fireplace insert efficiency - three questions

[rickw]

1. I have a Lopi Answer insert. I get the feeling that I burn more wood than I should be. It's in an exterior masonry chimney; and I suspect that I'm losing a lot of heat out the brick to the great outdoors. I sort of remember someone here talking about wrapping the insert in insulation (ceramic wool) or insulating the interior of the chimney. Has anyone actually done this? Did it seem to help?

2. The flue draws fine (6" SS liner all the way to the stove, with block off plate), but I'd like to insulate it to keep it clean. I've read on UK (British) hearth forums about pouring in vermiculite or something like it. I've seen vermiculite loaded cements for sale on the web. Does anyone have experience with pouring loose vermiculite/perlite around the liner from the block-off plate up? Or is a wet cement the better option?

3. are there any cat inserts currently made other than the WinterWarm or the Blaze King Princess?

How do I like the Answer? - Its fine as long as you keep throwing wood into it every 2-3 hours. Longest burn ever was 6-7 hours after cramming the firebox completely full (there's my clean flue, I know, but I'd like to sleep thru the night at least once a winter). On the other hand, relights in the morning are generally easy - especially with some ash in the bottom of the stove. The blower must be used.


Thanks

 

[karl]

I can't give you the best answer since I'm just now getting around to buying an insert, but I have researched them for a long time. I'm getting the Napoleon 1402. Everybody on here suggested I get an insert with a 2-2.5 cubic foot firebox for overnight burns. Originally, I was going to buy one with a 1.7 cubic foot box and thanks to the advice on here I'm getting a 2.25 box. The Lopi answer is only 1.6 cubic feet, so you might not be able to get overnight burns in it.

 

[rickw]

The Answer is too small - I know that now (believe me). That aside, even a larger insert in an exterior masonry chimney will have the same heat loss issues. So, anyone tried insulating the insert itself? The only reason I'd even consider it is that convective shroud will keep an air passage open.

Thanks

 

[Gooserider]

1. I have a Lopi Answer insert. I get the feeling that I burn more wood than I should be. It's in an exterior masonry chimney; and I suspect that I'm losing a lot of heat out the brick to the great outdoors. I sort of remember someone here talking about wrapping the insert in insulation (ceramic wool) or insulating the interior of the chimney. Has anyone actually done this? Did it seem to help?

Some do this, and reportedly it helps, but the bottom line is your real problem is a tiny firebox. Insulating may help you get more heat into the room from a load, but it won't significantly increase your burn times.

2. The flue draws fine (6" SS liner all the way to the stove, with block off plate), but I'd like to insulate it to keep it clean. I've read on UK (British) hearth forums about pouring in vermiculite or something like it. I've seen vermiculite loaded cements for sale on the web. Does anyone have experience with pouring loose vermiculite/perlite around the liner from the block-off plate up? Or is a wet cement the better option?

Using the cement is a BAD idea, as it will make your liner a permanent part of the chimney - future repairs will be impossible without demolishing the chimney. OTOH pouring vermiculite in (BTW the stuff you can get at the local garden center will work fine) works reasonably well at insulating, though again it won't help your burn times alot, and is repairable, although it's messy to get it out.

3. are there any cat inserts currently made other than the WinterWarm or the Blaze King Princess?

I believe Woodstock makes a cat insert or two.

How do I like the Answer? - Its fine as long as you keep throwing wood into it every 2-3 hours. Longest burn ever was 6-7 hours after cramming the firebox completely full (there's my clean flue, I know, but I'd like to sleep thru the night at least once a winter). On the other hand, relights in the morning are generally easy - especially with some ash in the bottom of the stove. The blower must be used.

Thanks

Bottom line - the biggest single influence on burn time is firebox size, the bigger the box the longer the burn. You basically have to burn so much volume / hour at a minimum to keep a cat lit or your secondary flames going, and the firebox has to have at least that much volume X the number of hours you want it to burn. Concensus here is that you need at least 2-2.5 cu ft of useable space to get an overnight burn with oak, more if you are using fast burning woods like pine.

