Hello, I'm new to this forum. I have the chance to purchase a used Regency gas insert (model U31, B-vent)) for my masonry fireplace from a seller on Craigslist for a good price, the insert is approximately 12 years old, in good working condition. The present owner is upgrading to a larger unit. I would use this unit to heat the lower level of my house which is about 700 sq. ft. (total square footage is approx. 1200 sq.ft.). My house was built in 1933. I've been reading a lot on the internet and on this site and plan on installing it myself, including the vent. As I said, the insert would be installed into an existing masonry firplace with a tile-lined flue. I have used the fireplace quite a bit over the years but would like to get more effeciency from the fireplace. I already have NG in the house for the HW heater and old, forced-air furnace. If anyone has an opinion on purchasing a used insert, I would like to hear it. I have priced new insert and the cost of this unit reperesents a considerable savings, VERY considerable. Thanks.