time!
A cheap combi will give you a twin shower effect on a par with that achieved by using an aged and incontinent rat in place of the shower head. Two electric showers (assuming you have a single domestic supply to the house and need both to operate together and with other appliances on) may have to be so small that their effect will be even worse.
There are a lot of issues here regarding adequacy of electric supply (for 2 electric showers), adequacy of cold water pressure, adequacy of gas supply at boiler for large combi or (whispering) 2 combis.
But to respond to your specific question it may be helpful to look at electrical shower outputs. These are commonly 8.5kW, 9.5kW or 10.5kW. A combi is 24kW, 28kW or 35kW electrical equivalent. So in heating terms a combi produces more hot water than 2 electric showers. If there is good mains pressure it should be easy to equitably share the flow by plumbing the showers in small enough bore. IME the Screwfix bar mixer works well across a range of pressures. Of course you have got to stop the other bath grabbing too much water as well. Its really a design problem which is probably why the plumber is struggling. He may also know a friendly electrician because for 2 electric showers you will definately need a good one. If there is poor cold pressure you are stuffed either way.
Anyway its rented accomodation, has to be safe but who says it has to be good? Or have matters improved since I was in rented accom....
Combi's are one box solutions, the simplest and easiest method of installation. This place is to have 6 people showering in the morning. Say the average shower is 100 litres of hot water. That is a 600 litres of water requiring storage. A hell of a lot. Even 500 litres is a hell of a lot, and expensive to provide storage for, with maybe the floor requiring strengthening. Only combi's with their infinitely continuous supply of hot water can provide the solution to this problem economically. Two combi's. One for each shower, join the outlets for the baths. Everyone satisfied, no digruntled tenants, no running out of hot water, and also backup. If one combi goes down, one will work giving a shower. So they will have to wait longer for a shower for a few days, but at least there will be hot water and heat in the house.
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A domestic supply gas supply can provide 212 cu foot an hour, about 62kW input. Two properly sized combi's can do the job no problem, with the average around 27kW.
This problem is crying out for two combi's as the solution.
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In this case, provided the cold supply is adequate I wouldn't dismiss the suggestion out of hand, neither would I advocate it. Although there is redundancy and you could employ smaller cheaper combis, two maintenance contracts would be required. That's a business case issue for the renter. As I said its really a design issue. There is more than one solution depending on the weight given to various factors.
What happens if either the gas or power fail, result no hot water unlike with a storage tank, OK there is only a limited supply but every one will be able to wash using flannel, soap and a bowl....
I also suspect that after the cost of running two water supplies from the company valve, two gas supplies from the meter together with all the extra CH/HW pipes one could have installed a large boiler and storage tank.
It's also crying out from an up rated electricity supply and electric showers, and if there is going to be more than one kitchen with full cooking facilities then that alone will probably mean that the cost of having the electric intake up rated has already been budgeted for.
It's also crying out for a storage tank so that there is at least some hot water if there is a major breakdown of either boiler(s) or power, also a storage tank will allow water to be heated in an emergency by electricity (although expencive it will be cheaper than pitting up to six tenants into a Hotel for how ever long.
This is not a clear cut plumbing decision, as someone else has said, it's a planning / business decision as well.
First, check the water psi in front of home; divide by two. Hot water usually comes out at lower psi than cold. Now, call your water supplier, ask them what is the psi to the water meter at your rental. If psi is 60 but 20 feet from the meter coming from your hose spigut, the psi is 40, than dig up water meter and take out old pipe.
You could, with a bit of plumbing have an unvented cylinder for the showers and baths, heated from the heating loop output of the combi, and just use the DHW output of the combi for kitchens. That way you can have lots of hot water for the baths and showers and still use the combi. Small note you will need a pressure ballanced type of shower mixer.
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for cylinders a 210L or 250L one. If the mains cold water flow is poor then you could have a conventional hotwater cylinder, aagin heated by the heating loop of the combi.
Point to remember, when the combi is heating the Domestic hot water output, it will not be heating the house, heating a bath can take some time and the house may get cold. A mains pressure hot water cylinder will need anual serviceing, and a large notice DO NOT TAMPER.
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