Most efficient boiler settings

Lox99

To achieve the best efficiency with your boiler, consider the following settings:

baxi.co.uk

Set the boiler temperature to at least 65°C to prevent bacteria growth.

baxi.co.uk

For optimal efficiency, reduce the flow temperature to 60°C or lower.

energyguide.org.uk

Lox99

Generally speaking, the most efficient temperature for your thermostat is between 18°C and 20°C.

Albermarle

Lox99 said:

To achieve the best efficiency with your boiler, consider the following settings:

baxi.co.uk

Set the boiler temperature to at least 65°C to prevent bacteria growth.

baxi.co.uk

For optimal efficiency, reduce the flow temperature to 60°C or lower.

energyguide.org.uk

Bacteria growth is only possible if you have a hot water tank. The advice to go to 65 is therefore irrelevant if you have a combi.

In any case 65 is not really necessary to kill the bacteria involved (which is legionnaires) in a domestic setting. A setting of 60 should be fine, especially if the system is in regular use.
Problems with Legionnaires is mainly in commercial settings, so there the 65 recommendation is more relevant.

FreeBear

Lox99 said:

To achieve the best efficiency with your boiler, consider the following settings:

Set the boiler temperature to at least 65°C to prevent bacteria growth.

For optimal efficiency, reduce the flow temperature to 60°C or lower.

Necro-posting on a 3 year old thread is usually frowned upon. On top of that, your "advice" is not precise.

Hot water does not need to be 65°C or higher. Anything above 50°C will kill bacteria, it just takes longer. On top of that, as you increase the temperature, the risk of scalding increases. So if you must heat your water to 65°C (and there is no reason to have it that hot), you should fit automatic thermostatic valves on every sink/bath to limit the temperature.

Optimal boiler efficiency will depend on the number of radiators in the system, their size, and whether TRVs are fitted. If your radiators are marginally sized for the room being heated, turning the flow temperature down may mean that the room never heats up. On top of that, there is a minimum amount of heat that a condensing boiler can produce - If the number/size of radiators is less, then the boiler will start to short cycle which will knock back efficiency and increase wear & tear on internal components. Yes, IF you have a condensing boiler that can modulate its output AND your radiators are appropriately sized, 60°C is good (or even 50°C). But when it is really cold outside, you may well need to increase the flow temperature in order to heat the house effectively.

Lox99 said:

Generally speaking, the most efficient temperature for your thermostat is between 18°C and 20°C.

Rubbish - The most efficient thermostat setting is a temperature that you are comfortable at. Some (e.g. very young, and elderly) need a higher setting of 21-22°C. Others can get away with 16-17°C or even no heating at all.

grumpypensioner

We have lived in our owned semi for 60 years so it is a bit late to make any radical changes to the heating system, but I have managed to tune it nicely over the years. Bearing in mind that we are now old and decrepit so cold is really painful, and we don't holiday or dine out, so our pension is now sufficient to cover energy/water/rates/food.

We have an old Baxi back boiler and conventional hot water tank and a two downstairs radiators (hall and dining room), supplimented with a Dakin air conditioner heat pump upstairs and a free standing (low cost) Wessex air heat pump conditioner in the lounge (brilliant device); the Baxi also has an open gas fire (also brilliant). All nearly zero maintenance so count  that against your expensive maintenance contract.

The gas back boiler is set to 70º to get efficient heat transfer to the radiators and hot water tank. The radiators have independent thermostats to control different area temperatures with the main thermostat on the wall in the dining room; the only bad aspect is that it measures the wall temperature more than free air!!! All heating is switched off for 11 hours at night because we retire early, but comes on at 6.30 before we get up (why heat when we are not there?). The hot water tank is set to 55º which provides our hot pressure shower in the morning. Note that listeria does not just die suddenly at the recommended 60º, it is dormant at low temperature, breeds when warm, and is killed off at higher temperatures at varying rates. So a hot water tank which is maintained at a lower temperature as well as being regularly flushed through should be ok.

