So I need a blockoff plate, but what to do NOW?

[HalJason]

So, despite what my installer insisted, I now believe I need a blockoff plate. Install of my insert (Jotul Kennebec) was in Oct 2005 with full 25' flex liner, sealed at the top. The installer told me that this was the right way to do it, but after reading here since then, I'm convinced that he was dead wrong (on more than one count, but lets start here).

My hearth is brick, and the surround isn't totally flush to the brick to begin with (1/4" gaps here and there) so between the gaps and the mortar joints, there is a lot of potential for air loss (and based on what I've seen, this potential is being realized).

I fully plan on building a blockoff plate in the spring, with several inches of ceramic fiber on top of it. After chatting with a few people with the same insert as I have, it seems like I'm not seeing the performance they are, and I'm wondering if the lack of a blockoff plate is accelerating the cooling of the insert as well. Could this be the case, or am I hearing "fish that got away" tales from other owners? Loading the stove up (not dead full, but 3-4 decent sized splits) letting everything char at about 80%, then bringing it back to 20% or so, I can see a peak of around 550 (where it'll stay for maybe 45 minutes if I'm lucky) then a gradual drop to 350 or so about 2-3 hours after loading.

The insert runs 24x7 most days (I work at home) so I'm not real keen on pulling it for a day or two while I make a permanent plate. I was wondering if it would make sense for me to get some ceramic fiber now, and shove it around the flex where it passes through the damper, as a temporary fix until the end of the burning season. I know this wouldn't stop air infiltration (which is my real problem) but I thought it may slow it down a bit. If I remove the surround (which I can do in the morning before firing the stove up, while the surface is 150 or so) I can probably pull this off with very little hassle.

On a somewhat related note, this stove allows installation with varying amounts of stove sticking out into the room. It's currently installed as far in the fireplace as possible, but when I built the hearth I allowed quite a bit of extra room so I could eventually pull it out a bit if I wanted to. Would it make more sense from a heating point of view to pull it out a bit? I'm going to have the stove out anyhow to put in the blockoff plate, so I could kill two birds with one stone if this makes sense.

Thanks for a terrific forum, I've learned a lot in the past 1.5 years.

-Hal

 

[Hogwildz]

I believe you could seal around the surround edges and that would also act as block off. At the very least cut down the draft if not eliminate it.
I know my Summit manual gives 2 options, seal around the surround, or install damper block off plate. If your just looking to temp until you can get the damper block off plate in. You can put some proper insulation (kawool, rock wool) arounf the surround edges.

 

[jjbaer]

So, despite what my installer insisted, I now believe I need a blockoff plate. Install of my insert (Jotul Kennebec) was in Oct 2005 with full 25' flex liner, sealed at the top. The installer told me that this was the right way to do it, but after reading here since then, I'm convinced that he was dead wrong (on more than one count, but lets start here).

My hearth is brick, and the surround isn't totally flush to the brick to begin with (1/4" gaps here and there) so between the gaps and the mortar joints, there is a lot of potential for air loss (and based on what I've seen, this potential is being realized).

I fully plan on building a blockoff plate in the spring, with several inches of ceramic fiber on top of it. After chatting with a few people with the same insert as I have, it seems like I'm not seeing the performance they are, and I'm wondering if the lack of a blockoff plate is accelerating the cooling of the insert as well. Could this be the case, or am I hearing "fish that got away" tales from other owners? Loading the stove up (not dead full, but 3-4 decent sized splits) letting everything char at about 80%, then bringing it back to 20% or so, I can see a peak of around 550 (where it'll stay for maybe 45 minutes if I'm lucky) then a gradual drop to 350 or so about 2-3 hours after loading.

The insert runs 24x7 most days (I work at home) so I'm not real keen on pulling it for a day or two while I make a permanent plate. I was wondering if it would make sense for me to get some ceramic fiber now, and shove it around the flex where it passes through the damper, as a temporary fix until the end of the burning season. I know this wouldn't stop air infiltration (which is my real problem) but I thought it may slow it down a bit. If I remove the surround (which I can do in the morning before firing the stove up, while the surface is 150 or so) I can probably pull this off with very little hassle.

