Legionnaires disease: why isn't there an increase?

Discussions about serious topics, for serious people
Post Reply
User avatar
lpm
Junior Mod
Posts: 5365
Joined: Mon Nov 11, 2019 1:05 pm

Legionnaires disease: why isn't there an increase?

Post by lpm » Wed Jan 18, 2023 2:36 pm

In the UK to prevent legionella hot water is supposed to be stored at at least 60 degrees. Health & Safety laws make this a requirement for office buildings etc and typically domestic plumbers have set home systems to do the same.

However in recent months there's been a load of ill-informed advice on Facebook and similar, recommending various money saving "hacks" such as turning down boiler temperatures. Legionella bacteria enjoy 37 degrees best and survive 20-50. I have no doubt that many households have reduced storage temperatures below 50. A sterilisation cycle of 60 degrees every two weeks would address the problem.

Almost half of UK households still have hot water cylinders.

Legionnaires is a communicable disease so any increase would be quickly apparent.

But there hasn't been. Why not?
⭐ Awarded gold star 4 November 2021

User avatar
dyqik
Light of Blast
Posts: 6458
Joined: Wed Sep 25, 2019 4:19 pm
Location: Masshole
Contact:

Re: Legionnaires disease: why isn't there an increase?

Post by dyqik » Wed Jan 18, 2023 3:34 pm

Two things come to mind:

Firstly, legionnaires is an airborne bacteria disease, that you catch by breathing in mist contaminated with it. The usual mode of transmission is via HVAC systems rather than hot water. The mere presence of it in water that you are in contact with is not sufficient to cause the disease. A shower may not produce enough fine spray to give a sufficient dose to cause problems (my shower, for example, doesn't produce much in the way of mist - I suspect that the modern low flow showers don't generally)

Secondly, pneumonia infections are also a symptom of CoVID and other respiratory diseases. Legionnaires from water mists may not show up against that background, and the pool of the most vulnerable individuals has likely been depleted by CoVID.

User avatar
dyqik
Light of Blast
Posts: 6458
Joined: Wed Sep 25, 2019 4:19 pm
Location: Masshole
Contact:

Re: Legionnaires disease: why isn't there an increase?

Post by dyqik » Wed Jan 18, 2023 3:36 pm

The recommended temperature for hot water in the US is 120°F, 49°C, to prevent scalding, and has been for quite some time. Defaults are often higher at 140°F/60°C, but 49°C is the recommended temperature here, as the best balance between bacterial build up and scalding.
Last edited by dyqik on Wed Jan 18, 2023 3:42 pm, edited 1 time in total.

User avatar
dyqik
Light of Blast
Posts: 6458
Joined: Wed Sep 25, 2019 4:19 pm
Location: Masshole
Contact:

Re: Legionnaires disease: why isn't there an increase?

Post by dyqik » Wed Jan 18, 2023 3:42 pm

Water treatment probably also has something to do with it. Domestic water is now more carefully treated with chloramine or chlorine, to suppress bacterial buildup, and that will carry through to domestic hot water heaters (particularly chloramine, which doesn't evaporate from standing water at 60°C).

IvanV
After Pie
Posts: 1759
Joined: Mon May 17, 2021 11:12 am

Re: Legionnaires disease: why isn't there an increase?

Post by IvanV » Wed Jan 18, 2023 4:01 pm

And before these regulations came in, was legionella a recorded problem of domestic water tanks?

Most of the known cases seem to be associated with situations where the water that gets warm is exposed to the environment allowing it to become infected relatively easily. The most common early cases were with things like the cooling systems of large air conditioning systems, where warm water vapour was exposed to the air, pumping it out onto the footway, and passers-by breathing it in. The domestic hotwater tank is within a controlled system without easy entry, fed by water which has been processed by a water treatment works to make it safe to drink. The likelihood of legionella getting into hot water tanks seems low. But that's me theorising, is there data?

One has to ask whether this is another case of UK regulations regulating what they can regulate instead of what they need to regulate, thus adding cost for little health and safety benefit. Legionella can, in principle, colonise a domestic hot water tank if kept at a somewhat lower temperature. But in practice, does it do that, given the difficulty of getting in there?

You write "still have" as though a hot water tank is a primitive thing to be avoided. I consciously refused to have a combi boiler when I replaced my hot water system, about 3 or 4 years ago, mainly because other family members had bad experiences with them, but also with half an eye on the possibility of later retrofitting a solar water heating system. In a decarbonised world, flexibility through heat storage is a benefit.

