Poor Drafting chmney

Mark Berry

I installed a replacement warm air furnace last summer, the old one was about 25 years old(1725 burner). When I set up the burner it was a hot humid day with little to no wind. My draft was -.01 in. w.c. I figured that when colder weather settled in that draft would naturally increase. I had to return for a delayed ignitin in feb. and rechecked the draft, still -.01 in. w.c.
The chimney is in the middle of the house and has a clay liner. I was wondering if a stainless liner would increase the draft or should I install an inducer motor.
Thanks,
Mark

Ken_8

A few observations...

1) If hot water is derived by a typical gas water heater, the draft hood will diminish draft of the oil furnace by about what you're experiencing.

2) If electric, the draft regulator should be stabilizing the draft and it should remain constant.

3) Please discern whether your measurement is at the breach - or over fire (in the chamber) for us all.

4) Is there a C/O door in the ash pit? Is it sealed?

5) Are you sure the flueway is not also shared by a fireplace or wood stove? If so, it is unsafe and must be changed.

6) Was the chimney designed for a coal system and sized accordingly? It may be so darn big that the chimney will never draw much.

7) .01" w.c. negative draft on a hot humid day is not abnormal - unless the A/C's on and/or a whole house fan kicks in and backdrafts the chimney. But the stink would get anyone's attention in that case. And you did not mention it.

8) Wassupwit the draft regulator? You didn't mention it. Does it just lay flat closed - or can you see it rock a tad?

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john@TR

chimney liners

The chimney needs to be sized correctly for the BTUH input of the equipment. It's likely too large for what you're venting into it now. Most liner manuf have sizing tables available (ask @ the supply house).
A draft inducer will probably just give you the opposite problem-too much (or too negative) draft. A flame retension burner will start to have "fame-detatchment" at or above -.04"WC draft (measured over-the-fire).

Jimmy Gillies

Mark

Chimneys rely on the change in temp inside to work well, so if you can't get the temp inside high enough because, say, the chimney is to big the the draft will be poor.
Is the chimney high enough? Is there any trees overhanging the chimney? Is the house prone to high winds?

There are many factors to consider with a poor draft chimney. Have a good look at the top of chimney first, 9 times out of 10 your problem will be there.

I hope that helps

Kind regards.
Jimmy Gillies.

Mark Berry

other info

The chimney is approx 20' tall. The chimney does not have a clean out it ends at the breeching. The -.01" w.c. is at appliance termination. Actual size of clay liner I did not measure. I have the damper fully closed and -.01" is max I can get, damper does not move. There is a fire place and it has it's own flue. It runs beside oil flue, the house is a ranch and you can see the top of the chimney from the ground. The oil flue is approx. 8" higher than the wood when it exits the chimney. No complaints of smokebacks from fireplace. The oil furnace is the only appliance venting into the chimney.

Ken_8

Depending on the furnace

BTU input, a normal 8X8 clay line should be visible exting out the roof?

What about the water heater? Is it gas, oil or electric? If gas or electric - is it too vented through the same chimney?

And is the furnace sealed lightly in the combustion area? Any sort of leak especially around the site door/plate would reduce draft readings considerably.

Also, check the draft at the site door to find the O.F. draft (Over fire) - just remember to put a rag/seal around the draft gage while doing this test.



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