I have an oil fired boiler and cylinder system, and all the upstairs rads run off 15mm branch from the boiler. There were 4 rads and I've just added another small one in a bedroom which didn't have one. Took a bit of balancing but they're all still getting to a good temperature, however I've since read that you shouldn't have any more than 3 rads off 15mm pipe. Will having 5 rads off 15mm cause problems for the boiler longer term? I could take the pipework from the new one out and connect it to the downstairs 22mm branch which has only 2 rads on it, however I will need to add at least 2 more rads downstairs.
How many rads off 15mm pipe?
- Thread starter rreanor
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I was under the impression you shouldn't have more than 3.
I had 4 in my last house and they just about worked, the main bedroom rad I never managed to get to heat up evenly.
It won't harm the boiler in any way, it's just the heat produced by the rads won't be so great, andd balancing them can be a bit of a pain if you can do it at all.
I had 4 in my last house and they just about worked, the main bedroom rad I never managed to get to heat up evenly.
It won't harm the boiler in any way, it's just the heat produced by the rads won't be so great, andd balancing them can be a bit of a pain if you can do it at all.
Depends on the system. The old "no more than X rads off 15mm" harks back to the days of standard efficiency systems, and was done to reduce noise created by water flowing quickly around the pipes. A modern well designed system set up for a condensing boiler runs at a much lower flow rate and so more rads can be run off 15mm. In fact, it's actually quite feasible to run entire systems in 15mm if they're correctly balanced and the pump is set correctly.
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I have found the TRV has changed to whole idea of how big and how many radiators. It was in the 80's a case of a boiler with 28 kW output wanted radiators just slightly over say 32 kW and you had a single thermostat for all.
Today likely you want double the kW on radiators to boiler, as the TRV's turn radiators up/down even off so you want to use the heat to speed up heating of other rooms. The whole idea has been turned on its head. Even the reason for central heating, back in the 70's central heating was often just back ground heat, I have not removed covers off the fire and used it since the day I moved into this house.
I will admit the on/off oil boiler is not as good as the modulating gas boiler for hysteresis free heating of the rooms, with my mothers old house with a modulating gas boiler the rooms stayed at the set temperatures all day, the boiler never switched off and radiators were rarely hot, they were just warm enough to keep rooms at set temperatures.
The oil fired boiler does not produce a steady heat in the same way, rooms do over shoot, but in the main that is my fault for selecting Nest Gen 3 thermostat which will not connect to the TRV heads, but the fault is not bad enough to be worth swapping thermostat to one which will link to TRV heads.
Today likely you want double the kW on radiators to boiler, as the TRV's turn radiators up/down even off so you want to use the heat to speed up heating of other rooms. The whole idea has been turned on its head. Even the reason for central heating, back in the 70's central heating was often just back ground heat, I have not removed covers off the fire and used it since the day I moved into this house.
I will admit the on/off oil boiler is not as good as the modulating gas boiler for hysteresis free heating of the rooms, with my mothers old house with a modulating gas boiler the rooms stayed at the set temperatures all day, the boiler never switched off and radiators were rarely hot, they were just warm enough to keep rooms at set temperatures.
The oil fired boiler does not produce a steady heat in the same way, rooms do over shoot, but in the main that is my fault for selecting Nest Gen 3 thermostat which will not connect to the TRV heads, but the fault is not bad enough to be worth swapping thermostat to one which will link to TRV heads.
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Personally, max of 4 ordinary sized compact rads. Column rads need 5 times as much water as compact.
I don’t like finely balanced systems, velocity noise from lockshields & people adjusting the wrong side of the rads (no matter how many times you tell them not to)
I don’t like finely balanced systems, velocity noise from lockshields & people adjusting the wrong side of the rads (no matter how many times you tell them not to)
That's the beauty of IMI Eclipse TRVs, the balancing happens under the TRV head and the stays fully open
Wow there's some odd logic on here
TRVs have nothing to do with it...if the house is cold all the rads need to heat up at the same time.
The theory hasn't changed for a hundred years...pipe sizing has got nothing to do with the no. of rads.
Pipe sizing is all about the volume of water required to circulate to provide the heat required and the friction in the pipework and boiler heat exchanger (water head loss).
Have a look on the web for the pipe sizing calculators/guides.
The only difference today is regarding the heat carrying capacity of the pipework, if your boiler and radiators are suited then the delta (the flow and return temperature difference)
can be increased to 20 degrees doubling the capacity.
TRVs have nothing to do with it...if the house is cold all the rads need to heat up at the same time.
The theory hasn't changed for a hundred years...pipe sizing has got nothing to do with the no. of rads.
Pipe sizing is all about the volume of water required to circulate to provide the heat required and the friction in the pipework and boiler heat exchanger (water head loss).
Have a look on the web for the pipe sizing calculators/guides.
The only difference today is regarding the heat carrying capacity of the pipework, if your boiler and radiators are suited then the delta (the flow and return temperature difference)
can be increased to 20 degrees doubling the capacity.
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One ginormous
Two large
Three (ish) mediums
Four titchty.
Or; heatloss calcs , ΔTs, mass flow rates as above
Two large
Three (ish) mediums
Four titchty.
Or; heatloss calcs , ΔTs, mass flow rates as above
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