We have both the Espar furnace and hydronic unit and regularly run B20 in our rig. We use only commercially produced bio that meets the ASTM standards and have had no problems to date..
When I had our van built I had SMB run bio compliant fuel lines to the Espar units, otherwise they use standard rubber fuel lines. Standard rubber fuel lines will be slowly dissolved by running bio, so if you intend to run bio diesel you will need to change these lines.
I did a lot of research on the web and did find reports of people having problems with bio-diesel in the Espar units. The reported problems were that the bio-diesel creates a build up of carbon on the atomizer screen. Unfortunately it did not specify whether they were running straight bio or a blend. It also did not specify if they were running home made bio or ASTM grade bio. Also, if you read the literature that comes with the furnace you will see that Espar specifies that the atomizer screen should be cleaned and the glow pin changed annually anyway.
The general consensus seems to be that most equipment designed to run on diesel should not see any adverse effect from a B-20 blend but only time will tell.
If thats not enough there is also the problem that if you are still under warranty and Ford finds out you have been running bio-diesel over B5 they may void your warranty. So be sure to fill with Dino diesel before dropping your rig off for service.