Gooserider

 

[rickw]

Gooserider - thanks for the reply.
OK - I fully understand that the stove is too small. I also understand that for longer burns I need a larger stove; and that I'd be generally happier with a larger stove. Got it. I was asking about insulating the insert based on efficiency concerns; and hoping for specific advice on types of insulation, placement,etc. I don't know, but I suspect that I'm throwing away a lot of heat right through the brick of the chimney.
Thanks for thoughts on vermiculite for insulating the flue. Is garden shop vermiculite asbestos-free?
I'm interested in a cat insert because I want a combination of modest heat output (small house) and longer burn; and I think that a cat will provide that (and of course will still need a larger firebox). Woodstock's website does not show any insert (or I didn't find any).

Rick

 

[R&D Guy]

Edit: Saw Ricks newest post.

 

[R&D Guy]

Rick IMO i'd stay away from a cat insert. Cat's are rather sensitive, and there's a lot of don't with them like burning paper with colored print, and with most there is a procedure to opening the door when they're hot or you can destroy the cat. As was said, they have to be really hot to work too. I think SS secondary pipes are more bullet proof.

 

[Gooserider]

Gooserider - thanks for the reply.
OK - I fully understand that the stove is too small. I also understand that for longer burns I need a larger stove; and that I'd be generally happier with a larger stove. Got it. I was asking about insulating the insert based on efficiency concerns; and hoping for specific advice on types of insulation, placement,etc. I don't know, but I suspect that I'm throwing away a lot of heat right through the brick of the chimney.
Thanks for thoughts on vermiculite for insulating the flue. Is garden shop vermiculite asbestos-free?
I'm interested in a cat insert because I want a combination of modest heat output (small house) and longer burn; and I think that a cat will provide that (and of course will still need a larger firebox). Woodstock's website does not show any insert (or I didn't find any).

Rick

Far as I know the garden shop vermiculite is asbsetos free, but it probably wouldn't hurt to check the label... I know a lot of people use it when building outdoor pizza ovens. I've seen it suggested several times here, primarily when either there isn't enough room for a regular insulation blanket (I.E. trying to get a 6" liner down an 8x8" clay tile flue) or where the liner is already installed as an easier solution to retrofitting than pulling the liner out to wrap a blanket around it.

On the insert, I guess I must have been thinking of Hearthstone, who does a couple of really nice BIG inserts, but presumably they would be too big for you, and they aren't cats. Sorry for the wrong answer. :red:

Gooserider

 

[stoveguy2esw]

look hard at soapstone units, there arent as many manufacturers out there as with cast and steel units (we do steel) the mention about the Ss tube units earlier has merit , however cats arent as sensitive as you might be led to believe providing the design of the stove is sound , my experience with a freestanding cat unit has been very favorable, the comment about the colored paper is valid and very important, catalysts are able to do what they do because of the compounds they are made of , the chemicals in dyed paper are destructive to these compounds so dont get rid of the christmas present wrappings in a cat unit, or you may have a bill by valentines day. getting back to the soapstone stoves , for long heat cycles they excel, cast running a fairly close second. there are steel units with EBT that do offer long burn times as well but you are looking for a larger unit and though the EBT offers pretty resectable burn times to get a 10 plus hour burn an EBT unit with a large firebox would likely have you sleeping in the yard from the heat output. i would listen to the members who have experience with medium sized soapstone units as with a smaller home you dont need massive heat output and you do want long duration , that says soapstone to me (even though i build steel) hows that for an endorsement, hope this helps ya

 

[wg_bent]

Woodstock doesn't make inserts, but Hearthstone does. Morgan and Clydesdale. The answer is a very small stove, but I get longer burns than that out of my Osburn and it's only slightly bigger. 1.8 cuft. That said I get 8 hour burns only if I'm burning very large chunks of elm, oak or locust.

If you can fit a larger unit, go for it. As for insulation I wouldn't do that. If the unit were intended to be more efficient through insulation blankets, Lopi would supply them. I think you'd be asking for trouble. If you have room, you might be able to attach some micore to the inside surface of the fireplace firebox. and that might help a little, but I think you problem is more related to the stove size. Inserts have air chambers that allow for the blower air to get heated and moved into the room. I'm not sure what percentage of heat goes out into the fireplace, but it's probably not a huge percentage.

