Hi Andy,

With respect to your first point, we have an oil-fired hot water heating system, but two 4.0 kW ductless heat pumps now supply virtually all of our space heating needs; the boiler only kicks on when temperatures remain below -10C for an extended period of time. An air-to-water system would be nice, but air-to-air units are far more affordable (the installed cost of our two units was $4,100.00 CDN/£2,270) and having two fully independent heating systems allows us to switch between fuels based on relative price.

Regarding your second point, ductless mini splits offer the added benefit of air conditioning and dehumidification. Our cooling requirements in Atlantic Canada are quite modest, but living in a maritime climate we would often run our dehumidifier non-stop from mid April through September. Dehumidifiers are loud, guzzle a tremendous amount of electricity and generate waste heat during the times of the year when you least need it. You also end up emptying the collection bucket every one to two days. Now, I run our heat pumps in "dry" mode -- no noise, far lower power consumption, no unwanted waste heat and, as an added bonus, no bucket to empty.

There would be some additional grid demand, but it should be manageable. Our newest ASHP is a high efficiency inverter system that constantly adjusts compressor speed in response to changes in heating demand. I have it plugged into a power monitor and it draws 200 to 300-watts under light load and as much as 1,500-watts when operating at maximum capacity. Continuous operation eliminates standby losses and makes for a smoother load curve. Also, for much of the winter, daytime temperatures are typically several degrees higher than what you would experience overnight; all else being equal, the highest ASHP demands occur during the overnight hours when overall demand is low and daytime COPs would presumably benefit from higher ambient air temperatures.

Last point and forgive me for stating the obvious. If I have a natural gas heating system, 100 per cent of my needs are met by natural gas, whereas with an ASHP, my needs are likely derived from a mix of fuel sources, some no doubt more desirable than others. A growing number of customers also have the option to purchase green power, so that nudges us a little further in the right direction.

Edit: Mini splits are fairly simple to install, but the work should be performed by a qualified technician. This video provides a good overview of what's involved: http://www.youtube.com/watch?v=PdMRVO_NOz4

Cheers,
Paul