What is the optimal temperature for boiler ?

FiFtHeLeMeNt · Dec 18, 2019

Hello guys,
We have a quite big boiler which circulates hot water in our hot water storage tanks and 80 apartments radiators.
We have currently set the boiler thermostat to 65 °C and the boiler Flue gases are between 250-350 °C.
The person who services our boiler insists that we lower the boiler thermostat even more and says it would prolong the lifespan of the boiler, but I have heard that boiler should not operate below 60 °C because it causes the Flue gas to form acidic chemicals and eat into the boiler pipes.
The service worker says because our flue gas temperature is so high, such acidic chemicals will never form and it is better to lower the temperature.
I would like to hear your advice on this matter, If you need more info or pics let me know.

Regards

Gasmk1 · Dec 18, 2019

if you lower it any more you may not get the desired stored hot water temperature which could lead to legionella problems

The primary method used to control the risk from Legionella is water temperature control.
Water services should be operated at temperatures that prevent Legionella growth:

Hot water storage cylinders (calorifiers) should store water at 60°C or higher
Hot water should be distributed at 50°C or higher (thermostatic mixer valves need to be fitted as close as possible to outlets, where a scald risk is identified).
Cold water should be stored and distributed below 20°C.

Last Plumber · Dec 18, 2019

FiFtHeLeMeNt said:
Hello guys,
We have a quite big boiler which circulates hot water in our hot water storage tanks and 80 apartments radiators.
We have currently set the boiler thermostat to 65 °C and the boiler Flue gases are between 250-350 °C.
The person who services our boiler insists that we lower the boiler thermostat even more and says it would prolong the lifespan of the boiler, but I have heard that boiler should not operate below 60 °C because it causes the Flue gas to form acidic chemicals and eat into the boiler pipes.
The service worker says because our flue gas temperature is so high, such acidic chemicals will never form and it is better to lower the temperature.
I would like to hear your advice on this matter, If you need more info or pics let me know.

Regards

On non-condensing Boilers (particularly ones with cast iron heat exchangers), running them at too low a temperature can cause them to suffer more corrosion internally to the flue ways and combustion chamber walls.

My opinion is that they should be run above the Boiler dew point point which is normally 55 degrees Celsius or thereabouts. Although the flue gases are at a higher temperature than that of a condensing Boiler, condensate can still form on the internal skin due to lower surface temperatures. I always run them at 60 degrees Celsius or above to help to prevent that.

doitmyself · Dec 18, 2019

Which boiler do you have? (make and exact model/kW)

centralheatking · Dec 18, 2019

Gasmk1 said:
if you lower it any more you may not get the desired stored hot water temperature which could lead to legionella problems

The primary method used to control the risk from Legionella is water temperature control.
Water services should be operated at temperatures that prevent Legionella growth:

Hot water storage cylinders (calorifiers) should store water at 60°C or higher

Hot water should be distributed at 50°C or higher (thermostatic mixer valves need to be fitted as close as possible to outlets, where a scald risk is identified).

Cold water should be stored and distributed below 20°C.

Absolutely correct, gas mark has it right on there is no margin beyond this criteria
chking
[automerge]1576687646[/automerge]

FiFtHeLeMeNt said:
Hello guys,
We have a quite big boiler which circulates hot water in our hot water storage tanks and 80 apartments radiators.
We have currently set the boiler thermostat to 65 °C and the boiler Flue gases are between 250-350 °C.
The person who services our boiler insists that we lower the boiler thermostat even more and says it would prolong the lifespan of the boiler, but I have heard that boiler should not operate below 60 °C because it causes the Flue gas to form acidic chemicals and eat into the boiler pipes.
The service worker says because our flue gas temperature is so high, such acidic chemicals will never form and it is better to lower the temperature.
I would like to hear your advice on this matter, If you need more info or pics let me know.

Regards

Your advisor is wrong its that simple. centralheatking

FiFtHeLeMeNt · Dec 18, 2019

centralheatking said:
Absolutely correct, gas mark has it right on there is no margin beyond this criteria
chking
[automerge]1576687646[/automerge]

Your advisor is wrong its that simple. centralheatking

As @Last Plumber suggested, we do have a non-condensing boiler with cast iron heat exchangers.
I have attached the boiler spec to this post, although you may not understand the language, I guess you would understand the specs as the numbers are in English.
Is the Legionella the primary reason to keep the boiler above 60°C ?
If we assume there is no risk of Legionella, is it still advised to keep the boiler above 60°C ?

