Advice on replacement Towel Rad on Gravity System heated by Multifuel Stove

[GeoffG]

Hello,

My current installation is an 8Kw Morso Stove, about 20 years old, connected to:

• An indirect coil in a vented cylinder (on the ground floor where the heater is, but raised by about 80cm), gravity fed with a bathroom towel rail upstairs also gravity fed.
• Once the gravity circuit is up to temp, a pump kicks in to circulate the heat around three radiators.

We have another heating system so we hardly ever use the Stove.

The hot water header tank (and the stove header) are in a cupboard only 2 meters from bathroom floor height, so the head is poor, and a shower (other than an electric one) is impossible upstairs.

So, we are having the vented cylinder replaced with an electric only unvented one, which does not come with an indirect coil. (This of course is not a DIY job!)

Where the coil was will be bypassed, and so there will be just the bathroom Towel Rad on Gravity, and the other rads will kick in sooner, once the towel rad circuit gets warm.

My Question.

I would like to install a replacement radiator in the bathroom for the following reasons:
1. I want to add an electric element to heat the bathroom via the bathroom rad, when the Stove is not in use.
2. There is not enough height in the alcove where the bathroom rad is situated, to add an element to the existing rad, as it is tall and narrow.
3. The rad looks like it is only 400-500 watts, and I would like to have a better heat sink, having removed the water cylinder coil. I read that about 10% of the Stove output is advised - so that would be 800 watts.

The current rad works fine, but it is not plumbed as a gravity rad - the input and output are both at the bottom. Also, it seems to be only 15mm pipework (about a metre) that is visible in the bathroom.

I found a bigger radiator that I liked to look of, a double 600x600, that is about 900W. But the makers say it will only work in my system if there is "good pressure". I don't know what that means, and my plumber seems possibly a bit unsure about the gravity side of the work.

So my question is - Can forum folk advise me what sort of rad will work in my situation?

(This is the one I like: Urban Horizontal Radiator | White Finish | From Victorian Plumbing )

 

[Chuck]

my plumber seems possibly a bit unsure about the gravity side of the work.

So my question is - Can forum folk advise me what sort of rad will work in my situation?

I wouldn't want to predict how a well a gravity circulation system will work with a modern emitter designed for pumped circulation and nor, it seems, do your plumber or radiator manufacturer. Unless you convert to a pumped system, which is what I'd want to do, I think you'll be in trial-and-error territory.

 

[GeoffG]

I wouldn't want to predict how a well a gravity circulation system will work with a modern emitter designed for pumped circulation and nor, it seems, do your plumber or radiator manufacturer. Unless you convert to a pumped system, which is what I'd want to do, I think you'll be in trial-and-error territory.

Thanks Chuck.
I'm wondering what my options are then, and what are the consequences of those options?
I don't especially mind if the bathroom emitter does not work brilliantly when powered by the stove (although that is obviously preferable).
The main thing is to have a system that works safely, and will not cause difficulties if we use the stove. Preferably that still is not dangerous during a power cut!
We do of course have a pumped part of the system, but I'm not clear how that circuit interacts with the Gravity circuit within the stove (or outside of it). Once the pump kicks in, will that assist the gravity circuit and the bathroom emitter on it at all?
What would be involved in changing the system to be all pumped?
Re: "with a modern emitter", the current emitter (small towel rad) does not look much different to one I might buy today, so not I'm sure what the difference would be in replacing it with a higher output one that is a different shape? Can you help me understand the issues involved and the differences?
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P.S. I have a deadline to meet, as the plumber is coming to install the cylinder a week today. So I need to select a radiator, and get it ordered for delivery in time, as soon as possible. Thanks.

 

[Chuck]

The main thing is to have a system that works safely, and will not cause difficulties if we use the stove. Preferably that still is not dangerous during a power cut!

If you are keeping the stove then yes, for safety, you have to have a working gravity circuit. My worry is that in your existing system you have an indirect cylinder to act as a heat sink, which will provide the main driving force for the circulation. I'm not sure whether a single radiator will be sufficient.

I'm sorry that I can't be more help.

 

[GeoffG]

If you are keeping the stove then yes, for safety, you have to have a working gravity circuit. My worry is that in your existing system you have an indirect cylinder to act as a heat sink, which will provide the main driving force for the circulation. I'm not sure whether a single radiator will be sufficient.

I'm sorry that I can't be more help.

Am glad to say that a 600W towel radiator in the upstairs bathroom replacing the smaller one that was previously fitted, has proved sufficient to make the gravity system still work, and the pumped circuit then kick in once the gravity circuit has heated up.