So our comfort depends on multiple sources of heating, each controlling their own specific zone with the radiators supplying background central warmth when needed. Not a fully automated system but it is simple to physically press a button when required! We find 21º to 23º comfortable which is achieved within an hour from the occasional drop to 15º when freezing outside when I get up and make the tea. We may not be energy efficient, but we are comfortable, and lucky enough not to have other expenses using our pension. We also add that we have plenty of ventilation so no funny growths anywhere.

I think the ethos of current green efficient energy usage is fraught with potential problems. Living in a sealed box reliant on a single energy source can cause problems, so spread the load and have backups, consider other mechanisms such as thermal solar panels. I still have a "green" 100% efficient emersion heater in the hot water tank as backup (make sure it can be set to lower temperatures than the standard 70º). Don't aim for the ultimate savings and design a bit of wastage into the house such as opening the windows! Following government guidelines may be green, but it can also lead to excess humidity with black mould and bug growth. And installing a £12k electric powered water heat pump system (having equivalent interest savings of nearly £500 pa) takes a long pay back period. And electricity energy costs are 4 times that for gas so add that into your calculations.

My wife reminds me of the early GoS treatment for TB, put them in a covered warm bed on the veranda to breathe the fresh cold air! Irrelevant I know but life is about compromise, just think/reason and lessen government/social media influence, every situation is different. Apologises for the diatribe, good luck.

grumpypensioner

I would add to my previous comment, that all is not what you might be told in advice about air to water heat pump technology, which is probably why the government offers a grant to entice you to change.
These heat pumps can have an efficiency of up to 400%, but this is a marketing optimum and only for a narrow range of weather conditions, and generally quite a bit lower. The associated heat losses from piping, pumping and storage will drop it further. Gas boilers can have an efficiency between 40% and 90%, so bearing in mind the 4x cost of electricity over gas, the cost of operating the two systems is probably about equal so no dramatic savings to offset capital outlay. They even quote a possible loss on cold days.
There is an important difference between heat pumps and gas, the operating temperatures. Gas flames are very hot so you can have wide range water temperatures and things heat up quickly. Heat pumps operate at much lower temperatures, generally a maximum of 60ºC, so everything is very much slower and your radiators and hot water tank will most definitely not exceed this. Actually running at these lower temperatures will be your main energy saving - so you could also lower the settings on your gas boiler to match! However radiators need to be correspondingly larger to provide equivalent warmth.
If you are considering an air to water heat pump, choose very carefully, like new EV technology things are improving but I think there is still a long way to go. It all depends on where you are coming from, what system you are replacing, and your motives for doing so. I personally like my air to air heat pumps, simple, very effective because they operate at lower temperatures and warm (or cool) the whole house. I think a compromise of using gas to provide hot bathing water and air to air heat pumps to control the house is optimum.
Read one example  https://sourceheatpump.com/air-source-heat-pump-minimum-maximum-temperatures/
Another. https://nef.org.uk/can-i-get-my-hot-water-from-an-air-source-heat-pump/

FreeBear

grumpypensioner said:

I would add to my previous comment, that all is not what you might be told in advice about air to water heat pump technology, which is probably why the government offers a grant to entice you to change.
These heat pumps can have an efficiency of up to 400%, but this is a marketing optimum and only for a narrow range of weather conditions, and generally quite a bit lower. The associated heat losses from piping, pumping and storage will drop it further. Gas boilers can have an efficiency between 40% and 90%, so bearing in mind the 4x cost of electricity over gas, the cost of operating the two systems is probably about equal so no dramatic savings to offset capital outlay. They even quote a possible loss on cold days.

If you want real, first hand data on how well a heat pump performs, I'd suggest having a look at https://heatpumpmonitor.org/

Or you can have a chat with local heat pump owners and get the low down of how well a system is performing in your area - https://www.visitaheatpump.com/

Then there is a section on this forum dedicated to heat pumps - https://forums.moneysavingexpert.com/categories/heat-pumps

grumpypensioner

FreeBear said:

grumpypensioner said:

I would add to my previous comment, that all is not what you might be told in advice about air to water heat pump technology, which is probably why the government offers a grant to entice you to change.
These heat pumps can have an efficiency of up to 400%, but this is a marketing optimum and only for a narrow range of weather conditions, and generally quite a bit lower. The associated heat losses from piping, pumping and storage will drop it further. Gas boilers can have an efficiency between 40% and 90%, so bearing in mind the 4x cost of electricity over gas, the cost of operating the two systems is probably about equal so no dramatic savings to offset capital outlay. They even quote a possible loss on cold days.

