Our propane tank was filled yesterday. Since then, the furnace occasionally howls when it starts up. I called the propane company, but they don’t know why.
My hypothesis is that there was moisture in the fuel that was added. Since it’s in the twenties outside, I hypothesise that the moisture is freezing in the line and causing a restriction as it enters the furnace causing the furnace to howl. Once the furnace has kicked on and the contaminated fuel is pushed through, the noise stops. The woman at the propane company said that if that was the case, all of their customers would be affected. (Maybe they are, but no one else has called?)
Is my hypothesis reasonable?
Does anyone have a factual answer as to why the furnace is howling?
Perhaps in this temperature range the chimney is creating the sound in one of several pyrophonic modes. A Rijke tube is an example of this. There are a variety of other pyrophone sound pipes. They can be as simple as an open flame in a pipe with the proper configuration. Usually this would require some kind of additional air inlet, and that might be an indication of a leak in the chimney.
When howling pour a pot of warm water over the tank. If it goes away then it most likely is water/moisture. If so they can add (I think) methanol to the tank to help, even if it’s something else there is a dryer chemical they can use.
Sometimes a clogged air filter will cause a furnace to whistle or howl. Yours might have coincidentally gotten dirty enough to howl when your tank was filled. Or, it could be, you know, a werewolf in the flue.
Back to the problem at hand. Does the howling start when the burner comes on, or when the fan comes on? And does the furnace have just the main fan that blows air in the house, or does it also have an induced draft fan on the flue?
Any other propane appliances in the house like a water heater or rangetop? If so, can you tell if the flames on those look or sound any different? Probably won’t be able to tell on a water heater, but it may be noticable on a stove burner. First thing a technician might check is the pressure of the propane line. Regulators are usually hassle free, but maybe something caused yours to change a little bit.
Oh, and liquid propane is lighter than water, so any water in the propane tank would be at the bottom. I don’t think it would cause problems even if there was water in the tank.
Speaking of density, gaseous propane is heavier than air, so it will accumulate in low places. Be careful if you suspect a propane leak. As in, get the hell out of the house careful.