A fireplace does not always need a chimney. You can have a vent, but there are some concerns with a vent when the fireplace is in use.
I often see problems with chimneys. On the metal units that have a flue going out of the roof, you will find a wooden box built around them. The box will be coming apart, so rain can seep into the house. The metal cap holds water and is rusting. Insulation is not correctly kept away from the flue. With brick chimneys, you find cracks in the bricks and the cement cap. Every once and a while I find that the chimney has no cricket or saddle (the roof framing to help divert water away from the chimney). I have discovered chimneys pulling away from the house. There are many small issues that can lead to bigger problems. One problem has nothing to do with my field, but rather with the design of the home. I saw a beautiful home that had windows surrounding the fireplace to provide a better view of the porch. In another home, the chimney would have cut down on living space or added a larger cost to the house. In these cases, we will see builders adding a fireplace vent.
Fireplace vents are an acceptable solution, but they come with two problems that I consistently find. One issue that I bring up on my home inspection reports is the nature of the vent itself. Look at the photo, and you will see a metal box coming out of the wall. Hard to see is the fact that this box is stamped with the word “hot”. The hot combustion air and particles are going through this vent to the exterior. This vent is placed at chest height for me (about five feet above the ground at its top edge). I have noticed similar vents placed closer to the ground. In either case, when a fire is burning, the vent will be quite hot. What is to prevent you or a child from touching the vent? Nothing. With the vent going out to the porch, you could burn someone during a party. With the vent in the photo that is against a rear wall, children could hit the vent while playing. Another vent may be near shrubs that could burn if they are dry. Having an extra protective measure to prevent contact with this vent when its hot is not in any building code that has been brought to my attention. I imagine that other home inspectors may not place this item on a report, but I do, because a hot vent can be dangerous.
The next issue has to do with the smoke coming from the fireplace. If you have a gas or wood burning fireplace, you will have a combustion gas (smoke) exiting through the vent. This particular vent was for a gas fireplace that was sealed on the interior. The vent had a good deal of creosote. This is the burned particles in smoke, and they can act like charcoal, meaning that they can catch on fire. As a side note, most smoke detectors that we have in our homes are not detecting a gas like oxygen. The detectors work by sensing particles in the air. This is why they can be set off with dust. All of these particles do not land on the walls of the vent; they go out of the building. If you have an operable window that is near this vent, you could have the smoke blowing back into the house. This does not always happen. Vents are placed a distance from the openings to prevent this from happening. Also, the fireplace is used when it is cold, and a window will not be open. However, the smoke flowing into the house can happen. The problem with smoke that builders ignore is the vent in a covered porch. The home with windows around the fireplace was meant to be inviting for entertaining. A door near this interior space led out to a porch that was covered by the roof. This home had a second story, so the porch roof was high up. Yet, I could already see signs of the soot on the ceiling over the porch due to the fireplace being used. There was about eighteen feet between the vent and the edge of the porch. Unfortunately for the homeowner, smoke goes up, not diagonally out to avoid the roof. Over time as the homeowner entertains, the creosote will build up on the ceiling of the porch.
Fireplace vents are not a bad idea. A vent can reduce the cost of installing a fireplace. They avoid problems which can ensue from a chimney. However, a fireplace vent can bring its own problems, and I just want you to be aware.