Fireplace insert: Insulate the exterior, or not?

[pdqdl]

OK! I have just about determined that I need 6" x 17' to 20' of chimney liner. Now for the tough choice. The kits will come with an attachment plate at the top, designed to suspend the liners, so this simplifies that question. So far as I can tell from the descriptions, there isn't much difference in the various attachments, and I won't even need the "T".

Selkirk brand kit from Menards, but 4-6 days later arrival at $356.00. The Selkirk has an extra 5' of liner in the kit, but is made of 304 Stainless steel, as best I can tell.
https://www.menards.com/main/heatin.../1768134/p-1444453715488-c-6895.htm?exp=false

Rockford brand from Home Depot, but it is only 20' long. Made out of 316 Stainless, however. At $538.00, I don't know if the "smooth wall" feature and the better grade of steel is significant enough to spend an additional $182.00.
https://www.homedepot.com/p/Chim-Ca...s-Steel-Chimney-Liner-Kit-SW620SSKF/204673930
(The same exact kit is available at Lowes for $568.00, but it seems to be privately branded)

(or $518.00 at Amazon, with lower tax rate!)​

Worthy of mentioning: the Home Depot, Lowes, Amazon, and Walmart kits all feature the same picture on the product, but Lowes and Walmart refer to their chimney as "Double ply", I suspect this is just a marketing trick, but don't know for sure.

If anyone has a brand preference or other recommendation, please let me know.

 

[gggGary]

On minor changes can make the difference:

This stove replaced a wood burner with a rusted out heat exchanger when I moved here.

It was where the furnace had been, about 3' out from the 6" square tile chimney flue opening, connected with 6" single wall smoke pipe.
Was an SOB to run, hard to light, fire would die, it would smoke up the house.
When I moved it tight to the chimney, using about 2' of double wall connector pipe/elbow. That fixed it, never a problem since.
It was previously in the living room,

and ran like a champ there on about 6' of triple wall from the ceiling straight up to a cap.

One trick I learned; if you can a get a fresh air vent at or near the basement floor then pipe it up to near the ceiling, it won't create cold drafts.

 

[pdqdl]

One trick I learned if you can a get a fresh air vent at or near the basement floor then pipe it up to near the ceiling and it won't create cold drafts.

Sorry, I'm not quite getting the picture on how that would help.

EDIT: It sounds kind of like an outside air connection, but attached high above the stove?

 

[pdqdl]

And... I've thought of another question.

I started this project thinking I would insulate everything as much as possible to improve the draft of the stove, but I am beginning to think that will be unnecessary and prove to be a waste of money. I figure that I haven't had any creosote for the last 22 years, so keeping the flue warm to prevent condensation shouldn't be an issue. To that extent then, all the heat in the flue will be somewhat trapped by a well insulated cap and the barrier I intend to put where the damper should be. That will be a significant savings.

Same story for insulating the outside of the fireplace insert. If I trap any escaping heat at the top of the hearth area with a good seal, the former fireplace will warm up pretty quickly off the exposed flex pipe, and this should make an adequately warm backside to the insert that it too will be more efficient.

@gggGary, you mentioned previously that I shouldn't insulate the flue. Have I seen the light at last, or do you have other comments?

 

[dboyd351]

View attachment 1222026

The doggies sure do love a fire, don't they?

 

[gggGary]

And... I've thought of another question.

I started this project thinking I would insulate everything as much as possible to improve the draft of the stove, but I am beginning to think that will be unnecessary and prove to be a waste of money. I figure that I haven't had any creosote for the last 22 years, so keeping the flue warm to prevent condensation shouldn't be an issue. To that extent then, all the heat in the flue will be somewhat trapped by a well insulated cap and the barrier I intend to put where the damper should be. That will be a significant savings.

Same story for insulating the outside of the fireplace insert. If I trap any escaping heat at the top of the hearth area with a good seal, the former fireplace will warm up pretty quickly off the exposed flex pipe, and this should make an adequately warm backside to the insert that it too will be more efficient.

@gggGary, you mentioned previously that I shouldn't insulate the flue. Have I seen the light at last, or do you have other comments?

