efficiency of an insert vs a stove

[karl]

I'm curious about how efficient inserts are compared to the same stove as a free standing model. I know the btu output is listed as the same because they are tested as stoves and not asinserts. I have a PE Summit insert and it works really well, but I don't get the crazy amount of heat out of it that other people say they do with the free standing version. I know the chimney and over insulation in the house plays a big part, but I just curious if anyone has any genera ideas.

 

[begreen]

A free-stander generally does better than the same box as an insert. Inserts are mostly convective heaters. There is usually more radiant heat with a freestanding stove and less heat lost to warming the masonry.

Some confounding factors that can make an insert an even poorer performer are: external chimney keeping the firebox cooler, no block-off plate, & poor blower convection system.

 

[Todd]

Do you have a blower for your insert? I think it's an absolute must have for inserts.

 

[webbie]

My guess is that the whole assembly could be as much as 20-40% less efficient than a free stander. Keep in mind that since most insert owners ONLY have the insert, they generally don't compare them to freestanders.

Some suggestions have been given here to mitigate the loss - everything from the tight sealing block-off plate, to blowers and to panels which do not fit tight against the fireplace so trapped heat can escape. I suppose you might get it down to only a 15% diff (on exterior fireplaces) Example - 70% freestanding, 60% insert (that is about 15% less)...

 

[BrotherBart]

Interesting question. Everybody always seems to assume that that wall, or walls with a corner installation, don't have any heat loss to the great outdoors but that an insert with a shroud around it and a blower does.

 

[begreen]

There's a whole lot more loss to an outdoor masonry wall behind an insert than to an interior insulated wall. And then there is a lot of territory in between.

If you stick your naked butt (a heat radiator) in an enclosed stone box on the exterior of the house vs having it exposed to the interior 70 deg. warmth of the house, you will feel the difference quickly. Yes, if we find you with your butt sticking in a cold stone box, we are to call the funny farm right away, but what the hey, this is stove science .

 

[karl]

Craig,

I think you might be right with the 20%-40% amount. I have a block off plate and my chimney is only exposed to the outside on one side, but then again It's a one story house so most of the chimney is above the house.

Now that I have a few months of burning experience I think I can make some decisions. And since Elk is gone I can discuss some modifications I want to make in the spring for next year.

1. I want to put a second blower on the insert. I have looked at the one thats on it and it looks as though I could buy a replacement and put it on the other side of the insert. The big advantage to me would be a higher volume of air with a lower and thus quieter fan setting. Also the Summit blower doesnt blow all the way across the top of the stove. It really only blows air across on one side. I think the second fan and reworking the baffles would help alot.

2. Insulating above the block off plate. I think I might insulate the whole liner next year. I have a short, 15 foot chimney.

3. Insulating around the insert portion that's enclosed. It's a zero clearance insert and if I use a fire proof insulation I think I'll be safe. Also the fireplace is large enough I could put it in there and still have it 8"10" away from the insert. I'm considering putting metal over the insulation to help reflect the radiant heat back to the stove. This would keep the stove hotter with a lower draft setting and also help prevent heatin the block around the chimney and thus loosing alot of that heat to the outside.

4. Make a different surround with louvers in it and maybe a small blower in it to help recover some of the heat.


5. Craig, please explain what you mean by "and to panels which do not fit tight against the fireplace so trapped heat can escape." My cold outside air intake comes from ash clean out, so thats a cold zone for me. However, I'm sure it's pretty hot in there and the heat is being lost to the block. Wouldn't it be better for me to rework the outside air intake and then treat that area as a hot area and try to recover the heat from it instead of sealing it in there to be lost?

Tell me what you think if you would.

I'm not knocking the Summit. It is a beast. I haven't had the furnace on yet this year. I can get a 30-35 degree temperature differential without any trouble. 40-45 degrees isn't much harder but not doable without loading every few hours: but then I have the coaling up problem. If I could a 50 degree swing with a good 6 to 8 hour load period, I would be extremely happy. 20 degrees is probably the average low around here. I'm going to work on the house insulation this summer too, but really it's not too bad.

