Combustion analysis on oil fired direct vent

Preiss

My son just bought a home with an oil fired direct vented furnace. A Kerr Eclipse Furnace with Riello BF3 Burner. Looks like a clean set up but there is no combustion analysis sticker. There is no barometric damper on the vent, Which may be normal. Where would a combustion analysis probe go? In the vent connector at the beech? I cannot see it inspection whole anywhere.

Preiss

 I meant breech. Sorry.

Steamhead

Found the manual online and here's what it says:

"On smoke/vent pipe, between appliance breech and draft control,
punch or drill a 1/4" round opening. Direct Vents have a sampling port
located on the breech connecting adaptor. "

So that's where the analyzer probe would go- look for the port in the adaptor.

It's extremely important to set this burner up with instruments, and to leave some headroom so if the oil or air supply changes over the course of the season, the air/fuel mixture won't get too rich and cause the burner to make soot, which will belch out the vent and discolor the side wall of the house.

STEVEusaPA

Never a baro on direct vent.

Preiss

Thanks guys, info much appreciated. I’ll look again for an inspection port. I didn’t think there was a damper on direct vents either so I imagine you set up your vent draft by using the burner air shutter adjust. I’ll check to make sure it’s got 0 smoke and a draft of around .04 IN/H2O at the connector. Please let me know if the draft should be different seeing how it’s a sealed vent. Thanks again guys.

Preiss

By the way I have a smoke pump and Testo  310 analyzer. Am I looking for approx 11 1/2 % CO2?

Steamhead

The way I was taught was, find the zero-smoke point and note the CO2 reading. Then open the air shutter enough so the CO2 drops by 1/2-1%. This will allow enough headroom so if the fuel-air mix should change during the season, it should not cause sooting. Zero smoke is the goal.

Soot is your enemy. Not only is it dirty, but it seriously reduces efficiency, and makes more work for us at the next servicing.

Preiss

I completely agree with you. I’ll make that adjustment. Thanks Steamhead.

Preiss

Should there be a firebox inspection sight to see the flame and do a draft over the fire check? I didn’t notice one when I looked at the furnace but there may have been a cover that was hiding it.

EBEBRATT-Ed

@Steamhead

Is correct. You have to make it smoke so you can see where you are, then open the air just enough to get 0 smoke. Take your Co2 etc and if combustion looks good open the air band enough to drop the Co2 about 1% from what you had.

Preiss

Thanks EBEBRATT-ED. In other words don’t worry about draft characteristics on a direct vent just be concerned with 0 smoke and then adjust CO2 down 1%. If smoke and CO2 are good draft will automatically be ok? I have my own Kerr-Comet Boiler. It does have a damper and I just the vent to .04 in/h2o, .02 in the fire with 0 smoke. It Works great, 87% efft, very happy with it. I’m running a Riello 40F5 on it. Thanks again for all your advice guys.

EBEBRATT-Ed

@Preiss
No, draft or over fire pressure whatever the unit is designed for always has to be considered. But direct vent it is what it is. If the flue is correct it should be ok.

Dropping the Co2 1% below what it is when you have a 0 smoke gives you a cushion. Without the cushion, dog and cat hair and lint in the blower wheel, changes in fuel and air temp could cause a soot up before the next cleaning

Preiss

Thanks again. 

EdTheHeaterMan

With a direct vent, the combustion chamber may operate under pressure. The exhaust may also be under pressure, so seal up the combustion sample port with that red RTV sealant. The burner fan is the device that is making the combustion process move. No chimney effect causing negative pressure (draft) when you have direct-vent.

Air volume will change with air temperature. Cold air is "more dense" than warm air. So the same cubic foot of air delivered by the fan on a warm day will actually have more weight (including more oxygen) when that same cubic foot of air is colder. This is all considered when the Burner/Boiler or Burner/Furnace is designed. Be sure to follow the manufacturer's instructions on the excess air adjustment.

As far as lint and pet hair build up on the fan... That should not happen on a direct vent because the air is firm outside. The location of the outside air inlet is to be considered here. Is it close to the clothes dryer vent? then you have a problem with lint buildup. Are there shrubs that give off large seeds, small leaves or excessive pollen at certain times of the year? this will be a problem. A customer of mine, with no problem for 8 years started to have a sooting problem after some new shrubs were introduced near the air intake. Remove the shrub and the problem stopped. You not only need to understand electrical controls, combustion theory, fan laws, and pump laws to be an HVAC tech. You also need to be an arborist or an ornithologist from time to time.

KEEP THE VENTS CLEAR. (both in and out)

Mr.Ed

Preiss

Thanks Mr Ed. I agree with you completely. The burner fan will be driving the combustion process and producing a positive draft throughout the vent system. Again just making sure to have no smoke and adjust for CO2 and of course sealing the sampling port. As far as the outside direct vent head, It is on the side of the house where there are no shrubs, bushes, trees, intake or exhaust vents of any sort, nice and clear of everything. Kerr-Eclipse furnaces are designed for use with their direct vent system. Whoever installed the furnace and direct vent did an excellent job. The supply air and vent are well supported With no soot whatsoever around the outside head. The furnace starts and runs well. I’ve had no problems with Kerr or Riello products so far. Cross my fingers. Thanks for your advice, much appreciated.