Bought a house a few years ago that has a BIS fireplace in it, decided to get it going this year. Cleaned it out pretty good and looked down the chimney to see if there were any obstructions before starting it. First few fires were perfect. Been burning wood off and on for about 3 weeks now with no problems. The last two times I tried to start a fire, I ran into an issue. I would get the fire going with no problems. Start with newspaper and kindling and would start to add a some larger kindling as the coals started to form. After an hour or so, the fire would just not burn anymore. It seems like the fire is not getting any oxygen as it grows. The front two vents on the front are really the only way this fireplace can transfer air to the inside of the fireplace as the outside air control is not ported anywhere. I have one question. Where do the front two vent on the unit vent to inside the fireplace? It looks to be sealed pretty good all the way around on the inside, just can't figure out if there is blockage inside the vents or if there is something else going on.