Gasmk1 · Dec 18, 2019

in your original post its says the boiler supplies hot water tanks so ther ewould be a legionella risk if you drop the temperature

FiFtHeLeMeNt · Dec 19, 2019

Gasmk1 said:
in your original post its says the boiler supplies hot water tanks so ther ewould be a legionella risk if you drop the temperature

You are right, but in our region the tap water is heavily regulated and chlorinated as everyone drinks tap water, so there is a very minimal risk of Legionella growth. Our plumber has 40 years of experience in this field and says he always sets the hot water tanks between 40-45°C and has never had an issue with Legionella.
Our main concern here is the longevity of the lifespan of our central heating system and minimizing the maintenance costs.

Gasmk1 · Dec 19, 2019

Fine then take his word for it but you are putting the cost of a boiler against the safety of your 80 tenants, just because it hasn't happened doesn't mean it won't. But if that's the risk you want to take for an unknown versus an unknown it may increase the life of the boiler Ortiz it may not the only known is if you lowere the temperature of the boiler you will save money on gas

centralheatking · Dec 19, 2019

Gasmk1 said:
Fine then take his word for it but you are putting the cost of a boiler against the safety of your 80 tenants, just because it hasn't happened doesn't mean it won't. But if that's the risk you want to take for an unknown versus an unknown it may increase the life of the boiler Ortiz it may not the only known is if you lowere the temperature of the boiler you will save money on gas

Dabbling with potentially infectious water in your own home is one thing however as soon as the public and customers become victims then legal obligations come into play raising the prospects of criminal
charges and civil litigation against the building owner, operator and engineer. Proper records of adequate inspections and treatments must be maintained. centralheatking

oz-plumber · Dec 19, 2019

While boiler flue temperatures are indicative of the efficiency of the appliance, stored potable hot water supply should not be altered to gain more efficiency from the boiler.

Storing hot water at 40C - 45C is perfect blooming temperatures for Legionella.
These sorts of temperatures are considered 'warm water systems'.
They, at the minimum, require UV filtration to kill off bacteria.
There's a lot more than that also - just basics posted.

I would get a new Engineer that knows how to operate the system safely.

It would only take one case of a Legionella type symptom occurring in one resident in the building and you would have to go through a complete flushing of the building.

You Stated
"Our main concern here is the longevity of the lifespan of our central heating system and minimizing the maintenance costs."

Get 1 person with 1 symptom of Legionella and every hot water tap in the building will have to be tested weekly or monthly for a period of probably 12 months.

That alone would cost you more than replacing the whole entire Plant for the building.

You really need the services of a qualified consultant to go over your system and implement changes that are required.
With a system of that size, you also need to keep and maintain a Log Book .

centralheatking · Dec 19, 2019

centralheatking said:
Absolutely correct, gas mark has it right on there is no margin beyond this criteria
chking
[automerge]1576687646[/automerge]

Your advisor is wrong its that simple. centralheatking

Looking over this post we are very carefull regarding Gas and boilers...GSR etc. but also this one highlights just how inexperienced people can 'get themselves into hot water' get my pun, over water issues as well ...the legionella list is endless...started in USA with their retired military at a convention
last big one was in Barrow in zFurness sports centre ...we need to be helpfull and vigillant chking

SJB060685 · Dec 19, 2019

You stated "your main concern is the longevity of the system". The main concern should always be the safety of all consumers.

FiFtHeLeMeNt · Dec 19, 2019

Thank you for your advice guys, you are right, the main concern should be the safety and health of residents and we will keep our hot water storage tanks above 60°C.

Stigster · Dec 20, 2019

FiFtHeLeMeNt said:
Thank you for your advice guys, you are right, the main concern should be the safety and health of residents and we will keep our hot water storage tanks above 60°C.

I think that is a very wise decision. Once legionella takes hold in a system, even if nobody gets sick, the monitoring and mitigation procedures can be expensive and time consuming. Also, the first thing that would be required would be to get your stored hot water temperatures back up to 60C+

Danb · Dec 20, 2019

40 to 45c prime for bacteria.
Do what the lads above have said.
Don't take a chance and penny pinch. Will cost you alot more than just cash if there's an outbreak!
[automerge]1576839054[/automerge]
If you temps have been low I would probably pasturise the tank for abit.

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What is the optimal temperature for boiler ?

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