Oil Furnace/OIl Hot Water Heater Fumes Back up

Old 01-13-20, 09:17 AM
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Oil Furnace/OIl Hot Water Heater Fumes Back up

Oil Furnace and new Hot Water heater Fume Back up – we have had this issue for years, but no one can find problem after several tech visits. Fumes from furnace issue enter house through ducts: · No issues at all if furnace temperature kept at daytime level (comes on frequently)· If furnace turned down at night to cool house (gets colder between firings) - so furnace only comes on occasionally the issue of fumes starts – to eliminate this we simply turn off the furnace before bed and have done so for years. Turn it to daytime temperature in the morning and no problem during the day.· New Hot water heater – same fumes but is only on for a short period (15 min max) so issue is minimal but there. It smells worst at the motor. Doesn’t get pushed upstairs.· No CO2 issues· Techs have checked whatever they do and no one can find any issues at all. Anyone with any ideas I can relate to my next tech visit?

Old 01-13-20, 10:04 AM
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This is just a thought since a problem like yours is very difficult to assess without being there.

First, I would look for something that is common to both the furnace and the HWH since both run independently of each other with 2 separate burners and individual settings. You mentioned it going on for years and you also said you have a new HWH so I'm guessing the old HWH was the same way.

One reason for fumes on an oil appliance is improper settings but with 2 separate units it sounds unlikely they both would be wrong plus as you said it's not consistent which bad burner settings would be. Another is poor draft.

Have you had your chimney checked for proper operation. Your chimney draft should be checked when they do your efficiency test when serviced. You are looking for something that is common to both units which is your chimney. If the chimney does not pull a draft then the fumes, instead of going up the chimney would stay in the basement and when the furnace comes on and the blower starts could be sucked up into the house which is why you may be getting them when the furnace is on and not the HWH, because there is no blower on the HWH.

This also could be the reason why it happens more at night when the furnace runs less than during the day settings. Once the chimney gets hot, that is what creates the draft. By turning down your furnace at night it allows your chimney to cool and not create that needed draft because your units do not run long enough to heat the chimney.

You may have a chimney flue too large for your units or too low a exhaust temp from your furnace and heater to create a proper draft.

I would start with a draft test and a chimney inspection. Also, the fumes getting up through the ducts concerns me since your heat exchanger is sealed from the ductwork unless there is a crack in it allowing combustion fumes to enter. There are smoke bombs available you can use yourself to check this or it could be just the fumes being sucked in by the blower. It would be good to verify though. Your tech would know about this.

The bottom line is it is something that is common to both and has been going on for years and mostly does it when the furnace is not running constantly which allows the chimney to cool. The thing with oil fired HWH's is, on there own they don't run long enough to heat the chimney to create a draft and warm air furnaces, depending on how well they are sized for your home may not run long either. The fastest way to heat your home is with warm air because it heats so quickly so burner cycles can be short.

Check your chimney. Hope this helps a little.
Old 01-13-20, 01:18 PM
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I had a fume problem with my boiler (after burner shut down) and cured it by installing a control with a 15(?) second valve-on delay and a 2 minute motor off delay.
I suspect your problem may be caused by insufficient combustion air (tight basement).

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