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Old 11-15-2011, 03:37 PM   #16
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Combustion Air Intake


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For the benefit of other readers the furnace has a pressure switch and intake screen to protect it and you from blockage. Cheap builders s**k.
Very good point yuri.....so if that "screen" is lets say just part blocked.....then what happens.........? what happens is the furnace is starved for combustion air, it runs rich, and soots up the primary, and secondary heat exchanger, fouls the drains and the exaust pipe, and ruins a perfectly good furnace due to it being run improperly and against what the manufacture had intended............and all of this because a builders sub was to cheap to put in a few feeet of low cost pvc pipe. Have I made my point ?

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Old 11-15-2011, 03:43 PM   #17
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Combustion Air Intake


Combustion 101:

The pressure switch proves the CORRECT amount of draft=air for combustion=proper combustion. Plus it has a safety margin. The only variable is the gas pressure and whether the burners are dirty. If it is overfired then it can soot up and overheat. As long as the pressure switch closes and is not faulty then it is safe to use even with a half blocked pipe. Happens all the time here with snow and hoar frost etc.

To get even more technical they use a differential pressure switch and measurement across the heat exchanger in high efficiency furnaces. The heat exchanger essentially works as an orifice and flow can be measured across an orifice. Bernoulli's principle etc.
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Old 11-15-2011, 03:45 PM   #18
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Combustion Air Intake


A bit off topic but I am expecting someone to come in to my home tomorrow to install a 4" PVC fresh air intake to my boiler room due to an occurrence of backdraft that shut my boiler down on me.

Should I be rightly concerned about this big 4 inch hole straight from the outside to the floor of my finished basement? It can get quite cold here, like -30C cold... I've been so busy and all over the place that I neglected to ask the technician for details about what exactly they were going to do but I can only assume that since they are completely certified to do this stuff that it will be done in the right way and the "right" way certainly can't end up making your home freezing cold can it?
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Old 11-15-2011, 03:50 PM   #19
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Combustion Air Intake


I take it your are in Canada eh? You should check with the gas co if they are sizing it properly as it needs to be looked up in the code book and depends on whether the boiler is natural draft or power vented. Should get it inspected by them for liability reasons and to make sure they did it properly. The minimum I use is 5 inch and a lot of 6 inch or larger depending on the BTUs of the boiler. 4 inch is probably good for up to 100,000 BTUs if it is natural draft. We use an insulated flex pipe and goose neck it like a sink drain and run it to the floor level near the burner. The goose neck part is at floor level and prevents cold air rushing in. When there is a negative pressure it will rush in. Still will get cold in that area but not as bad as without one. If the PVC is not insulated it will sweat all over the place and drip. That is why we use insulated flex pipe.

There is a much better system called a Hoyme motorized damper (Google it, made in Canada) which interlocks with the boiler and only opens when the boiler is on. You may want to put the job on hold and investigate one of them.

http://www.hoyme.com/
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Last edited by yuri; 11-15-2011 at 04:01 PM.
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Old 11-15-2011, 03:58 PM   #20
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I take it your are in Canada eh? Where are you and how many BTU's is the boiler? You can check with the gas co if they are sizing it properly as it needs to be looked up in the code book and depends on whether the boiler is natural draft or power vented. The minimum I use is 5 inch and a lot of 6 inch or larger depending on the BTUs of the boiler. 4 inch is probably good for up to 100,000 BTUs if it is natural draft. We use an insulated flex pipe and goose neck it like a sink drain and run it to the floor level near the burner. The goose neck part is at floor level and prevents cold air rushing in. When there is a negative pressure it will rush in. Still will get cold in that area but not as bad as without one.
It's a mid efficiency (85%?) natural draft slantfin galaxy, it says it has an output of 80,000 btu but now I'm concerned since I may eventually build an addition onto the house (though not a huge one) in the future and who knows, the size of the boiler my increase, I may go higher efficiency... yadda yadda. Should I have asked them to upsize the intake?

Thing is, the backdraft sensor has only tripped once in the 2 months or so we've been here during an extended bout of cooking with the exhaust fan going for hours so it's not like it's totally starved for air as it is.

