Fast recovery cylinders - advise and recommendations

[Alan]

Hello group,

I'm researching a replacement hot water cylinder as an upgrade / replacement for the existing aging one. The current one is roughly 1m high and 400mm wide.

Current config is gravity circulated from bolier on 28mm pipework, no HW thermostat.

This works OK, but water takes ages to heat, and often isn't quite enough, hence upgrade.

Plan is to replace with a fast recovery cylinder and convert system to fully pumped at the same time. Pump is currently situated near boiler, and a "T" downstream to send water to upstairs / downstairs circuits.

I'd like to change to upstairs / downstairs zones also, so shopping list will include suitable motorised valves to allow this.

Bolier is a Baxi back-boiler about 5 years old, so no plans to replace this. Programmer is of similar age and has facility to control valves etc. House currently has 1 thermostat in downstairs hall, all rads have TRVs apart from hall and bathroom.

I've looked at the "Superduty" cylinder offerings from Albion:

there and other makes / models you can recommend? Any other things I need to consider or buy to do this?

Many thanks,

Alan.

[David Hansen]

On Mon, 10 Apr 2006 14:34:27 GMT someone who may be "Alan" wrote this:-

If your house is suitable for solar heating (southish facing roof for example) then you may want to consider fitting a solar ready cylinder. The price of sunshine is not going to change, unlike that of gas and it should provide most of your hot water in the summer and a substantial contribution for much of the year. One supplier is

I'd like to change to upstairs / downstairs zones also, so shopping list

Three zone valves and a little pipework re-arrangement then. Presumably you want all the heating on all the time, with each zone just controlled by its thermostat. An alternative would be a three channel controller so you could have the upstairs and downstairs heating on at different times.

Check how the boiler is fed and vented. This is often with via the pipes to the hot water cylinder, which are teed off at the cylinder and then continue to the loft.

[Andrew Gabriel]

I think you'll have problems here due to gross mis-match of the power of the two items. Your back boiler is probably something like 6-8kW output, and a fast recovery cylinder can probably take at least 25kW. This means that when run from such an under powered boiler, the return temperature will be very low, and will force the boiler into condensing mode, which could quickly wreck a conversional boiler.

I would suggest only using a fast recovery cylinder with a condensing boiler, and stick to a regular Part L cylinder if you have a convensional boiler, which requires a return water temperature of at least 60C to avoid condensing.

[Alan]

Andrew - good point, I'll check the power output. So returning water which is vastly lower in temperature to the output of the boiler can / will cause condensing where it's not wanted, as it's not a condensing boiler? I hadn't considered this. Plan "B" would be a regular cylinder as you say, but still go fully pumped and zoned then.

David's suggestion a solar ready cylinder is interesting - I'll research this option also.

Alan.

[mike]

"Alan" wrote in news:LwM_f.6120$ [e-mail]:

My slightly older Baxi Bermuda comes in 2 flavours, 57/3 with a max o/p of

21 kW, and the 45/3 with a max o/p of 16.5 kW

I use it with a Superduty CF80, and it works fine.

I've never checked the return temperature, as it's only on for 2 spasms a day, but it runs good and hot.

mike

[Doctor Drivel]

A fast recovery cylinder greatly reduces inefficient boiler cycling. Worth fitting and setting up the temp differential across the flow/return to the max the makers say. Most will go to 15C on non-condensing boilers.

[Alan Deane]

OK, bolier output is 14.65 kw - so should be OK, similar to Mike's setup.

I've investigated the dual-coil solar cylinders, and am more likely to go this route now for future solar heating. The tanks have 60mm insulation vs ~22mm on standard ones which will help retain heat no matter what the heat source is.

Alan.

[Andrew Gabriel]

OK, I've only limited experience of back boilers, and it was only 7kW -- I didn't realise they were available at significantly higher outputs.