CH flow temp's
- Thread starter bster
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Am I right in thinking it would use less fuel, so it'd be cheaper?? 
well yes, but would it heat your home that has had its rads sized using the standard deltaT value of XX (or whatever) the rad manufacturers use for specifying outputs.
also at 60 flow the boiler will fire for longer to meet room stat temp than it would when at 82degrees (i think).
BTW - can someone explain deltaT50, i know its something to do with the difference between flow temp and room temp or something
also at 60 flow the boiler will fire for longer to meet room stat temp than it would when at 82degrees (i think).
BTW - can someone explain deltaT50, i know its something to do with the difference between flow temp and room temp or something
On the majority of condensing boilers it is advantageous to run the heating temperature as low as possible (but sufficiently high to heat the house) in order to allow the maximum time the boiler fully condenseses.
Top end boiler do this automatically and are fitted with an external temperature sensor.
Delta T is just the temperature difference. Hot water performance of combis is often qouted at a delta T of 35 centigrade, eg 9.5 lites/min @ delta 35 meaning it will raise the inlet water temperature by 35 centigrade with a flow rate of 9,5.
Several manufacturers quote a delta T of 30 centigrade in order to "exaggerate" the boiler performance to the public and uninformed installers.
Top end boiler do this automatically and are fitted with an external temperature sensor.
Delta T is just the temperature difference. Hot water performance of combis is often qouted at a delta T of 35 centigrade, eg 9.5 lites/min @ delta 35 meaning it will raise the inlet water temperature by 35 centigrade with a flow rate of 9,5.
Several manufacturers quote a delta T of 30 centigrade in order to "exaggerate" the boiler performance to the public and uninformed installers.
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You don't! the boiler's flue gas heat exchanger reduces the heat of the flue gas to the dew point, thus returning useable heat to the system. It can usually only do this efficiently when the system is going full whack and has not been modulated down.
If you want to see it happening on a combi, just open a hot tap to full flow and then watch the flue.
If you want to see it happening on a combi, just open a hot tap to full flow and then watch the flue.
Elite - thank you,
i've remembered now that is why rads should be oversized using deltaT50, as this will overload the condenser and result in max efficency, but are rads now sold with outputs rated at delta TXX specifically for condensing systems.
Any thoughts on original post?
i've remembered now that is why rads should be oversized using deltaT50, as this will overload the condenser and result in max efficency, but are rads now sold with outputs rated at delta TXX specifically for condensing systems.
Any thoughts on original post?
Set the boiler flow temperature at a temperature so the return water drops below the dew point.
For most of the heating season a flow temperature of say 60 degrees with a delta of 10 to 20 across the radiators will ensure a return tempearture sufficiently low enough to allow the boiler to condense. It is only necessary to raise the flow temperature on very cold days. Weather compensated boilers do this automatically of course.
For most of the heating season a flow temperature of say 60 degrees with a delta of 10 to 20 across the radiators will ensure a return tempearture sufficiently low enough to allow the boiler to condense. It is only necessary to raise the flow temperature on very cold days. Weather compensated boilers do this automatically of course.
In the real world, we live with what we get. Most customers will not appreciate the irony of paying extra ££££££'s to achieve modest savings on replacing all of their radiators. Mind you, if the cost of gas goes up any more .......
Eliteheat said
The boiler heat exchanger can only extract the latent heat of evaporation from the flue gas if the return water is below the dew point. This means the boiler flow temperature must be significantly below its maximum setting. Much of the water seen eminating from the flue is due to water vapour condensing in the flue itself and not on the heat exchanger.
This is why all condensing boilers have a higher Kw output at lower flow and return temparatures.
The most efficient ones also have a much larger plate exchanger to run the flow and return temperatures lower in hot water mode.
The larger radiators debate comes from the fact that to run the boiler in condensing mode for as much time as possible the flow tempeartures must be lower. Since the average temperature of the radiator is then lower its output is correspondingly lower.
In reality for most of the heating season the radiators can be run at reduced average temperature and the house will heat up fine. When the weather is really cold the flow tempearture can be turned up.
Replacing all the raidors for larger types just to allow the boiler to condense fully during the few weeks a years when it is really cold is fruitless. They would never pay for themselves. It was another myth put around when condensers arrived on the scene.
Where are you getting the delta 50 from? Are you taking an average radiator temperature of 70 (with flow at 80, return at 60) and a room temperature of 20 centigrade?
The boiler heat exchanger can only extract the latent heat of evaporation from the flue gas if the return water is below the dew point. This means the boiler flow temperature must be significantly below its maximum setting. Much of the water seen eminating from the flue is due to water vapour condensing in the flue itself and not on the heat exchanger.
This is why all condensing boilers have a higher Kw output at lower flow and return temparatures.
The most efficient ones also have a much larger plate exchanger to run the flow and return temperatures lower in hot water mode.
The larger radiators debate comes from the fact that to run the boiler in condensing mode for as much time as possible the flow tempeartures must be lower. Since the average temperature of the radiator is then lower its output is correspondingly lower.
In reality for most of the heating season the radiators can be run at reduced average temperature and the house will heat up fine. When the weather is really cold the flow tempearture can be turned up.
Replacing all the raidors for larger types just to allow the boiler to condense fully during the few weeks a years when it is really cold is fruitless. They would never pay for themselves. It was another myth put around when condensers arrived on the scene.
Where are you getting the delta 50 from? Are you taking an average radiator temperature of 70 (with flow at 80, return at 60) and a room temperature of 20 centigrade?
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Not forgetting guys that underfloor heating workis at 60c which is why many boilers have the adjustment for flow temp
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