To be honest I had to jog my wood heating info /lore brain cells, it's been a while since I had to do much to my systems. Your plan sounds good/great. But I might insulate the back (and side?) walls of the fireplace, no sense trying to heat masonry that's exposed to the outside. You can see I have a piece of fireproof insulation behind my basement stove, for the same reason, heating a concrete wall doesn't add much benefit. I don't run that basement stove all the time just when I'm down in my shop working or when it's super cold, for plumbing protection and to warm the floors a bit.
On the vent pipe; Let's say somewhere in the basement punch a 4" hole in the wall, then on the inside add a 4"elbow and pipe pointed up to 6'. the warm inside air acts like a stopper that keeps cold air from moving up and constantly flowing out at floor level.
I figured this out when a required 12"square boiler room outside air opening would freeze fuel oil at floor level in sub zero temps, I added a 12" elbow with an open pipe that went 6' up the wall. That stopped air flow unless the boiler was running pulling it in past the resistance of buoyant warm air inside the pipe. IE a thermal trap.
On not insulating a flue; chimney fires are always a possibility, insulation can let the pipe overheat and melt or collapse, free air around it will circulate and keep it below red hot much longer than if it's insulated. Free air within the chimney will still allow the pipe to quickly get and stay warm enough to aid draft.
hope that helps.

Just for fun, my current living room stove.

The air channels and vents in the masonry induce enough airflow that I have no need for a circulating fan.
The orange is a steel wood box with an outside loading door and top door.

Heated this house with 100% wood except for long trips away for 20 years now.

 

[pdqdl]

The air pressure balancer pipe makes perfect sense, but cannot work at my house. All my interior walls are below ground, and probably run at about 50°- 60° year round. A bit cool in the summer, and damned cool in the winter. There is only a sheet of paneling covering the 45" tall foundation wall.

You asked for pics:
The fireplace, hearth landing, and mantel




Good thing you suggested the sawzall. I couldn't get to all the parts with either the grinder or the sawzall. I did get it done, though. It took me longer to get that little stub of pipe out of the stove than it took me to cut the whole flue pipe off.

Here are the two pipe sections I couldn't pull out from the top of the chimney. Notice how little creosote was in them. Nothing sticking to the sides of the chimney, either. Not bad for 22 years of burning, eh?
.....

Now it's damned chilly in the basement. I plugged it up with the cover plate until some parts show up.

 

[pdqdl]

...The orange is a steel wood box with an outside loading door and top door.
View attachment 1222107 View attachment 1222108 View attachment 1222109
Heated this house with 100% wood except for long trips away for 20 years now.

I like that idea. Not too practical for my house, however. I've thought about knocking out a section of the basement wall and building an extra room underneath the deck to store stuff in, and maybe give in a back yard exit. The City would never find out, and we could use the space. Unfortunately, I've never gotten that ambitious.

 

[JRM]

To insulate the back of your box why not just tack weld short bolts to the exterior. Wrap in kaewool and fix with fender washers/nuts. You could always cut off excess length once the blankets are installed if clearance is an issue.

 

[pdqdl]

That was exactly what I was thinking, too. I just haven't yet decided to do it.

I've been wondering why none of the insert manufacturers seem to do that. Insulating against the cold behind the stove makes sense to me, and I don't know why it isn't done. They even publish efficiency statistics for these wood burners, so I'd think there would be motivation to insulate the exterior to control the heat delivery better.

There has got to be a reason it isn't done by all of the manufacturers, but I haven't worked it out yet.

 

[JRM]

I've been wondering why none of the insert manufacturers seem to do that.

My guess is bean counter economics. I have an outdoor wood stove that I have had to make several modifications to to improve it's efficiency. Mainly poor insulation in key areas and draft control. My first clue on the insulation was how quickly the snow would melt off of it in certain places.

 

[TNTreeHugger]

I am re-habilitating my fireplace insert, a Quadrafire 4100. It's been a great heat supplement to the house, but has really sucked since the stovepipe up the chimney went bad. Yeah, I know. I should have fixed it a long time ago. Still, apart from the fact that it was hell to get started, it burned clean and added heat to the house. I also need to replace the firebrick and backer board & blanket on the inside.

Rignt now I have it pulled out, with plans to install new, stainless steel double-wall stovepipe to the top of the chimney. Something like Menards' 6" pipe.

I also intend to modify the stove to take the makeup air into the firebox from the holes I intend to punch through the fireplace walls. I really don't like the fact that I am burning wood with warm "inside" air, instead of taking it from the outside.