Thanks for everybodies input.

 

[iceman]

Craig,

I think you might be right with the 20%-40% amount. I have a block off plate and my chimney is only exposed to the outside on one side, but then again It's a one story house so most of the chimney is above the house.

Now that I have a few months of burning experience I think I can make some decisions. And since Elk is gone I can discuss some modifications I want to make in the spring for next year.

1. I want to put a second blower on the insert. I have looked at the one thats on it and it looks as though I could buy a replacement and put it on the other side of the insert. The big advantage to me would be a higher volume of air with a lower and thus quieter fan setting. Also the Summit blower doesnt blow all the way across the top of the stove. It really only blows air across on one side. I think the second fan and reworking the baffles would help alot.

2. Insulating above the block off plate. I think I might insulate the whole liner next year. I have a short, 15 foot chimney.

3. Insulating around the insert portion that's enclosed. It's a zero clearance insert and if I use a fire proof insulation I think I'll be safe. Also the fireplace is large enough I could put it in there and still have it 8"10" away from the insert. I'm considering putting metal over the insulation to help reflect the radiant heat back to the stove. This would keep the stove hotter with a lower draft setting and also help prevent heatin the block around the chimney and thus loosing alot of that heat to the outside.

4. Make a different surround with louvers in it and maybe a small blower in it to help recover some of the heat.


5. Craig, please explain what you mean by "and to panels which do not fit tight against the fireplace so trapped heat can escape." My cold outside air intake comes from ash clean out, so thats a cold zone for me. However, I'm sure it's pretty hot in there and the heat is being lost to the block. Wouldn't it be better for me to rework the outside air intake and then treat that area as a hot area and try to recover the heat from it instead of sealing it in there to be lost?

Tell me what you think if you would.

I'm not knocking the Summit. It is a beast. I haven't had the furnace on yet this year. I can get a 30-35 degree temperature differential without any trouble. 40-45 degrees isn't much harder but not doable without loading every few hours: but then I have the coaling up problem. If I could a 50 degree swing with a good 6 to 8 hour load period, I would be extremely happy. 20 degrees is probably the average low around here. I'm going to work on the house insulation this summer too, but really it's not too bad.

Thanks for everybodies input.

i have one too it does a great job of heating
however yes you can insulate above the block off plate but there is only so much it will help ...meaning no more than 2 inches anything after that won't help
2 fans is a good idea but even though you don't feel the fan all the way acroos heat is still coming out naturally.. if you add another fan the turn them both down to a lower speed so you don't cool off the box in theory you will still have more cfm
if you insulate the box make sure you don't cover the hole in the back as that is where the stove gets its combustion air
also you could simply take your shroud to a metal fabricator and where the indentation is on the panels have one made so there is a screen type look so it will allow air to come out... that will prolly be the cheapest and best way to get more heat
another way to find out is simply take your shroud off and burn it for a day and see how much more heat comes out... i have thought of this too.. by insulating the outside you can keep the box a little warmer yes but the only way it would make a diff is if its an external chim...(that was right from pe people)
we can tweak it to make it run more eff a little bit but he also said that it was going to make the cold end of the house go up 15 degrees the room its in might go up a few but on an inetrior chim taking off the shroud and having a block off might do something ... however they can't recc. burning without a shroud
so when you try it let me know how it works for you!!

 

[sgcsalsero]

If you stick your naked butt (a heat radiator) in an enclosed stone box on the exterior of the house vs having it exposed to the interior 70 deg. warmth of the house, you will feel the difference quickly. Yes, if we find you with your butt sticking in a cold stone box, we are to call the funny farm right away, but what the hey, this is stove science .

that is freakin' hilarious BG . . .

