Expert: James Ball - 1/13/2009

Question
Dear James,
We have a 1961 single story ranch home with basement and a single masonry fireplace which has two flues, one for the oil-fired boiler and one for a wood-burning FP (the FP has a larger flue). We have recently (in the past 2 weeks) been experiencing an oil smell when our oil-fired boiler is running.  The smell is only in the room directly above the boiler (which is located in the basement), and is the room with the fireplace.  The oil smell is difficult to notice when standing next to the boiler in the basement (i.e. orders of magnitude less than the floor above).  This led me to think that something is wrong with the flue or chimney.  We had the boiler cleaned by a licensed company 2.5 months ago and had both flues cleaned by a certified sweep ~1.5 months ago.  Both flues checked out fine according to the sweep.  The sweep also installed a stainless cap on the FP flue (previously it had none).  The FP flue has a top-mounted damper. The oil-fired boiler flue has a vacu-cap.

It is difficult to ascertain what could have changed in the past few weeks, though it seems that if we open the glass doors to the fireplace and stick our head down there, the oil smell is very strong.

Could the oil fumes be coming down the FP chimney, even though the top-mounted damper is closed?  Did installing the FP flue cap create a better avenue for the fumes to transmit by?  I believe we do have somewhat a negative pressure problem, since after we burn a wood fire, there is a burned wood smell for a few days afterwards (especially if there is any unburned wood left on the rack, that seems to exacerbate the burned wood smell).  On a few occasions when we were burning a wood fire during strong winds, we would get downdraft and smoke would blow into the room.  This has gotten better since the cap was installed, does the cap act as wind-brace?  Though, this negative pressure problem would have been going on for over a year, while this is the first time we have had oil smell coming from the FP.

Any suggestions would be helpful.

Answer
Hello CK, you have a lot going on here so lets see if I can help, lets say every thing is clean and working the way it should, lets start with cleaning the firebox out of all ash and unburnt wood and then close the top-mount damper. then light a piece of insence and put in the fireplace opening (3" from the top  in the middle, then move it to different areas of the firebox and re test) and see what happens to the smoke does it go up the chimney, blow back into the room or just seem to go straight up and flow both ways. If it just flows (no real direction) then the air is not moving up or down in the fireplace flue. that is good. if it is going up the chimney or if it blows back down then it is not sealing that well (get that sealed or fixed), then if you smell the "oil" open a window in the fireplace room and see if it improves? if so the you might have a negative pressure issue(Negative Pressure in your home (house stack effect) that is hot air raising in your home (and getting out through the attic vents, doors, lights) your house is a better chimney than your chimney. Also kitchen/bathroom exhaust fans, cloths dryers and the boiler/furnace all take house air out of the house (mechanical negative pressure) your house might need make up air, maybe open a window in the oil units room)
if you still have the problem have the oil flue and fireplace flue video scanned to assure the flues integrity and it it is not right repair it. (certified sweep should be able to help)
James