Use deep discharge marine battery as emergency power source?

Yeah, forgive me for being confused. You've spent so much time telling us how that wondeful ECM blower runs 24/7 and only draws 100Watts..... I guess you forgot the part where that's only in fan only mode, where the fan barely moves the air. The other part of that 24/7, when the furnace is actually heating, it draws 8 times that. But wait, we're supposed to use a two stage furnace that spends a lot of time on lower output heating so that furnace is firing a lot of the time. Some would say it should be firing all the time during the coldest days. So there goes that miracle ECM blower that only uses 100W, 24/7.

Uh huh, according to you.... Last time I checked the poster was asking about using a simple inverter, not a UPS. A full UPS was never a requirement. But you do have a way of taking threads into your own little world. But even playing by your rules, what's this, which I found in 2 mins with google?

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Samlex TN-1500-112F, Off Grid Inverter, 1500 Watt, 12 Volt, Pure Sine Wave, w/Solar Charge Controller/AC charger & Transfer Relay for UPS function

Pay attention. He didn't say he wanted to use an auto battery. The question was about using a marine deep cycle battery. And you can get deep cycle batteries that will supply 150AmpHr. Use a couple of them and you have an hour or two of furnace run time. Economical or practical compared to a generator? No. But not totally out of the realm.

I know you think you Canadians are very smart up there. So, I'm sure you'll like this source straight from Canada. They say you can power a furnace with a battery/inverter:

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1A =97 Battery backup with inverter/charger for short blackouts of 12 =96 48 hours: $2,350 Essential AC loads only. Furnace, sump pump, well pump, fridge, plus efficient lights and small DC appliances.

Again, I'm not saying it's cost effective, or practical. I'd go with a generator. But it shows that once again, contrary to your shoot from the hip comments, it can be done. BTW, have you gone down to the auto parts store to see those batteries with the removable cell caps?