User avatar
lpm
Junior Mod
Posts: 5365
Joined: Mon Nov 11, 2019 1:05 pm

Re: Legionnaires disease: why isn't there an increase?

Post by lpm » Wed Jan 18, 2023 4:33 pm

Yep, hot water storage is a semi-battery for storing cheap overnight electricity and it's a shame there was a trend to getting rid of them. Far better way to balance day/night than resource-heavy batteries. But once an airing cupboard has been converted to something else, few households will want to reverse.

If domestic hot water has been excessively heated to 60 degrees for decades then there's a clear CO2 win (and financial win) from changing guidance. 45 degrees is basically what's wanted for showers.
⭐ Awarded gold star 4 November 2021

User avatar
nekomatic
Dorkwood
Posts: 1125
Joined: Mon Nov 11, 2019 3:04 pm

Re: Legionnaires disease: why isn't there an increase?

Post by nekomatic » Wed Jan 18, 2023 7:26 pm

I haven’t read all the ill-informed advice on Facebook but hopefully it talks about reducing the heating flow temperature, not the hot water temperature.

As I understand it vented hot water cylinders, like what many UK households still have, are not all that efficient. Pressurised system cylinders like what the Europeans have are better but take up even more space. We got one of these on the basis that it was the most efficient and would allow us to add solar thermal in future (as we got one with a spare coil for the purpose) but we never did. The programmer has an anti-legionella setting which can heat it up above 65 degrees for a couple of hours every Wednesday afternoon (or something) but we’ve never used that either.
Move-a… side, and let the mango through… let the mango through

User avatar
bob sterman
Catbabel
Posts: 965
Joined: Mon Nov 11, 2019 10:25 pm
Location: Location Location

Re: Legionnaires disease: why isn't there an increase?

Post by bob sterman » Thu Jan 19, 2023 7:56 am

A few quick thoughts...

- People may still have water at a temperature, while not high enough to kill all the bacteria, that is high enough so that growth isn't optimal (e.g. 45-50C).
- Undiagnosed non-pneumonic legionellosis being more common than we think.
- As dyqik suggests - domestic showers may not produce a sufficiently fine mist for optimal spread.
- Older age groups - most vulnerable to the disease - having baths and not producing mist at all.
- If it lives in shower heads, domestic showers may be used less frequently than those in gym, hotel, hospital - so the fittings may have a chance to dry out between uses.

User avatar
headshot
Dorkwood
Posts: 1170
Joined: Tue Nov 12, 2019 9:40 am

Re: Legionnaires disease: why isn't there an increase?

Post by headshot » Thu Jan 19, 2023 11:46 am

nekomatic wrote:
Wed Jan 18, 2023 7:26 pm
I haven’t read all the ill-informed advice on Facebook but hopefully it talks about reducing the heating flow temperature, not the hot water temperature.
It’s this. The advice is to set your central heating boiler temperature to 60c and it’s is specifically aimed at condenser boilers. It means that the water coming back into the system is cooler - which in turn aids the condenser’s efficiency.

Details here: https://www.boilercentral.com/boiler-ad ... mperature/

Our condenser boiler has separate dials for hot water from the taps and the radiator flow temp.

IvanV
After Pie
Posts: 1759
Joined: Mon May 17, 2021 11:12 am

Re: Legionnaires disease: why isn't there an increase?

Post by IvanV » Thu Jan 19, 2023 11:53 am

nekomatic wrote:
Wed Jan 18, 2023 7:26 pm
As I understand it vented hot water cylinders, like what many UK households still have, are not all that efficient. Pressurised system cylinders like what the Europeans have are better but take up even more space. We got one of these on the basis that it was the most efficient and would allow us to add solar thermal in future (as we got one with a spare coil for the purpose) but we never did. The programmer has an anti-legionella setting which can heat it up above 65 degrees for a couple of hours every Wednesday afternoon (or something) but we’ve never used that either.
I have a pressurised system, and my previous system was pressurised too, right back to 2007. I had thought that was normal now. Especially since many of us are now aware how nice a pressurised shower is, given they so common in hotels, etc. Now I have a boiler and separate pressurised tank, and know how big that tank is, I can understand why others are reluctant to install such a system. There are maintenance requirements for pressurised tanks, whereas vented tanks can carry on unexamined for decades. I also had to ask around a bit to find a plumber willing to install it ("you really want a combi, so much easier for me to install...."). It explains, I suppose, why some well-educated friends, when recently replacing their ancient system, installed a new vented cylinder, to my horror.