Now that you got the picture, here's the question: This fireplace insert is basically a steel box inside of a steel box. The heater blower circulates warm air into the house from the space between the two boxes. The outside shell, however, is sitting in a damned cold fireplace with cold air coming in from above, and theoretically, from the holes I intend to make in the rear. This means that a significant amount of heat will be shed to the outside, when I'd rather keep it inside the house.

I wish to insulate the outside of the fireplace insert with some inch thick kaowool ceramic fiber blanket, something like this stuff:
https://brickwoodovens.com/products...ilns-ovens-pizza-ovens-furnaces-forges-stoves. I haven't decided whether or not to attempt attaching it physically with metal screws and galvanized roofing washers, or perhaps some other scheme that hasn't yet occurred to me.

I figure all the heat I can keep in the house will be an improvement, especially since that insert lets tons of cold air into the house when isn't burning. Your comments and advice are welcome!

Have you asked Montana resident?
Just kidding!

 

[Section VIII]

Definitely not as drastic as the 50,000 BTU roofing torch, but this what i use to get a draft going in my woodstove chimney. I build the fire, then stick this up the entrance to the chimney for about 30 seconds, then immediately light the fire. Works for me.
Also, your chimney is tall enough, isn't it?
when I first installed my woodstove, the guy that helped me do it had done many up in New York before moving down here. He told me how high he thought the chimney pipe needed to be, and we initially went with that, even though it was less high than the woodstove manufacturer recommended.
I had major problems with downdraft getting a fire started with that chimney and I ended up adding another 6 feet of pipe, 3 feet at a time and have never had a problem since. My experienced installer buddiy swore that wasn't the issue but firsthand experience and the stove manufacturer's instructions gave a much different answer.
I realize you have likely checked the chimney height, just passing on my experience.

I just use this to start the fire. Ex father-in-law used something similar to start the fires in his free-standing wood stove in the basement...although his didn't have the integrated ignition.

 

[Section VIII]

Nope! The brick chimney is pretty much outside the walls of the house. Obviously from the outside.
View attachment 1221957
I also see that the top of the chimney isn't quite as tall as the roof peak. Is ok, as that fireplace always drafted nicely with a fire going. Like the insert, however, not so good when starting cold!


Hmmm... Hadn't considered it. I have both, will try both.


Not sure what you mean. Please explain.


An excellent suggestion. I wish I had thought of that putting it in the first time. One thing I cannot do is raise the insert any higher than previously. The faceplate is tucked right up against protruding bricks at the top.


6" liner to top is what I had originally, but not recently. I even sealed the top of the chimney so that no air was flowing down the outside of the 6" liner. Originally, it worked fine, but rust had its way with my cheap install.


You guys are more familiar with many different intake systems than I am envisioning. This will only be a few holes poked into the back wall of the fireplace to allow outside air into the open ports on the back side of the insert. I'm currently re-thinking that plan anyway. 25 cfm seems to be the accepted flow rate into this kind of stove. That's about the equivalent of a low speed computer fan; not too much in the big scheme of air flow inside the house. I am beginning to think that sealing up the chimney real tight to cold air flow might be better for the total heat exchange than making the backside of the insert frigidly cold with outside air.


I have no backdraft issues on this contraption, once the fire is well started. Obviously, turning on the attic fan is a smoky disaster, though. Both my house furnace and water heater use outside air and induced flue pipe venting, so that never affects the woodburner.

I love my Ruud on-demand water heater, too. I even have a water circulation pump connected to a flow detection switch, with a fancy timer. It will stay on for any time that I dial in, then remain off until cycled on again. I also have a thermostat on the circulation line, to prevent activation of the circulation system when it isn't needed. This is the problem with these on-demand water heaters! It can seem to take forever for the hot water to arrive. My circulation pump cuts that down to about 5-10 seconds for every faucet in the house except for the downstairs bathroom sink. Additional benefit: the circulation pump is switched on at 1/4 gpm, but the on-demand water heater doesn't come on until 1/2 gallon per minute. The low-flow faucet in the kitchen sink was tricky to get any hot water when initially put in. I fixed that pretty quickly! ​

This is what I was referring to regarding chimney height
As initially installed the chimney only extended about as high as the 2 support poles attached to the chimney pipe. Didn't draw worth a crap and was several feet shorter that the stove manufacturer's recommendation based on top of the roofline and slope of the roof.
My "installer" friend was adamant the chimney height was not the problem and threatened to quit helping if I went to a taller chimney.
I ordered the extra pipe, installed it and my draft problem vanished.

