I believe the manual states static pressure in duct work should be at least .2 IWC. To measure accurately you put one line in the blower housing box (to account for air filter restrictions) and one line in your plenum or in the ductwork close to the plenum. I doubt that is your problem though. I've tempararily run my system at .1 IWC before without an issue.
My Heat Commander blower turns on about 10 minutes after starting a fire with a cold start. If I do a terrible job building a fire it might take a half hour for the blower to kick on. No idea where they pulled the 1-4hr warm up time from, unless they are accounting for a poorly built fire that just smolders for 4 hours.
I have the most heat available while the fire is actively burning and there are visible flames. As long as there are active flames I always have heat available. There is less heat available once it gets to coaling stages. Assuming the thermostat is calling for heat, the blower will remain on until probably the last hour or so of the burn. During the last hour the blower will have to cycle on/off due to lack of available heat. If my thermostat was calling for heat the entire duration of the burn, from a cold start, 20lbs of oak would probably last 3 hours.
Something isn't adding up if you have a hot fire and your plenum is not getting up to temp. Either something is blocking the heat from reaching the plenum, or the hot air in the plenum is being moved elsewhere before it has time to reach the desired temp. Does your ductwork have a natural draft to it? Does air come out the registers when the blower is off but the furnace is hot?
Also, make sure your baffle plates above the secondary air injection tubes are in the right spot and seated properly. I seemed to lose a lot of heat when mine were pushed all the way forward by accident.
I have not yet measured my static pressure in the plenum, but the subject did come up while on the phone with the SBI techs. They mentioned it in passing, but said that the 0.2" WC is for when the blower is running on low speed. Since I'm having issues getting it to come on at all, the static pressure wouldn't be causing my current issue.
I did notice something important over the weekend. When the unit is relatively cool, the servo for the grate draft is on continuously as I've already described. When it does get up to temp and the blower does kick on, that servo shuts off. From that point on, so long as the RTD probe was seeing enough heat, it was the P servo that was running continuously. I was hearing the same sound, but didn't realize it was coming from the other servo. I adjusted the tab on that draft so that it made its limit switch correctly, and that problem stopped. Now the unit works as expected so long as the RTD says that the plenum is up to temp. When the RTD temp drops below 105, the G servo turns back on and runs non-stop again (still a problem). Overall, this has drastically improved how the HC is working for me.
My plenum feeds into the trunk line for my central air system. I run the blower on the central air system constantly pretty much year round. The main outlet on my HC plenum has a backdraft damper installed to keep the central air system from blowing air backwards through my plenum. That means if the HC blower isn't on, there's practically no air flow in the plenum, and I think this is a problem. On Saturday I installed an additional 6" outlet (with a manual damper) that feeds into the cold air return for the central air system. My goal here was 2 fold. First, it allows, and even creates some air flow in the plenum when the HC blower isn't running. Second, on warmer days and with smaller fires, it allows me to pull some heat off the fire box and circulate it through the house. This seems to work well when there's only a bed of coals, and its enough to maintain the heat in the house when the outside temps are in the mid 20s if the damper is completely open. I can close the damper down noticeably and still get enough heat for the house when the temps are up in the 30s. This requires more effort on my part because I'm only adding a couple of splits ever 3-4 hours (just enough to ensure there's a good bed of nice hot coals). Doing this with a hot bed of coals doesn't seem to put enough heat into the cold air return to prevent my gas furnace from kicking on as needed. If I have the HC up to full temp, I think this would no longer be true, so when the temps drop down lower I will need to close that manual draft down quite a bit. Even if its only open a little though, it should still create the airflow needed for plenum to heat up better.
Currently, my coals are lasting a LONG time unless I go down and pile them all up on top of the grate. I'm not sure if that will change once the G servo is fixed or not. I'm hoping it will stay the same because I don't get any smoke off of a bed of coals, and that low, slow heat is very useful to me on most days through out the winter. While it does get cold in this part of Indiana, most of the time the high temps during the winter are in the mid 30s. Later this week the over night lows will be down in the single digits, so I'll see now this setup runs with a nice hot fire at that point.
From a cold start, I'm not getting up to temp in anywhere near 10 min. More like 30 min to 45. With that said, I haven't tried to build a big hot fire fore the past few days because the over night lows are only down to about 20 deg, and the highs are getting up near 40. At 45 and sunny, the sun heats my house enough to keep it up near 70 degrees without any kind of furnace running.
A full load of oak only running 3 hours might be problematic for me. My old wood furnace would run well with up to a 24" log, and a full load would provide good heat for at least 6 hours when the temps were below zero. On an average day, it would provide good heat for 10-12 hrs. The fire box on this system is noticeably smaller, but I was really expecting the "higher efficiency" to help offset that difference. If I can only get good heat for 3 hours when the temps are down around zero, that could become a problem for me since I'm usually gone (at work) for 10-12 hrs during the week. Then again, since we normally only have 5 to 10 of those days a year, this may work out better overall. My wife does not like messing with the wood burner, but the HC IS easy to deal with so having her add 4 or 5 pieces in the early afternoon wouldn't be a big deal. Since the HC blower is driven by the thermostat, and my gas furnace can jump in and supply heat if the HC isn't hot enough, I think it will all work out for the best.
