How to measure Hot Water Head

[pooksahib]

Hi. I've just had a Trevi Boost shower fitted and the temperature is very disappointing. I'm going to ask my builder to check it out but I'd like to be a bit more informed before I do so. The instructions contain a graph with Hot Water Temperature on one axis and Hot Water Head on the other.

It's the latter I'm wondering about as it's given in Metres. What exactly is Hot Water Head and how (in metres) is it measured?

Many thanks.

 

[steved101]

it's the heigh from the cold water tank (go from the bottom) to the shower rose. you want with most showers at least 1 metre, or a pump will be needed. some showers use only 600mm head but flow may be poor/poorish.

 

[doitall]

The head is from the bottom (some go middle) of the storage tank, to the highest part of the system, could be a shower rose or a pipe in the loft.

More info on what you have would be an idea.

 

[pooksahib]

Thanks, both. The building is all one one level and the Trevi is in the newly built extension. Distance from hot water tank to Trevi is 7 metres. My builder connected the new pipework in the loft space i.e. there's nothing new to be seen by looking at the hot tank, it's all up above. The cold tank is in the loft as you'd expect - almost, but not quite, above the hot tank. The new pipes run along the rafters and then down to the Trevi. The hot tank temperature is set at 60c, hot enough for the house.

Given that the pipes are in the loft, can I clarify who's right as regards 'Head' - is it the height of the showerrose or the overhead pipe? (Obviously, 'cold water head' will be negative. It's just Hot water head I want to measure.)

One matter I'll be asking my builder about is the temperature control knob. It's supposed to go from 1-5 but I can only rotate between, say, 2 and 4.5. Perhaps he's done something wrong here...

Thanks again for the prompt reply to my initial post.

 

[doitall]

See, you didn't read what I said after all.

To answer the question again "The highest part of the hot water system"

I also asked for more info, as I have a feeling the cylinder may also be stood up in the loft.

In which case the head will be from the bottom/middle of the storage tank, to the pipe out of the top of the cylinder.

 

[maltaron]

The head of water is from the top of the water in the header tank to the outlet point measured verticle. This will obviously be variable according to the level in the tank and the lowest point would be the level used in calculations. Any pipework in between is irrelevant to the head allthough it could add resistance to flow. With a power shower both hot and cold are fed from the same tank (the hot via the cylinder) so are the same head.

 

[doitall]

The head of water is from the top of the water in the header tank to the outlet point measured verticle. This will obviously be variable according to the level in the tank and the lowest point would be the level used in calculations. Any pipework in between is irrelevant to the head allthough it could add resistance to flow. With a power shower both hot and cold are fed from the same tank (the hot via the cylinder) so are the same head.

Wrong big time maltaron

 

[Tipper]

I thought it was a good description assuming a pump is being added.

But a Trevi Boost uses cold water at mains pressure via a venturi to pull the HW into the shower mixer thus improving the performance.

Therefore you need a good mains pressure for it to work and you need enough HW via pipework without too much resistance for the resulting water to be hot enough. If the available head of HW at the shower mixer is low, due to low cold tank height and poor pipework then not enough HW will get through to mix with the CW resulting in a cool shower.

Might be worth trying restricting the cold flow to the mixer by shutting any inlet isolating valve a little. Too much though and it won't work any better than a standard mixer.

 

[doitall]

I thought it was a good description assuming a pump is being added.

How do you work that out Tipper.

The water level measured to the top of the storage tank will only give you static pressure, not working pressure which is what you need to know. At best you can go the center of the tank, depending on the recovery.

The head to the cold will be greater,even though it's from the same tank, as the highest point will be lower than the top of the cylinder.

To improve the venturi you have to increase the head, this can be by raising the tank or lowering the cylinder.

Some improvement could be gained by increasing the cold feed to the cylinder.

 

[cmother1]

I'm with malatron on this. I've an upstairs and a downstairs shower, both run off the same cylinder& CWS tank. Guess what? - there's loads more pressure on the downstairs one. Don't know what all this guff about top of cylinder and pipes in the loft is about. It's the point to point vertical distance that counts.

