# Hvac/co mystery



## MTN REMODEL LLC (Sep 3, 2010)

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)

TIA

Peter

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


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## tjbnwi (Feb 24, 2009)

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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## The Coastal Craftsman (Jun 29, 2009)

So are they 100% sure they have enough make up air coming in? Does the furnace and water heater use a concentric flue?


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## MTN REMODEL LLC (Sep 3, 2010)

tjbnwi said:


> 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.
> 
> ...


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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## tjbnwi (Feb 24, 2009)

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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## MTN REMODEL LLC (Sep 3, 2010)

tjbnwi said:


> 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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## MarkJames (Nov 25, 2012)

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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## MTN REMODEL LLC (Sep 3, 2010)

MarkJames said:


> 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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## tjbnwi (Feb 24, 2009)

MTN REMODEL LLC said:


> 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)?
> 
> ...


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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## tjbnwi (Feb 24, 2009)

According to the Rheem website the blower is 4 speed 2 heat 2 cool. Controls are on the board and also through an optional thermostat.

Tom


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## Tom M (Jan 3, 2007)

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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## tjbnwi (Feb 24, 2009)

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


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## flashheatingand (May 3, 2008)

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?


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## MTN REMODEL LLC (Sep 3, 2010)

tjbnwi said:


> 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.... 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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## tjbnwi (Feb 24, 2009)

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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## MTN REMODEL LLC (Sep 3, 2010)

flashheatingand said:


> 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.????


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## MTN REMODEL LLC (Sep 3, 2010)

tjbnwi said:


> 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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## griz (Nov 26, 2009)

This confounding stuff usually turns out to be something simple....

Anyone check the appliances for complete/proper combustion?


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## tjbnwi (Feb 24, 2009)

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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## MTN REMODEL LLC (Sep 3, 2010)

griz said:


> 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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## Tom M (Jan 3, 2007)

If you think you were benefiting from incidental venting by the old furnace, then your backing up claims that the flue being used is a problem. Too much money to just replace all kinds of working equipment.


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## beenthere (Mar 5, 2009)

There are power ventors that can be used.


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## MTN REMODEL LLC (Sep 3, 2010)

MTN REMODEL LLC said:


> Does anyone think this senario might be the cause:
> 
> Facts: No problem with CO untill new 96 sealed furnace replaced a natural exhausted conventional furnace was replaced.
> 
> ...





Tom M said:


> So has it tripped since you allowed original venting? And not to beat a dead horse but did anyone visually look up into that chimney?


Tom Yes, it went from Sat to Wenesday fine, then was tripping in the house at 20 to 40 ppm... no strange weather involved. And I have not been up on the roof or chased the vent, but I've been asured that both GB3 and Walreath have thourouly inspected it


??????


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## beenthere (Mar 5, 2009)

Might also want to stick a low level in the crawlspace, and see what the CO is in it.


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## MTN REMODEL LLC (Sep 3, 2010)

Tom M said:


> If you think you were benefiting from incidental venting by the old furnace, then your backing up claims that the flue being used is a problem. Too much money to just replace all kinds of working equipment.


T.... Yes.... Just surmizing/guessing at this point.... and I (and GB3 and Walreath) have no idea why the present wh/boiler venting would not be functioning satisfactorily.

Thanks


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## MTN REMODEL LLC (Sep 3, 2010)

beenthere said:


> There are power ventors that can be used.


BT.... are those just power combustion air fans.... or are they somehow integral with the vent stack.... and does it matter.

Just curious....

TIA


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## Tom M (Jan 3, 2007)

And what was the weather like during this time? I disregard the Hot water heater because they the the flue year round with less volume.

I forget already. Did you say the boiler shuts down or just that the CO sensor alerts?


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## MTN REMODEL LLC (Sep 3, 2010)

beenthere said:


> Might also want to stick a low level in the crawlspace, and see what the CO is in it.


Yes... Exactly my curiosity when I spoke with Jim yesterday.... but he had brought both up into the Kitchen and bedroom primarily for double safety.

They have a high reading hold on them too... don't know if he is going to put one down there or not..... hate to say/recommend he not have the double safety


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## beenthere (Mar 5, 2009)

MTN REMODEL LLC said:


> BT.... are those just power combustion air fans.... or are they somehow integral with the vent stack.... and does it matter.
> 
> Just curious....
> 
> TIA


You can get them to use for side wall venting. Or as a booster to help a chimney that doesn't have good draft.


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## MTN REMODEL LLC (Sep 3, 2010)

Tom M said:


> And what was the weather like during this time? I disregard the Hot water heater because they the the flue year round with less volume.
> 
> I forget already. Did you say the boiler shuts down or just that the CO sensor alerts?


T... weather was moderate, no strange winds or temps.... night temp was probably around 25 degrees. Jim has not detected any correlation with a weather effect correlation with the many times it has tripped.

The primary correlation is morning fire-up timing, thus the thought of cold air having to heat up for drafting, but it is extreemly erratic and does not appear correlated to actual night coldness/warmness.(I'm also wondering that on colder nights the boiler is running more and the venting is never getting cold?)(Part of the problem "mapping" this is that the crawl space is not that easily accesable, and consequently Jim checks the HW baseboards heating but is not necessarily certain of exactly when the boiler is fireing)

No the boiler does not shut down (what trip would cause it to?)... just the CO monitors going off.

Thanks


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## SLSTech (Sep 13, 2008)

Ahh I thought it was just the How Water Heater - sorry missed seeing the boiler but my recommendation would still stand - either find a way to isolate both from conditioned areas (aka inside the thermal envelope) or go with direct vent

As for CO - as mentioned it is cumulative & the UL listing is based off of ASHRAE which was based on a study done back during Vietnam if memory serves me correctly. Per the study conducted on military personnel or those at that age - 70 PPM was ok for the time period listed. 