That hoyme damper thing is all over the internet but somehow I doubt they are planning on putting any kind of interlock damper on this thing when they come and it's going to end up in a bucket which doesn't seem to work at all from what I'm reading. I'm starting to freak out that I'm going to be spending all this money and get a cold basement in return.
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Old 11-15-2011, 04:04 PM   #21
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Combustion Air Intake


Reread my post I added some important info to it.

The Hoyme is the BEST way to go. The other system is bush league and TOTALLY in-efficient. You will end up with a cold floor. Some contractors are too lazy or dumb to know how to install a Hoyme so you may want to shop around for one. Lots of them will just blow you off so you need to do the research or regret it later.

Most cases of CO poisioning are from spillage/backdrafting and poor combustion from a lack of oxygen. You may have had this case for a longer time than you know. Should have 2 new accurate non cheap CO detectors in the house too.
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Last edited by yuri; 11-15-2011 at 04:07 PM.
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Old 11-15-2011, 05:01 PM   #22
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Reread my post I added some important info to it.

The Hoyme is the BEST way to go. The other system is bush league and TOTALLY in-efficient. You will end up with a cold floor. Some contractors are too lazy or dumb to know how to install a Hoyme so you may want to shop around for one. Lots of them will just blow you off so you need to do the research or regret it later.

Most cases of CO poisioning are from spillage/backdrafting and poor combustion from a lack of oxygen. You may have had this case for a longer time than you know. Should have 2 new accurate non cheap CO detectors in the house too.
Yeah, when I moved in the previous owner had CO detectors throughout the house but shockingly all of them were expired and their solution to their constant beeping due to that was to just remove the batteries from all of them. I have since installed new not-inexpensive ones on every floor, and I haven't had any alarms.

They also had a Y fitting on the boiler flue going into the chimney cavity where one side was not connected to anything (probably connected to previous hot water tank which at some point was replaced with a direct vent model) and it was left completely uncapped so it must have been spewing CO from the boiler all over the basement. First thing I did when I moved in was cap that, but holy how stupid is that?

I guess at the end of the day it's better to have a cold floor in the basement than to die of CO poisoning... but in your experience, will the cold air coming into the boiler room really travel outside of it? I assume when it's cold enough outside for the cold air to be a big bother the boiler will be firing quite often and sucking the cold air back out. Perhaps just putting a rubber weather strip at the bottom of the door to the boiler room will mitigate the cold air from going all over the living area of the basement?
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Old 11-15-2011, 05:33 PM   #23
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I had a house in Calgary with a mid eff furnace and that gooseneck system and I hated the way air flowed in in the off cycle. Worse on windy days. Houses have a natural convection current to them and 2 stories are worse. Hot air rises and cold settles so there was air coming from that pipe 90% of the time. If you seal the room then the floor above the boiler gets cold along with everything in the room. Not so bad if you are in Southern BC or Ontario but when it gets below -10C I would want a Hoyme. They are INCREDIBLY well built and reliable and have been around for 20 yrs or more. They power closed and fail open so you will always have heat and have an end switch to prove it is open and then fire the boiler. If you plan to get a sealed combustion over 90% eff boiler in the future and the water htr is sealed then the bucket, gooseneck pipe works and is cheaper.
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Old 11-15-2011, 07:31 PM   #24
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I had a house in Calgary with a mid eff furnace and that gooseneck system and I hated the way air flowed in in the off cycle. Worse on windy days. Houses have a natural convection current to them and 2 stories are worse. Hot air rises and cold settles so there was air coming from that pipe 90% of the time. If you seal the room then the floor above the boiler gets cold along with everything in the room. Not so bad if you are in Southern BC or Ontario but when it gets below -10C I would want a Hoyme. They are INCREDIBLY well built and reliable and have been around for 20 yrs or more. They power closed and fail open so you will always have heat and have an end switch to prove it is open and then fire the boiler. If you plan to get a sealed combustion over 90% eff boiler in the future and the water htr is sealed then the bucket, gooseneck pipe works and is cheaper.
I'm in Toronto, closeish to the lake, so while there are times it does get pretty bitter overall it's not too bad compared to some other places in Canada. Still, I actually work out of my home office in the basement and we have our home theatre and do a lot of our living down here so I'm definitely going to ask 1001 questions about this install before they do anything. I would have assumed some kind of damper would have been standard fare until I started looking this up more.
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Old 11-15-2011, 07:49 PM   #25
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Plus you don't want hot humid air migrating in there thru an open pipe in the Summer and you have lots of that if you are close to the Lakes. We sell a LOT of them on fresh air pipes with our new furnaces for that reason. They are expensive and less than 10% of the guys know how to wire them up properly so you may get some resistance. Not difficult if they follow the instructions but a lot of guys can't be bothered to take an active interest in their trade (a whole other story).
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Old 11-16-2011, 06:32 AM   #26
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Plus you don't want hot humid air migrating in there thru an open pipe in the Summer and you have lots of that if you are close to the Lakes. We sell a LOT of them on fresh air pipes with our new furnaces for that reason. They are expensive and less than 10% of the guys know how to wire them up properly so you may get some resistance. Not difficult if they follow the instructions but a lot of guys can't be bothered to take an active interest in their trade (a whole other story).
I don't understand why the wiring would be confusing. Can't you just take power at the boiler, and then wire the interlock directly to the same pins that the thermostat leads to? What is it, 5 wires in total?