. . Hey Craig, if ever you had an excuse to start a Hall of Fame quotation list

 

[sgcsalsero]

5. Craig, please explain what you mean by "and to panels which do not fit tight against the fireplace so trapped heat can escape." My cold outside air intake comes from ash clean out, so thats a cold zone for me. However, I'm sure it's pretty hot in there and the heat is being lost to the block. Wouldn't it be better for me to rework the outside air intake and then treat that area as a hot area and try to recover the heat from it instead of sealing it in there to be lost?

I believe Web might be speaking of letting some air getting around panels (shroud) . .my installer put insulation around panels to 'plug' any gaps . . what he really should have done was install a block off . . I now have a block off and NO insulation around panels to hopefully let more heat out (the gap is not huge, maybe 1/2")

btw, I left all the panels off for a week . .it did make a difference (felt more heat radiating off) . .I didn't notice if the thermostat reacted quicker . . stands to reason that with the panels off more heat radiates more quickly off steel insert

I'm not knocking the Summit. It is a beast. I haven't had the furnace on yet this year. I can get a 30-35 degree temperature differential without any trouble. 40-45 degrees isn't much harder but not doable without loading every few hours: but then I have the coaling up problem. If I could a 50 degree swing with a good 6 to 8 hour load period, I would be extremely happy. 20 degrees is probably the average low around here. I'm going to work on the house insulation this summer too, but really it's not too bad.

35 degree differential ??? . . . can you explain that a little more, do you let your house get down to 50 then crank your PE up to get the house to a sauna like 80 ?? . .

 

[JimWalshin845]

An insert is like putting your beer can in a cozy, expose 6 sides of a cube with circulated air and you will definitely get more BTUs.

 

[karl]

what I mean by a 35 degree temperature differential is that when it's say 40 degrees outside I can keep the house 75. 35+40=75 If it's 20 out I can keep the house 55 degrees. Actually, it's been down to the high teens and I was able to keep the 65, so that's a 45 degree differential but I had to load the stove every few hours. I hope this explains it for you.

 

[iceman]

what I mean by a 35 degree temperature differential is that when it's say 40 degrees outside I can keep the house 75. 35+40=75 If it's 20 out I can keep the house 55 degrees. Actually, it's been down to the high teens and I was able to keep the 65, so that's a 45 degree differential but I had to load the stove every few hours. I hope this explains it for you.

is your house isulated well?
it is hard for me to keep the house warm when its 0-25 degrees the upstairs i can get the hallway to 68-72 and bedrooms 64-68 but at night when we sleep it drops of course and the furnance is set at 64 and it did kick on a couple of times early in the morning right before i got up
but when i had the insulation guy come and check my house which i thought was insulated he told me by todays code i needed another 6 inches and he was going to put something inbetween the joists (ceiling) to help it vent a little better
the moral of the story is the rooms that are the coldest are at least almost 50 feet from the stove i believe adding 6+ inches of insulation will have a affect on the colder nights

 

[webbie]

Karl, sounds like you are on the right track. If you do use outside air, you might want to think again about it, as it may actually be lowering your total efficiency.

What I meant by the panels....was that they should not provide the seal, the damper block off should do it. Loose panels and a good damper seal can, in some situations, let some of the trapped heat (from behind the panels) move into the room.

As to your other ideas......is your fireplace a pre-fab? If so, I doubt you will gain much by wrapping the pipe - having a few dead air spaces makes for quite decent insulation. Your draft might slightly increase....but IMHO (if unit is operating properly now) it will not increase the total efficiency much.

An improved blower might help - I have seen lots of blowers and convection chambers that were not well thought out. Insulating the unit could help a lot - especially the top of the unit. I know some units (Winterwarm?) come with a 1/2" insulation on top.

If you do have a metal prefab fireplace, I think the downside of an insert may not be as large.....well, to explain further, I would say that the prefab itself without any insert is pretty bad (at radiating cold), but at the same time it does not have the capacity to soak up as much heat as masonry does. So while it is stealing some efficiency, it is going to do the same (to your house) even without an insert.