If you want real, first hand data on how well a heat pump performs, I'd suggest having a look at https://heatpumpmonitor.org/

Or you can have a chat with local heat pump owners and get the low down of how well a system is performing in your area - https://www.visitaheatpump.com/

Then there is a section on this forum dedicated to heat pumps - https://forums.moneysavingexpert.com/categories/heat-pumps

Thank you for the links which I have read in part, a lot of data not always in the ideal format. You have probably realised that I am a little cynical due to the laws of physics and absence of any air to water heat pumps experience. I have two different types of air to air heat pumps, both have been impeccable with a short ramp up to heat our house. And both can be used to dehumidify and cool in hot weather - perfect. I am just concerned with the low operating temperature offered by air to water systems, it does not seem to be "quite there" for efficient heat transfer to maintain a tank of hot water at say 55ºC let alone hotter radiators (seems they appear to need an emersion heater to occasionally boost temperature to kill legionnaire). Any links to a list of problems encountered by users that I can read as there seems to be a paucity of those? As for all product "star" ratings I always read the grumbles first!

FreeBear

grumpypensioner said:

FreeBear said:

grumpypensioner said:

I would add to my previous comment, that all is not what you might be told in advice about air to water heat pump technology, which is probably why the government offers a grant to entice you to change.
These heat pumps can have an efficiency of up to 400%, but this is a marketing optimum and only for a narrow range of weather conditions, and generally quite a bit lower. The associated heat losses from piping, pumping and storage will drop it further. Gas boilers can have an efficiency between 40% and 90%, so bearing in mind the 4x cost of electricity over gas, the cost of operating the two systems is probably about equal so no dramatic savings to offset capital outlay. They even quote a possible loss on cold days.

If you want real, first hand data on how well a heat pump performs, I'd suggest having a look at https://heatpumpmonitor.org/

Or you can have a chat with local heat pump owners and get the low down of how well a system is performing in your area - https://www.visitaheatpump.com/

Then there is a section on this forum dedicated to heat pumps - https://forums.moneysavingexpert.com/categories/heat-pumps

Thank you for the links which I have read in part, a lot of data not always in the ideal format. You have probably realised that I am a little cynical due to the laws of physics and absence of any air to water heat pumps experience. I have two different types of air to air heat pumps, both have been impeccable with a short ramp up to heat our house. And both can be used to dehumidify and cool in hot weather - perfect. I am just concerned with the low operating temperature offered by air to water systems, it does not seem to be "quite there" for efficient heat transfer to maintain a tank of hot water at say 55ºC let alone hotter radiators (seems they appear to need an emersion heater to occasionally boost temperature to kill legionnaire). Any links to a list of problems encountered by users that I can read as there seems to be a paucity of those? As for all product "star" ratings I always read the grumbles first!

I used to have a Baxi back boiler (with the gas front). Radiators roasting hot, and the house was always cold. Over the last 10 years, I've upgraded insulation and killed off all the cold draughts I could. Finally managed to kinda get the place warm, but lacked good control over the boiler. Bit the bullet back in 2023 and had a new boiler installed. Took the opportunity to replace most of the radiators and replumb the system. This winter, I've been experimenting with low flow temperatures in an attempt to push the efficiency as high as I could. Running at 45-55°C flow temperature seems to be the sweet spot. No more roasting hot radiators, yet the house is a comfortable temperature (some days, flow temperature is down to just 40°C).

Low flow temperatures do work to keep a house warm. But the radiators need to be quite a bit larger in order to emit the same amount of heat - Most of mine are 30-50% larger than one might expect.

