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Discussion Starter · #1 · (Edited)
A good friend and I have been conversing over his problem. I'm a GC and sub all my HVAC/tinning work... so I'm a layman in this regard.

Jim may have gotten long winded in his e-mail, but I've tried to synopsize it: as follows......

Have a situation and would appreciate input from you.

(Lots of background and then just a simple question.)

Last December, we had the crawl space and attic sealed and insulated. The company that did the work (GB3 Energy Solutions) preformed before and after CO and air leakage tests and installed two outside combustion air vents for the furnace, boiler and water heater. We also purchase a CO-Experts low level CO monitor.

We recently (on Oct 18th) had a new high efficiency furnace installed by Walrath Heating.

Since that time, the CO monitor alarm has gone off several times with readings of 58, 20, 17, 37 & 39 ppm.

A Walrath tech came out using a Bacharach Monoxor III which reads as low as 1 ppm and checked the new furnace, the boiler and the hot water heater, but was unable to get any reading. He suggested that perhaps the monitor was defective.


Meanwhile, early morning on 11/30, our Kidde CO monitor alarms went off. They go off at a level of 70ppm. We opened doors and windows, went outside and called 911. Fire Department came but by that time could only get a reading of 12 ppm in the crawlspace.

They called Xcel who sent a tech out and checked all three appliances and again could not find any readings.

We again called Walrath who sent another tech out. He spent a couple of hours testing and checking stuff and came to the conclusion that there is not adequate combustion air being provided to the boiler and water heater. He surmised that since most of the alarms were going off early in the morning that when those devices were firing up early in the morning, the vent stack was cold and we were experiencing back-drafting. He proposed running additional combustion air vents. He also left a CO-Experts model 2014 CO Monitor.

That monitor alarm promptly went off the next morning with a reading of 13 ppm.

The rep from Walrath called me on Monday, restating what the tech had said. . It was suggested that I contact GB3 to see if they would stand behind their work and install the additional venting.


One of the owners from GB3 called and scheduled an appointment yesterday morning to find the source and cause of the CO.

That tech ran numerous tests on the devices and determined (and then showed me the tests and readings) that the problem is not inadequate combustion air, but rather that the new furnace fan is so much more powerful that the old furnace fan that it is creating negative pressure in the crawl space as it is drawing air from the gaps in the return ductwork which in turn is causing the water heater to back draft. The recommended solution is to seal the return air ducts.

The GB3 owner called this afternoon to confirm the techs findings. He indicated that since they are in the business of sealing homes, they need to be aware of air flow requirements, etc, and are trained and have the equipment to run the tests.


Thanks in advance,

UPDATE: Since this time, or at my questions, some other points.

1) Jim had (GB3) do his return airducting in the crawl space completely sealed (in hopes of alleviating an negative pressure and backdrafting)

The co monitors still went off at 25-50 ppm, even with his trap door open to the crawl space.

2) Both companys have inspected his current boiler and WH venting and found it to be properly functioning.

3) His new furnace is a 96% Rheem with dual stage, properly vented to outside. Jim did mention that it was very noisy and seemingly more powerfull blower than old furnace, when he had no problem and it was conventionally vented thru a separate chase than the boiler and WH currently.

4) Although a big crawl space, it was insulated and sealked, but the GB3 put in both a high and low 6" combustion air supply venting.

5) The new furnace is horizontally set, and there appears with testing to be no leaks causing a negative pressurization.

6) The new furnace has a PSC motor... not a variable speed... but I am unaware if that can be set to different speeds with jumpers. Jim notes that it blows like all hell.

Any ideas.... Jim is about to install more combustion air venting (after sealing the crawlspace which runs under main living quarters:censored:)

TIA

Peter

EDIT: Additionally, the CO going off does not seem related to any strange windy occurances.
 

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If all of these appliances are sealed combustion how is any CO getting into the space? Combustion air should be from the exterior. Exhaust should have no way back in. I'd be looking for a leak in one of the induced draft flues.

Have them down one of the units for a few days, see if it affects the readings. Then swap the operation.

Try staggering the start up times.

Is one of the 6" inlets to close to an exhaust?

Tom
 

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Discussion Starter · #4 ·
If all of these appliances are sealed combustion how is any CO getting into the space? Combustion air should be from the exterior. Exhaust should have no way back in. I'd be looking for a leak in one of the induced draft flues.

