I inspected a home that had a fireplace on the main floor with a gas water heater and furnace in the basement that were both venting into the fireplace chimney (from below). I couldn’t tell if the masonry chimney was lined because they had a board fixed in place at the top of the fireplace firebox.
Am I correct in thinking they need to keep the fireplace blocked off (as it currently is) to prevent gases from the appliances below from finding their way into the house through the fireplace?
I realize I should have had a mirror, but let’s assume I was a better-prepared inspector and using my mirror I was able to see just one flue. In that situation, am I correct in thinking they need to keep the fireplace blocked off (as it currently is) to prevent gases from the appliances below from finding their way into the house through the fireplace?
Yes, I agree with Scott, that chimney is 32" wide which is enough for two flues. Plus you can look through the spark arrestor screening to see in there to verify.
There should have been a clean out door in the basement also for at least the fireplace or outside, and one for the other flue.
There was no cleanout in the basement. Not sure if this is helpful, but here’s a pic of the two flues going into the chimney in the basement: Furnace in the front and water heater in the side. (Both pipes were centered.)
Gases can find there way into the house through other means e.g.loose brick, missing mortar, etc.
That chimney needs to have a Level 2 inspection:
A Level 2 inspection is required when any changes are made to the system. Changes can include a change in the fuel type, changes to the shape of, or material in, the flue (i.e. relining), or the replacement or addition of an appliance of a dissimilar type, input rating or efficiency. Additionally, a Level 2 inspection is required upon the sale or transfer of a property or after an operation malfunction or external event that is likely to have caused damage to the chimney. Building fires, chimney fires, seismic events as well as weather events are all indicators that this level of inspection is warranted.
If I was you, I would recommend that before the inspection contingency ends.