I've asked around too and everyone has a different answer. I've heard 1.3, 1.5, 1.7 but can't find anything concrete. The Seminole POH says its heater burns half a gallon an hour but it doesn't say how many BTU the heater is. I've also seen in an Aztec POH that the fuel consumption is small enough that it doesn't matter and I'm pretty sure that's a bigger heater than the heater in the Seminole. So who knows?
½ gallon an hour is what I remember. By the way, be sure you know which tank from which the Janitrol draws fuel. I am sure it is also the right tank on the Seminole.
I would also add that some examiners have a real fetish (?) about the Janitrol. Some examiners have been known to consume most of the oral on the Janitrol. They ask question after question about the heater. Such as, how it is ignited (I recall it has two electrical "points"), what you do if the heater won't fire (Reset the points - the breaker may be a button you push under the nose gear. Don't quote me on that; it's been nearly nine years since I even thought about Seminole systems). The long and short of it is know the Janitrol inside and out before you take your practical. And that goes for both Private and Commercial multi applicants.
bobbysam - at least regarding the Duchess, you're right about the breaker. Your memory is good for nine years! There's a round access panel on the belly, just aft and to the right of the nosegear that you can remove to get access to the button to reset the breaker. I have to do it all the time in the winter months, and with the 8 screws or whatever to remove the access panel, it's kind of a pain. After landing, we're told to run the blower with the heater off for a few minutes to avoid tripping the breaker. Many pilots forget to do this and keep the heater going until shut down. Then I either get stuck resetting the d*mned thing or flying with my jacket on.
Your memory is good. I don't think it matters where the fuel is supposed to come from because the thing is never going to work when you need it On the P-baron I flew I spent most of my time in the nose well resetting the button. The Cheyenne II we had, the heater would quit at the most inopertune time. At night, at the flight levels, with over two hours of flying to do. Building a fire in the trash can was a thoughtful option because we did not have enough blankets and coats and the weather below was not an option to go into.
If the Janitrol heater keeps popping the overheat breaker, located outside of the cockpit normally on the heater, it is BROKE and should be repaired before further use. It is located on the heater to prevent inflight FIRES and by reseting it at each landing you are just bypassing this important safety feature. I have well over 5000 hr in light twins with Janitrol or Southwind heaters and have never had one that blew the breaker regularly that did not have a mechanical problem. Do not keep reseting the breaker and do not let anyone tell you it is normal. If anyone remembers the actor Ricky Nelson, his DC-3 caught fire because the crew kept resetting the breaker on a heater located under the cabin floor secured by a screwed down panel. It popped so often they just removed the screws so they could access the overheat switch as required. The crew survived the pax did not.
When you fly with a Janitrol heater dress like you don't have one. I have too many hours with frosted headset mike and frozen feet when the thing blew out, wouldn't lite or the infamous cb popped.Make sure the AD is complied with every 100 hours, very important to make sure that you don't get any carbon monoxide in the cabin. On the Aztec and PA-31 it was one gallon an hour out of the right tank if I remember correctly.