Legionnaires and heat pumps
I'd like to find out what people think about the Anti-Legionnaires settings on the Ecodans (& probably other ASHP's too). Look at @rv3's power usage graph a few posts back. Look at the orange DHW (Hot Water) readings. Every 15 days, look at the Anti-Legionnaires peak. I'm not advising anyone to do anything that might pose a health risk, but I am interested in an honest discussion about it. Particularly since the insulation on those tanks means that it keeps heat in beautifully. Does anyone know how long & at what temp we have to keep it to be safe? Also, how often?
Good topic.
I think the risk of catching Legionnaires from an ASHP heating/DHW system is very, very small. It's primarily an airborne pathogen and since most ASHP systems are unvented, it's hard to see how it would get into the water. It could concievably enter at the water treatment plant but these are quite sterile environments and a lot of our water has stuff added to it that is likely to kill off any nasties.
If any make it into your DHW, they won't be very happy. This from Wikipedia.
Temperature affects the survival of Legionella as follows:[3]
- Above 70 °C (158 °F) – Legionella dies almost instantly
- At 60 °C (140 °F) – 90% die in 2 minutes (Decimal reduction time (D) = 2 minutes)
- At 50 °C (122 °F) – 90% die in 80–124 minutes, depending on strain (D = 80–124 minutes)
- 48 to 50 °C (118 to 122 °F) – can survive but do not multiply
- 32 to 42 °C (90 to 108 °F) – ideal growth range
- 25 to 45 °C (77 to 113 °F) – growth range
- Below 20 °C (68 °F) – can survive, even below freezing, but are dormant
So the Legionnaires cycle decreases the risk from very, very small to vanishingly small. If your DHW is at 50C constantly anyway, 60C for 3 hours once a week isn't going make a lot of difference.
Should you do it/keep doing it?
Only you can decide. 😉
@kev-m, that’s all bang on. I didn’t realise Legionnaires died so quickly at over 60C. Interesting.
Our DHW is set to 44C. The heat pump was set to take it to 60C for a least an hour once a week. I changed that to 10 days. We have an iBoost that heats our hot water to over 60C using excess solar - today we produced loads of solar so the ASHP system has reset its 10 day countdown.
The likelihood of getting Legionnaires via your tank is slim, but I still keep our settings activated and let the iBoost do its thing, as we’d rather be safe than sorry. In a world that’s going more and more bonkers with each passing day, we’ve opted to be cautious.
Buy Bodge Buster – Homeowner Air Source Heat Pump Installation Guide: https://amzn.to/3NVndlU
From Zero to Heat Pump Hero: https://amzn.to/4bWkPFb
Subscribe and follow our Homeowners’ Q&A heat pump podcast
The risk is very very small in catching legionella, in the whole of England and wales for 2016 there were 208 cases (most recent data found)
- 22 Forums
- 2,096 Topics
- 46.2 K Posts
- 58 Online
- 3,384 Members
Trusted Installers
Struggling to find a reliable heat pump installer? A poor installation can lead to inefficiencies and high running costs. We now connect homeowners with top-rated installers who deliver quality work and excellent service.
✅ Verified, trusted & experienced installers
✅ Nationwide coverage expanding
✅ Special offers available
Latest Posts
-
If you are thinking of heating on the immersion conside...
By JamesPa , 2 hours ago
-
RE: Surface mount or bury primaries for heat pump installation?
@tomasmcguinness, I think your best bet would be using ...
By Aventus Eco , 11 hours ago
-
RE: Solar Power Output – Let’s Compare Generation Figures
@toodles all depends on asking the right questions! And...
By Tim441 , 13 hours ago
-
RE: Mitsubishi cycling while on chilled water output
I absolutely wouldn't remove the buffer altogether, I'd...
By JamesPa , 20 hours ago
-
RE: Commencing on an ASHP Installation Process
I received confirmation this morning that my Greener Ho...
By Sheriff Fatman , 22 hours ago
-
@jamespa Thanks for the advice - very helpful. I had al...
By abam48 , 2 days ago
-
RE: Weather compensated secondary circuits with Biomass
Hi @andycoo we do an LK 110 standalone weather compensa...
By Sune , 2 days ago
-
RE: Adding battery storage to SolarEdge PV system
@chandykris No need to apologise at all! I forgot to ad...
By Toodles , 3 days ago
-
RE: Say hello and introduce yourself
Yes please do Suggesting a loss in the region...
By JamesPa , 3 days ago
-
As I have reported elsewhere we turned on the cooling o...
By downfield , 4 days ago
-
-
@el3b Hi, sorry to hear that, it is advisable to instal...
By ASHP-BOBBA , 5 days ago
-
RE: Difficult positioning of air source heat pump
@rikiarn Out of intrigue, the thread reads as though Ai...
By Sheriff Fatman , 5 days ago