My previous system was an integrated boiler and pressurised hot water store all in one box. That was a good idea in terms of minimising space requirements, at a time when combis were not common or reliable. But it added complication - you had to get specialists to maintain it, and it was also unreliable. The first time it broke down, I called in a normal plumber, not knowing about the specialists, and he failed to repair it having separated me from a lot of money. But at least I had hot water from the immersion heater in the tank, during the 4 weeks it eventually took to get it fixed. It seems that the problem that integrated product tried to solve was eventually more cheaply and reliably solved by a combi. So such integrated products are no longer in the market, as far as I can see. A lot of us who had those integrated systems also suffered from the ill-designed new flue regulations of about 2012, which eventually wrote mine off when it still probably had about 5 years useful working life remaining.

User avatar
lpm
Junior Mod
Posts: 5365
Joined: Mon Nov 11, 2019 1:05 pm

Re: Legionnaires disease: why isn't there an increase?

Post by lpm » Thu Jan 19, 2023 12:33 pm

headshot wrote:
Thu Jan 19, 2023 11:46 am
nekomatic wrote:
Wed Jan 18, 2023 7:26 pm
I haven’t read all the ill-informed advice on Facebook but hopefully it talks about reducing the heating flow temperature, not the hot water temperature.
It’s this. The advice is to set your central heating boiler temperature to 60c and it’s is specifically aimed at condenser boilers. It means that the water coming back into the system is cooler - which in turn aids the condenser’s efficiency.

Details here: https://www.boilercentral.com/boiler-ad ... mperature/

Our condenser boiler has separate dials for hot water from the taps and the radiator flow temp.
No, there are "instruction" videos showing how to turn down the temperature on the hot water tank. Nothing to do with Combi boilers.
⭐ Awarded gold star 4 November 2021

User avatar
headshot
Dorkwood
Posts: 1170
Joined: Tue Nov 12, 2019 9:40 am

Re: Legionnaires disease: why isn't there an increase?

Post by headshot » Thu Jan 19, 2023 1:42 pm

Well, if it’s advice people are taking from Facebook, I’ll consider it a Darwinian issue.

User avatar
lpm
Junior Mod
Posts: 5365
Joined: Mon Nov 11, 2019 1:05 pm

Re: Legionnaires disease: why isn't there an increase?

Post by lpm » Thu Jan 19, 2023 1:55 pm

But the Facebook advice might be correct. Save money and CO2 at infinitesimal extra risk.
⭐ Awarded gold star 4 November 2021

User avatar
headshot
Dorkwood
Posts: 1170
Joined: Tue Nov 12, 2019 9:40 am

Re: Legionnaires disease: why isn't there an increase?

Post by headshot » Thu Jan 19, 2023 2:01 pm

My condenser boiler is set to 60c for flow temp and hot water on the advice of our plumber friend.

User avatar
Grumble
Stummy Beige
Posts: 3909
Joined: Mon Nov 11, 2019 1:03 pm

Re: Legionnaires disease: why isn't there an increase?

Post by Grumble » Fri Jan 20, 2023 6:19 pm

headshot wrote:
Thu Jan 19, 2023 2:01 pm
My condenser boiler is set to 60c for flow temp and hot water on the advice of our plumber friend.
No offence, but your plumber friend might not be all that well up on efficiency. We’ve reduced our flow temp to 43°C and improved our comfort. Also reduced the heat output from the factory setting of 30kW to 15kW (guess).

On a condenser boiler hot water can be reduced to whatever gives you the temperature you need at point of use without mixing with cold.
A bit churlish

User avatar
headshot
Dorkwood
Posts: 1170
Joined: Tue Nov 12, 2019 9:40 am

Re: Legionnaires disease: why isn't there an increase?

Post by headshot » Fri Jan 20, 2023 6:56 pm

Grumble wrote:
Fri Jan 20, 2023 6:19 pm
headshot wrote:
Thu Jan 19, 2023 2:01 pm
My condenser boiler is set to 60c for flow temp and hot water on the advice of our plumber friend.
No offence, but your plumber friend might not be all that well up on efficiency. We’ve reduced our flow temp to 43°C and improved our comfort. Also reduced the heat output from the factory setting of 30kW to 15kW (guess).
Everything I’ve read online, and on our boiler manufacturer’s website, has suggested not setting below 60c.

monkey
Dorkwood
Posts: 1567
Joined: Wed Nov 13, 2019 5:10 pm

Re: Legionnaires disease: why isn't there an increase?