Have them down one of the units for a few days, see if it affects the readings. Then swap the operation.

Try staggering the start up times.

Is one of the 6" inlets to close to an exhaust?

Tom
Tom..... Thanks for the ideas/discussion/interest....

No.... only the NEW furnace is a 96% sealed combustion /exhaust... neither of which is close to the combustion air intake for the boiler/WH.

No.... Combustion air (for boiler and WH) is supplied at foundation level.... exhaust is conventional thru the roof.

I do like your idea of shutting down a system to test... just not practical at our current temps........................................................

In a sense, that has occured in that everything was fine prior to the NEW (Oct 18) install of the new furnace.

I, (and apparently two specialists in HVAC) are stumped.

Best

Peter
 

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Have the HVAC contractor set the DIP switches to a lower blower speed on heat call. Sounds like the blower is causing an exhaust rollout. The rollout switch may not be catching it with the CO readings being so low. May need more return air than combustion air.

Tom
 

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Discussion Starter · #6 ·
Have the HVAC contractor set the DIP switches to a lower blower speed on heat call. Sounds like the blower is causing an exhaust rollout. The rollout switch may not be catching it with the CO readings being so low. May need more return air than combustion air.

Tom
T.... Thanks.... I think you may be on to it.... Couple questions

1) Will there be a DIP/jumper for a lower sped on a PSC motor.... (funny I asked Jim to find out but had not heard back as yet)?

2)Could you explain exhaust roll out to me a little bit?

3) And the roll out switch?

Thanks

Peter

Your idea, seems to be on the right tract as 1) it ws new furnace that started this....and 2) it's blower seems over strong.
 

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I know nothing, but maybe this will jar some new ideas.

I observed something vaguely related in a home sale last year. In that case, inspector reported backdrafting from the water heater flue, so we trimmed branches away from the chimney. No improvement. Next, had the slope and run of the vent checked, and also for obstructions - no improvement. Then a wise old HVAC man noticed the difference in the sizing of the ductwork on a transition (boiler and WH shared ductwork to flue. That transition difference turned out to be quite important to him, telling me something like you can't go from 4" to 7" diam...or whatever the step-up was - I forget....and he recommended it be changed/increased, as I recall. So they did it, and that finally solved it.....

So.....maybe you're also backdrafting the water heater exhaust somehow in the morning, and it has something to do with the duct sizing, and on top of that the new furnace isn't completely sealed...so WH isn't venting quite as it should....I'd maybe turn down the water heater thermostat early in the morning to cut off the burn (maybe to "vacation" level) and see if that affects the CO alarm in any way. See what I mean? Sorry i don't know squat about this, but maybe there's a kernal of an idea there somewhere.
 

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Discussion Starter · #8 ·
I know nothing, but maybe this will jar some new ideas.

I observed something vaguely related in a home sale last year. In that case, inspector reported backdrafting from the water heater flue, so we trimmed branches away from the chimney. No improvement. Next, had the slope and run of the vent checked, and also for obstructions - no improvement. Then a wise old HVAC man noticed the difference in the sizing of the ductwork on a transition (boiler and WH shared ductwork to flue. That transition difference turned out to be quite important to him, telling me something like you can't go from 4" to 7" diam...or whatever the step-up was - I forget....and he recommended it be changed/increased, as I recall. So they did it, and that finally solved it.....

So.....maybe you're also backdrafting the water heater exhaust somehow in the morning, and it has something to do with the duct sizing, and on top of that the new furnace isn't completely sealed...so WH isn't venting quite as it should....I'd maybe turn down the water heater thermostat early in the morning to cut off the burn (maybe to "vacation" level) and see if that affects the CO alarm in any way. See what I mean? Sorry i don't know squat about this, but maybe there's a kernal of an idea there somewhere.
Mark..... Actually... You also are on to something.....

The parellel here is pretty close. I failed to explain the Boiler/WH are drafted same flue. And in an energy audit Jim did, the auditor questioned the slope (and hood) on the WH.

Now both GB3 and the furnace installer said the exhaust/flue was fine... but you and I know that tech's are not always right.

I have not seen the exact installations, plan to Saturday (for Xmas drinks), but I'll sure look.

With a little backdrafting negative pressuization from the new furnace, and a weak exhaust draftinhg from a less than great WH/boiler flue draft... maybe that's the answer.

