Dropping the flow temperature to 60c

diystarter7

[Deleted User] said:

Norman_Castle said:

Deleted_User said:

Norman_Castle said:

fly-catchers said:

Given that combi boilers have been around for years now why are they only now going on about dropping the flow temp? The advice for dropping the thermostat temp by 1 degree to save 10% has been around for years. 

"They" being the government? Its public information offered now due to the fuel crisis. The information has been around for years. The heating or installation industry should have advised homeowners when the installations were done but from experience many did not give this advice or advised wrongly.

Why can't boilers measure the return temperature and adjust their output automatically?

Public information about  would be equally useful as would stopping homeowners drying washing on radiators.

I'd suggest public information about how TRVs work and what their function is would be more important than saying "set them all halfway".

The full quote rather than your omissive quote, "setting TRVs to halfway which is 70 degrees then adjusting in small amounts over time"

Suggesting 70 degrees as a starting point rather than set to maximum as they often seem to be. I agree educating their purpose and that the setting makes no difference to how quickly the room will warm up.

So, I should go and turn up every TRV in my house then?

Surely saying "your TRV determines the temperature where your radiator turns off - here is the range" is far more useful.

Hi

I agree

To turn them up and then halfway is very poor and serious money-wasting advice. People already in fuel poverty and others
would not thank anyone for poorly though out advice.

TVR's are puka when it comes to saving money via CH and if your already have them, utilise them as they can save you loads of money. If you don't have TVR's, IMO, gov should give targeted help as not only TVR's and good practices will save money but the planet as well.

Thanks

Steve182

For a condensing boiler you will achieve optimum efficiency with a flow temp of around 50°C. At this temp the return will hopefully be as low as 30°C but with low load could be a bit higher, maybe 40°C

The reason for increased efficiency at low temps is the secondary heat exchanger, in the flue (the condensing part) which works much more efficiently when water is cooler.

The flue gases may be at perhaps 75°C after leaving the main heat exchanger. Condensing boilers have a main and a secondary heat exchanger. If you run your boiler at  80°C flow with a return of say 65°C, there is only a 10°C temp difference between return water at 65 and flue gas at 75 in the secondary heat exchanger. Not much heat is extracted from the flue.

On the other hand, if your return water temp is much lower, say 35°C, achievable with a 50°C flow, and your flue gasses enter the secondary heat exchanger at 75°C,  well happy days, 40°C temperature difference! You'll see a huge plume of condensed flue gasses exiting your flue terminal confirming that you're extracting every possible BTU from that boiler!

Edited to say that 50°C flow temp is unlikely to give you enough radiator output  in very cold weather, but may be OK in milder temperatures.

This is the same reason that ASHP's don't usually perform satisfactorily when connected to radiators when it's cold.

pensionpawn

Steve182 said:

For a condensing boiler you will achieve optimum efficiency with a flow temp of around 50°C. At this temp the return will hopefully be as low as 30°C but with low load could be a bit higher, maybe 40°C

The reason for increased efficiency at low temps is the secondary heat exchanger, in the flue (the condensing part) which works much more efficiently when water is cooler.

The flue gases may be at perhaps 75°C after leaving the main heat exchanger. Condensing boilers have a main and a secondary heat exchanger. If you run your boiler at  80°C flow with a return of say 65°C, there is only a 10°C temp difference between return water at 65 and flue gas at 75 in the secondary heat exchanger. Not much heat is extracted from the flue.

On the other hand, if your return water temp is much lower, say 35°C, achievable with a 50°C flow, and your flue gasses enter the secondary heat exchanger at 75°C,  well happy days, 40°C temperature difference! You'll see a huge plume of condensed flue gasses exiting your flue terminal confirming that you're extracting every possible BTU from that boiler!

Edited to say that 50°C flow temp is unlikely to give you enough radiator output  in very cold weather, but may be OK in milder temperatures.

This is the same reason that ASHP's don't usually perform satisfactorily when connected to radiators when it's cold.

There's also the issue, for boilers that can't set independent h/w / c/h temperatures, that the flow temperature shouldn't be less than 60c (ideally 62c) to protect against legionella build up in the H/W tank.

Reed_Richards

Steve182 said:.

This is the same reason that ASHP's don't usually perform satisfactorily when connected to radiators when it's cold.

And up until there you had me convinced you knew what you were talking about.  I presume what you mean is that ASHPs don't usually perform satisfactorily as a drop-in replacement for a gas or oil boiler when it's cold - which is true.  I replaced my oil boiler with an ASHP and it has kept us perfectly warm during the recent cold weather.  But we also replaced all the radiators with ones having a much larger surface area.         

[Deleted User]

pensionpawn said:

Steve182 said:

For a condensing boiler you will achieve optimum efficiency with a flow temp of around 50°C. At this temp the return will hopefully be as low as 30°C but with low load could be a bit higher, maybe 40°C

The reason for increased efficiency at low temps is the secondary heat exchanger, in the flue (the condensing part) which works much more efficiently when water is cooler.

