Hot water tank cold water feed NRV

[Peter]

Fitting a new hot water tank, one question do I need to fit a NRV to the tank cold water feed, as 2 sets of fitting instruction give different advice, one to fit one, the other no real advice either way.

Peter

 

[pvb]

Yes, it's a good idea, but then you ideally need an expansion tank on the hot outlet.

I fitted a new calorifier a year or so ago, without an NRV on the cold inlet, and I find I get hot water out of the cold tap for a while. I've bought an NRV, but general sloth has prevented it being fitted yet.

 

[nedmin]

Last 2 boats I,ve had do not have a non return valve.Why put in another complication.

 

[nedmin]

Not sure what you mean by an expansion tank on hot outlet.You need an accumalator on the cold side to keep pressure constant.

 

[Sandyman]

The purpose of a NRV is to prevent hot/warm water gravitating up into the cold tank.
This does not happen on all systems. It depends on the pipe layout.
I would fit one. Its a simple device & not likely to cause problems.

 

[Jean]

Better to get the pipework right (to minimise gravity circulation), but if you do choose to fit one, remember that the pump head will have to overcome the NRV spring, and this can be quite significant, so much so that the flow rate may be much lowere than without it.

 

[Golf Charley]

They are used on domestic installations to prevent contamination of the supposedly clean mains water, with water from your hot water system header tank in the roof which may have a dead pigeon or mouse in it.

If you rely on your water tank for drinking water, it would be advisable to fit one, and they are not expensive. If you have microbial activity in your water tank, adding heat to it will only make the microbes breed faster

 

[Golf Charley]

Jean makes a valid point with regard to plumbers merchants type fittings.

The squeeze bulb of an inline fuel pump, as used for an outboard, contains a simple rubber (?) nrv, so no "spring" to overcome

 

[david_bagshaw]

Fitting a new hot water tank, one question do I need to fit a NRV to the tank cold water feed, as 2 sets of fitting instruction give different advice, one to fit one, the other no real advice either way.

Peter

we had one & removed it 20 years ago as a temporary measure,because the pressure release valve would dribble to the bilge every time the tank was heated. Never had problems with hot from the cold tap. Did similar in the 70s with a system with a small expansion tank,which always overflowed.

So my vote---- don't fit.

 

[vyv_cox]

If I can to some extent summarise what others have said and add a bit of my own, you have several options. Your current cold water system (?) may or may not have an accumulator to reduce cycling of the pump for minor tap openings or leaks, usually close to the pump. You would be advised to fit one if adding a calorifier to absorb the thermal expansion of the water. In this case the pump acts as a NRV for the system.

Adding a NRV on the hot water side before the calorifier, as said, prevents hot water from expanding back into the cold supply. But in this case the thermal expansion of the water cannot be accommodated by the accumulator near the pump, so you may need to fit a second one. Sometimes there is sufficient elasticity in the hot water hoses that it is not necessary, but if the blow-off pressure of the calorifier's safety valve is close to that of the pump you may suffer constant dribbles of water from it.