Post by monkey » Fri Jan 20, 2023 7:34 pm

headshot wrote:
Fri Jan 20, 2023 6:56 pm
Grumble wrote:
Fri Jan 20, 2023 6:19 pm
headshot wrote:
Thu Jan 19, 2023 2:01 pm
My condenser boiler is set to 60c for flow temp and hot water on the advice of our plumber friend.
No offence, but your plumber friend might not be all that well up on efficiency. We’ve reduced our flow temp to 43°C and improved our comfort. Also reduced the heat output from the factory setting of 30kW to 15kW (guess).
Everything I’ve read online, and on our boiler manufacturer’s website, has suggested not setting below 60c.
Do you get an increase in CO with burning less fuel?

User avatar
dyqik
Light of Blast
Posts: 6458
Joined: Wed Sep 25, 2019 4:19 pm
Location: Masshole
Contact:

Re: Legionnaires disease: why isn't there an increase?

Post by dyqik » Sat Jan 21, 2023 5:32 am

monkey wrote:
Fri Jan 20, 2023 7:34 pm
headshot wrote:
Fri Jan 20, 2023 6:56 pm
Grumble wrote:
Fri Jan 20, 2023 6:19 pm


No offence, but your plumber friend might not be all that well up on efficiency. We’ve reduced our flow temp to 43°C and improved our comfort. Also reduced the heat output from the factory setting of 30kW to 15kW (guess).
Everything I’ve read online, and on our boiler manufacturer’s website, has suggested not setting below 60c.
Do you get an increase in CO with burning less fuel?
You should get a reduction. CO gets produced when the burn is rich, while a lean burn goes to completion (but may produce more NO2).

There is a risk though it's that there's not enough heat to pull air through, so that the burn is actually rich due to air starvation. That shouldn't happen with a boiler that is vented directly.

monkey
Dorkwood
Posts: 1567
Joined: Wed Nov 13, 2019 5:10 pm

Re: Legionnaires disease: why isn't there an increase?

Post by monkey » Sat Jan 21, 2023 8:52 am

dyqik wrote:
Sat Jan 21, 2023 5:32 am
monkey wrote:
Fri Jan 20, 2023 7:34 pm
headshot wrote:
Fri Jan 20, 2023 6:56 pm


Everything I’ve read online, and on our boiler manufacturer’s website, has suggested not setting below 60c.
Do you get an increase in CO with burning less fuel?
You should get a reduction. CO gets produced when the burn is rich, while a lean burn goes to completion (but may produce more NO2).

There is a risk though it's that there's not enough heat to pull air through, so that the burn is actually rich due to air starvation. That shouldn't happen with a boiler that is vented directly.
That was pretty much my first thought, but I know very little about boilers, and they're probably more complicated than I expect.

Just thought it might be a reason to have it hotter than the hot water needs to be.

User avatar
headshot
Dorkwood
Posts: 1170
Joined: Tue Nov 12, 2019 9:40 am

Re: Legionnaires disease: why isn't there an increase?

Post by headshot » Sat Jan 21, 2023 9:18 am

Grumble wrote:
Fri Jan 20, 2023 6:19 pm
headshot wrote:
Thu Jan 19, 2023 2:01 pm
My condenser boiler is set to 60c for flow temp and hot water on the advice of our plumber friend.
No offence, but your plumber friend might not be all that well up on efficiency. We’ve reduced our flow temp to 43°C and improved our comfort. Also reduced the heat output from the factory setting of 30kW to 15kW (guess).

On a condenser boiler hot water can be reduced to whatever gives you the temperature you need at point of use without mixing with cold.
Are you talking about radiator flow temp, or hot tap water?

I actually don’t think our hot tap water is set to 60c thinking about it. That advice is only for boilers that supply tanks - ours is hot water on demand, straight from the boiler.

43c for radiators seems very low.

User avatar
Grumble
Stummy Beige
Posts: 3909
Joined: Mon Nov 11, 2019 1:03 pm

Re: Legionnaires disease: why isn't there an increase?

Post by Grumble » Sat Jan 21, 2023 1:22 pm

headshot wrote:
Sat Jan 21, 2023 9:18 am
Grumble wrote:
Fri Jan 20, 2023 6:19 pm
headshot wrote:
Thu Jan 19, 2023 2:01 pm
My condenser boiler is set to 60c for flow temp and hot water on the advice of our plumber friend.
No offence, but your plumber friend might not be all that well up on efficiency. We’ve reduced our flow temp to 43°C and improved our comfort. Also reduced the heat output from the factory setting of 30kW to 15kW (guess).

