Hot Water Pipe supplied by 2 Different Boilers

[nb99]

Hi

This is a theoretical question for now, so no need to worry about the "whys" of the situation! If I have an existing fuel-fired boiler providing the hot water to a tap, and I "T" in another pipe (to the pipe going from the boiler to the tap) supplied by an emersion heater, will the water coming out of the tap be roughly 50% from the emersion heater and 50% from the fuel boiler? If not, what will dictate which supplies more?

My guess is that given both are pressured by the mains cold water pressure that they will roughly contribute 50% each to the tap, but I'd love another opinion on this please.

Many thanks

NB99

 

[Gasguru]

It will depend on the head loss (friction through the pipework/heat exchanger) between the tee joints before and after the water heaters ie. if the flow resistance is higher through the boiler then the flow will favour the easier route through the immersion heated tank.

Sounds like a bodge job (that may be unsafe).

 

[Agile]

Far better to have taps which you use to select which source you want to use.
Or boiler for kitchen and cylinder for bathrooms!

For those who dont know, in France they use an unvented cylinder and a pressure release valve which drips to allow expansion. Most dont have any P&PV.

TONY

 

[nb99]

Thanks for the comments. Yes I could see taps working in certain situations but the aim here would be to have the water heated by 2 different sources (roughly 50/50) rather than just one or the other.....

 

[nb99]

gasguru - why do you assume it would be unsafe? What is the worst case?

 

[Agile]

Those of us who work on heating systems will not understand why you, who don't have that knowledge, think that there can be any advantage is supplying hot water from two different sources at 50% from each.

The actual flow from each will depend on the comparative resistance from each source.

This is unlikely to be linear either as boilers usually have flow limiters so the proportions from each will also vary according to the flow rate.

Generally not a good idea!

Tony

 

[nb99]

For the record, in case anyone else finds this thread, I set up the system with both fuel boiler and electric emersion heater joining the hot water supply tap for the house. Works a treat. Mix is roughly 50/50 and we can turn off either boiler to make it 100% either system. Gives our system a lot more flexibility and options going forward.