On Saturday, September 26, 2015 at 12:14:12 AM UTC-5, micky wrote:
My neighbor tells me he needs a new Honeywell oil burner control unit,
and they come in 3 time lengths, 15, 30, and 45 seconds. How do I
know which length to buy? I know it doesn't say on the furnace itself
and I'm 99% sure it doesn't say on the control box.

Is there a model number anywhere on the furnace? I'm down South where I've never seen Oil heat in a home. If you can find a model number, you could call a supply house or service company and perhaps find someone who could tell you the most common parameters used in your area. If you can't find a model number, describe the furnace to one of the service company techs and he might be able to tell you. A picture posted on an image sharing site would help an experienced oil burner make a suggestion. ^_^

[8~{} Uncle Oil Monster