You might want to try extending the height of the chimney/vent like dboyd351 did. Code is primarily to prevent embers from falling back on the roof but it also helps with exhaust flow from the flue as nearby obstructions can deflect/effect flue exhaust.

 

[pdqdl]

"Extending the height of the chimney" is what this thread is all about. I didn't used to have nearly as severe a smoke problem. For the last couple of years, I've been running "header dumps" into the brick chimney, with too large a cold space to overcome with a tiny startup fire.

 

[pdqdl]

Gentlemen, I think I have corrected my stove problems, and made additional improvements. I think the conversations in this thread have been quite helpful, so thanks to all of you.

Here is what I did:

1. I installed a flexible 6" stovepipe up to the top. It made tremendous improvements in how well the stove burned. The improved draft made it easy to start, and it kept the window much cleaner, too.

This was the best price & product I could find.​

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2. I bought a roll of rock wool and made enough 2' wide rolls to stack them one upon the other until I reached the top of the flexible stovepipe. I bought a 2' long section of 7 inch stovepipe, and it made a perfect template for rolling up the rock-fiber insulation.​

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3. Then I capped it with two 12"x12" chimney plates, made to accommodate the 6" hole up the middle. I put a nice fat layer of rock wool between the two stainless plates so as to somewhat insulate the chimney from cold drafts on the outside of the stovepipe.​

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4. Then I capped it with a square chimney cap from Menard's to keep the rain out.​

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Sorry, I didn't take any pictures of the last couple of steps. I was kinda preoccupied with not falling off the roof in the dark.​

Some notes:

• I gave up on insulating the outside of the fireplace insert. It just wasn't practical without making holes in the metal or welding to it. I figured that would cause more problems that it would solve.
• I couldn't figure out any way to insulate or seal the firebox behind the insert. It was all firebrick, and again, it looked like more trouble than it was worth.
• I settled on capping the chimney real well. I figured the space between the stovepipe and the chimney would get warmed up if it was well sealed, then more heat would go out to my living quarters and less would go out the uninsulated backside. So far, that seems to have been a good call.
• My decision to insulate the flexible stovepipe was based mostly on my desire to keep the exhaust gases as hot as possible, in order to reduce future accumulations of creosote. Time will tell, but it cannot hurt that I have even better draft since I insulated the stovepipe and capped the chimney.
• In case you are not familiar with it, the rock wool is pretty much impervious to any temperature that will be found in a fireplace. It is kind of fragile though. I'm concerned how long it will last. The fireplace insert had some 22 years old in it, and it was still intact, so I'm hopeful the chimney outlasts me.

I'll admit I didn't quite understand how profoundly a cold column of air was pushing down on my cold chimney when I tried starting it up. It's fixed now, and starts up better than the day I first installed it.

I started it up this evening, having made all the improvements. Not a single puff of smoke comes inside the house now.

 

[Del_]

Gentlemen, I think I have corrected my stove problems, and made additional improvements. I think the conversations in this thread have been quite helpful, so thanks to all of you.

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I started it up this evening, haveing made all the improvements. Not a single puff of smoke comes inside the house now.

Looks great!

 

[pdqdl]

Side benefit to having a really good draft: When you shovel out the ashes, even the dust goes up the flue.

 

[dboyd351]

Pretty work PDQDL! I especially like the rock wool insulation and template to cut it.

 

[pdqdl]

You should have seen me stitching the insulating rolls together with 3 bands of 16 guage wire around the outside and 20 gauge wire wires tied loosely to the bands to keep them all together. It took me about 75 minutes per roll, although the bulk of the time was cutting and straightening the thin wires. If there is the slightest bend in the tips of my thin wires, it wanders off course when I poke it through the wool, and then ends up where I can't tie it down. I didn't expect that impediment.

I kind of "stitched" the rock wool to the circular bands, as I fear that any vibration or movement will cause it crumble. I gave up on doing that to the last two rolls, as I was running out of time, and I didn't need to worry about the long slide down the stovepipe damaging them.