If you want to do an experiment to prove this turn on an upstairs un-pumped shower run off a static tank and raise the shower head as high and as low as it will go. You can actually see the pressure reduce the higher you get.

Anyone with another variant on this topic?...

 

[doitall]

I'm with malatron on this. I've an upstairs and a downstairs shower, both run off the same cylinder& CWS tank. Guess what? - there's loads more pressure on the downstairs one. Don't know what all this guff about top of cylinder and pipes in the loft is about. It's the point to point vertical distance that counts.

If you want to do an experiment to prove this turn on an upstairs un-pumped shower run off a static tank and raise the shower head as high and as low as it will go. You can actually see the pressure reduce the higher you get.

Anyone with another variant on this topic?...

Don't talk rubbish, and better still don't contradict your own statement.

You can actually see the pressure reduce the higher you get.

The outlet from the cylinder is the highest point, that is the head, what you get at that point is all you get anywhere, at any level.

Connect a hose to your shower and take it up to the top of the cylinder if you want a test.

 

[maltaron]

Sorry I have to argue the point again. The head is from the highest point i.e. water level in header tank to the outlet point. Providing that the hot water cylinder is below the header tank (it would not work otherwise) the cylinder can be on the ground floor of a two story house and the head would still be from the header tank. I have been involved in two houses plumbed in this way and if Doitalls' reasoning applied there would be no hot water upstairs. It is often piped this way to give almost instant hot water at the kitchen sink.

 

[doitall]

Sorry I have to argue the point again. The head is from the highest point i.e. water level in header tank to the outlet point. Providing that the hot water cylinder is below the header tank (it would not work otherwise) the cylinder can be on the ground floor of a two story house and the head would still be from the header tank. I have been involved in two houses plumbed in this way and if Doitalls' reasoning applied there would be no hot water upstairs. It is often piped this way to give almost instant hot water at the kitchen sink.

I don't have a problem with you arguing a point if you can't see or get the point, surely that's what a forums for.

Understand this comment by tipper "You can actually see the pressure reduce the higher you get." Yes because he is reducing the head, the higher you go the lower the head.

The head is from the storage tank, we won't argue about where at this point, to the highest part of the hot water system.

In your argument you say the cylinder is in the basement, fine, the head will now be different on each floor as you go up the building.

Send me an email, in my profile and I'll do you a drawing

 

[maltaron]

Just go back to school and learn physics. The head as you say is the vertical distance between the highest point and the point of delivery. The HW tank is effectively a U tube with no effect on the head.
I think that perhaps its time to agree to differ and close this thread.And yes, the higher you go the lower the head i.e. the distance from the highest point to the point of delivery is smaller and you will still get some delivery until your point of delivery is above the header tank, not the cylinder.

 

[pooksahib]

I certainly seem to have started something here...

See, you didn't read what I said after all.

You'd said 'head' could be from cylinder to loft pipe, steved101 had it only as far as showerrose. I was just double checking who had it right...

... I have a feeling the cylinder may also be stood up in the loft.

All that's in the loft is the cold storage tank. How water cylinder is in the utility room.

As far as this thread goes, can I take it that 'cylinder' = Hot, 'tank'=Cold? Maltaron speaks of a 'header tank' - is that another term for cold tank?

Anyway, I have this graph from the manufacturer - temperature of water in hot cylinder on one axis, 'Hot water head' (in metres) on the other. I just want to know if I fit into the area on the graph of 'acceptable performance'. So there's my hot cylinder in the utility room, cold tank in loft, H&C feeds to the new Trevi have been made in the loft space. Trevi is on same level as hot cylinder (bungalow).

I'm guessing my Hot Water Head is just over a metre (distance between showerhead and the pipe running along the rafters). Can anyone confirm or suggest otherwise?

Sincere thanks to all contributors - for the entertainment as well as the info.