As for the risk of legionella, if you have a heat pump, you'd normally have an unvented tank. The incoming water (assuming you are on mains) will be treated before it is piped to your house. Almost zero risk of the bacteria getting in to the system. And as long as you maintain a DHW temperature of 50°C or higher, the little blighters will die. OK, at 50°C, it takes hours to kill the bacteria. At 60°C, the bacteria is killed withing 30 minutes. But as you increase the water temperature, the risk of scalds also increases (a real danger for the very young and the elderly).

A heat pump is very capable of proving hot water at 50-55°C. And if you really want a weekly legionella kill cycle, an immersion heater can be used to boost the water to 60°C and use just under 1.2kWh (to heat 200l from 55°C to 60°C). And to be quite honest, the risk of legionella is extremely low in the UK - Some 400 cases reported annually, and half of those, the infection is contracted overseas. You have a better chance of being hit by a No.13 bus !

grumpypensioner

FreeBear said:

grumpypensioner said:

FreeBear said:

grumpypensioner said:

I would add to my previous comment, that all is not what you might be told in advice about air to water heat pump technology, which is probably why the government offers a grant to entice you to change.
These heat pumps can have an efficiency of up to 400%, but this is a marketing optimum and only for a narrow range of weather conditions, and generally quite a bit lower. The associated heat losses from piping, pumping and storage will drop it further. Gas boilers can have an efficiency between 40% and 90%, so bearing in mind the 4x cost of electricity over gas, the cost of operating the two systems is probably about equal so no dramatic savings to offset capital outlay. They even quote a possible loss on cold days.

If you want real, first hand data on how well a heat pump performs, I'd suggest having a look at https://heatpumpmonitor.org/

Or you can have a chat with local heat pump owners and get the low down of how well a system is performing in your area - https://www.visitaheatpump.com/

Then there is a section on this forum dedicated to heat pumps - https://forums.moneysavingexpert.com/categories/heat-pumps

Thank you for the links which I have read in part, a lot of data not always in the ideal format. You have probably realised that I am a little cynical due to the laws of physics and absence of any air to water heat pumps experience. I have two different types of air to air heat pumps, both have been impeccable with a short ramp up to heat our house. And both can be used to dehumidify and cool in hot weather - perfect. I am just concerned with the low operating temperature offered by air to water systems, it does not seem to be "quite there" for efficient heat transfer to maintain a tank of hot water at say 55ºC let alone hotter radiators (seems they appear to need an emersion heater to occasionally boost temperature to kill legionnaire). Any links to a list of problems encountered by users that I can read as there seems to be a paucity of those? As for all product "star" ratings I always read the grumbles first!

I used to have a Baxi back boiler (with the gas front). Radiators roasting hot, and the house was always cold. Over the last 10 years, I've upgraded insulation and killed off all the cold draughts I could. Finally managed to kinda get the place warm, but lacked good control over the boiler. Bit the bullet back in 2023 and had a new boiler installed. Took the opportunity to replace most of the radiators and replumb the system. This winter, I've been experimenting with low flow temperatures in an attempt to push the efficiency as high as I could. Running at 45-55°C flow temperature seems to be the sweet spot. No more roasting hot radiators, yet the house is a comfortable temperature (some days, flow temperature is down to just 40°C).

Low flow temperatures do work to keep a house warm. But the radiators need to be quite a bit larger in order to emit the same amount of heat - Most of mine are 30-50% larger than one might expect.

As for the risk of legionella, if you have a heat pump, you'd normally have an unvented tank. The incoming water (assuming you are on mains) will be treated before it is piped to your house. Almost zero risk of the bacteria getting in to the system. And as long as you maintain a DHW temperature of 50°C or higher, the little blighters will die. OK, at 50°C, it takes hours to kill the bacteria. At 60°C, the bacteria is killed withing 30 minutes. But as you increase the water temperature, the risk of scalds also increases (a real danger for the very young and the elderly).

A heat pump is very capable of proving hot water at 50-55°C. And if you really want a weekly legionella kill cycle, an immersion heater can be used to boost the water to 60°C and use just under 1.2kWh (to heat 200l from 55°C to 60°C). And to be quite honest, the risk of legionella is extremely low in the UK - Some 400 cases reported annually, and half of those, the infection is contracted overseas. You have a better chance of being hit by a No.13 bus !

Thank you for your excellent reply, points noted.