Hot water cyl to cwt min dist for pwr shwr

[wakeyomega]

Hi All
Firstly, I'm not a plumber, so if I'm not supposed to be here please let me know, in which case, apologies and I'll back off.

I am a competent DIY'er (and apprentice trained sparkie, albeit 39 years ago!)

Question.
I am fitting a pump for a power shower, I have a gravity fed system and the pump instructions suggest 1M min distance between the top of the hot water cylinder and the bottom of the cold water storage tank. Because of the quirky way my victorian house is built, the bathroom is on a half landing, the cold water tank is above the bathroom ceiling and the hot water cylinder is on the upper floor. The result of this is that the distance between the hot water cyclinder and the cold tank is only 0.7M. I have limited options to lift the tank and was wondering how critical this minimum distance is? I've lived with this set up for 20 + years for delivering hot water to the bath and sink with no problems. Any thoughts from our friendly plumbers out there? Should I suck it and see?

Thanks Pat

Other
1.The distance between the bottom of the cold tank and the shower head is 500mm, which is double their minimum, so i shouldn't need a negative head kit.
2. The pump will be sited at the base of the hot water cyl.

 

[bathroomboy]

Check out the salamander pump website for installation instruction and advice, also is the cws big enough for the pump, should be at least 50 gall.

 

[wakeyomega]

Hi Bathroom Boy
Thanks for the rapid reply.
I'm pretty clear on the installations requirements of my kit, what I'm really looking for is what the impact may be of having the distance between hwc and cwt 300mm less than the minimum in my paticular installation. Any thoughts?

Thanks Pat

 

[bathroomboy]

I have fitted pumps with the cws being just above the cylinder and have not had a problem, but this depends on the pump you are installing, it may be that the manufacturors instructions are trying to ensure that you have enough head to enable the flow sensors to activate and start the pump, hope this helps.

 

[johnmcginty]

If the difference between the The distance between the bottom of the cold tank and the shower head is 500mm then your pressure will only be 0.05 bar so the cold will need to be pumped too , I take it you are going to pump it from the tank and not from the main ? also 300mm less will mean 0.03 bar differential. and give you only 0.07 bar pressure.

 

[wakeyomega]

Hi
I'm installing the Bristan duraspeed 70 twin impeller (2 bar), so will be pumping both Hot & Cold. The Cold will be from the CWT, via a seperate 22mm flange (e.g. seperate from the feed to the hwt). I was assuming this would give me a balanced feed to the pump.

 

[johnmcginty]

make sure the cold feed to cylinder is higher than the cold feed to the shower. This is a reg to prevent scalding.

 

[wakeyomega]

Good point, thanks for the input

Pat

 

[justlead1]

Hi, I think you will find the reason for min distances is to ensure the pump does not draw air ( pulls water out quicker than goes in.) Increasing the size of the cold feed to cylinder may overcome the potential problem. Good Luck

 

[stevetheplumber]

i would use an essex flange into the side of the cylinder to ensure no pull on the vent rather than the more popular surrey flange

 

[NickH]

Like Justlead says, the likely problem will be that the pump will draw more water from the hot cylinder than the cold feed can replenish and so you will get a tendancy to draw water down from the vent pipe, if this isn't very long then you will draw out all the water in it and then start to suck in air. Its important to ensure that the cold feed to the cylinder is as large as possible, at least 22mm but preferably 28mm. Obviously the pump size is an important factor so dont go mad and put a 3 bar on it.

 

[wakeyomega]

Thanks, I now understand the reasoning. I'll devlop a contingency plan to install a new tank at the top of the house if required.

Thanks again

Pat