So, I don't really have a major complaint with the furnace....in fact, my wife and I are loving it! However, there are a couple little things that bug me about it, and a couple other things that I wish were improved:
1. The first time the blower kicked on, I was shocked to feel a bunch of air escaping from the seams between the sheet metal that makes up the air jacket. I should have expected it, I guess, but I had assumed that it would be a bit more airtight. It's not a big deal, except if I'm refilling while the furnace is still hot and the temp is keeping the blower running, as one seam directs air across the door opening. The turbulence (or the Venturi effect or Bernoulli principle of the air blowing across the opening, can't remember which its called), causes some smoke to escape. I can work around it by unplugging the blower motor, but that get's old. I may have to wire in a switchable outlet so I can just flip a switch rather than unplugging it every time (aren't outlets designed for a 1,000 insertion/removal cycle lifespan?). My second option is to remove the sheet metal (held with sheet metal screws), and use furnace cement to caulk the seams. I imagine this would also get more air out of the registers, not that I need it...
2. My biggest complaint is that the openings in the grate that allow the ash to fall through are wider than the ash pan! Seriously, what's with the design?! I like to stay on top of the ash buildup, but this design means I have to reach way into the bottom of the furnace to clean out the ash that misses the pan each time I want to dump ashes. It defeats the purpose of the pan. If I don't clean it out each time, when I push the pan back in it pushes the spilled ash to the back, which prevents the pan from going in all the way, which prevents me from fully closing the ash door!
3. A suggestion for improvement. The fire box is so massive, it seems like there is enough space below the baffle that I could add a second row of firebrick laid end-to-end on edge above the existing row. This would require a adding slight lip to to the existing clip (easy enough by just making it a "T" instead of right-angle stock), and adding another right-angle clip to hold the top of the bricks. I assume this would help keep the firebox temp up. Also, since the Add-on can simulate secondary burn at good temps because the air supply is above the door (e.g. it mixes the incoming combustion air with the combustible gasses off-gassing from the wood below the baffle and gets a good sheet of "secondary burn" sometimes) this firebrick would probably help get and keep those temps, right?
4. As others have mentioned, adding secondary burn tubes would be nice.
5. I can't believe how hard it is to keep even a trace of humidity in the air now that we've added the Add-on on top of our 30-NCP. I think I'm going to install an outside air kit (OAK) to the 30 NCP to try to reduce the amount of air-turnover that's going on in our drafty house. It probably won't make a huge difference, but even a tiny bit will help. Right now we have one big humidifier going downstairs, and 3 in the bedrooms upstairs, and it's still really hard to get the humidity to 30% on days when it's below 20 degrees outside. We've probably gone through well over 200 gallons of water this season so far (daily refills of all humidifiers). An option for an OAK for the Add-on furnace would be nice, but that would be an even bigger re-design than secondary-air tubes.
Having said all that, we still really love the furnace! We can now keep the whole house well over 70 degrees even when it's below zero, when the last couple of winters we were lucky to stay above 60 (at the same outdoor temps) in the rooms near the 30-NCP, and had to run a propane wall furnace to keep the bathroom and utility room above freezing (no fun taking a shower in a room that's between 50 and 60, but we didn't want to spend any more on propane than absolutely necessary). I ran a register into the bathroom, and it now stays above 80 when the Add-on is running.
P.S. I'm running the add-on as a stand alone unit.
1. The first time the blower kicked on, I was shocked to feel a bunch of air escaping from the seams between the sheet metal that makes up the air jacket. I should have expected it, I guess, but I had assumed that it would be a bit more airtight. It's not a big deal, except if I'm refilling while the furnace is still hot and the temp is keeping the blower running, as one seam directs air across the door opening. The turbulence (or the Venturi effect or Bernoulli principle of the air blowing across the opening, can't remember which its called), causes some smoke to escape. I can work around it by unplugging the blower motor, but that get's old. I may have to wire in a switchable outlet so I can just flip a switch rather than unplugging it every time (aren't outlets designed for a 1,000 insertion/removal cycle lifespan?). My second option is to remove the sheet metal (held with sheet metal screws), and use furnace cement to caulk the seams. I imagine this would also get more air out of the registers, not that I need it...
2. My biggest complaint is that the openings in the grate that allow the ash to fall through are wider than the ash pan! Seriously, what's with the design?! I like to stay on top of the ash buildup, but this design means I have to reach way into the bottom of the furnace to clean out the ash that misses the pan each time I want to dump ashes. It defeats the purpose of the pan. If I don't clean it out each time, when I push the pan back in it pushes the spilled ash to the back, which prevents the pan from going in all the way, which prevents me from fully closing the ash door!
3. A suggestion for improvement. The fire box is so massive, it seems like there is enough space below the baffle that I could add a second row of firebrick laid end-to-end on edge above the existing row. This would require a adding slight lip to to the existing clip (easy enough by just making it a "T" instead of right-angle stock), and adding another right-angle clip to hold the top of the bricks. I assume this would help keep the firebox temp up. Also, since the Add-on can simulate secondary burn at good temps because the air supply is above the door (e.g. it mixes the incoming combustion air with the combustible gasses off-gassing from the wood below the baffle and gets a good sheet of "secondary burn" sometimes) this firebrick would probably help get and keep those temps, right?
4. As others have mentioned, adding secondary burn tubes would be nice.
5. I can't believe how hard it is to keep even a trace of humidity in the air now that we've added the Add-on on top of our 30-NCP. I think I'm going to install an outside air kit (OAK) to the 30 NCP to try to reduce the amount of air-turnover that's going on in our drafty house. It probably won't make a huge difference, but even a tiny bit will help. Right now we have one big humidifier going downstairs, and 3 in the bedrooms upstairs, and it's still really hard to get the humidity to 30% on days when it's below 20 degrees outside. We've probably gone through well over 200 gallons of water this season so far (daily refills of all humidifiers). An option for an OAK for the Add-on furnace would be nice, but that would be an even bigger re-design than secondary-air tubes.
Having said all that, we still really love the furnace! We can now keep the whole house well over 70 degrees even when it's below zero, when the last couple of winters we were lucky to stay above 60 (at the same outdoor temps) in the rooms near the 30-NCP, and had to run a propane wall furnace to keep the bathroom and utility room above freezing (no fun taking a shower in a room that's between 50 and 60, but we didn't want to spend any more on propane than absolutely necessary). I ran a register into the bathroom, and it now stays above 80 when the Add-on is running.
P.S. I'm running the add-on as a stand alone unit.
