My house has 14 rads from the 70's and 80's and I've noticed the heat up time is around an hour to full working temperature, I guess due to the volume of water in the system. Boiler size is a combi 36k btu. Do new high efficiency rads contain less water if so by how much?
Heat efficient rads
- Thread starter RichD1
- Start date
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1. Unlikely to be a 36k Btu boiler. More likely to be 36 kW.
2. There isn't really any such thing as a high efficiency radiator. They all convert heat in the water to heat in the room in pretty much the same way.
3. Radiators which heat up quicker also cool down quicker.
4. If you want a quicker heat up time, increase the flow temperature of the boiler.
2. There isn't really any such thing as a high efficiency radiator. They all convert heat in the water to heat in the room in pretty much the same way.
3. Radiators which heat up quicker also cool down quicker.
4. If you want a quicker heat up time, increase the flow temperature of the boiler.
The higher the temperature the less efficient the boiler becomes. Do all the radiators heat evenly? Have the radiators been balanced properly?
Likely the bigger part of the hour, will be the thermal lag, due to the thermal mass of the fabric of the house itself. The volume of water, will get to up to temperature, fairly quickly. The only way to speed things up, is with larger radiators, or increasing the temperature of the water in the radiators. Doing the latter is a bad idea, because that will probably mean the boiler not working in it's most efficient condensing mode - the cooler, the better, but generally below 55C return.
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If it took a hour to heat the rads from say 25C to 75C with a 36kw boiler output then the system contents are 619L, very unlikely IMO, are you sure the boiler output isn't range rated, assuming a more realistic max of 125L system contents = a boiler output of 7.3kw!!, somethings not adding up here.
Is the boiler cycling on/off due to lockshield valves being throttled?.
Putting it like that there does appear to be a mismatch somewhere.
When I put the boiler on tomorrow I’ll check to see if the boiler does go into a cycle mode.
I’m pretty sure the system is fairly well balanced but I will check that to. Out of interest there are several ways to balance a system. I don’t have any temperature measuring equipment so I’ve used the method of fully opening the TRV’s and then closing down the lock shields until they are all a half a turn open. Then run round checking to see what rads heat up first and opening up the lock shield on those which aren’t getting hot. Continue that process until all rads heat up together. Is there any better method?
When I put the boiler on tomorrow I’ll check to see if the boiler does go into a cycle mode.
I’m pretty sure the system is fairly well balanced but I will check that to. Out of interest there are several ways to balance a system. I don’t have any temperature measuring equipment so I’ve used the method of fully opening the TRV’s and then closing down the lock shields until they are all a half a turn open. Then run round checking to see what rads heat up first and opening up the lock shield on those which aren’t getting hot. Continue that process until all rads heat up together. Is there any better method?
LSVs a 1/2 turn open should still give a fairly high flowrate, os assuming the total rads output at 21 kw at a dT of 15C then the flowrate will be 20LPM and a 36kw boiler set to 75C will give a dT of 26C and will start modulating when the rads return temp reaches 49C, a hour heat up time means the rads might emit a average of ~ 10kw while heating up, add the ~ 7.5kwh to heat up the system water so boiler output ~ 17.5kw and not just 7.5kw as I said originally. Once up to temperature then the boiler output might be ~ 21kw at rad and boiler dT of 15C and flowrate of 20LPM.
The boiler should give the flow/return temperatures, the flowtemp should be displayed and the return shown in some menu or other.
I have 10 rads ~ 15kw output and a 20kw oil fired boiler set to 75C will heat the system contents of ~ 90L from a cold morning start in 25 to 30 minutes.
The boiler should give the flow/return temperatures, the flowtemp should be displayed and the return shown in some menu or other.
I have 10 rads ~ 15kw output and a 20kw oil fired boiler set to 75C will heat the system contents of ~ 90L from a cold morning start in 25 to 30 minutes.
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Thanks John, I think I have seen the boiler temp display flicking from a figure of around 50ish when in cycle mode. The boiler is a Vaillant 835?EcoPlus and I’m not sure if there are hidden menus to let you the flow and return temps. I’ve also reduced the boiler temp to 65C to try and save on gas.
Let me monitor it a bit more and I’ll report back.
Let me monitor it a bit more and I’ll report back.
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