Have I got a fast recovery cylinder?

[pm]

Is there an easy way of telling the difference between a DHW fast recovery cylinder and a ... don't know the terminology. Slow recovery cylinder?

My cylinder is pre-insulated and has 22mm coil connections near the bottom and about half way up.

Thanks

Pete

[EricP]

The answer to your question is:

When you run the water out, does it reheat quickly? If yes, you probably have a fast recovery one.

[Tony Bryer]

Not that I know of, unless there's a label with useful information

[pm]

Don't know. In the summer I use an immersion heater. In the winter the CH and DHW is on constantly so it doesn't really run out. I am converting my CH system to S-plan and putting a tank stat on the tank, the instructions state different mounting locations for fast recovery and non fast recovery.

[mike]

pm wrote in news: [e-mail]:

My fast recovery cylinder uses a pipe, or immersion thermostat.

This plugs in right at the bottom, not straps on at the side.

I've no idea if all fast recovery cylinders are like this, or any conventional ones.

But it may give you a clue

mike

[marvelus]

unlikely, how old is you system?

[pm]

The cylinder is about 4 years old. The boiler was over 20 years old.

[Andy Hall]

There are a couple of ways:

- Drain the cylinder, take out the immersion and look inside with a torch.

- A science experiment.

• Block the bottom connection of the coil with a bung.

• Attach a length of transparent plastic tube plus a funnel to the top coil connection.

• Place a measuring jug under the lower connection.

• Fill the coil slowly with water using the funnel until you see the transparent tube just beginning to fill.

• Pull out the bung and measure the volume of water.

• Unless you have one of the cylinders with a group of small tubes as a coil (one manufacturer does these - can't remember which), the coil typically consists of 22mm tube.

• From the volume of water, and the tube diameter (radius to calculate cross sectional area - pi x radius squared) you can determine the length of tube.

• The diameter of the coil is typically half to two thirds of the cylinder diameter.

• Therefore, from the length of tube you can calculate both the number of turns and surface area of tube.

A fast recovery cylinder has a large surface are of tube and many coil turns - perhaps 10+. A conventional one generally has three or four.

While this is far from precise science, it should be close enough to work out what you have.

[pm]

I would rather not disturb the connections now so can I ask a slightly different question - does it make a huge difference where the tank stat goes? The instructions say half way up, unless it is a fast-recovery type in which case at the top.

[Christian McArdle]

The tank stat should go nearish the bottom, but a couple of coils worth above the bottom coil connection. If you put it near the top, you'll only use a fraction of the capacity.

Christian.

[manatbandq]

Doesn't sound right to me. You want the water to be heated down to the bottom (or near) of the cylinder before the stat turns off the heat.

MBQ

[pm]

I've just looked at the online literature

the bit about mounting near the top is not in there, the date on the online guide is

08/00 whereas the booklet that came with the unit is 06/06.

The details in my booklet are more like

page 2 "Electric Immersion and fast recovery systems".

Also would it make a difference whether the flow is top to bottom or bottom to top?

[marvelus]

But the water is heated from the bottom.

[manatbandq]

OK, there will be convection but that aside think of the following...

The hot water is drawn off from the top with cold entering at the bottom. If the stat is at the top then the heating will not kick in again until you've emptied the cyclinder and the stat sense the cold water reaching the top. With the stat in the usual place the heating will kick in before you exhaust the supply of hot water.

MBQ