Please help!

[bholler]

If you cut the firebox and leave the vents open unless you completly seal the cut area you are bypassing your block off plate. And if the fireplace is on an outside wall leaving them open will probably do more harm than good

 

[Hogwildz]

If you cut the firebox and leave the vents open unless you completly seal the cut area you are bypassing your block off plate. And if the fireplace is on an outside wall leaving them open will probably do more harm than good

The block off plate seals the old firebox below the cut area, and doing it's job of keeping direct heat where it is intended to flow. The vents are only doing what they did prior with heat from the shell of the the old fireplace. Works as was originally intended, just not getting the heat direct from the source any more, only from the residual heat from the shell.

Don't think it makes much of a considerable difference either way, I just know the vents do work from testing them. Plus I ran power for the blower cord to an outlet I installed in the lower vent opening. then ran the blower cord to the outlet. All hidden, yet accessible if need be.

 

[bholler]

The block off plate seals the old firebox below the cut area, and doing it's job of keeping direct heat where it is intended to flow. The vents are only doing what they did prior with heat from the shell of the the old fireplace. Works as was originally intended, just not getting the heat direct from the source any more, only from the residual heat from the shell.

Don't think it makes much of a considerable difference either way, I just know the vents do work from testing them. Plus I ran power for the blower cord to an outlet I installed in the lower vent opening. then ran the blower cord to the outlet. All hidden, yet accessible if need be.

Ok the vents circulate air through the inner and outer wall of the fireplace. You then cut through those walls and blocked off the bottom. But you didn't block off the top. So yes heated air is no longer sucked up through the damper area but it is sucked through the lower vents and some of that goes up around the liner through your cut. That is why I said you are bypassing your block off plate.

 

[Dix]

Mine are open ... the passive system works.

A big plus, is the chimney radiates heat long after the fire is out, and the vents help. Really helps on "Iffy" days.