The flue gases may be at perhaps 75°C after leaving the main heat exchanger. Condensing boilers have a main and a secondary heat exchanger. If you run your boiler at  80°C flow with a return of say 65°C, there is only a 10°C temp difference between return water at 65 and flue gas at 75 in the secondary heat exchanger. Not much heat is extracted from the flue.

On the other hand, if your return water temp is much lower, say 35°C, achievable with a 50°C flow, and your flue gasses enter the secondary heat exchanger at 75°C,  well happy days, 40°C temperature difference! You'll see a huge plume of condensed flue gasses exiting your flue terminal confirming that you're extracting every possible BTU from that boiler!

Edited to say that 50°C flow temp is unlikely to give you enough radiator output  in very cold weather, but may be OK in milder temperatures.

This is the same reason that ASHP's don't usually perform satisfactorily when connected to radiators when it's cold.

There's also the issue, for boilers that can't set independent h/w / c/h temperatures, that the flow temperature shouldn't be less than 60c (ideally 62c) to protect against legionella build up in the H/W tank.

For a system boiler with a HW cylinder, there must be a temperature difference between the boiler flow temperature and the cylinder set temperature. If not, the boiler will just keep cycling when the two temperatures reach near parity. 

grn99

Dolor said:

pensionpawn said:

Steve182 said:

For a condensing boiler you will achieve optimum efficiency with a flow temp of around 50°C. At this temp the return will hopefully be as low as 30°C but with low load could be a bit higher, maybe 40°C

The reason for increased efficiency at low temps is the secondary heat exchanger, in the flue (the condensing part) which works much more efficiently when water is cooler.

The flue gases may be at perhaps 75°C after leaving the main heat exchanger. Condensing boilers have a main and a secondary heat exchanger. If you run your boiler at  80°C flow with a return of say 65°C, there is only a 10°C temp difference between return water at 65 and flue gas at 75 in the secondary heat exchanger. Not much heat is extracted from the flue.

On the other hand, if your return water temp is much lower, say 35°C, achievable with a 50°C flow, and your flue gasses enter the secondary heat exchanger at 75°C,  well happy days, 40°C temperature difference! You'll see a huge plume of condensed flue gasses exiting your flue terminal confirming that you're extracting every possible BTU from that boiler!

Edited to say that 50°C flow temp is unlikely to give you enough radiator output  in very cold weather, but may be OK in milder temperatures.

This is the same reason that ASHP's don't usually perform satisfactorily when connected to radiators when it's cold.

There's also the issue, for boilers that can't set independent h/w / c/h temperatures, that the flow temperature shouldn't be less than 60c (ideally 62c) to protect against legionella build up in the H/W tank.

For a system boiler with a HW cylinder, there must be a temperature difference between the boiler flow temperature and the cylinder set temperature. If not, the boiler will just keep cycling when the two temperatures reach near parity. 

On my system that difference is a minimum of 10 degrees; otherwise as you say, it will go on forever burning gas and the cylinder water never reaching temp. The other thing I've noticed since fitting a thermometer onto the h/w cylinder next to the stat (cylinder is insulated by manufacturer) is how quickly that temp drops, (withour water being used and new cold topping up) which made me think of those who only heat h/w cyl until low 50's. Yes, I have a supplementary h/w jacket on order, now that I know how much heat is lost without the tank water being used, over a day. Will only increase the cylinder stat temp once I've added the jacket.

Astria

pensionpawn said:

Steve182 said:

For a condensing boiler you will achieve optimum efficiency with a flow temp of around 50°C. At this temp the return will hopefully be as low as 30°C but with low load could be a bit higher, maybe 40°C

The reason for increased efficiency at low temps is the secondary heat exchanger, in the flue (the condensing part) which works much more efficiently when water is cooler.

The flue gases may be at perhaps 75°C after leaving the main heat exchanger. Condensing boilers have a main and a secondary heat exchanger. If you run your boiler at  80°C flow with a return of say 65°C, there is only a 10°C temp difference between return water at 65 and flue gas at 75 in the secondary heat exchanger. Not much heat is extracted from the flue.

On the other hand, if your return water temp is much lower, say 35°C, achievable with a 50°C flow, and your flue gasses enter the secondary heat exchanger at 75°C,  well happy days, 40°C temperature difference! You'll see a huge plume of condensed flue gasses exiting your flue terminal confirming that you're extracting every possible BTU from that boiler!

Edited to say that 50°C flow temp is unlikely to give you enough radiator output  in very cold weather, but may be OK in milder temperatures.

This is the same reason that ASHP's don't usually perform satisfactorily when connected to radiators when it's cold.

There's also the issue, for boilers that can't set independent h/w / c/h temperatures, that the flow temperature shouldn't be less than 60c (ideally 62c) to protect against legionella build up in the H/W tank.

