Mums House - low pressure to bath

[kay-jay]

what he means if the you had a seperate cwsc the higher you can raise it above the cylinder the greater the pressure into the cylinder thus giving greater pressure to the taps but as its all in one you cant increase the the pressure to the cylinder no matter how high you lift it

correct, or at least that is my understanding of it.

 

[tamz]

Would this not be negligible though? The head in this case will be operating on the distance between the water level in the cwsc and the connected cylinder. Therefore being the same whether in the loft or on the roof. There may be a small advantage gained from an increased drop on the pipework but imo not worthy of the effort involved.

The height of the cwsc above the cylinder is irrelevant to the head of water (pressure) available at the taps as it just runs through it.
The head at the taps is determined by the height of the cwsc, or in this case the water level in the combination cylinder, above them.
A combination tank will not give any less pressure at the taps than a separate tank and cylinder. The higher you lift it the better the head of water so it is worth doing.

Think of it like this.
A cwsc fitted in the loft of a 3 story building, 3m ceilings, and the hot water cylinder fitted on the floor of the ground floor and a shower head on the top floor.
Discounting pressure drop due to resistance, the pressure on the bottom of the hwc would be just under a bar. The pressure at the hot tap on the ground floor perhaps about 0.85 bar, the pressure at the shower head would be around 0.1 bar.
Same scenario with a combination cylinder in the loft, The pressure at the bottom of the cylinder would be around 0.08 bar, pressure at the hot tap on the ground floor is the same 0.85 bar and same 0.1bar at the shower head.
Same pressure at the outlets.

 

[tamz]

correct, or at least that is my understanding of it.

See above :wink:

 

[Simon F]

agree with Tamz about the pressure,
possible issue with complete combi move to loft space is suffient structure to carry the combined weight

 

[rocketmanbkk]

So, as Tamz and others say, it would be better to to fix a tank in airing cupboard and new cwsc in loft to provide better pressure to bath taps.

It's as I thought and wanted to thank all for their comments.

I'll see what she wants to do but want to get it done for her as a bath takes a lifetime to fill.

Thanks again

 

[kay-jay]

The height of the cwsc above the cylinder is irrelevant to the head of water (pressure) available at the taps as it just runs through it.
The head at the taps is determined by the height of the cwsc, or in this case the water level in the combination cylinder, above them.
A combination tank will not give any less pressure at the taps than a separate tank and cylinder. The higher you lift it the better the head of water so it is worth doing.

Think of it like this.
A cwsc fitted in the loft of a 3 story building, 3m ceilings, and the hot water cylinder fitted on the floor of the ground floor and a shower head on the top floor.
Discounting pressure drop due to resistance, the pressure on the bottom of the hwc would be just under a bar. The pressure at the hot tap on the ground floor perhaps about 0.85 bar, the pressure at the shower head would be around 0.1 bar.
Same scenario with a combination cylinder in the loft, The pressure at the bottom of the cylinder would be around 0.08 bar, pressure at the hot tap on the ground floor is the same 0.85 bar and same 0.1bar at the shower head.
Same pressure at the outlets.

Thanks tamz makes sense, was thrown at first cos its contrary to what i was taught.

Sent from my GT-I9100 using Tapatalk

 

[tamz]

What would happen in reality if you sat a combination cylinder in the loft in the above scenario and opened the hot tap on the ground floor is that it would draw air as the water would run out the cylinder faster than it could fill due to the pressure difference.
If you ever have to sit a hwc under a cwsc in a loft use a 28mm feed to the cylinder to overcome this.