I use the Dwyer Mark 25 also as do many on here.. I would think its perfect for any coal appliance. But hopefully someone that's more knowledgeable with a direct vent could advise..
As far as tips are concerned, most of us hook them up "backwards" so that the reading is on the positive side of the zero even though its measuring negative pressure. The reason is that the negative side of the scale only goes to -.05 where the positive side goes higher than you'll ever need to get a reading.. See pic.