And that ties in and is related/consistant with Tom's ideas.

Thank Ya

Peter
 

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T.... Thanks.... I think you may be on to it.... Couple questions

1) Will there be a DIP/jumper for a lower sped on a PSC motor.... (funny I asked Jim to find out but had not heard back as yet)?

2)Could you explain exhaust roll out to me a little bit?

3) And the roll out switch?

Thanks

Peter

Your idea, seems to be on the right tract as 1) it ws new furnace that started this....and 2) it's blower seems over strong.
The DIP switches or jumpers are on the board.

Rollout is when exhaust or burner flame leaves the combustion area. It is caused by a negative pressure in the building. There is a rollout switch that senses flame rollout, but would not sense a slight exhaust backdraft.

Tom
 

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Oversized blower drawing the back draft hence tripping the roll out. It must be a sealed exhaust if its a cat3 system because a cat vi is pvc intake and exhaust from the out doors. Direct vent.

In any event a few months bcak I had a roll out switch constantly tripping. Pulled out the duct and found a masonry shard in the chimney obstructing the flow. Clear and a day later it happened again. I went on the roof, dropped a light down and saw a solid squirrels nest. Fished it out, put a cap on and called it a day.
 

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Discussion Starter · #14 · (Edited)
The new furnace is a 96% with PVC intake and exhuast according to the info from Rheem. It appears as if the new blower is back drafting the other 2 appliances which appear to have standard draft flues.

Tom
Yes... The unit is dedicated combustion air and direct vent, both in PVC (and with a condensate pump)

So....:censored: I have to think the same way....:thumbsup: but I have been assured the furnace bottom plate is attached, return air is sealed..... how is it backdrafting (negatively presurizing the crawl space) the other flue(s).

Honestly Thanks..... (The censored thingy is for the GD problem/issue)

But I'm going to call the tech's myself to see if that blower can't be adjusted down.


(Many years ago I had two Rudd two stage furnaces installed in my home.... the tech's seemed nicest, neatest workers. Upon checking their install, I found numerous install errors. From not running new thermostate 5 wire for two stage operation, delivering 100 BTU unit instead of 125K, to no shutoff or drip leg.......) Point being, maybe the furnace unit is not well sealed off... and the reports that Jim is getting from GB3 and the furnace installer is not correct... DUH... Wake up Peter
 

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Get a smoke stick, fire up the furnace and hold the stick near the draft hoods on the water heater and boiler. Watch which way the smoke goes. If it enters the living space, follow it to leak.

Do the test with the appliances running also.

Tom
 

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Discussion Starter · #16 ·
2 combustion air vents @ 6" it's supposed to be 1 square inch per 1,000 btu. doing a little high school math, pi r squared, thats roughly 30 square inches. Isn't that a little low for all three appliances?
Flash..... Thanks.... I was not aware of 1"/1k ratio. I will check.

Although I had assumed the furnace installer had actually calcked the correct figure.

Incidentally, it would apply to only two appliances (WH/Boiler) as new furnace is direct PVC vented both combustion/exhaust. (Don't know their exact BTU's)

Also interesting is that before new replacement of furnace, old furnace was conventiional 80% so/and with three units and present venting, there was no CO tripping.????


:rolleyes::rolleyes::rolleyes:
 

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Discussion Starter · #17 ·
Get a smoke stick, fire up the furnace and hold the stick near the draft hoods on the water heater and boiler. Watch which way the smoke goes. If it enters the living space, follow it to leak.

Do the test with the appliances running also.

Tom
T... That has been done by either GB3 or furnace installer.... yes their is leakage/backdrafting...... not always.... despite pro's assertion that combustion air is sufficient, new furnace cold returns are sealed, and exhaust venting is fine.


Can't really follow backdrafting smoke to anywhere creating a negative pressurization.
 

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With a smoke pen you can hold it and watch where the smoke goes. It will move to the lowest pressure.

The installers were thinking return air leak, they may have missed something. This will also show a backdraft which must be corrected. There should be no CO in the home.



Tom
 

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Discussion Starter · #20 ·
This confounding stuff usually turns out to be something simple....

Anyone check the appliances for complete/proper combustion?

Ya know Griz...... Good point.... I don't know..... but will bring it up.... and it is often something so obvious that we've overlooked and let recent changes or other deetails to get in the way.
 
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