On a somewhat related note, this stove allows installation with varying amounts of stove sticking out into the room. It's currently installed as far in the fireplace as possible, but when I built the hearth I allowed quite a bit of extra room so I could eventually pull it out a bit if I wanted to. Would it make more sense from a heating point of view to pull it out a bit? I'm going to have the stove out anyhow to put in the blockoff plate, so I could kill two birds with one stone if this makes sense.

Thanks for a terrific forum, I've learned a lot in the past 1.5 years.

-Hal

I'm looking at purchasing the Jotul 450 also and when I install mine I'll put a lower block-off plate in it and I'll insulate the liner. Also, since you have 25 feet of chimney, there's plenty of length for cooling to occur (and therefore you'll get poor draft) if you have NOT insulated the pipe and especially so if it's an outside chimney (3 sides of the chimney exposed to the outside as opposed to a chimney that is entirely surrounded by the house except where it pierces the roof).

So...after you've exhausted all other possibilities for diminished performance, check to see if your liner is insulated. I found a couple of sites where 25 ft of insulation for a 6" in pipe can be had for $250.


BTW...how do you like your Jotul 450 and what are the pros/con's of owing it? I saw your comments above but if you have any more comments from your friends who also own it, I'd like to hear all of these. What length burns are they getting out of it???.

 

[Gooserider]

To answer your question about pulling the insert out of the fireplace more or not... From all I've seen it probably depends on where your fireplace is in the house.

If the fireplace is in the middle of the house, not on an exterior wall, then it shouldn't make a big difference, but it will change the nature of the heat you get. With the insert pulled out, most of the heat goes directly into the air, which will warm things up faster, but not be as "lasting" a heat. With the insert pushed in, you won't get as much direct air heating, but will get more radiant heating as the insert's heat gets absorbed by the mass of the fireplace and re-radiated. This will give you a more stable temperature, sort of like a soapstone stove or a masonry heater.

If you have a fireplace on an exterior wall, especially if it sticks out from the wall to the outside, you will be best off to pull the insert out as far as you can. Any heat that is dumped into the fireplace mass is mostly going to be heating the outdoors, so you want to get as much heat out into the inside air as you can.

As a temporary measure, until you get the blockoff plate installed, I'd recomend trying to seal the gap between the surround and the fireplace wall as much as you can.

Gooserider

 

[HalJason]

I get plenty of draft, that's truly not an issue. In fact, the burn times are right in line with what I'd expect with a firebox this size. I can keep flames for 2-2.5 hours, and very bright coals for another 2. With a last load at about 9pm, there's no problem with having enough coals around at 7am to rake forward and get it roaring again in no time.

What concerns me performance wise is the speed that the insert cools. I keep reading about people (not just with the Kennebec, but all stoves) with hours of 600 degree temps. I'm lucky if I can get 600 for 30 minutes before it cools. My thought was that if cool (relatively) air was exiting around the surround, it'd cool off the outside of the sleeve which would just help suck heat from the stove as well. This may just be how the stove behaves, but I'll know once I have it installed properly. On the same token, if I'm losing a lot of room air up the chimney, it means I'm also pulling in a lot of cold air from elsewhere.

The stove IS on the wall between the house and an attached garage. Technically it's an outside wall (garage is unheated, but _is_ insulated) but the chimney isn't subject to outside temps, at least for the first half of its height (the garage rarely goes below freezing unless outside temps are in the single digits.. even before we got the stove).

I'll try to find a way to seal around the surround, but since it's not a flat wall (bricks, so there are horizontal mortar joints) it may be a bit tricky to not only do, but do in a way that doesn't look like heck, that's why I was considering shoving something up the chimney instead.

