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Protecting 95% furnace exhaust in winter

2K views 18 replies 9 participants last post by  ktownskier 
#1 ·
Had a heck of a time trying to log back on here,after a long time away! Anyway,I just had a new 95% efficient furnace installed. My brother warns me that the inlet or exhaust needs to be extended,or it will freeze up in the winter!
Then my sister says,she had to break ice off of hers last year[she lives near Madison Wi.when she had no heat.
Can I do something to prevent a freeze-up,or do I just have to inspect it when the weather gets rough?
[I'm in north central Illinois]
 
#7 ·
Neither did I in several houses until I had to relocate my vents in our current place. It's near an inside corner on the lee side from the prevailing wind so on a still night the exhaust would just hang around in a cloud. Normally, there is probably enough air movement to prevent it.
The first couple of times it happened it was always overnight, so I got to wake up to a cold house and run outside and into the garden to clean out the intake. Fun.
 
#5 ·
The longer the exhaust outside in the cold, the cooler the gases will be and more likely to freeze in the off cycle and may not thaw on the next cycle. When it terminates closer to the wall, the gases remain a bit warmer and keep from freezing.

I get long icicles on mine during cold spells. (-20 to -15 *C daytime highs.) As it warms up, they fall off. You do want to keep some distance above the snow line.

Cheers!
 
#6 ·
The icicle on the exhaust is not a problem and the Lennox Pulse units all had them.

You knock it off once a month.

The intake is the problem and you need to keep it clear of snow and recirculating exhaust gases.
 
#12 ·
The biggest problem I have with our 95% condensing furnace is the condensate drain freezing. Water backs up in the pipe until it gets back up to the furnace and then the system switches itself off.

Keep an eye on the drain where it exits the house and if you get an icicle forming there, you're about to have a problem!
 
#16 ·
With a new furnace installation the question becomes do you have a naturally drafted gas water heater that was sharing the same exhaust flue? If yes, did they install a smaller chimney lining for that appliance? More details if you now have what is called an orphaned water heater. If not, enjoy the new furnace and be safe.

Through one form or another we seem to have at least one CO tragedy every year here in Maine.

Bud
 
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#3 ·
Like Yuri says, if the exhaust and intake are close together and at the same rough level, the moisture in the exhaust can get picked up by the intake and freeze unless there is a good cross-breeze to carry it away. If they are both 90* elbow down or straight out, I suggest snorkeling the exhaust up about a foot (90* elbow up>straight section>90* elbow out.
Also, check to see if the intake has a screen in it. Some have a moulded grid in the plastic fitting, others just a piece of stiff steel screening. Take it out. If you're worried about critters, take it out after the first frost and put it back in the spring.


Looking at your handle - do we own an Ultra?
 
#19 ·
This doesn't just apply to 95% effecient furnaces, it applies to any device that uses sealed combustion. Like my 82% tankless water heaters. Or 80%+ furnaces.

Before I replaced my 80% effecient furnace with my 95% one, They had run the 3" PVC pipes a pretty long way. About 30'. Which was within tolerances. My Mom was living in the house at the time and it was a very cold winter.

Since I am the youngest, I was the one she called to come and fix things. So when she called saying it was cold in the house, I came over and checked. The exhaust had dripped down and iced mostly over the intake. The installers had put the exhaust on two 90* so that it went up then out and the intake on a 45* point down. In the same plane so when the moisture from the exhaust came out and condensed in the bitter cold it froze on the exhaust and kept building up and eventually built up so that it came over the inlet and started cutting of the intake air.

I broke the ice off and power cycled the furnace. (OK, I turned it off when I started looking for problems and then turned it back on when I cleared the ice)

Checked to make sure the burner came on and that there were no more errors and changed the filter and told Mom that it should be better now.

When it warmed up a bit, I came back and changed the PVC ends so that they didn't align anymore.
 
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