I was in a small greenhouse the other day that had a warm air lowboy oil fired furnace. When it fired up the oil burner lit and started warming the heat exchanger as I'm used to seeing in residential furnaces. After a short time the fan kicked on and started blowing heat down the duct - all good. But then what I found odd was the fan shut off but the burner kept running until the heat exchanger warmed back up, then the fan kicked back on again. This cycle continued for half an hour till the greenhouse was up to temp (55° F). I'm just used to seeing both the fan and the burner run till the t-stat no longer calls for heat. Is that lowboy hooked up wrong and running up against a high limit or something or is that possibly normal operation. The owner said all warm air furnaces run like that... I've never seen one do it.