How to model water flow when only a couple of sample points available?

Chimney sweating

• Our house has a 3 chamber chimney that was built in the 1950's that is constructed from the basement floor up through the 1st floor and out the roof.The 1st floor is an old coal fireplace using the middle chamber.In the basement the water heater is vented through one of the chambers and the gas furnace is vented through the other.This year we replaced our very old furnace with an 80% efficiency model that is also vented through the chimney.We also insulated our attic with blowin insulation.We are in the middle of long cold spell with temps in teens at night and 20's during the day.I noticed in our living room a couple of spots of moisture coming through the chimney stone up close to the ceiling.I got up in the attic and pulled away some of the insulation from the chimney and found moisture on the side where the furnace was vented.So I swept away the insulation from the chimney on that side, believe giving it air flow would fix the problem.It has not fixed the problem.I am wondering what is causing this.Is it the moisture from the gas exhaust building up on the inside walls of the chimney and finding its way through cracks?Or is it just a temperature thing?Also can I place a metal flue inside this chimney chamber down to the furnace ,that way the exhaust would just be in the flue and not exposed to the inside wall of the chamber and keep the moisture away and the temperature of the chamber wall at more of a constant level?

• Answer:

  yes it is condensation from the gas and its because of the cold temperatures we've been having. gas is almost all mopisture and if it cant get out the chimney fast enough it cause moisture on the walls and find a way either down to the bottom or leach out the bricks. with a condensation problem, a stainless steel lining is the easiest and most affordable way to fix the problem. now...only use a licensed chimney repairman, go on the B.B.B. or consumer affairs to find a couple in your area. ALWAYS GET MORE THAN ONE ESTIMATE!! now its hard to give you a price that something like this should cost but i can try to give you a very general price idea. a chimney up to 25' with a double connection(one for the oil and one for the gas, they must go in separately and the gas must be on top) should cost anywhere from $950.00 to up to $1400.00 a higher chimney will cost more they say they charge by the foot but its pretty much B.S. most likely they'll tell you its 316L stainless steel and it might be, but in any case when they get there put a magnet to it, if it sticks tell them you dont want it its not 316L. also make sure they check the BTU on both units and make sure they're using the right size diamater liner.