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What is head?

What is head when talking about water systems in a house? How does it relate to hot/cold water and water for radiators? Thanks in advance,

CM.

Reply to
Charles Middleton
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Simply head equals pressure. In a house with tank in the loft the presure is "x" head. The head refferes to the height of the tank from its water line. The higher the more the pressure. 1 bar is approx 30 foot. If the tank is 30 foot above you the pressure where you are will be 1 bar. That is why in 3 story house when the tank is in the loft, on the 4 th floor, the pressure in the basement is high and on the top floor very low.

A man I know, to increse the pressure on his shower installed another large

100 gallon water tank in the loft. He was confued at why the pressure had stayed the same.

So if you have a 4 floor house and the pump and boiler in the basement the pump may not reach the top floor radiators. The more bends and elbows in a pipe, the more the pressure is reduced, so a punmp has to be sized with the pipe run taken into acciount. Lots of elbows and the 20 foot head pump may only raise water 15 foot.

A pump may be rated at 20 foot head. If a 40 foot clear plastic tube is attached to the outlet of the pump and it runs up directly vertical, if the pump pumps water from the same level the pump is on, the water should rise up 20 foot in the plastic tube.

You must have heard the term "a head (pressure) of steam" on films, when the train driver or ships engineer waits for the steam pressure to build up to move the ship or train. Or the fireman shovels coal in like hell to keep "the head up" to keep up the speed.

Reply to
IMM

It's a measure of static pressure expressed in terms of the pressure which will exist at the bottom of a vertical column of water of specified height. For example, the head of water at your kitchen tap (for a stored hot water system) may be about 15 feet (roughly 0.5 bar in pressure terms) - being the vertical distance of the surface level of the water in the header tank above the tap.

The static head of water in your central heating system is measured in the same way (assuming a vented system with a small F&E tank in the attic). The static head in the downstairs rads will be greater than that in the upstairs rads due to their relative vertical positions. In a pumped central heating system there will, of course, be a dynamic pressure which is exerted by the pump and superimposed on the static pressures.

Hope this makes sense!

Reply to
Set Square

That might be true if the pump was picking up its water from an open-to-atmosphere trough in the basement. But, of course, it isn't! It's being fed with a static head of water commensurate with the 4-floor house - and only has to generate sufficient *dynamic* pressure to overcome the flow losses.

Back to your Physics text book, Mr IMM - if you ever had one!

Reply to
Set Square

The *pressure* is reduced by bends and elbows, is it?

Remind me again of what you claim to earn a living at?

Reply to
Dave Plowman (News)

The term Head, when used in plumbing, is the height you have from a static feed tank which is above all other appliances. So, the higher the head of water, the more pressure you get in the pipes to move the water below it.

Reply to
BigWallop

Hum, you have got a couple of different concepts mixed up here.

Yes, but the central heating pump is responsible for circulating the water in the system, not keeping the upstairs radiators filled up. Central heating pump only has to overcome the dynamic pressure drop of the system at the operating flow rate which is normally of the order of a few feet of head, and is not related to the hight of the header tank or the fill pressure of a sealed system. A central heating pump won't normally generate anything like the head required to pump water from the ground floor to a loft header tank or even upstairs radiators, and doesn't need to.

Reply to
Andrew Gabriel

I'm trying to remember my basic physics about the maximum head an impeller pump can generate? I'd think it unlikely to be more than 1 bar?

Reply to
Dave Plowman (News)

I can't think of a reason for a limit. It basically uses centrifugal force at the outer edge of a volume of spinning water, and if you make the diameter larger or the angular velocity higher, the pressure should increase. Maybe there's some factor I'm overlooking (cavitation)? Of course, there's a limit to what a 3" diameter impeller on a 100W motor in a central heating pump can achieve. I just looked up the spec of one typical heating pump, and it's 0.5m head.

Reply to
Andrew Gabriel

You need to know more about heating and the many plumbers who have had to replace a pump with a more powerful version because the tops rads only get warm, or not at all

Reply to
IMM

What the f**k do you know about heating? err, err, er...nothing.

Not twiddling a knob.

Reply to
IMM

Thanks. Whilst he started well when talking about the roof tanks, the plot got lost on CH circulators.

IMM has some agreement with higher powers than I deal with that exempt him from the known laws nature.

Reply to
Ed Sirett

Depends. A pump will have "x" head on it inlet and oulet, in theory balanaced out. In practice the the boiler gets in the way and a lot of piping. From what you say a pump need only just move a water a little. If the restriction is high on the inlet, the suction side you may find there will be little flow, if any, at the far end.

Reply to
IMM

Likely because they're the furthest from the pump and the longer the pipework, the greater the resistance to the flow.

Reply to
Dave Plowman (News)

Obviously rather more than you, though, then?

You'd not last five minutes at it. It's something that requires skill. Not just quoting reams from websites and brochures without understanding a word of it.

Reply to
Dave Plowman (News)

The important point - which you need to get into *your* head - is that this has nothing to do with *static* head (which is self-cancelling in a circulating system) - but is simply a function of circuit resistance.

If you took all the pipework in your notional 4-storey house, and laid it out in one *horizontal* plane, you would have exactly the same relationship between pump dynamic pressure and cricuit flow as you had with the original vertical pipework.

Reply to
Set Square

The pump head overcomes that. Duh!

Reply to
IMM

That is a question. Answer NO.

Stop commenting on fields you know sweet FA about.

Keep twiddling the knob.

Reply to
IMM

Go way....you don't say! Duh!

Reply to
IMM

In message , IMM writes

It's you who claims to be able to give head

... but whose, we must ask?

Reply to
raden

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