Flow and return temperatures for optimum efficiency

[sgs2009]

My Ideal combi boiler has a maximum flow temperature of 55 degrees and a minimum flow temperature of 15 degrees set on it. Are these values ok? Thanks

 

[ScottishGasMan]

My Ideal combi boiler has a maximum flow temperature of 55 degrees and a minimum flow temperature of 15 degrees set on it. Are these values ok? Thanks

Is your house warm enough?

If it is then yes they are ok, if it isn't then it may need to be higher. There is no right or wrong broad figure, it will depend on the systems design and the heat loss of the house.

 

[sgs2009]

Thanks

 

[Johntheo5]

Those temperatures sound more like DHW to me, although 15C isn't much use in either CH or DHW mode.

 

[sgs2009]

Those temperatures sound more like DHW to me, although 15C isn't much use in either CH or DHW mode.

That's what I thought - hence the question - they are the settings shown when I access the menu - seems odd

 

[Johntheo5]

What boiler/model/power output?

 

[JonathanM]

My Ideal combi boiler has a maximum flow temperature of 55 degrees and a minimum flow temperature of 15 degrees set on it. Are these values ok? Thanks

Which Ideal combi is it? I've not seen that minimum setting before.

 

[Londoner2]

My Main eco compact is set to 55c in my terraced house, house does take a bit longer to heat up and the rads dont get really hot like old heating systems.

In my opinion condensing mode savings were calculated way back in 2009 when energy pricess were really low, a saving today of £150 is paltry.

 

[sgs2009]

Which Ideal combi is it? I've not seen that minimum setting before.

It's an Ideal Logic Combi 30. I accessed the settings through the Honeywell wireless.

 

[old duffer]

My Ideal combi boiler has a maximum flow temperature of 55 degrees and a minimum flow temperature of 15 degrees set on it. Are these values ok? Thanks

I run my home on flow temperature rather than room thermostat.
I have an auto option that determines incoming air and flow return temp. It's been -4.7 degrees outside here for the last few days and nights and the max flow temp the auto setting has given is 56 degrees.
If I opt for the eco mode for flow settings, I can reach a max of 60 degrees.
For flow circuit heating you need to size the rads to account for the lower temp (you need to use heat loss and water temp calcs to determine what these are)
I find that auto setting keeps the house @ 16.5-17 degrees and combined with a humidity of around 44%, the entire house is comfortable.
18 degrees is the cozy room temp and this is achieved (in these very low temps at the moment) by switching to eco mode @ 60 degrees flow on an evening.
Readings at the boiler side show flow at 60 degrees and return @ 28 degrees....rad surface temps are 30-32 degrees

 

[ericmark]

I have wondered many times about saving when gaining latent heat, but much depends on how the boiler is set up to start with. Both by manufacturer and installer.

I know my mothers did not have option for an electric modulating thermostat, latter Worcester Bosch do, but not OpenTherm which it seems means only controls one room, there may be one which links to TRV's but I have not seen one.

This means you have to decide either/or. Modulating thermostat, or linked to TRV's the control with TRV's will cause the boiler to modulate, but it will cycle in warmer weather without a wall thermostat, so the two need careful balanced, and I managed with mothers house, but failed with this house.

But boiler in this house does not modulate, so TRV control not so important. Mothers house once set, radiators always warm, very rare hot, or cold, just warm enough to maintain room temperature.

But is the saving enough to be worth swapping to a modulating thermostat? Having programmable TRV's yes, cost me £15 each in 2019, but paying £200 for new thermostat, that's half the years oil bill, not sure it will save enough?

 

[old duffer]

I have wondered many times about saving when gaining latent heat, but much depends on how the boiler is set up to start with. Both by manufacturer and installer.

I know my mothers did not have option for an electric modulating thermostat, latter Worcester Bosch do, but not OpenTherm which it seems means only controls one room, there may be one which links to TRV's but I have not seen one.

This means you have to decide either/or. Modulating thermostat, or linked to TRV's the control with TRV's will cause the boiler to modulate, but it will cycle in warmer weather without a wall thermostat, so the two need careful balanced, and I managed with mothers house, but failed with this house.

But boiler in this house does not modulate, so TRV control not so important. Mothers house once set, radiators always warm, very rare hot, or cold, just warm enough to maintain room temperature.

But is the saving enough to be worth swapping to a modulating thermostat? Having programmable TRV's yes, cost me £15 each in 2019, but paying £200 for new thermostat, that's half the years oil bill, not sure it will save enough?

how can a thermostat interact with a boiler that does not support high modulation? A thermostat is on/off...its the boiler that does the work

 

[vulcancontinental]

It turns it off

 

[johnny2007]

1. Probably the most important feature from an efficiency standpoint is to ensure that the boiler runs for as much time as possible in condensing mode.
2. To run in condensing mode, the return water temperature as it reaches the boiler should be no more than 55 degrees.
3. You can work back from that to calculate what the flow temperature should be. This isn't a simple calculation as it depends on how the system (assuming radiators) was sized in the first place.
4. If the radiator system is modern, and was correctly sized originally, then the temperature drop across each radiator should be around 20 degrees, giving a flow temperature of 55 + 20 = 75 degrees.

Does this apply to combi boilers?
If so, do we measure temperatures at the radiator pipes (flow and return?) Or at the boiler?

 

[JonathanM]

Does this apply to combi boilers?

You don't want a flow temperature of 75C with any type of condensing boiler. You really only need the flow temperature to be high enough to keep you comfortable, because the lower the return temperature, the more it will condense, and the more efficient it will be. A flow of 55C, or even lower, is often recommended these days.

If so, do we measure temperatures at the radiator pipes (flow and return?) Or at the boiler?

At the boiler is more important.