Boiler Flow Temperature for Different Outside Temperatures

nxdmsandkaskdjaqd

A question for those that have a central heating system (weather compensator) where the boiler flow temperature is set by the outside temperature (i.e cold outside higher flow temperature, warm outside then a lower flow temperature).  I would be interested to know the flow temperature for different outside temperatures:
-5C = x flow temp
0C = x flow temp
5C = x flow temp

Astria

It depends on your individual property and CHS. You would use the lowest flow temp that will still keep your property warm.

Mine kicked in at 60c this morning when it was warming the house up, but now it's running at 50c even though the outside temperature hasn't really changed. The only difference is that this morning it was increasing the temperature of the house from 14 - 17, but now it's just maintaining that temperature so it doesn't need to be as high.

Doing this yourself will be a hassle, so if your boiler can keep your property warm at 50c then leave it at that, but if it takes too long or is on constantly and can't keep the property warm then increase it to 55c, etc.

Reed_Richards

Astria said:

Mine kicked in at 60c this morning when it was warming the house up, but now it's running at 50c even though the outside temperature hasn't really changed. The only difference is that this morning it was increasing the temperature of the house from 14 - 17, but now it's just maintaining that temperature so it doesn't need to be as high.

That's Load Compensation, not the same thing as Weather Compensation.  

Astria

Reed_Richards said:

Astria said:

Mine kicked in at 60c this morning when it was warming the house up, but now it's running at 50c even though the outside temperature hasn't really changed. The only difference is that this morning it was increasing the temperature of the house from 14 - 17, but now it's just maintaining that temperature so it doesn't need to be as high.

That's Load Compensation, not the same thing as Weather Compensation.  

Correct, I have both, I was just saying that the outside temperature doesn't really matter, it depends on your individual property and equipment. A 50c flow temperature for one property might not be the correct flow temperature for another.

Qyburn

I did this for commercial builds, using mixing valve rather than varying boiler temperature but the final effect is the same. We used a ratio of 2:1, a 1 degree change in outside temperature made a 2 degree change in flow temp. With a design upper and lower limit. 

nxdmsandkaskdjaqd

Astria said:

It depends on your individual property and CHS. You would use the lowest flow temp that will still keep your property warm.

Mine kicked in at 60c this morning when it was warming the house up, but now it's running at 50c even though the outside temperature hasn't really changed. The only difference is that this morning it was increasing the temperature of the house from 14 - 17, but now it's just maintaining that temperature so it doesn't need to be as high.

Doing this yourself will be a hassle, so if your boiler can keep your property warm at 50c then leave it at that, but if it takes too long or is on constantly and can't keep the property warm then increase it to 55c, etc.

By way of background.  I have a 7 year old condensing boiler in 20 year property using on average 20000kw a year.  The boiler is in the utility room and I have been adjusting the flow for the last 7 years.

This morning I had a a flow of 53C, house was at 16.3C and outside was -4.2C.   It did however take 2 hrs to raise the temperature to 20C and used 38kw of gas.  But I am OK with that length of time.  I use the analogy of 2 cars on a journey, one at 70mph and the other at 55mph, the car travelling at 55mph would use less fuel.

The reason for the post was to check my flow rates based on modern compensators.

nxdmsandkaskdjaqd

Qyburn said:

I did this for commercial builds, using mixing valve rather than varying boiler temperature but the final effect is the same. We used a ratio of 2:1, a 1 degree change in outside temperature made a 2 degree change in flow temp. With a design upper and lower limit. 

Is it possible for you to say the following:
-5C = x flow temp
0C = x flow temp
5C = x flow temp

Londoner_1

nxdmsandkaskdjaqd said:

Astria said:

It depends on your individual property and CHS. You would use the lowest flow temp that will still keep your property warm.

Mine kicked in at 60c this morning when it was warming the house up, but now it's running at 50c even though the outside temperature hasn't really changed. The only difference is that this morning it was increasing the temperature of the house from 14 - 17, but now it's just maintaining that temperature so it doesn't need to be as high.

Doing this yourself will be a hassle, so if your boiler can keep your property warm at 50c then leave it at that, but if it takes too long or is on constantly and can't keep the property warm then increase it to 55c, etc.

By way of background.  I have a 7 year old condensing boiler in 20 year property using on average 20000kw a year.  The boiler is in the utility room and I have been adjusting the flow for the last 7 years.

This morning I had a a flow of 53C, house was at 16.3C and outside was -4.2C.   It did however take 2 hrs to raise the temperature to 20C and used 38kw of gas.  But I am OK with that length of time.  I use the analogy of 2 cars on a journey, one at 70mph and the other at 55mph, the car travelling at 55mph would use less fuel.

The reason for the post was to check my flow rates based on modern compensators.

Yes but the higher gas setting means house will warm up quicker but use more gas, the lower setting means more time to reach temp hence using more gas over longer run.

End result is same amount of gas used overall.

markin

Just keep a log and you will soon figure it out for your home.

Reed_Richards

Londoner_1 said:

Yes but the higher gas setting means house will warm up quicker but use more gas, the lower setting means more time to reach temp hence using more gas over longer run.

End result is same amount of gas used overall.

No, the lower the return water temperature the more efficiently your gas boiler will work.  And the lower the output water setting the lower the return water temperature.  The analogy with the two cars is exactly right.

nxdmsandkaskdjaqd said:

  I use the analogy of 2 cars on a journey, one at 70mph and the other at 55mph, the car travelling at 55mph would use less fuel.

 

Astria

Reed_Richards said:

Londoner_1 said:

Yes but the higher gas setting means house will warm up quicker but use more gas, the lower setting means more time to reach temp hence using more gas over longer run.

End result is same amount of gas used overall.

No, the lower the return water temperature the more efficiently your gas boiler will work.  And the lower the output water setting the lower the return water temperature.  The analogy with the two cars is exactly right.

nxdmsandkaskdjaqd said:

  I use the analogy of 2 cars on a journey, one at 70mph and the other at 55mph, the car travelling at 55mph would use less fuel.

 

Lower return water temperature is known to:

• Slower corrosion rates
• Less O2 released to attack metals
• Less Thermal Shock to the system and components
• Better on the expansion vessel as the membrane is kept cooler
• Reduces cavitation at pump and fittings
• Less noise/ creaking in the system
• Increased comfort through reduced heat gradient in the room
• Increased comfort through steady emitter output
• Safer
• Cleaner Air within the house
• Less loss through pipes in unheated areas
• higher comfort at lower room temperatures
• More efficient combustion/ heat transfer
• Condensate can clean heat exchanger and ensure better heat transfer
• More extracted latent heat from added condensing
• Longer burn times, less cycling of the boiler and boiler wear and tear from turning on and off the ignition sequence.

The list goes on...