Furnace Problem Observation - Page 2

Eastham · 01-23-2020, 05:43 AM

I used the same screen on the fridge .last summer the fridge would not get to the cold blue section on the thermometer. I Removed the screens to see if it helped and the next day it was in the blue section and a lot colder.it made a believer out of me.I still have one on the furnace when it is stored.Also the fridge screen was like new and not clogged up at all.

**flybouy** · 01-23-2020, 06:16 AM

If you do some simple math you can calculate the the area of restricted airflow, i.,e. take the diameter of the wire used in the screen X the length of the vertical + horizontal wires X the number of wires = the area. Then take total area of the vent divided by the area of the wire to get the % of blockage per tube.

Given the relative small area of the intake and exhaust I think the % blocked would be eye opening.

Brentw · 01-23-2020, 07:50 AM

And here's another note on how little restriction it takes to affect them. I installed a 45 degree deflector plate on the exhaust port, that was enough to keep tripping the furnace. They definitely do not tolerate much restriction.

travelin texans · 01-23-2020, 08:47 AM

I've had 3 5th wheels since '05 all with screens on the furnace intake/exhaust, fridge vents & put fine screen on the Suburban water heater vent as well, never an issue with any of them, without I'm positive that mud daubers &/or wasp would've been a much bigger problem.

sonofcy · 01-30-2020, 11:41 AM

Quote:

Originally Posted by sourdough

It is wintertime and from time to time there are different posts about various problems with furnaces. Sometimes they are pretty clear cut; I've replaced fans, control boards etc. But something a little sneaky happened to me last night that might be valuable to tuck away if one isn't aware.

A year or so ago I put the little mesh "bug screens" over my hot water heater and the exhaust on the furnace. Never had a bug get in either but thought I would be proactive. Last winter the furnace sort of acted weird but continued to heat and function. Last night got pretty cold for here (about 31) and the furnace was running quite a bit, until I woke up about 3am freezing. Wondering what was going on I listened for the furnace; the fan was running but the burner would only kick on for a few seconds then go back off. The air would not get warm. It did not cycle off, just kept firing up, burner run for a few seconds then stop. Turned off the thermostat thinking that would be the issue (replaced 4 times at the moment) but didn't fix it. Turned on the fireplace and a little heater and went to sleep figuring I would look at it today.

This morning turned on the thermostat and it fired up, kept blowing, got hot and heated the room. On the 2nd attempt to fire up and run it did the same thing it did during the night. Fan comes on, burner kicks in full blast, runs a few seconds and shuts down. Thinking through it I figured it was the limiting switch so opened up everything dreading tearing that thing apart...and then, a thought (somewhat rare these days)!! Limit switch faulty? Limit switch "activated"? It wants input, output and through put. Now you know where I'm going.

Out of curiosity I went outside and removed the mesh screen from the heater exhaust cover. A fairly fine mesh thinking it might be causing the heat to back up running as much as it was. Ran all day today and all evening without a hiccup so figure that was it. I'll know 100% in the morning but as consistently as it was failing I'm 99% sure. Just wanted to throw that out in case someone might fall into a similar predicament. Looks like it saved me tearing that furnace apart and I'm all about that.

Highly unlikely that extremely coarse mesh is the issue. I had similar symptoms and had to replace the board months ago to fix it. A dinosaur board is MUCH more reliable than the factory boards.

**sourdough** · 01-30-2020, 12:11 PM

As of today it hasn't faltered once since removal of the screen. I've already replaced the board on it.

sonofcy · 01-30-2020, 12:43 PM

Quote:

Originally Posted by sourdough

As of today it hasn't faltered once since removal of the screen. I've already replaced the board on it.

Maybe the fact that it's a 35k model has something to do with it. Is the exhaust opening any bigger than the usual 20 something k furnace?

**sourdough** · 01-30-2020, 12:52 PM

I'm not sure about the size difference in openings but I'm pretty sure it being 35k has a bearing on it.

pdaniel · 02-01-2020, 11:06 AM

The owner’s manual for my furnace, a Suburban, states to not place bug screens on the exhaust and inlet of my furnace and the Suburban water heater manual states the same.
Some people ask me how I get rid of the nests in my furnace-fire up the furnace and watch it cook.

**chuckster57** · 02-01-2020, 11:47 AM

Quote:

Originally Posted by pdaniel

The owner’s manual for my furnace, a Suburban, states to not place bug screens on the exhaust and inlet of my furnace and the Suburban water heater manual states the same.

Some people ask me how I get rid of the nests in my furnace-fire up the furnace and watch it cook.

That works if you catch the nest in time. Typically, mud dawbers go as far into the combustion chamber as possible and since the burner is a nice flat piece it makes an excellent base to start piling the mud. Once there is enough, the furnace will not light.

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