To answer the question of what I think of the stove, it's a wonderful stove and really kicks out heat when it's going. I'm pretty sure that any performance issues I have are related to the install, not the stove. The firebox is on the small side, so don't expect to heat a 3200 ft^2 house with it, but it does an OK job of heating my 2200 ft^2 almost on it's own (we bought it for supplemental heat, and it's done wonderfully). Definitely double-check the install though. It's door gasketing is a bit tricky (2 doors, one closes on top of the other) and mine was installed with a poorly adjusted door latch. The manual talks about adjusting the latch if the dollar bill test fails, but doesn't explain how (took me a while, but I finally dug in and figured it out). It wasn't until recently that I realized the gaskets were leaking, runs much better now, but still cools faster than I'd expect.

-Hal

 

[jjbaer]

To answer the question of what I think of the stove, it's a wonderful stove and really kicks out heat when it's going. I'm pretty sure that any performance issues I have are related to the install, not the stove. The firebox is on the small side, so don't expect to heat a 3200 ft^2 house with it, but it does an OK job of heating my 2200 ft^2 almost on it's own (we bought it for supplemental heat, and it's done wonderfully). Definitely double-check the install though. It's door gasketing is a bit tricky (2 doors, one closes on top of the other) and mine was installed with a poorly adjusted door latch. The manual talks about adjusting the latch if the dollar bill test fails, but doesn't explain how (took me a while, but I finally dug in and figured it out). It wasn't until recently that I realized the gaskets were leaking, runs much better now, but still cools faster than I'd expect.

-Hal

Thanks. My house is much smaller (1650 sq ft) so I should have no problem heat wise but with my set-up (smaller rooms and not as open) it will be more of a heat distribution issue. I partially address that now by using my furnace fan to help distribute heat. As to why your unit cools down so fast, I'm not sure. Although it has a cast iron surround and cast iron doors, I believe the firebox itself is steel but it would also seem that the firebricks would help stabilize the temperature. let us know what you find out.

 

[jjbaer]

I get plenty of draft, that's truly not an issue. In fact, the burn times are right in line with what I'd expect with a firebox this size. I can keep flames for 2-2.5 hours, and very bright coals for another 2. With a last load at about 9pm, there's no problem with having enough coals around at 7am to rake forward and get it roaring again in no time. -Hal

I know you said it was cooling too fast and this might cause it to cool even faster however, as far as heat is concerned, do you have a fan on this unit? Reason I ask is because the fan is optional on this unit.....

 

[HalJason]

Thanks. My house is much smaller (1650 sq ft) so I should have no problem heat wise but with my set-up (smaller rooms and not as open) it will be more of a heat distribution issue. I partially address that now by using my furnace fan to help distribute heat. As to why your unit cools down so fast, I'm not sure. Although it has a cast iron surround and cast iron doors, I believe the firebox itself is steel but it would also seem that the firebricks would help stabilize the temperature. let us know what you find out.

Unfortunately my floorplan isn't as open as I'd like either. There are 2 rooms (furthest from the stove on the same floor) that stay colder. Fans help quite a bit, but since the entry to one of the rooms has a gaping hole in the ceiling (stairs to next floor, which stays nice and warm) a fan can only do so much.

I do have the fan, which I generally keep on low, but I have run without it. Temps stay high a bit longer, but still drop off fast.

-Hal

 

[My_3_Girls]

Hal and Cast,
Here's my deal:

- installed a new kennebec 9/06 in living room of a 1600 sf colonial, two story. It was built in 1996
- at 20 degrees f and up, it heats the whole house.
- sealed only at the chimney cap, chimney is in the unheated garage - I call it exterior
- this stove/insert is perfect for this house - anything over 40 degrees, it coasts on about 8 splits a day
- I do not have the cold air intake, I depend on the "leaks" around the surround for my combustion air. The air intake (from memory) is in the center of the back of the stove. If you block off the chimney, and you also block off the suround, you will likely not have enough combustion air to feed this heat beast.
- after this season, I will be pulling the unit out and installing a block off plate. I had the same experience with the installers saying I didn't need two block offs. It works fine now, but I work pretty hard for my wood, and would like to get the optimum performance out of the stove.

