Could I / should I fill the space between insert and fireplace with bricks?

[TradEddie]

This shoulder season, I've experimented with switching off my insert blower once the room begins to heat up in an attempt to prevent the house overheating. There certainly is a significant difference in heat output, but as someone here pointed out recently, that heat is going somewhere, either up the flue, or into the surrounding brickwork. I expect that some of the "lost" heat is going up the flue, but without a doubt, the surrounding brickwork gets much hotter when the fan is off, and maintains significant heat for almost a day after the last log has been loaded. Even in mid winter, this could be very useful way to control heat.

I was thinking, could I improve this heat sink by filling the large space between the insert and my old fireplace with more bricks? I can't see much problem with filling around the sides or rear, but where they would be much more useful, and much more potential for problems would be on top. If I was doing it on top, I'd build a frame to hold the bricks.

Any thoughts/concerns/experiences? Should I do it at all, and if I do, should I pack them tight, or leave air spaces?

TE

 

[Ram 1500 with an axe...]

I ran my insert with the surround off for a week or two, I found out I was losing no heat out from the sides, the inside of the fireplace did not heat up, there were only a few cobwebs in there.

 

[firebroad]

I ran my insert with the surround off for a week or two, I found out I was losing no heat out from the sides, the inside of the fireplace did not heat up, there were only a few cobwebs in there.

I have always wondered about this. My insert surround does not seal against my flagstone fireplace, I was considering stuffing some rolux or gasket rope in there. Good to know it isn't necessary.

 

[Ram 1500 with an axe...]

I have always wondered about this. My insert surround does not seal against my flagstone fireplace, I was considering stuffing some rolux or gasket rope in there. Good to know it isn't necessary.

Maybe different inserts will give off different results, but this is why I believe I do not ne a block off plate that many on here preach..... Try running the insert with no surround and an ir gun in hand.....Suzy q

 

[bholler]

I am sorry but I feel that every insert should have a block off plate. If it is an internal chimney it is not quite as important but it doesn't cost much and it is easy so why not do it? And fire broad it you have a block off plate there is no need to seal the face plate. As for the original question I would say that adding brick would not make much of a difference. Is it an internal or external chimney? If it is external I would say that putting insulation behind the insert would benefit you much more than brick.

 

[Ram 1500 with an axe...]

If the heat is not escaping from the sides or back, why would you need a block off plate?

 

[bholler]

well I find it hard to believe no heat is coming off the outside of the insert I have never seen one that didn't. But regardless heated room air will go up the chimney and if it is an external chimney it will get cooled and then drop back down out of the fire place. Like I said if it is internal it is not as important but still a god idea

 

[begreen]

I don't know of any insert that has an insulated jacket. Some heat will always radiate from the convective jacket of the insert. Keeping that heat in the area you want to heat with a block off plate is a good idea, especially if the chimney is on an exterior wall. But even with an interior chimney it can help if the primary goal of the insert is to heat the same floor. If the goal is to heat upper floors too then heating up the chimney may be helpful, if the chimney has some exposed surfaces upstairs. If it is framed in behind walls and there is an air gap between the framing and the chimney, it's possible that a lot of the heat can go up to the attic and out the vents. The benefits will vary and depends on the house construction, chimney location, chimney exposure etc..

 

[TradEddie]

I do know that with the fan on, very little heat reaches the metal sidewalls of the fireplace firebox, what I need to check is if this is true when the fan is not running, and whether the top gets hot with or without the fan. With 70's in the forecast, this experiment may need to wait a few months, but I'll be on the lookout for cheap bricks.

TE

 

[firebroad]

I don't have a block off plate, but my installer shovedplenty of rolux down the sides of the chimney. Had I known at the time, I would have insisted on the plate.
I was concerned about convection sucking the heat back through the gaps in the surround.

 

[Grisu]

This shoulder season, I've experimented with switching off my insert blower once the room begins to heat up in an attempt to prevent the house overheating. There certainly is a significant difference in heat output, but as someone here pointed out recently, that heat is going somewhere, either up the flue, or into the surrounding brickwork. I expect that some of the "lost" heat is going up the flue, but without a doubt, the surrounding brickwork gets much hotter when the fan is off, and maintains significant heat for almost a day after the last log has been loaded. Even in mid winter, this could be very useful way to control heat.

I was thinking, could I improve this heat sink by filling the large space between the insert and my old fireplace with more bricks? I can't see much problem with filling around the sides or rear, but where they would be much more useful, and much more potential for problems would be on top. If I was doing it on top, I'd build a frame to hold the bricks.

Any thoughts/concerns/experiences? Should I do it at all, and if I do, should I pack them tight, or leave air spaces?

TE

That's pretty much what I see with my insert. I now turn the blower on when the stove is at temp and turn it off about 2 hours later when the peak burn is over. The blower serves more to heat up the room fast and to avoid potential overfire temps. It means I have less blower noise and the masonry will radiate the heat for a long time. A good block-off plate with some Roxul above is key, IMHO. With that I doubt you lose much if any more heat up the flue than when you use the blower. If that would be the case, stoves with large thermal mass (like soapstone) would be less efficient than simple steel stoves. I don't think I have ever seen someone make such a correlation.

If your fireplace is at an exterior wall, I would rather put some Roxul behind it than brick. The sides you can give it a try with the brick but I would leave some airspace to not trap too much of heat in there. Maybe check the minimum fireplace opening given in your manual as the minimum space the insert needs to have. Please be aware that just stacking bricks in there will leave an airspace between them and the fireplace masonry. Hence, it may take a long time until that heat makes it into the room. Thus, on the top I would think about adding insulation more than bricks. That way you will reduce the amount of heat that goes up along the flue.

 

[Grisu]

If the heat is not escaping from the sides or back, why would you need a block off plate?

Why do people not make holes in the ceiling of their living room other than for aesthetic reasons? Because they don't want to have room heat going up into the attic. The air around your insert is at least at room temp.