Is solar air heating for a floor as efficient as solar hydronic?

Thanks for your question, and I would start here in general terms of efficiency in heat delivery - there is no great difference in the energy efficiency between air heated floors or hydronic (liquid) radiant floors, at least when they are heated with the same fuel. Meaning – a boiler heating water that is circulated through radiant tubing in a concrete floor will not be any more or less efficient that a boiler heating a water coil that blows air through a floor.

The fuel source (gas, electricity, propane etc) will affect cost and efficiency, but differences in how you deliver heat isn’t as big a factor in determining efficiency. This page discusses the differences and pros and cons of each system – 

Radiant floors heated with air tubes

Moving into a solar solution though and choosing between a solar water heater and a solar air heater, there you would for sure have more variables in terms of the initial cost of the system, return on investment time, maintenance and lifespan. 

I assume you saw our page on solar air heated radiant slab on grade floor. I would personally lean towards that because they address a lot of the issues that come up with solar thermal water heaters – read more here, which can have a lot of maintenance issues. The thermal solar air panels we installed in that prefab kit house obviously don’t leak water, freezing is not a concern, and even summer overheating has been solved because that system has been adapted to generate solar hot water in summer in part to cool the system.

Solar thermal water heaters can, in a bizarre twist, need to be covered often during summer to avoid overheating. I hope this helps, check out those pages and if you have more questions let us know, but include your climate zone as well and we can better help you decide.