Cold weather furnace problem - Canadian TV, Computing and Home Theatre Forums
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post #1 of 19 (permalink) Old 2018-01-02, 04:12 PM Thread Starter
 
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Cold weather furnace problem

On New Year's morning our gas furnace wasn't working (13-year-old high efficiency Rheem). Checked the usual suspects, no snow around the vents. It would start, run the pre-purge cycle, then no flame and shut down. When I had the covers off and held the cover switch, it actually started, but would not keep running after I replaced the covers. Since I have a Reliance service contract I called and a tech was promised for the next day. So we used the woodstove and fireplace. Near the end of the day, on a whim, we checked inside the intake pipe and found crusty snow. After poking it out, the furnace started and ran. When the service tech called today before arriving I explained what happened, but he should look at it anyway, since it hadn't been serviced in 6 years. He cleaned out the intake with a brush, checked the furnace over and cleaned the flame sense rod. He also told me if the intake has ice and snow in it, the furnace will run with a cover off using inside air. Good to know. Apparently this can happen in cold blustery weather.
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post #2 of 19 (permalink) Old 2018-01-02, 05:12 PM
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so the problem was the intake pipe was blocked somehow with ice causing the furnace to not combust but when you took off the cover it combusts with the inside air, sounds to me its not a manufacturers defect but a result of mother nature wreaking havoc on our homes

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post #3 of 19 (permalink) Old 2018-01-02, 05:21 PM Thread Starter
 
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Yes, Mother Nature. First time it happened in 13 winters. Freaky cold blustery weather, snow gets sucked into intake pipe as furnace is shutting down, then crystallizes. The intake and exhaust for this furnace is nor a fancy manufactured one, but something the installer fabricated from PCV pipe.
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post #4 of 19 (permalink) Old 2018-01-04, 11:31 AM
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I've seen some type of grilles that go over the intake/exhaust pipe to prevent things like birds and critters from going inside, but I am not sure if they will help prevent ice buildup. I would have to do more research first but ya it wold be interesting

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post #5 of 19 (permalink) Old 2018-01-04, 11:58 AM
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Most of the installer fabricated intakes and exhausts I see don't meet code or, sometimes, even common sense. The code is very specific regarding spacing of intakes, exhausts, possible snow levels and other objects such as windows. I've seen intakes and exhausts that were less than 2" apart, allowing exhaust moisture to be drawn into intakes and freeze. I've also seen exhausts and intakes about a foot off the ground in places where snowfalls can reach 3', not including snow drifts.
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post #6 of 19 (permalink) Old 2018-01-04, 01:32 PM Thread Starter
 
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Here is a picture of my intake and exhaust, fabricated by the installer 13 years ago,



The intake is the closest and the exhaust is the one with the icicles. I painted the white piping with primer to blend better with the brickwork. After the installation I did check the venting layout and dimensions against code and it conformed. But I can see an east wind blowing the exhaust towards the intake.

As for some kind of grille at the intake, that may be a starting place for ice accumulation.
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post #7 of 19 (permalink) Old 2018-01-14, 07:54 PM
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Minimum code is to have both intake and exhaust terminate 12" above grade..

Those don't look to be at 12" above

The other thing to look as is the separation between the two pipes. Your installation manual will shoe examples of what is allowed.. The picture u posted is not typical of most installations.. Rheem may all this.. But typically the exhaust will be 12" above the intake.. The prevent recirculation wich will frost up an air intake



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post #8 of 19 (permalink) Old 2018-01-14, 09:15 PM Thread Starter
 
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Bad angle in picture, but definitely 12" above grade. When it was installed I was expecting some fancy combined intake/exhaust, which is why I checked it against the installation instructions and it's to code.
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post #9 of 19 (permalink) Old 2018-01-14, 09:25 PM
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Perfect

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post #10 of 19 (permalink) Old 2018-01-15, 03:26 PM
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Minimum code is to have both intake and exhaust terminate 12" above grade.
The version I read said 12" above the maximum expected snowfall for the location. For much of Ontario that would be 24" above grade. We occasionally have 36" snowfalls here so that would be 48"
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post #11 of 19 (permalink) Old 2018-01-15, 03:39 PM
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B149.1-15
8.14.8. F
A vent shall not terminate less than 1ft above grade level.

Installation manuals may recommend or require more.

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post #12 of 19 (permalink) Old 2018-01-15, 03:44 PM
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What about the intake? I've got to wonder how many vents and intakes 1' off the ground get blocked by snow.
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post #13 of 19 (permalink) Old 2018-01-15, 07:19 PM
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12" for intake..

Typically if close to grade you will see intake at 12" exhaust at 24" but each manufacturer has its own requirements..

Depending on the manufacturer the separation between the intake and exhaust will vary. But the constant is 12" above grade for both minimum..

The whole anticipated snow level is a number that is not constant or in writing within the code or installation manual. So it's hard to enforce.. Its rare installers aim to be exactly at 12" logic and good workmanship normally prevail

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post #14 of 19 (permalink) Old 2018-01-15, 07:55 PM Thread Starter
 
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Originally Posted by ExDilbert View Post
What about the intake? I've got to wonder how many vents and intakes 1' off the ground get blocked by snow.
The constant warm exhaust keeps the snow down. In my case it's sheltered too and drifts don't build up.
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post #15 of 19 (permalink) Old 2018-01-15, 10:43 PM
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But the intake does not emit warm air. There are people who shovel snow against walls where intakes are present. I've seen people pile snow up against a wall with a direct vent intake and exhaust that was just over 12" off the ground (I'm pretty sure that is against code.) Then there are people with snow blowers and plows that put snow in stupid places. 12" off the ground just seems too low for a furnace intake or exhaust in Canada. It's not a good idea to count too much on common sense from installers either. That's why regulations and inspectors exist in the first place.
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