It depends on the ambient temperature and the setting of the thermostat.
24 hours a day
In most cases 24 hours per day!
that would depend on the size of the blast furnace.
The filter should run for at least 6 hours a day, preferably during the day as this is when it is needed the most. Of course, the longer you run it, the better it wil lbe.
no hours
its depend on the stamina of the horse but horse can run a lot.
A photo shoot can run as long as 16 hours and at all times
Well, if by the question, you mean, how many hours a day should you run your filter and chlorinator, the answer is 8 hours per day in summer; half early morning, half late afternoon, 6 hours per day in winter; half early morning, half late afternoon
You should not run gas from the furnace to any appliances.
On average, a 45,000 BTU furnace will consume about 0.046 gallons of propane per hour when running. Therefore, 1 gallon of propane should last for around 21.7 hours of continuous operation for a 45,000 BTU furnace.
If your furnace is opperating correctly and the vent is in good opperating condition, You can run the furnace non stop forever.
Not if the furnace exceeds 5000 watts.