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Investment in hydrogen boiler's or air source heat pumps


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Just put in an ashp on the barn conversion I'm building, does have ufh and insulated to a bit better than building regs. Makes sense. But hard work for older properties or if using radiators. Amazes me how it strips the heat from the air, and the panel shows how much heat it is getting from the environment relative to electricity consumed.

Regarding hot water you do need a bigger cylinder because it won't heat it to the temperatures of gas/oil. 

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7 hours ago, Teal said:

Regarding hot water you do need a bigger cylinder because it won't heat it to the temperatures of gas/oil.

The more serious problem with hot water is to ensure it gets hot enough to kill Legionella bacteria.  I'm not sure what the official temperature needs to be.  This https://www.hse.gov.uk/legionnaires/things-to-consider.htm states 60C.  Some other sources say 65 of 66C.  This may require something (immersion heater?) to boost it from what the heatpump can manage.

Obviously, if the water is cooler, you need to add less cold at the bath or shower mixer, so you need to draw more hot - which might suggest a larger cylinder.  Also, if the reheat time is slow, you may want a larger reserve of hot to allow for peaks in demand (multiple baths/showers in a short period).

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No "eco" heating system will be an upgrade as such....listen to almost every pusher of it.....its a lifestyle choice that we will all have to buy into....it certainly will not be cost effective compared to what we have now......think of your low cost heating at the minute as the "Concorde" moment for our current lifestyle!!

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On 26/10/2021 at 05:15, JohnfromUK said:

The more serious problem with hot water is to ensure it gets hot enough to kill Legionella bacteria.  I'm not sure what the official temperature needs to be.  This https://www.hse.gov.uk/legionnaires/things-to-consider.htm states 60C.  Some other sources say 65 of 66C.  This may require something (immersion heater?) to boost it from what the heatpump can manage.

Obviously, if the water is cooler, you need to add less cold at the bath or shower mixer, so you need to draw more hot - which might suggest a larger cylinder.  Also, if the reheat time is slow, you may want a larger reserve of hot to allow for peaks in demand (multiple baths/showers in a short period).

So certainly my ASHP has a program (think they all do) that runs weekly to boost it to 65degrees to do this.

However, I think this is a relic, because so long as your hot water cylinder is not air vented (which it won't be)- it is chlorinated supply from mains that feeds it, and a sealed unit. So it's an inert holding tank that remains chlorinated where legionella could never establish or survive. 

However, under RHI requirements you have to have the weekly boost anyway - so even if it were an issue, you have the weekly heat boost cycle. My ASHP can actually do 65degrees on its own - most use immersion though. That said ASHP efficiencies drop off the higher temp you go, so you lose some efficiencies if you hold the tank at higher temps than required - hence you have a bigger cylinder than normal so you don't have to keep it at 65degrees at all time.

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1 minute ago, Teal said:

However, I think this is a relic, because so long as your hot water cylinder is not air vented - it is chlorinated supply from mains that feeds it, and a sealed unit. So it's an inert holding tank where legionella could never establish or survive.

Interesting thought - and probably true in all normal practice.  I have a sealed (i.e. direct from mains water, no header tank) system and heated by normal (non combi) gas boiler.  I was told - may be wrongly - that the hot water still needed to meet the minimum temperature to avoid legionella.  I have also read that cold feed pipes running through a loft where the temperature is very probably above the lower 'safe' limit of below 20C can also be a risk.  Seems a greater risk when things like showers are unused for a period (guest rooms etc.)

The fact seems to be that legionalla are not normally a problem in a small domestic system, but are (at least theoretically) a risk.  My former system (now replaced) had a tank in the loft which in the summer used to get very warm - and fed the 'cold' of the shower feed directly with luke warm water in summer!

These people have an axe to grind as they are flogging test kits!  https://hydrosense-legionella.com/legionella-legionnaires-disease-risk-sectors/domestic-water-systems/

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