15mm hot water supply to existing 22mm piping - problems ?

[3point14]

The piping from my old immersion heater tank is 22mm (or imperial equivalent) for some length before reducing as it feeds different places and the outlet from my proposed instantaneous water heater replacement is only 12/15mm.

I do not want to rip out pipework unnecessarily but canI live with this, just stepping up from 12mm to 22mm and leaving the existing pipework where it is ?

Cheers

 

[Agile]

You can but at the disadvantage that it will take longer, waste water and gas, before the water comes out hot!

If you are not going to replace it then at least lag the hot pipes.

Tony

 

[3point14]

I take your point on the lead in cold water but we'd have that to get through in any case, though pushed through at 22mm and not 15mm I agree, thus delaying somewhat the hot water at the faucet / shower head.

New system is electric (as is old, no gas on site). Stiebel Eltron DHF 12C1 http://www.directtradesupplies.co.u...heater.html?___store=default&___store=default

 

[Agile]

I would never make that change!

As electric then the advantage of making the water pipes 15 mm is far more important.

Tony

 

[3point14]

Wouldn't change what ?

Current system is defunct or thereabouts, putting in a new immersion heater is just old technology (and always limited quantity) and I've used instantaneous heaters for years with great success.

I would obviously prefer 15mm pipes all around but that would vastly increase the budget and at the moment, I'm trying to keep it all down as far as possible.

I've just got some 22mm piping out ofthe old heater with compression fittings on it and I can self plumb this in with 15mm to 22m at near zero expense versus bringing in a plumber and so forth.

Might not be perfect but I'm hoping it will do.

 

[looneyfitter]

You may also find that you get a drop in water pressure in the hot feed to the bath etc. I would recommend you change the pipework to 15mm.

I cant understand why you don't want to use an immersion and tank?

 

[3point14]

You may also find that you get a drop in water pressure in the hot feed to the bath etc. I would recommend you change the pipework to 15mm.

I cant understand why you don't want to use an immersion and tank?

Why would there be a loss of pressure ? As I see it, the current piping is 22mm down to 15mm. The proposed will be 22mm to 15mm to 22mm (short run) to 15mm. The minimum size remains the same in both cases.

Why would you use an immersion and tank ? You limit the amount of hot water you have. You have a quick tail off in temperature. You have to heat water you may not want. You have to wait. The list goes on an on with negatives.

It is old technology for a bygone era.

 

[looneyfitter]

Will you not be feeding your water heater off the 15mm cold main? Most gravity hot water installations will be in 22mm, especially to the bath, thus if you pipe from 15mm to 22mm you have an increase in volume, decrease in pressure.

How big is the water heater you are proposing to fit? L/kw? A good insulated indirect cylinder shouldnt cause any problems if sized correctly. Why not go invented?

 

[3point14]

In an ideal situation I'd invest more money and effort and do a complete overhaul but the property is rented and we'll not be there that long, though long enough to benefit from these modifications.

I am not removing the current immersion tank (decades old) and I can either tap into the 22mm (or near imperial equivalent) just before the heater or more easily just tap into the outlet (also 22mm), essentially placing the new heater after the immersion outlet. I can then easily return the original piping when I leave.

The water heater is 13.2kw.

So the only 22mm piping I will have after the heater is a couple of metres before it reduces to 15mm. By my reckoning, this 22mm pipework after the heater, between two 15mm sections, will not reduce the flow at all as it will always be full.

It will mean a delay in hot water feeding through but I cannot escape that I am afraid.

 

[looneyfitter]

You will need to isolate your cylinder from the heater as the water heater (I presume) is mains fed? If you want to do it the way your suggesting, then you would need to fit a 22mm gate valve, double check valve then another 22mm gate valve before the 22x15mm tee your going to fit on the hot out of the cylinder ( after the expansion ) !!!!!!

If it's As you say, 22mm then 15mm feeding everything including the bath then you should be ok. It's rare you would only find 15mm at the bath tho.

Also what type of flow rates does your heater give? 15kw is still An awful lot of power over short periods. May want to do some math matey.

 

[3point14]

I don't get your logic I'm afraid.

There is a 22mm supply to the existing immersion tank. I simply propose turning that heater off, letting water flow through it at mains pressure and tap into it at the top, which is nearer where I want to join the new heater.

Then simply put on a 22mm to 15mm tee and hook up the flexi hoses from the new heater. Do the same at the output end. I don't see the need for any gate or other valves.

Heater gives 7.9 l/min at 38c and 4.6 l/min at 55c. Max 13.2kw.

 

[looneyfitter]

So you plan on putting mains pressure through you immersion tank and then tapping off that to your new heater?

If that's the case, I suggest you STOP what your doin right now and getting someone in who KNOWS what there doing!!!!

 

[looneyfitter]

Problem solved then?

 

[M0NBRAVE]

I was fascinated to read the above exchange initiated by 3point14. Going by the information supplied, I can't see any problems and the replies seem largely irrelevant. Yes, there will be slight changes in time lag and heat loss but these would be minimal over such a short distance.

Before running the cold water supply through the existing water tank, of course you want to be sure that it is tight and can hold mains pressure. If in doubt, by-pass it!

I would be interested how you get on. I am about to fit the same instant heater (Stiebel Eltron), mostly because it is the largest capacity (13.2 kW) single-phase unit I could find.