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Fitting central heating radiators

I have a 50 foot cruiser stern narrowboat heated by a multi fuel stove and Alde boiler driven gas central heating via a skirting radiator running most of the interior length of the boat. The gas system is ineffective, the radiator barely getting warm; using it to supplement the stove in this extremely cold weather is not working and the system won't work well enough on chilly Spring mornings, for example. I want to replace the skirting radiator with conventional panel ones. My questions are:
1. How large can the radiators be to be driven efficiently by the Alde boiler and circulation pump?
2. How many radiators can I sensibly install (I am thinking 3).
3. Anything I need to be aware of in undertaking this work, e.g. there can't be a return flow on the system because the skirting radiator (onto whose pipework conventional rads would be fitted) flows only one way to and from the boiler)?
Thank you.

Asked by: Paul Taylor  | 7.53pm, Sunday 24 February

WW says:

You haven't mentioned the type of boiler, but assuming it is the tall slim Comfort boiler- though much applies to the newer Compact unit.
If sufficient skirting convectors are used, it should be quite possible to effectively heat a boat. They transfer about 400W per metre length. To heat a boat properly, you need around 8 to 10 metres of convector. They also need good airflow above and below the convectors in order to work well.
You can use radiators (convectors) to an effective transfer of around 6.5 kW, which would then allow for the reduction in efficiency. You can find how much each convector can shift by looking at the pack, in a DIY store like B&Q.
Although these are connected via 15mm plumbing, it is essential that the rest of the plumbing is in 22mm pipe work, with no reducers. Using 15mm pipe work for the while system can reduce circulation and cause very poor performance.
The system should ideally be a two-pipe system- if you use a single pipe system then there should be no valves fitted to the radiator- you can fit valves to a two-pipe system.
You might also find that if the central heating boiler also heats a coil in the calorifier (hot water tank) it might be short circulating through the, which means that very little heat passed through to the convectors.
To cure this, fit a control valve into the supply line from the boiled into the calorifier branch. Start up the boiler (which a cold calorifier) and slowly open the contriol valve a bit at a time. Feel the pipe that leaves the calorifier and once you can feel it slightly warm, leave the valve in this position. A calorifier can only absorb around 800W of thermal load, so if to much heating fluid passes round the calorifier, it just causes the boiler to short circuit and prevents flow in the rest of the system.
You might find that looking tat how your system is fitted might mean you can alter it to work better. Checking the pipe work and calorifier balance valve are often the main issues.
Also check for any Air bubbles - which can lead to poor circulation. You might find that any loops prevent proper circulation- check that you are also using a proper antifreeze solution as well, which can help prevent gassing.
Let us know if you need any further help.

Mark Langley  | 8.28PM, Sunday 24 February

Just to add, you can fit panel Convectirs onto a single pipe system, by using a 22mm-15mm-22mm t-fitting. I cannot stress how important it is that the entire heating system is plumbed in 22mm pipe work

Mark Langley  | 8.31PM, Sunday 24 February

You can also use as many panel convectors as you see fit within reason- or combine panel Units with the inline fin rads.

Mark Langley  | 8.33PM, Sunday 24 February

You can also use as many panel convectors as you see fit within reason- or combine panel Units with the inline fin rads.

Mark Langley  | 8.33PM, Sunday 24 February

If the Alde is not heating the existing radiators, changing the type of radiators will not improve matters. It is likely that as Mark says; the heating pipe work is 15mm not the recommended 22mm (this is a common fault), or that there is some other restriction stopping the water flow. Another possibility is that the circulating pump is not working properly or there is an air lock in the system. This can happen if the header tank is not kept topped up; if it is dry when the heating is used for the first time, air can be drawn in and bubbles can get stuck, stopping the flow even if it is subsequently topped up. Careful bleeding will cure this problem. If it is a single pipe system, it is unlikely to work well as the Comfort boiler circulating pump does not produce much flow. Probably the best course of action would be to re-jig the pipe work, adding a proper return (in 22mm) pipe.
It is possible to see how much heat is being drawn from the boiler by looking to see how much time the main flame is firing; if it stays lit for a lot of the time, the boiler is working hard; if however it keeps switching off, only a small amount of heat is being demanded by the heating system.

Rupert Smedley  | 10.57PM, Sunday 24 February

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