That's the easiest way to combat legionella build up, but realistically, it's incredibly rare for legionella build up in any residential property to cause any problems and typically the worse place isn't the hot water cylinder but the shower which normally runs at the ideal temperature for legionella growth and also isn't used for long periods of time. If you use the entire hot water cylinder every day then build up isn't going to happen, alternatively increasing the temperature to 60c once a month (or week if you use little of the stored water) is typically enough.

pensionpawn

[Deleted User] said:

pensionpawn said:

Steve182 said:

For a condensing boiler you will achieve optimum efficiency with a flow temp of around 50°C. At this temp the return will hopefully be as low as 30°C but with low load could be a bit higher, maybe 40°C

The reason for increased efficiency at low temps is the secondary heat exchanger, in the flue (the condensing part) which works much more efficiently when water is cooler.

The flue gases may be at perhaps 75°C after leaving the main heat exchanger. Condensing boilers have a main and a secondary heat exchanger. If you run your boiler at  80°C flow with a return of say 65°C, there is only a 10°C temp difference between return water at 65 and flue gas at 75 in the secondary heat exchanger. Not much heat is extracted from the flue.

On the other hand, if your return water temp is much lower, say 35°C, achievable with a 50°C flow, and your flue gasses enter the secondary heat exchanger at 75°C,  well happy days, 40°C temperature difference! You'll see a huge plume of condensed flue gasses exiting your flue terminal confirming that you're extracting every possible BTU from that boiler!

Edited to say that 50°C flow temp is unlikely to give you enough radiator output  in very cold weather, but may be OK in milder temperatures.

This is the same reason that ASHP's don't usually perform satisfactorily when connected to radiators when it's cold.

There's also the issue, for boilers that can't set independent h/w / c/h temperatures, that the flow temperature shouldn't be less than 60c (ideally 62c) to protect against legionella build up in the H/W tank.

For a system boiler with a HW cylinder, there must be a temperature difference between the boiler flow temperature and the cylinder set temperature. If not, the boiler will just keep cycling when the two temperatures reach near parity. 

Indeed. Flow 62c, boiler belt stat 60c. Boiler comes on, boiler goes off. 2/3 of the year the tank is heated by excess solar only.

Norman_Castle

[Deleted User] said:

Norman_Castle said:

Deleted_User said:

Norman_Castle said:

fly-catchers said:

Given that combi boilers have been around for years now why are they only now going on about dropping the flow temp? The advice for dropping the thermostat temp by 1 degree to save 10% has been around for years. 

"They" being the government? Its public information offered now due to the fuel crisis. The information has been around for years. The heating or installation industry should have advised homeowners when the installations were done but from experience many did not give this advice or advised wrongly.

Why can't boilers measure the return temperature and adjust their output automatically?

Public information about  would be equally useful as would stopping homeowners drying washing on radiators.

I'd suggest public information about how TRVs work and what their function is would be more important than saying "set them all halfway".

The full quote rather than your omissive quote, "setting TRVs to halfway which is 70 degrees then adjusting in small amounts over time"

Suggesting 70 degrees as a starting point rather than set to maximum as they often seem to be. I agree educating their purpose and that the setting makes no difference to how quickly the room will warm up.

So, I should go and turn up every TRV in my house then?

Assuming you understand how TRVs work that would obviously be a backward step. The advice would be for people who don't know what they are and from experience have them set at maximum.

Norman_Castle

For anyone unsure of how to use their thermostatic radiator valves. Offered on a take it or leave it basis.

https://tmhughesandson.uk/thermostatic-radiator-valve-hack/

Unfortunately, most homeowners don’t know how to get the very best from their thermostatic radiator valves a lot of people turn them to the maximum or minimum setting, which is unnecessary. The idea of thermostatic radiator valves is that they adjust themselves, here’s how best to use them for energy efficiency

In every room, you don’t want

• No heat
• Some heat but not enough
• A little to much heat
• Far to much heat

You want the exact temperature that matches your comfort preferences, the amount of heat will be different for every room in your house

In every room turn your radiator valves to the halfway point this will likely be level 3, leave for 6-24 hours, it’s up to you but 6 hours is the minimum

After the 6-24 hours has elapsed sit in each room for a while (around 15 minutes will work with this hack) and decide whether the room is too hot or to cold

• To hot? turn the valve down to 2.5
• To Cold? turn the valve up to 3.5

Leave again for 6-24 hours after this time sit in each room again and monitor the temperature

• Still too hot? turn the valve down to 2
• Still too cold? turn the valve up to 4

Perfect Temperature? the radiator is set and can be left alone

Repeat this method until you have your ideal temperature for each room you also have the option of working in smaller increments when adjusting the valves (0.25 instead of 0.5 for example) if you want a more precise setting.

This simple method will make you very comfortable and make sure you’re not wasting in money on your heating bills.