Following a nationally certified home inspector's inspection

Dave Yates (PAH)

Unlined brick chimneys - especially in row homes at the bottom of a hill - have been prone to draft issues on start-up. Older equipment with fairly large standing pilots helped keep things rolling. But, in this case, I had an interior (centrally located in the home) terra cotta lined chimney exhibiting good draft prior to either appliance firing. Although it settled down to fairly low levels of exhaust, the delay was from the damper & not the chimney and at all times throughout every run cycle there was small stream of exhaust with 40- to 50-PPM of CO being ejected into the basement.



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Dave Yates (PAH)

CO

Both the water heater and boiler flues have the old Ameri-Therm bi-metal dampers installed in them. The systems got a green light from the home inspector, but the buyers wanted the HVAC equipment tested.

On start-up, the boiler spilled 300+ PPM CO until the damper's "fingers" curled back. It slowly settled down to a point where it averaged 40- to 50-PPM & remained at that level over the course of the entire run cycle of 45-minutes. Burner clocked within limits & combustion analysis was good following a run-in of a few minutes.

The water heater spilled CO until the damper was fully opened.

Dilution polution rendered 2-PPM CO in the basement room air. There's a bedroom down there too.

Can't know if they don't test & they can't test if they don't know.



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Jim Bennett

Wow!

Those Ameri-Therm dampers were the hottest thing going in this area 25 odd years ago. I wonder how many of them are still out ther in "service"

Jim

Steamhead

Sounds like a \"rough start\" on both units

I have an old Ameri-Therm on my water heater, and it never does that. Also I wonder if the chimney was restricted in that house?

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Dave Yates (PAH)

chimney

was free & clear with no obstructions (mirror view to sky above from access door). Draft was quite pronounced.

The damper's "fingers" never quite flatten out to avoid some interference with draft and the boiler's draft hood construction (internal to the jacket with open sides) led to this being a mis-application. Looks like a sheet-metal box with a v-shaped diverter - take away the two sides along the V-side of the diverter & that should help you to see its design. My suspicion is that this diverter design is marginal at best and operated at the fringe without any flue or chimney obstructions. Toss in a reduction of flue diameter from the Ameri-Therm damper's "fingers" and that marginal performance falls below acceptable standards. I should add that observation of the damer's internal components was possible due to the diverter's construction. Moisture from the initial combustion left a dancing vapor trail along the boiler's jacket - immediately above the side-wall grille stamped into the jacket - during each initial firing after allowing the damper to close.

The thermal reaction time is quick, but not fast enough to avoid a wee bit of initial spillage at the water heater's draft diveter.

Never yet saw a motorized damper that openes AFTER the burner fires. We too installed tons of the Ameri-Therms, but that was a long time ago & long before we ever thought of testing for CO. Absent a combustion-overflow-chamber, it seems likely most appliances would see momentary spillage on initial start-up. No safey interlock if the bi-metal should fail to curl.

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Boilerpro_3

Timmie would best answer this,but...

I believe flue gas spillage for a period of five minutes at start up is considered acceptable according to safety standards as is occasional backdraft during regular operation. I believe most boiler installation manuals say this. A chimney will never draft well on initial cold start unless you have a good wind over it, even with a motorized damper.
Another reason to begin installing power vented equipment.

Boilerpro

Boilerpro_3

Ah, didn't notice that it was continuous

That is certainly beyond the five minute requirement I've seen.

Boilerpro