We have an existing radiator system in our house but nothing to heat it right now (we removed the old cooker). We have 12 radiators and approximately 18-20 KW of heat output @ 60 degrees.
Looking to install a heat pump system that would give us from 9-13 KW heat output and cost $10,000 to $13,000 installed. So it's a big up front install cost but if we ran this on an off peak 2 tariff (up to 18 hours a day) and with a COP ~3-4 our annual heating cost might be as low as $400.
Compare this to an LPG boiler either 18 KW or 30 KW and installed would be around $6500-8000. Ongoing costs per year would be around $600-800 depending on LPG prices for the same heating as above. The pros of the boiler is it's 'simple' technology (=easy to repair etc), known to be reliable, is powerful at 18 KW, and has a fast response time.
Over ten years the heat pump system just wins out on cost but the big question for me is: does a heat pump hydronic system really cut it?! Every local plumber I talk to reckons they dont run as well as the theoretical COP and can be disappointing + cost a lot to have installed. The argument is good - heat pumps are newer technology and more complex, but maybe they've only experienced the poorer performing domestic hot water heat pumps vs units designed for hydronic heating.
Costs aside, can anyone highly recommend a heat pump hydronic system? Do they deliver on the theoretical outputs and heat the radiators well?