Furnace backdrafting into home.

I had a furnace backdrafting into the home today. Discovered the reason was the exhaust fan for the kitchen was creating a negative pressure in the home. The fan was a dual fan and pulled at 90 CFM. I beleive in my report I will instruct my client to replace the fan with a smaller unit. Any thoughts??
If anyone has a good narrative it would be appreciated.

I believe I would hand it off to a qualified professional to correct…

The furnace was backdrafting exhaust (carbon monoxide) into the home. It appeared some of the cause may have been due to the kitchen fan running at the same time. Carbon monoxide is deadly, colorless, odorless, poisonous gas. Immediate correction by a qualified professional is needed.

Thanks larry

Interlocking mechanism needed with Kitchen range hood! This is new to the Inspection world so just mention it but don’t try to say it needs to be done. This is usually done in a very tight house with a HRV.
I also agree with Larry to hand it over to a Professional.

Was there a combustion air intake present for the furnace?

· **Repair, Safety Issue: **The heating system shows evidence that exhaust products have been “back drafting”. ***This is a safety concern. ***This condition results from any of a number of improper and potentially unsafe system conditions. Immediate repair by a qualified service technician is needed.

The answer to that would be no.
My report said this:
The furnace was observed to be backdrafting. Upon further investigation, the fan from the kitchen was on and creating a negative pressure. No combustion intake was found in the furnace room. This is considered a serious safety concern and needs to be repaired as quikly as possible by a licensed heating contractor.

I gotta think unless you have some special training on this and have proof of a negative pressure should avoid that language as it is diagnosing a safety hazard and giving the correction.
Was the furnace in the Kitchen?

There could many other factors involved .

Guessing this would be a overly tight home for something like that to have any effect.

This would mean bathroom fans or a number of other circumstances may also cause the issue.
Did you calculate vent sizing for the furnace unit and was it combined with water heater?

I would just report the reading and recommend the HVAC Tech examine the cause.

When the fan was on it backdrafted. When it was off it performed properly. I don’t see an issue with reporting that condition.

I agree Greg. The Kitchen exhaust fan may be contributing to the backdrafting and should be noted in the report, this is a life safety issue.

This makes it sound like the kitchen fan was the only fan causing the back drafting. Did you test the other fans? How about the dryer? The buyers may just not use the kitchen fan and think it is safe now.

Combustion air needed, check all conditions that may cause back drafting . recommend License contractor to repair.

How did you determine l test for back draft condition, was there visible evidence you can mention, a CO reading, or smoke test. Was the furnace running when you discovered back draft.? Also was there back draft at the WH when furnace running?

I would report back draft evidence by XXXX but not mention cause, there just to many as mentioned and leave to professional to determine.

I had the kitchen exhaust fan running when I turned on the furnace. It began to backdraft into the home. My co detector went through the roof. I went back upstairs and shut off the fan and it stopped. I then turned on the bathroom fan and rechecked it. No issues. The water heater did the same thing. I then turned on the dryer and checked it. No issues. The only thing that made it back draft was the kitchen exhaust so that is what went into the report.

That is fine but if you say that is the only cause I hope you are 100% correct .
It should not backdraft no matter what you are running and the vent may not be drafted correctly to begin with so I repeat (did you do a flue size calculation)?
Did you check for obstructions ?

[quote=“belliott, post:14, topic:72641”]

I repeat (did you do a flue size calculation)? No, That is not my job.
Did you check for obstructions ? Yes, I always check the flue by opening up the bottom or top.

[quote=“gmathias1, post:15, topic:72641”]

OK the reason I asked is because if it is a flue size /run issue the kitchen draft hood has no bearing on the correction and is simply a symptom.
Maybe I misinterpret but my impression is you are calling out the hood as the issue.

[quote=“belliott, post:16, topic:72641”]

The kitchen exhaust is the issue I found so it is mentioned. The root cause may be something else but that is for a HVAC tech to decide and repair.

OK that is your call.

I have yet to see a house so tight that just a 90 CFM fan makes a properly designed furnace back draft.

I see no information that qualifies for more than “the furnace back drafts”.

Nothing else in the house should be questioned at this point till you get all the facts straight.