Hotbed for greenhouse

I am constructing a reclaimed greenhouse on my allotment. There is no electricity so to generate some winter warmth I want to make a hotbed.

Instead of manure I'm thinking of using the free wood chips we have on-site. The pile gets very hot under the surface. Too hot to touch. So I reckon it could work in a hotbed. If I add some chicken manure pellets we may even have some usable soil conditioner after 12-18 months.

I see a couple of advantages namely:
1. the wood chips are free
2. They are lighter than manure so easier to wheelbarrow around
3. As they reduce in volume I can keep adding more on top and won't empty till next year.
4. The heat should go out of them by summer and the box can just be left in the greenhouse

Does anyone have any thoughts on this idea?