On a condenser boiler hot water can be reduced to whatever gives you the temperature you need at point of use without mixing with cold.
Are you talking about radiator flow temp, or hot tap water?

I actually don’t think our hot tap water is set to 60c thinking about it. That advice is only for boilers that supply tanks - ours is hot water on demand, straight from the boiler.

43c for radiators seems very low.
Radiator flow temp depends on the size of the radiators in the house. Ours (installed by previous owner) were well over sized, many people’s are. At a flow temp of 60 they were too hot to touch. The main thing that matters is whether your house gets to a comfortable temperature, and ours does with a 43C flow temp. Once you’re comfortable then optimise for efficiency - lower flow temp is better for condensing and hence efficiency. Houses vary, obviously. Our hot water is set higher because we do all our washing up by hand.
A bit churlish

User avatar
shpalman
Princess POW
Posts: 7567
Joined: Mon Nov 11, 2019 12:53 pm
Location: One step beyond
Contact:

Re: Legionnaires disease: why isn't there an increase?

Post by shpalman » Sat Jan 21, 2023 2:06 pm

I have my hot water set at 45°C, which is just a little bit hotter than I need and means I can add a trace of cold to get the temperature I want but go hotter if I like. I can't stand it when hot water just isn't quite hot enough.

I had my radiator flow temperature set to 50°C but I've just reduced it to 45°C so we'll see how that goes.

Don't know what this kind of boiler is called but it's gas fired and there's no hot water tank. The advantage is being able to shower at a decent water pressure for as long as I like, the disadvantage is that it works best with a constant flow of hot water, you can't really get away with turning the tap off and on again a lot (you'll get really hot water for a moment and then it'll be cold for a while).
having that swing is a necessary but not sufficient condition for it meaning a thing
@shpalman@mastodon.me.uk

IvanV
After Pie
Posts: 1759
Joined: Mon May 17, 2021 11:12 am

Re: Legionnaires disease: why isn't there an increase?

Post by IvanV » Mon Jan 23, 2023 9:06 am

shpalman wrote:
Sat Jan 21, 2023 2:06 pm
Don't know what this kind of boiler is called but it's gas fired and there's no hot water tank. The advantage is being able to shower at a decent water pressure for as long as I like, the disadvantage is that it works best with a constant flow of hot water, you can't really get away with turning the tap off and on again a lot (you'll get really hot water for a moment and then it'll be cold for a while).
It's called a "compact instantaneous wall-hung room-sealed (type C) fan-assisted boiler" according the English language documentation.

My experience of using similar primitive objects of this nature, when taking a shower in medium income countries, is that the flow rate is inversely related to temperature. But trying to adjust the amount of cold water mixed into the shower adjusts the flow rate through the boiler in the same quantity. So, whatever ratio of hot and cold you choose at the mixer tap, the output temperature of the shower remains stubbornly constant.

User avatar
shpalman
Princess POW
Posts: 7567
Joined: Mon Nov 11, 2019 12:53 pm
Location: One step beyond
Contact:

Re: Legionnaires disease: why isn't there an increase?

Post by shpalman » Mon Jan 23, 2023 10:42 am

IvanV wrote:
Mon Jan 23, 2023 9:06 am
shpalman wrote:
Sat Jan 21, 2023 2:06 pm
Don't know what this kind of boiler is called but it's gas fired and there's no hot water tank. The advantage is being able to shower at a decent water pressure for as long as I like, the disadvantage is that it works best with a constant flow of hot water, you can't really get away with turning the tap off and on again a lot (you'll get really hot water for a moment and then it'll be cold for a while).
It's called a "compact instantaneous wall-hung room-sealed (type C) fan-assisted boiler" according the English language documentation.

My experience of using similar primitive objects of this nature, when taking a shower in medium income countries, is that the flow rate is inversely related to temperature. But trying to adjust the amount of cold water mixed into the shower adjusts the flow rate through the boiler in the same quantity. So, whatever ratio of hot and cold you choose at the mixer tap, the output temperature of the shower remains stubbornly constant.
Well, that's not my experience with it here.
having that swing is a necessary but not sufficient condition for it meaning a thing
@shpalman@mastodon.me.uk

Post Reply