I have a gas fireplace in my sunroom right now, maybe in a year or 2 I was considering switching it to a wood burning stove, will the existing flue work with a wood or pellet burning stove?

Probably not. Most gas fireplaces installed are really gas appliances that are vented. If it is a true fireplace, it should say so on a metal tag attached to the fireplace. Other clues are, the flue will be much larger A' vent on a wood burning fireplace, (8-12 inches when viewed from the smoke chamber) and there will be a damper installed. Gas vented flue will be small B' vent. Be sure before you build a wood fire!

Have a pro inspect your home and make recommendations. No, you cannot use gas 'vent' in lieu of 'chimney'. Gas B-vent or direct vent pipe are not substitutes for stove pipe. There is much planning when installing a woodstove including floor, wall and possibly ceiling protection, location and type of chimney, firestops, support, termination, single vs. double walled pipe, clearances to furniture and furnishings, etc. then the stove selection itself. FYI, most EPA Phase II stoves use 6" pipe; most fireplaces start at 8". If you are looking for heat but like the open hearth fire look, consider a hybrid fireplace/ stove. Many good choices out there. Visit your local hearth retailer.

Just one other example why gas vent is not interchangeable with wood: a single walled connector for wood carries an 18" clearance to combustibles.

Pellet vents are special pipe, too. Most require the joints to be sealed with hi-temp. RTV silicone. Speclal venting rules, too.

Bob

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Keep the fire in the fireplace.