Hi All,
I plan to renovate my toilet. Currently using instant water heater so I plan to change to storage water heater. I have a few questions

This is my original piping plan from developer. My shower is directly from main pipe so no pressure issue.




If I want to add storage water heater, what is the correct connection should be. Option A, I keep existing plan just add additional copper pipe to the mixer for shower and water basin




or option B where I connect the shower to the water tank instead of main pipe




what are the pro and cons? I'm thinking of option A should be ok since I've been using main pipe as my shower with no pressure issue. Do I still need a water pump for option A? if yes, where do I put it? before water heater or after?

why can't your storage tank direct from main?

I don't know, should it be from main pipe? From what I read around mostly say from water tank.

Where you intend to install water heater tank? Also if option A no shower when main no water

some people uses tank purely for standby purpose.

your house, your decision but taking into consideration, why not consider a pump after water tank?

Its not advisable to use water direct from outside main immediately to your water heater storage tank.

This is because in the event of water disruption, and you accidentally left the heater turned on, the heater unit would overheat and you would end up with a burned fuse...which costs RM100+ to replace (price inclusive of water heater tech installer)

From my point of view, both your plans: A & B will work. Depends on how much work it is to create additional piping + expenses if you decide to go with B.

Ultimately you'll have to weigh the pro and cons yourself (cost, hardship, mess, etc)

Option B, basically SH inlet take from water tank, SH heated output to mixer tap (eliminate risk of dry burn), and for cold water you can either use from mains or water tank (no risk) to the mixer tap.

Any water heater instant or storage pls ensure to have 10mA RCD/RCBO installed at DB box. Statutory requirement. Without it can die one.

This post has been edited by ceo684: Mar 2 2021, 04:18 PM

Please check if you facing any pressure problem from tank itself. Base on both Option A & B, the SH is connecting to tank, you might need a pump if the pressure is insufficient. The pump will put right after the tank and before SH, and you can use the pump for all water lines. SH usually install above/near to the ceiling and not too far from the mixers.

Option A - If water disruption in the middle of shower, you might get burn because no cold water reach the mixer.
thus i would recommend option B, to get water from tank

For mixer, you cannot have cold water from main and hot water from water tank (through storage water heater) as both water pressure differs, won't work as intended even with check valve.

i dont think there will be enough water pressure to have a good shower experience in b

if you want to install like a, make sure there is a check valve at outlet of water tank. even better if you install a pump.

Thanks all for the replies. Water disruption is very uncommon at my place, so I'm not too concern about it. My main concern with option B is water pressure for the shower may not be sufficient. Adding a pump is an option but I'm afraid extra pressure will cause leaking in the future. the existing piping in my house is quite old, does additional pump will put more stress to it? The tank is connected to 3 bathroom, I don't have the budget to change all the piping to newer one.

Hi, can you explain a little bit why it wont work? what is the drawback if mixing main pipe cold water with hot water from storage heater?

Yes, pump will cause additional stress. It is recommended the pressurised section pipes are easily accessible and not all buried inside the wall. It definitely increase the chances of pipe joint leaking especially with PVC pipe.

Depending on the pressure (standard PVC pipe takes 4bar Syabas water no issue)
you may need to upgrade to either Class 7 PVC pipe, (not the elcheapo class 0 thin wall pipe)
or change to High Density Polyethylene HDPE Pipe 25MM x 100M PN12.5 PE80 (SIRIM) - meaning this pipe can support up to 12.5bar

Spec wise - https://www.engineeringtoolbox.com/pe-press...ades-d_668.html

This post has been edited by ceo684: Mar 2 2021, 08:31 PM

or you can get pump that can select pressure.........

grundfos scala 2 can go as low as 22 psi or 1.5 bar......which is lower than incoming water supply

I think it's because of water pressure differences..?

My house both cold water and storage heater are connected to main pipes (higher pressure). So when you turn on shower both are push by the same water pressure

I think you either choose both from main pipes or both from storage water tank (cold)

You can Google 'Hot cold water pressure mixer different', there's quite a lot of information.

I installed quite a few sites, both the hot and cold water pressure are different, you can't really control the mixing properly with the mixer as the source with higher pressure will limit the other source.

thanks all. man I thought it would be straight forward to re-pipe just for the water heater lol. Who knew the water pressure difference will impact so much. I really not keen on connecting the storage heater directly to main pipe, as others have mention it may cause issue if there is water disruptions. So I was browsing through YouTube, and found this method where they install check valve (basically its like 1 way valve) where they connect the main pipe and tank pipe together. so in the event of water disruption it will use the tank as water supply. is this better? Does check valve last long or it requires frequent maintenance?

I haven’t experience any check valve failure before. Make sure to use good quality ones.

A check valve plus a stopcock is recommended at the grey pipe before the storage heater.

Reasoning for stopcock is to shut off water in case of storage heater leakage or maintainence and the checkvalve is for prevent back flow of water to mains in case of water supply disruption. Although the water meter has a built in check valve, I won’t trust that one.

yes, agree on the check valve and stop cork at the main pipe. I will add that as well. I guess this settles all my questions. Thanks all!

Dear sir please save your money if you are not going to change the old pipes.
That new storage heater will not last more than 5 years before the inside are fill with corrosion and heaters burnt out.
I learn it the hard way. Had to change the pipes and buy a new storage heater.

You will still need a water pump, but most important also a water filter to help prevent the water heaters from dying faster than normal.
And nowadays most storage water SHOULD have a safety switch that prevent dry heating - when there is no water supply.

Hope my bad experience help you.