 

[PAJerry]

We also have a very small insert - I think the firebox is 1.3 cu. ft. It heats our house just fine, but does not have long burn times. I have put 3" of ceramic fiber on the top of the insert and it helped with the heat output to the room and seemed to keep the bricks around the chimney a bit cooler. I want to do the sides with an equal amount over the summer. I have found that I can get better burn times with slab wood than cord wood, maybe because I can stack more slab wood in the unit. I firmly believe that using a smaller stove, and keeping it burning pretty hot all the time, is a lot more efficient than having a larger stove that spends a lot of time dampered down and smouldering. I checked my chimney last week and it is very clean.
Regarding heat losses to the masonry chimney: our chimney runs up the middle of the house and is exposed on the back side by the upstairs steps. The masonry was very warm when using the stove 24/7 like we did. You are probably losing a considerable amount of heat out the back of the masonry. In our case, the only issue was huge ice dams on our roof from the warm second floor and the problems with insulating a cape-style house. Our new metal shingle roof should eliminate that problem. I would check to see where the intake air enters your insert, then insulate the whole thing, being careful not to block the intake. It certainly won't hurt anything and, although it won't help with the burn times, it should keep more of the warmth in the house.

 

[Gunner]

You said the house is small. How many sqft is it ?

Where is it located?

Insulation?

Layout?

 

[rickw]

Thanks much for all the input.

The house is in eastern Ma (Acton). It's a 1200 sq ft ranch, with the stove on one end. The house is insulated (blown-in fiberglass), but could stand more in the attic (which I'll be adding this summer). I'm going through 2-3 cords a year (well, for two years) - and this reduces my oil usage by 1/3-1/2 (actually the cost savings of $250/cord wood over oil was basically nothing - meaning it was a wash). I've got a nice Exel plot of oil use - but can't seem to attach it here.

As a side note - this year I got a little smarter about it and loaded up on unseasoned oak at $150 a cord. I'm aiming at a two year supply (with annual replenishment), so in 2008 I'll be burning really dry wood.


The little Answer insert works well for daily use, and I understand that reliable overnights aren't going to happen until I get a bigger firebox. I'd love to get a large freestanding cat stove (Woodstock, Blaze King, or Intrepid for example). Longer burns would be good; but more peak heat isn't necessarily good - using the stove steadily with outside temps over 45F is questionable.

Space is an issue, with the small size of the house the insert is favored. Which leads back to the efficiency issue. I wonder how much more wood I am burning by having the insert in the exterior chimney (or how much less heat I am getting for the same amount of wood)? This is a separate issue from burn time, and will remain a concern even with a larger insert (even though I would be enjoying overnight burns). Any thoughts?

Rick

 

[begreen]

A little clarification, the Intrepid is a small stove with a big heart. The cat version can go about 6 hrs on a load so you won't get overnight burns, but better than the Answer.

I think a Woodstock stove could be the ideal stove here. In the shoulder seasons, you can burn smaller fires and/or let them go out.

 

[webbie]

I would not fiddle with vermiculite, etc.

You have two problems - one being the firebox size and the other being a large masonry mass on an outside wall which may be soaking up a lot of the heat and wicking it outside.

A "Hearth Stove" would work better than an insert in such a case - something with no panels around it. This could be an insert that you leave the panels off and seal at the damper area or a stove which sits in front or partway in-out. Stoves which are designed to throw heat forward would be preferable to those which radiate strongly out the rear......because that heat will likely soak outside.

A problem with efficiency numbers on fireplace inserts is that they are usually not tested in a real world (outside fireplace) situation, in fact they are often tested as freestanding stoves! This means that actual efficiency numbers you might get from certain installations are much lower than quoted.

As BG mentions, the Intrepid is quite a small firebox. If you are going to step up from what you have, I'd suggest at least 2.4 cubic feet.

Cats will burn longer with lower output, so that does fit your scenario well.