It's my understanding that the Harman recommended units are not sine wave and only provide backup power to allow an emergency shutdown ( thus preventing smoke escaping into a house). Otherwise, the source of power - wall outlet or generator - is passed through to the stove. Wall outlet (from power company) - no problem, but generator, if it's not an inverter, is not "clean" power to the stove. There are Ups units that convert "dirty" to "clean" , but they're much more expensive ($600 +). So, short answer, your Champion will pass its "dirty" power through to your stove. Anyone out there - correct me if I'm wrong.
I've often wondered if the Ups will "clean up" the generator power. I have one of the harman recommended ups units and would love to know if I can use my cheap Champion generator so long as I'm going through the ups.
Well, a lot depends upon what you mean by "clean". "clean" could mean a pure sine wave. It also could mean keeping the voltage within spec, boosting low voltages and lowering voltage spikes.
Most of the UPSes you hear referred to are APC Smart-UPS, which are pretty basic modified-wave, standby units. When your power goes off, or the voltage goes out of range, like below 75v or above 140v, the UPS takes over.
For a little more money, you can get an AVR, automatic voltage regulator, UPS. They boost low voltages and reduce spiky voltages without switching over to the battery. This can extend your battery life, but it uses a modified sine wave.
And for a little more money than an AVR UPS, you can get a Pure Sine UPS. Those have pure sine waves and typically are AVR too.
I've had at least 4 APC Smart-UPS over the years, usually bought on sale on Black Friday, when you can get an $80 for about $40 at Staples. However, 3 of mine just died in the last year, which made me go looking for something better, like an AVR or Pure Sine model. For APC, those were quite a bit more expensive, so I decided to look at TrippLite and CyberPower.
I found an awesome CyberPower AVR, the AVRG750U, which I use for my computer, which has 12 outlets. I got it at Staples for $45. It's normally $70, but I get a $25 off $75 coupon thru the Staples Rewards program almost every other week via email.
For the pellet stove, I got a Pure Sine model, the CyberPower CP1000PFCLCD. It was $130 at Newegg. There's also a smaller model the 850 for about $115. The LCD display is like having a Kill-a-watt built-in. Tells me how long the stove will run on its current draw. I'm very happy with both units.
Now, you're going to have to test any configuration you go with, because not all UPSes will charge while on generator power. I don't even know if mine will charge, since I haven't had an outage since I got my new UPSes earlier this Fall. Having said that, the input voltage range in the specs is very wide, 78v - 142v, so I'm hopeful. The key will be whether they will accept the modified sine wave coming from the generator.