Cast, buy this stove and don't look back. I looked at a bunch of them and narrowed it down to the kennebec due to size, quality and looks, in that order. The fan is a must on an flush insert. The cool thing about this fan is that it has a "snap-stat" - you leave the switch on. When the stove heats up enough, it turns the fan on. I load it at 10pm, rake the coals at 7am, throw two full size splits in, wait about 3 minutes and I have flames. Most of the time, the fan is still blowing thru the night.

 

[jjbaer]

Hal and Cast,
Here's my deal:

- installed a new kennebec 9/06 in living room of a 1600 sf colonial, two story. It was built in 1996
- at 20 degrees f and up, it heats the whole house.
- sealed only at the chimney cap, chimney is in the unheated garage - I call it exterior
- this stove/insert is perfect for this house - anything over 40 degrees, it coasts on about 8 splits a day
- I do not have the cold air intake, I depend on the "leaks" around the surround for my combustion air. The air intake (from memory) is in the center of the back of the stove. If you block off the chimney, and you also block off the suround, you will likely not have enough combustion air to feed this heat beast.
- after this season, I will be pulling the unit out and installing a block off plate. I had the same experience with the installers saying I didn't need two block offs. It works fine now, but I work pretty hard for my wood, and would like to get the optimum performance out of the stove.

Cast, buy this stove and don't look back. I looked at a bunch of them and narrowed it down to the kennebec due to size, quality and looks, in that order. The fan is a must on an flush insert. The cool thing about this fan is that it has a "snap-stat" - you leave the switch on. When the stove heats up enough, it turns the fan on. I load it at 10pm, rake the coals at 7am, throw two full size splits in, wait about 3 minutes and I have flames. Most of the time, the fan is still blowing thru the night.

Thanks. We narrowed it down to only two units...the VC WWL and the 450 and my wife likes the 450 so that's what we'll probably get. Right now the fan on the 450 has three settings: 1) off, 2) lo and 3) high but both "lo" and "high" only activate when the box is hot enough. I wish they'd add a fourth setting: a "manual" setting whereby the user can turn the fan to the "on" position (not controlled by temperature but always "on") and have infinite control over the speed.........other than that, it appears to be a well built unit and looks great. From the reviews I hear here, it also appears to be a great performer. Any more pros/cons you could tell me about this unit, feel free to do so.

As to why HalJason is having the problem, I have a thought: without a block-off plate installed, the back of the insert heats the air in the rear insert area, the heated air rises up past the damper and into the colder chimney, this air in-turn is cooled by the cold chimney surface and then sinks as new hot air is rising from the back of the insert. This process taps heat from the rear of the insert which in-turn causes the insert to cool slightly faster. Installing a block-off plate lets this hot air only rise a foot or so before it is forced back down. In this limited distance it can rise, the air can't cool as much and won't suck as much heat from the insert.

 

[HalJason]

Thanks. We narrowed it down to only two units...the VC WWL and the 450 and my wife likes the 450 so that's what we'll probably get. Right now the fan on the 450 has three settings: 1) off, 2) lo and 3) high but both "lo" and "high" only activate when the box is hot enough. I wish they'd add a fourth setting: a "manual" setting whereby the user can turn the fan to the "on" position (not controlled by temperature but always "on") and have infinite control over the speed.........other than that, it appears to be a well built unit and looks great. From the reviews I hear here, it also appears to be a great performer. Any more pros/cons you could tell me about this unit, feel free to do so.

As to why HalJason is having the problem, I have a thought: without a block-off plate installed, the back of the insert heats the air in the rear insert area, the heated air rises up past the damper and into the colder chimney, this air in-turn is cooled by the cold chimney surface and then sinks as new hot air is rising from the back of the insert. This process taps heat from the rear of the insert which in-turn causes the insert to cool slightly faster. Installing a block-off plate lets this hot air only rise a foot or so before it is forced back down. In this limited distance it can rise, the air can't cool as much and won't suck as much heat from the insert.

I think the fan works the way it does, to minimize the amount of time a fire is burning in a cool stove (and therefor without the advantage of a secondary burn). I'd bet the end result would be a lot smokier, and a lot less heat inside the house, if the fan was running before the stove got up to temp.