I don't see why anybody who has replaced a light fixture or power switch wouldn't be able to do it themselves or am I missing something tricky?
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Old 11-16-2011, 12:28 PM   #27
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What they ended up installing is insulated flex pipe across the room and along the ceiling and then down again near the boiler with a big loop upwards at the bottom. The guy assured me that while some cold air will come out of it all the time that it won't be much and it won't affect the comfort of my basement... I guess time will tell. I guess the original tech was mistaken when he was talking about PVC to me. It's kind of mild today, 10C, and I can feel a little bit of draft from it but not a lot and it doesn't seem to draft any more than the power vent for the hot water tank does.
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Old 11-22-2011, 09:36 AM   #28
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So after all of the work done installing the air intake that was promised to me would eliminate the boiler from shutting down due to the spill switch, it happened again last night. The boiler will work fine for weeks (I think it had been a week before they installed the intake and a week since) where there were no occurrences of the spill switch tripping but now even after post intake install to my boiler room I found myself with no heat again and pressing the reset button.

So it seems to me that my boiler was getting enough air just fine before and they have basically done nothing other than cost me money and adding a new hole to my home. I left them a message of complaint and I'm waiting to hear back from them now but I'll be damned if I'm going to pay them to come back and figure out what is really going on here instead of just guessing and charging me for it. I did have their techs back on two separate occasions before the installation one for the original diagnosis that resulted in the recommendation for the intake and a second time for the annual boiler inspection and tuneup and neither time were any other problems noted.

Is it possible that the spill switch is simply just going south and popping open for no reason at all? I don't see how it can operate just fine for such long stretches if there is something else wrong like a blockage. There is an interlocked damper on the flue and I suppose that it could be closing early or not opening properly sometimes but there must be some kind of interlock on the position of the damper as well to prevent that situation.

I have a CO sensor right next to the boiler room that records peak CO levels detected in memory and it has never registered anything above 0 according to its record and I haven't had any alarms on any level of the house.

Any advice on how to handle the HVAC company on this? In my mind I have spent hundreds of dollars on something unnecessary and I kind of expect them to come back and rediagnose and solve the real problem at no cost of it is less than what I paid for the intake installation because honestly unless I really needed that intake I didn't really want it in the first place and was just going on the insistence of their technician that I needed it.

Last edited by chiefswabjockey; 11-22-2011 at 09:38 AM.
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Old 11-22-2011, 10:40 AM   #29
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Combustion Air Intake


Do you have any thing in the house that may cause occassional depressurization when the boiler may come on such as a jennair range, large range hood, big exhaust fan, additional chimney system like a fireplace, wood stove, etc.
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Old 11-22-2011, 10:42 AM   #30
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Do you have any thing in the house that may cause occassional depressurization when the boiler may come on such as a jennair range, large range hood, big exhaust fan, additional chimney system like a fireplace, wood stove, etc.
Sure, every house has some of these items these days but this house is nearly 80 years old and with the fresh air intake installed right next to the boiler I thought that would take negative pressure out of the equation. I should be able to have commercial blowers shooting out of the house without negative pressure developing at the flue now which leads me to believe it has to be something else entirely.

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