As for assuming they tested - I would ask if it has been scoped & looked at, just because they measure a draw & it doesn't backdraft doesn't mean it is all leaving out the top - seen plenty of disconnected pipes & other issues 

The reason I asked about the attic is that this is wintertime & wintertime stack effect is in full force - if they only sealed up the crawl but not the attic (sorry but most insulation doesn't count as air-sealing) they didn't really cut down on it & instead of pulling air into the crawl & up, they are pulling it up from higher & creating a slight vacuum which is exacerbated by the equipment kicking off & trying to pull its own air. 

As for it shutting off, I think he is referring to a low level oxygen one, but that would take a lot for that to be tripped & 20 to 70 ppm would not cause that to happen


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## beenthere (Mar 5, 2009)

_*CO exposure chart
*__*exposures at 1 hour*_*0-9 ppm (parts per million) CO:* no health risk; normal CO levels in air.​ *10-29 ppm CO: *problems over long-term exposure; chronic CO problems such as headaches, nausea- not the most dangerous level​ *30-35 ppm CO*: flu-like symptoms begin to develop, especially among the young and the elderly​ *36-99 ppm CO:* flu-like symptoms among all; nausea, headaches, fatigue or drowsiness, vomiting; *most CO detectors sound off here*​ *100 ppm + CO:* severe symptoms; confusion, intense headaches; ultimately brain damage, coma, and/or death, especially at 300 to 400 ppm+​A few things should be said about the above statistics. The above symptoms are for exposure to carbon monoxide for one hour. Symptoms may become more severe at levels such as 36-99 or 100+ ppm (parts per million) over longer exposure. There will always be a problem, for almost any amount of time, if the CO levels in a particular space exceed 400 parts per million. Any room with levels of carbon monoxide at 400 ppm is an extreme emergency.​ It should also be noted that the symptoms to each level of CO in the air is for a typical, healthy adult. Certain population groups, such as unborn babies, infants, children, the elderly or people with respiratory diseases may be more susceptible to low levels of carbon monoxide; 30 ppm and higher.


The above is from the CLBM Foundation.​


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## flashheatingand (May 3, 2008)

Could somebody use one of those infra-red thermal devices to see if the system may be leaking someplace mid-stream? Is one appliance power draft, and the other nat. draft? How frequently does the boiler cycle? Just have seen some holes in vent pipe before, and that acid from the nat gas can be corrosive.


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## pappagor (Jan 29, 2008)

what did you find out and did you get it fixed update


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## MTN REMODEL LLC (Sep 3, 2010)

UPDATE: EVERYONE.... Thanks for your input:thumbsup::thumbsup::thumbsup:

As you may remember, after X-mas Jim had all the original crawl space venting opened, but still had the CO tripping.

He subseqently had the furnace installer 1) turn down the new 95 2-stage furnace blower speeds (which a tech had previously told him were already on low speed!!) 2) rebuilt the boiler to wh venting and sealed (don't know in what manner yet 3) apparently found another leak to seal in the cold air return.

To date.... NO CO

Unfortunately, we can't quite be sure of exactly the cause. 

Sounds to me that basically we had a very weak draw up the boiler/wh vent,(especially in the morning when the flue was cold) and the new 95 furnace did place just enough negative presurization (thru return air duckts and minor draw leakage) to trip the CO.




FRIEND/JIM writes:


Hi Peter,
Hope you guys are better soon!
Can't remember if I told you what Walrath did when they were out on Monday the 30th - turned down the fan speed (both high and low settings), re-did the venting from the WH to the boiler, sealed one remaining leak in the return register and put mastic on the joints on the boiler flue.
So far, knock on wood, we have not had any alarm go off or even any reading show.
Am hoping we are aok.
Still seem to feel that Walrath is somewhat to blame - no problem before new furnace, bunch of info out there that states that installing new high efficient furnace can have a depressurizing effect in the CAZ, additional combustion air (after opening crawl space vents) was not necessary, etc.
Still have not received any bills from either company.
Will keep you posted should problem re-occur.
Thanks again for your input and for asking for help from your contractor site!
Jim


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## beenthere (Mar 5, 2009)

Thanks for the update.


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## MTN REMODEL LLC (Sep 3, 2010)

MTN REMODEL LLC said:


> UPDATE: EVERYONE.... Thanks for your input:thumbsup::thumbsup::thumbsup:
> 
> As you may remember, after X-mas Jim had all the original crawl space venting opened, but still had the CO tripping.
> 
> ...


Just additional update FYI

From Friend/Jim

Hi Peter,

Should have mentioned more detail on the change in the WH flue.

Walrath was able to somewhat increase the height of the rise from the top of the WH to the position of the 90 degree turn for the run over to the boiler. Tech also noted that the old elbow was severely crimped and actually was smaller than 3" at that point.

After all the changes were made, there was zero spillage from the WH.

Jim



I have no idea why the two HVAC companies (G3 and Walreath) did not notice this earlier?

Thanks for the help


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## flashheatingand (May 3, 2008)

Not that the gas line had anything to do with this,but, leaking gas can cause monoxi poisoning as well.


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## tjbnwi (Feb 24, 2009)

flashheatingand said:


> Not that the gas line had anything to do with this,but, leaking gas can cause monoxi poisoning as well.



How? 

Natural gas is odorless and colorless. It is 95% methanine, the balance is Ethane, Propane, Butane and Pentans, all hydrocarbons (there are also traces of water and carbon dioxide). 

Tom


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## flashheatingand (May 3, 2008)

The will eat jp the oxygen. Back during the gas light days many people died of carbon monoxide poisoning due to gas leaks


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