Truth be told, the snapstat is easy to get to though (I've replaced mine once already), so if you wanted to bypass it with a toggle switch, it'd be a 10 minute job. Assuming you don't have the parts onhand, you'll spend more time in radio shack explaining what parts you need to the "help", than you'll spend doing the work.

When I do install the blockoff plate, I will _NOT_ be sealing the surround to the wall (as was mentioned, combustion air needs to come from somewhere). What I will be doing though, is converting the fireplace's firebox to "part of the room", by putting quite a bit of ceramic fiber insulation on top of the blockoff plate (the blockoff plate stops air infiltration from the fireplace to the chimney, but does nothing for heat transfer, that's where the insulation comes in).

We looked at the VCWWL too, but steered away from it due to reviews, and between the fiddling required + the fact it has a cat, we figured it would be like tending to a third kid, and 2 was enough We both liked the Kennebec's styling, and once we saw one in person the decision was easy. Getting used to running a new EPA stove was a bit like learning to ride a bike all over again, but this time peddling with your hands and steering with your feet though. I grew up with an old 70's stove (also an insert) and I'm not sure much of what I knew applied, short of "you light it with a match" and "you put wood in it".


-Hal

 

[jjbaer]

Thanks. We narrowed it down to only two units...the VC WWL and the 450 and my wife likes the 450 so that's what we'll probably get. Right now the fan on the 450 has three settings: 1) off, 2) lo and 3) high but both "lo" and "high" only activate when the box is hot enough. I wish they'd add a fourth setting: a "manual" setting whereby the user can turn the fan to the "on" position (not controlled by temperature but always "on") and have infinite control over the speed.........other than that, it appears to be a well built unit and looks great. From the reviews I hear here, it also appears to be a great performer. Any more pros/cons you could tell me about this unit, feel free to do so.

As to why HalJason is having the problem, I have a thought: without a block-off plate installed, the back of the insert heats the air in the rear insert area, the heated air rises up past the damper and into the colder chimney, this air in-turn is cooled by the cold chimney surface and then sinks as new hot air is rising from the back of the insert. This process taps heat from the rear of the insert which in-turn causes the insert to cool slightly faster. Installing a block-off plate lets this hot air only rise a foot or so before it is forced back down. In this limited distance it can rise, the air can't cool as much and won't suck as much heat from the insert.

I think the fan works the way it does, to minimize the amount of time a fire is burning in a cool stove (and therefor without the advantage of a secondary burn). I'd bet the end result would be a lot smokier, and a lot less heat inside the house, if the fan was running before the stove got up to temp.

Truth be told, the snapstat is easy to get to though (I've replaced mine once already), so if you wanted to bypass it with a toggle switch, it'd be a 10 minute job. Assuming you don't have the parts onhand, you'll spend more time in radio shack explaining what parts you need to the "help", than you'll spend doing the work.

When I do install the blockoff plate, I will _NOT_ be sealing the surround to the wall (as was mentioned, combustion air needs to come from somewhere). What I will be doing though, is converting the fireplace's firebox to "part of the room", by putting quite a bit of ceramic fiber insulation on top of the blockoff plate (the blockoff plate stops air infiltration from the fireplace to the chimney, but does nothing for heat transfer, that's where the insulation comes in).

We looked at the VCWWL too, but steered away from it due to reviews, and between the fiddling required + the fact it has a cat, we figured it would be like tending to a third kid, and 2 was enough We both liked the Kennebec's styling, and once we saw one in person the decision was easy. Getting used to running a new EPA stove was a bit like learning to ride a bike all over again, but this time peddling with your hands and steering with your feet though. I grew up with an old 70's stove (also an insert) and I'm not sure much of what I knew applied, short of "you light it with a match" and "you put wood in it".


-Hal

Update.....Just bought a C450 and it arrived two days ago. Am looking forward to installing it in about two weeks.....

 

[Hogwildz]

Congrats, don't forget photos of it & FIRE!

 

[jjbaer]

Congrats, don't forget photos of it & FIRE!

Hog...will do...now I need mother natures help to get the snow off the roof to make it easier.....LOL