What size is the pond? Does it have fish in it?. I ask these questions as just when you want the heat, cos' its -10 outside, the top of the pond is frozen so the maximum temperature of the water at the bottom will be +4, so if you cool this the depth of ice will increase and eventually the fish will die and you will freeze. At most other times the pond will gain heat from the sun, depending on its area and shading so would be very useful and efficient in terms of pipe length. Writing (and thinking on the fly) the above, has caused me to change my mind, it goes like this:- If you put your pipes on the bottom of the pond, you cool the lower volume of water, so it sinks. This cold water then sits around your pipe, until its temperature gets to below 4 deg C, then it expands and rises, but when its temperature hits 4 deg C, when water is at its densest, so it sinks again to your pipework.
Now if you can mount your pipework higher up in the pond, the cold water from it will sink and warm water will come in to replace it, so there will be movement of the water and some mixing. So the system will work providing you do not hit the 4 deg C point when it will fail again.
Very Fraught!!
Frank

My own situation is not dissimilar, but the pond is further away. Have considered both G and ASHP but am not convinced, though I am still mulling it over - sufficient to experiment with the lowest CH (lpg) water temperature I could get away with so as to estimate how much more radiator area I would need. As we are, it works not too badly at 60C, so doubling the area of rad should do it. Or I wonder about fan assisted rads where space is short.

Others here may know more, but I'd guess the pond would chiefly save on installation cost. How big is it? A small lake might be more the thing....

I put in a new condensing boiler 2 yrs ago and I recon it was worth it. If I did use a heat pump, I should almost certainly want a peak-demand-lopping boiler in the system. Something that burns wood could do this as well, but I might not want to depend on that when I'm older.

Brace yourself for a loud chorus of 'insulate the roof!' from all and sundry. Me too. Even some is going to be way better than nothing and its not so dear, I think.

A low investment possibility with high instantaneous returns is the traditional one of simply hunkering down a bit in the winter. Wear more, and heat fewer rooms. Get headphones so people can listen/watch without going to another room to do it, electric blankets in the bed, that sort of thing.

I do have loft insulation already but will look at installing more. The question I have about water sourced heat pumps is to do with the distance from a sea loch with a strong current. It is around 100m from our house and down a drop of 50m. Would the pump have to work so hard to overcome the distance/drop it would be less efficient than an air source? Am I wrong to think that the only part in the water are the pipes? Would there be anything else in the water that would be liable to corrosion.

Our local installers are not terribly enthusiastic and I don't know if it's because they don't fancy doing something different or if there is a sound reason for sticking to air source.

I'd appreciate some impartial advice from any of the knowledgeable folk our there.

Thanks Paul,
I suspect there will be a few times in the year when the tide will be too low to cover the top of the slim jim which is why I was thinking of a closed loop system. I had hoped that the exchanger wouldnt need to go in the sea as I'm sure the corrosion will have too damaging an effect. Wishful thinking I guess.
Out of interest how far is too far to be practical?

Air source remains a viable option but would very strong winds have a damaging effect. eg. on the fans?