Moving bathroom radiator to hot water circuit

[scratch]

Hi,

I have a fairly traditional heating/hot water system were the boiler heats a circuit for the central heating and another circuit goes to a vented hot water cylinder. The only slightly unconventional thing about it is that the hot water circuit is pumped with its own pump controlled from a thermostat on the hot water cylinder.

There is a single radiator/towel rail in the bathroom, close to the hot water tank. This is currently part of the central heating system but I am interested in connecting it to the hot water circuit instead. I am interested in doing this because there is a horrendous pipe run to this bathroom radiator from another room and because I would like to be able to heat the bathroom when the central heating is not on (I grew up in a house where this was the case and I have got attached to a warm bathroom all year round). I would of course put a TRV on the radiator in the bathroom and put the radiator into the hot water ciruit in parallel with the tank.

Is this a sensible proposal? What do I need to look out for?

Cheers,

Dan

[Set Square]

Given your description of your setup, I'm afraid that it's an extremely

*bad* idea.

True, it would give you warm towels in the summer when the CH is off. But what about the winter? It takes a relatively short time to heat a tank of water. If you do what you suggest, your bathroom radiator will *only* be hot for that short time - the rest of the time the bathroom will be freezing cold!

A lot of people with more conventional setups have a bathroom radiator which is effectively connected to *both* circuits. Where there is a single pump, and zone valves, the rad is fed from a point after the pump but before the valves - so that it gets hot whenever either or both circuits are operating.

The nearest you could get to that would be to connect it to *both* circuits through a pair of back-to-back non-return valves - but that wouldn't allow you to dispense with your 'horrendous' pipe run, and you'd have to be very careful with the return connection in order to prevent reverse circulation under some circumstances.

[Rick]

This is a very good idea providing you use the right type of rail.

I have 2 towel rails in the house and they are on the pumped DHW circuit, it adds extra heat when bathrooms are cold ... but very useful having these warm in the summer - great for drying out towels.

My DHW comes from a thermal store, and all Hot water is at mains pressure ... as this Hot water is also pottable, the towel rails are brass (chrome finish) .... I got mine form Nu-Heat thay sell a wide range.

[scratch]

Rick, I guess that your system works fine because the pump is on a lot of the time or is controlled by a thermostat on the hot water circuit pipe? I think that the problem that I will have, as Set Square points out, is that with my system, as soon as the tank is up to temperature then the pump will switch off and my radiator will get no flow. On reflection, I think that if I had a gravity fed hot water circuit then my proposal would work OK. Can anyone suggest why I may have a seperate pump in the hot water circuit. What are the distance or height limits for a gravity fed hot water circuit?

[Christian McArdle]

You need to put it on the unzoned part of the circuit, before any zone valves, but after the pump. If the zone valve is next to the cylinder, then you're laughing. If it is near the boiler, and the boiler is miles away, you're not.

Christian.

[scratch]

I do not have a zone valve. Both CH and HW circuits are completly seperate right back to the boiler. Each has its own pump.

[Christian McArdle]

Ah. You may have problems, then.

You'd really need to run it as its own zone with its own pump, then.

You might consider retrofitting a heating element into the rad. Then you can have electrical boost when the heating is off. Running it off the hot water would only be marginally better than you have already. It would only heat up when hot water is used. Admittedly, this means it warms up during a bath or shower. However, it is useless for drying towels afterwards, as it will soon cool down again.

Christian.

[Rick]

No Thermostat ... there is a 3 port temperature blending valve on theDHW take off, the DHW pumped loop is a very low speed Grundfoss unit specifically for the task (descibed as zero head, low speed circulator) ... just about keeps water moving ... water is at mains pressure, so pump just has to keep it moving to keep DHW loop hot. As soon as any taps open ... mains pressure takes over and you get full flow & pressure, pump is irrelevant at that point.

The pump is quite neat as it has a built in multi time time switch in the end of the pump(Grundfos UPS20-14)

So the towel raisl are warm when the pump is running.

The way it achives this is simple ... I have a 20mm feed to all DHW take off points, one nice long serial run of pipe ... at the last take off point, I then run a 15mm pipe back to DHW blending valve via circulator pump .... i.e. pumped HW loop.