Getting more heat out of an insert

[Nick Mystic]

My post commenting on how much I am enjoying the quiet of my wood stove after having had an insert with a fan for eleven years morphed into a thread talking about getting more heat out of an insert. A few times now in different threads I've read comments where people have said they have burned their inserts for one reason or another with their surrounds removed for a time. Since most inserts don't look very attractive with their surrounds off it got me wondering if it would make sense to cut some slots or drill some holes in the top section of an insert surround to let some of that trapped heat escape back into the room? Of course, you would have to have a stop plate installed, but it's best practice to have one anyway. If the surround was raised an inch or so off the hearth it should get a nice convection current started that could move some hot air out the holes.

 

[rideau]

As long as there is no ash spillage on loading that gets under the insert. Then you'd be blowing ash all over your home. Someone posted with such a problem fairly recently.

 

[Nick Mystic]

Good point. My old insert was installed slammer style, so I shoved some insulation under the insert, which sat about an inch off my hearth in an attempt to seal it up so air wouldn't be sucked up my chimney. Instead of having an air opening at the very bottom of the insert, which could create the ash blowing problem you mentioned, perhaps some additional slots or holes could be drilled in the side pieces of the surround near the bottom, but away from the hearth where ashes could be sucked in and blown back out into the room.

 

[Jon1270]

I doubt that a few holes / slots would help much. Convection alone doesn't work well even with the higher temperatures inside the insert's air jacket, which is why a fan is necessary. What you're suggesting is essentially using the space between the insert and the original fireplace as a second air jacket, but temperatures would be lower and convection would be even less effective, especially since the space won't have been designed for easy air flow. If the brick (or other material) of the old fireplace soaks up heat and chills the adjacent air, that would shut convection right down; the convection can't start until the brick warms up, at which point the heat is already being lost. So there's a built-in conflict here -- you need the bricks to stay warm, so that convection will work to move heat, so that the bricks will stay cool.

I think it would help more to insulate around the insert so that less heat is lost into that space in the first place. And of course put in a block-off plate; it amazes me that people think of them as optional.

 

[TradEddie]

I think that putting Roxul between the insert and the original fireplace would have to help efficiency, keep that heat in the convection chamber where it can be used, but is there any danger that it might cause damage by overheating?

TE

 

[Jon1270]

I think that putting Roxul between the insert and the original fireplace would have to help efficiency, keep that heat in the convection chamber where it can be used, but is there any danger that it might cause damage by overheating?

No promises, but I don't see how. The outer shell of my insert (and I'm assuming this is pretty standard) is steel, and it's insulated from the firebox by a layer of air except at a few contact points; it can't get any hotter than the air moving through the air jacket, which I can't imagine getting to steel-damaging temperatures.

 

[HotCoals]

I never really understood the decorative plate deal around a insert.
I would have the block off plate but that would be it...then again I hate blowers..lol.

 

[WoodpileOCD]

Depending on the insert I like the way they look without the surround. Mine is designed to be either a free standing or an insert and has the bay front. I painted the inside of the FP black and without the surround I'm convinced I get more heat coming from behind and around it. Very satisfied with my setup right now.

 

[HotCoals]

Looks good Woodpile!
You would have to think it works better that way..run the blower much?

 

[Hogwildz]

No promises, but I don't see how. The outer shell of my insert (and I'm assuming this is pretty standard) is steel, and it's insulated from the firebox by a layer of air except at a few contact points; it can't get any hotter than the air moving through the air jacket, which I can't imagine getting to steel-damaging temperatures.

My insert has a casing with air space between it and the the firebox shell. The surround attached to the outer casing. The air space is for convection air flow. Filling that space would counter what it is intended for. I think many other inserts are set up the same way. At least the newer ones. I have no desire to insulate between the outer case and the fireplace walls. Sometimes it is better to leave the design the way it was made o intended to use. I also don't mind the masonry around the old fireplace holding & releasing heat, now that is it enveloped inside the house.

 

[Jon1270]

My insert has a casing with air space between it and the the firebox shell. The surround attached to the outer casing. The air space is for convection air flow. Filling that space would counter what it is intended for.

Yeah, that's not the space I was referring to. It would be nuts (and also difficult) to fill that space. I meant the space outside the insert, between the outer shell and the original fireplace.

I also don't mind the masonry around the old fireplace holding & releasing heat, now that is it enveloped inside the house.

My chimney's on an outside wall. The vast majority of the heat that soaks into the brick goes right outside. But I can see it being different for an interior chimney.

 

[mellow]

If you have an exterior fireplace it only makes sense to insulate the fireplace with roxul, it makes a huge difference.

 

[Jon1270]

Yep, that's my plan. Initially I followed the insert manual to the letter, and since it didn't say to insulate I didn't do it. But the heat loss is obvious, and I will be correcting the situation before next season.

 

[WoodpileOCD]

Looks good Woodpile!
You would have to think it works better that way..run the blower much?

I run the blower most of the time but usually on low setting. It's pretty quiet and it's a trade off. Low volume of higher temp air or higher Vol of cooler temp air. Low keeps it plenty warm in here.

I measured the air coming out not long ago. Maybe I'll start a thread on that topic.

 

[PLAYS WITH FIRE]

Mine is an exterior insert also...there is never any snow within 2'+ around the chimney that protrudes out about 2'. You can feel the warmth from it on the outside. This spring i am using an offset box to move my insert out 1' out of the fireplace and will fill the area behind with Roxul and then cover with sheet metal.
I figure the heat that is being sucked up by the masonry is enormous! I bust my butt for my wood and if I can burn more efficiently in any little way, I am!
If anyone is looking to buy an offset box, have it welded or pop rivet it together. Otherwise you suck air through it and not the insert.

 

[etiger2007]

I have a heatform steel box that the insert sits it. I did insulate the sides with Roxul but didnt really notice that big of a difference in heat out put, or how long the stove stayed hot. I think being it sits in a steel box the heatform probably reflects the heat better than if it was brick. I did put Roxul in the cavitiy between the heatform and the masonary chimney in the back of the old fire box and took out the Roxul on the sides so it could radiate more.

 

[Jon1270]

I have a heatform steel box that the insert sits it. I did insulate the sides with Roxul but didnt really notice that big of a difference in heat out put, or how long the stove stayed hot.

Before you did this, was there already Roxul above the block-off plate, between the liner and original chimney? I didn't even do that, and my Heatform was so badly rusted out that the smoke shelf was virtually nonexistent so heat that is absorbed into the heatform has a very easy escape route up the chimney.

I think being it sits in a steel box the heatform probably reflects the heat better than if it was brick.

I doubt this is true. Steel is a much better heat conductor than brick.