No. Get a model that operates on low pressures.
You can fit an auto booster pump from the tank to the combi cold inlet, eliminating the cylinder. It comes in automatically. After the pump, tee off this pipe and take it to cold on the shower and higher pressure shower. This should be the only tee off on the combi supply pipe. Look at:
Also with a cold water tank supply, the flowrate will higher as the water temperature is the tank is usually far higher than the cold water mains. This means the combi doesn't have to raise the water temperature so high giving higher DHW flowrates.
Would plumbing in two cold water supplies to the kitchen come from the same school as your twin combis? Your hacksaw must be red hot.
Please eff off plantpot.
Right, we're getting somewhere! I now have the pressure gauge and took a couple of readings from the garden tap:
11pm: 1.8 bar 8am: 1.6 barIf we were to put a larger diameter pipe in from the main inlet do you think this would be enough for a good shower with just a combi?
That does not look promising... but it is difficult to do any calculations without knowing things like the length of the pipe, and the standing pressure in the main at the other end of it.
no because at that static pressure the water will hardly reach the upper floors.
Jim A
Does he live in a block of flats?
You need to know the flow rate too.
At the top of the first floor shower head the static head will be down to about 1 bar and we have earlier established the flow was very poor. My point is it's hardly worth the expense of trying to improve the flow through larger bore supply pipework since the residual static pressure would remain poor where it was required in the OPs original brief.
Jim A
Must have many floors or high ceilings then. 1.6 bar will reach 50 feet. 3 average floors up it will still be higher pressure than that available on the ground floor of a 3 storey house from a loft tank.
But you miss the point of what is the residual static pressure at the storey height and the achieveable flow rate which was extremely low even at gf level. A proper storage solution can deliver a designed flow rate including a pumped shower solution. An enhanced supply pipe option may or may not match that performance at some considerable cost.
Jim A
What is important within the house at the end of the day is the flow rate. And this is determined by both the pipe size, pressure and of course any restrictions caused by the pipe runs and taps. With mains this is usually fixed by the incoming one - which can be changed, at a cost, if the flow rate is too low. A storage system should have the correct sizes etc as part of the design. What can be a problem these days is sourcing taps designed for low pressure - most seem to be made for countries which have a higher pressure than the minimum in the UK.
Thanks for all your replies. I'm still unsure which system will work best. Here's an overview of the project.
3 storey victorian terraced townhouse in London Toilet on the ground floor, bathroom with a shower on the first floor Pressure on ground floor is 1.6 - 1.8 bar depending on time of day Flow rate from kitchen tap (ground floor) is around five and a half lpm Main water pipe in the house is 15mm Existing heating system is 15 year old gas boiler on ground floor, with cylinder and tank on first floor and a further small tank (for rads I think) on the 2 floor.Issues:
Aims:
1, Good shower (essential)We are ripping out the ground floor so we will replace the boiler. The question is, what type of system should we install? Some people suggest that 1.6 bar won't be enough pressure for a good shower on the first floor, but if it drops to 1.3 bar (3m additional height) would that not be enough? We would replace the main 15mm pipe. That's the equivalent of having a tank 13m above the shower right?
If we have to go for a storage tank and pump, can you tell me exactly how it would be setup, and would we still use a combi??
Cheers.
Unless it has been upgraded it's probably lead and furred up.
Not quite that simple. The 1.6 bar is a static pressure but flow through any restriction results in a pressure drop. Stick your pressure gauge on your garden tap, run your 5.5 lpm from your kitchen tap, measure the pressure and report back. As a matter of interest what is the flow rate to your DHW header tank?
Jim A
Pretty well the same as me - including the poor mains pressure.
Ah. My storage tank is near the top of the house.
I have an Aqualisa designed for low pressure. It has 22mm feeds to it. The flow rate is superb.
Right - then the only real option is to go to a combi if you need to get rid of both.
You can increase the flow by having the incoming main replaced - if you're certain that's where the restriction is. You can also use 22mm pipe to help flow to critical areas like the shower etc. And choose a shower specifically for low pressure use.
On my storage system I do have a pump - but just for the kitchen hot water where the 'designer' tap is designed for high pressure. The one before it was fine without it.
There is another problem here that will affect any type of system. If the available static pressure can only achieve under 6lpm at ground floor level, how fast will it replenish a loft cistern? It will need to be a big tank, and you will hear water dribbling into it for ages!
I did as you suggested, and when I turn on the kitchen tap the pressure reading drops a tiny amount, less than 0.1 bar.
Also I tested the flow rate of the garden tap - 8 lpm. This suggests that the kitchen tap/pipework must be restricting the flow.
I think I would be inclined to talk to your supplier and see if you can get them to agree that the supply is not good enough. Otherwise you are between a rock and a hard place.
Getting acceptable performance could work out quite expensive. Upgrading your supply pipe looks like it will be necessary regardless of the type of system you go for in the end. Having done that you may find the flow rate rises to the point where a combi would be feasible, or you may have to stick with a storage system and use a pump for adequate shower performance.
With that data, even after upgrading the mains pipework you wouldn't have a good enough supply.
You will have to have traditional (storage cistern) based plumbing. You will be able to use a booster pump to get a good shower. Although with the shower(s) on the lower floors and the cistern in the roof space you should be able to get what many people would think was quite good.
You might not even have to change much of the existing equipment. You need minimum 22mm feeds from the cistern to the HW cylinder and the shower room, a wide bore shower hose and carefull selection of the shower head. Slightly less care will be needed with a boost pump.
If you had less incoming pressure you would also have to look at arrangement for boosting the mains pressure.
Alternatively you could look to work with a cellar/ground floor booster set (Armstrong Pullen is a possible manufacturer) the idea being that a low level cistern is installed and a powerful negative head (i.e. output pressure drop activated) pump is used. After which you can use whatever plumbing/heating system you wish. Normally this sort of equipment is used in medium sized blocks of flats.
HTH
Only partly. Fraid the 0.1 bar result indicates the main restriction is between the kitchen/garden tee-off and the supply side.
Jim A
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