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Welcome to the forum. Although you can post in any forum, the USA forum is here in case of local regs or laws

No problems just wondered how good they were
The one I thought about (Ariston) had a CoP (coefficient of performance) of 3.0, i.e. 3kW of heating for 1kW of electricity. To compete with gas I needed CoP > 4.0. Another issue was that unless you have its inlet and outlet terminating outside the thermal envelope of your house, you are paying to heat the air it is extracting its 'free' heat from. And you needed a 12 Amp supply electrical supply, and have long reheat times (4.5 hours), etc.

So, I loved the theory, but CoP > 1.0 is the only upside and IMO that's not enough to win if you have a gas supply and have to pay the going rate for grid electricity.
 
It doesn't qualify for RHI if it's only DHW, has to include Renewable space heating.

 
The concept of recovering unused heat from within the building is excellent - the Ecocent (Earth Save Products) range are the only ones we have fitted. From a financial perspective the payback period is significant (12 to 15 years) for a capital expenditure of £10k plus.

Without eligibility for RHI they only appeal to people who seek renewable energy at any cost.
 
It doesn't qualify for RHI if it's only DHW, has to include Renewable space heating.

Sorry didn’t realise he was wanting DHW only. I read cylinder and assumed heat store/buffer tank.
 
The one I thought about (Ariston) had a CoP (coefficient of performance) of 3.0, i.e. 3kW of heating for 1kW of electricity. To compete with gas I needed CoP > 4.0. Another issue was that unless you have its inlet and outlet terminating outside the thermal envelope of your house, you are paying to heat the air it is extracting its 'free' heat from. And you needed a 12 Amp supply electrical supply, and have long reheat times (4.5 hours), etc.

So, I loved the theory, but CoP > 1.0 is the only upside and IMO that's not enough to win if you have a gas supply and have to pay the going rate for grid electricity.
Typical salesman's gumpf. COP of 3.0 at what air temperature and relative humidity? Internal water temperature of what? And so in real-world conditions, what is the COP?
 

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