I have a Hampton HI300 insert installed in a tall exterior chimney. The unit's performance is very good, but I always felt like it could be better. I get 8 hr burn times on a good day, and the unit produces a lot of heat. One problem I have struggled with is difficulty controlling the fire. It had a tendency to run hot, and occasionally would run up to 800F or more if I reloaded too soon (like above 400F). This didn't seem right to me. My expectation was that I should be able to control the fire pretty well and prevent the temperature from getting out of control by limiting the air supply. Also, the stove seemed to have only one mode of operation - rapidly shoot up to 650 - 750F and then slowly drift back down. If I attempted to get a longer, slower burn, say keeping the temperature in the 500-600F range, the results were poor.
The installer said a block-off plate wasn't necessary as long as the chimney was sealed at the top. I was ignorant at the time so I didn't insist on it. But after using the stove for a couple of years, I became convinced I must be losing a fair amount of heat up into the dead air space in the chimney surrounding the liner. From there it just conducts away through the cold masonry. Finally after reading enough stories on Hearth.com about people putting in block off plates, or stuffing Roxul, I decided to give it a try.
I pulled the insert out this fall and stuffed a bunch of Roxul up the chimney to block off the space where the installers cut through the damper to get the liner in. I plugged it up pretty good. . .satisfied that there would be minimal escape of hot air up into the chimney. I also took this opportunity to block the auxiliary air port too because I have a strong draft and I would prefer to have a little more "dynamic range" with the air control, rather than always fiddling with the push rod between 90% and 100% closed.
I have only anecdotal evidence to offer, but I am convinced that the stove is producing more heat for the house, and burning better in several regards.
1. Fire is definitely more controllable. I can get very nice clean burns at much lower temperatures (500F) than I could before. I think this is because the Roxul block off helps keep the heat in and around the stove, meaning the firebox can sustain secondaries with less heat input needed from a high burn rate. Less heat input needed due to less loss of heat. Now I cruise with the air supply 75-95% closed, as opposed to 90-100% closed since I don't have the constant additional secondary air supply to contend with. I can also stop the fire quickly by shutting the air off completely if I need to (thanks to plugging up that auxiliary air supply hole). I like having that kind of control.
2. Significantly less ash production. Before I was accustomed to shoveling out the ash every 5 or 6 fires. So far this year I have only taken out a few shovelfulls after ~20 fires. I think my wood is pretty much the same as previous years, so I can only attribute this to the stove modifications. I think I am getting a longer, slower temperature drop off, allowing a more complete burn at the end of the cycle. It's been a big difference, and one that I didn't anticipate.
3. Somewhat improved burn times. I used to get 8 hours on a good night. Now I would say I am getting 8 hours without having to work very hard. The improvement in burn times hasn't been as significant as I had hoped, but I think it's still there.
Overall, I am quite pleased with the changes. If you are installing an insert in an exterior chimney, I would definitely insist on a block off plate of some sort.
-Jim
Pre-emptive disclaimers
1. Yes, I am burning dry wood. Doug Fir CSS for over a year.
2. Yes, I did the dollar bill test on my door and it passed.
3. All the temperatures I am quoting are measured with an IR thermometer in the center of the glass door. . . and yes, I know that the door temp. is not the same as the firebox temp., but I have calibrated all my burning habits based on the glass temp. as it is easy to measure (accessible), repeatable, highly correlated to the firebox temperature, and generally works great as a proxy.
4. My definition of burn time is the time from getting the stove up and burning clean to the time that I can come back and toss on a few splits and have it start right up again. Usually that means the temp. is around 250-300. It also means that my furnace hasn't needed to run at all.
The installer said a block-off plate wasn't necessary as long as the chimney was sealed at the top. I was ignorant at the time so I didn't insist on it. But after using the stove for a couple of years, I became convinced I must be losing a fair amount of heat up into the dead air space in the chimney surrounding the liner. From there it just conducts away through the cold masonry. Finally after reading enough stories on Hearth.com about people putting in block off plates, or stuffing Roxul, I decided to give it a try.
I pulled the insert out this fall and stuffed a bunch of Roxul up the chimney to block off the space where the installers cut through the damper to get the liner in. I plugged it up pretty good. . .satisfied that there would be minimal escape of hot air up into the chimney. I also took this opportunity to block the auxiliary air port too because I have a strong draft and I would prefer to have a little more "dynamic range" with the air control, rather than always fiddling with the push rod between 90% and 100% closed.
I have only anecdotal evidence to offer, but I am convinced that the stove is producing more heat for the house, and burning better in several regards.
1. Fire is definitely more controllable. I can get very nice clean burns at much lower temperatures (500F) than I could before. I think this is because the Roxul block off helps keep the heat in and around the stove, meaning the firebox can sustain secondaries with less heat input needed from a high burn rate. Less heat input needed due to less loss of heat. Now I cruise with the air supply 75-95% closed, as opposed to 90-100% closed since I don't have the constant additional secondary air supply to contend with. I can also stop the fire quickly by shutting the air off completely if I need to (thanks to plugging up that auxiliary air supply hole). I like having that kind of control.
2. Significantly less ash production. Before I was accustomed to shoveling out the ash every 5 or 6 fires. So far this year I have only taken out a few shovelfulls after ~20 fires. I think my wood is pretty much the same as previous years, so I can only attribute this to the stove modifications. I think I am getting a longer, slower temperature drop off, allowing a more complete burn at the end of the cycle. It's been a big difference, and one that I didn't anticipate.
3. Somewhat improved burn times. I used to get 8 hours on a good night. Now I would say I am getting 8 hours without having to work very hard. The improvement in burn times hasn't been as significant as I had hoped, but I think it's still there.
Overall, I am quite pleased with the changes. If you are installing an insert in an exterior chimney, I would definitely insist on a block off plate of some sort.
-Jim
Pre-emptive disclaimers
1. Yes, I am burning dry wood. Doug Fir CSS for over a year.
2. Yes, I did the dollar bill test on my door and it passed.
3. All the temperatures I am quoting are measured with an IR thermometer in the center of the glass door. . . and yes, I know that the door temp. is not the same as the firebox temp., but I have calibrated all my burning habits based on the glass temp. as it is easy to measure (accessible), repeatable, highly correlated to the firebox temperature, and generally works great as a proxy.
4. My definition of burn time is the time from getting the stove up and burning clean to the time that I can come back and toss on a few splits and have it start right up again. Usually that means the temp. is around 250-300. It also means that my furnace hasn't needed to run at all.
