Home heating issues - poor airflow

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Quattro Pete

Quattro Pete

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Oct 30, 2002
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The place we are renting has gas forced air heat. For the past few days, I feel like the amount of air being blown out of the vents/registers isn't anywhere close to what it used to be. Very weak. The system still maintains my desired 70F temperature in the house, but it seems like it needs to run longer to achieve it.

Maintenance guy came over, looked over the furnace, and concluded that it's working fine. He said it's the extreme cold that we've been having that may be responsible for what I'm seeing. Somehow, I am not convinced.

What could cause greatly diminished airflow? My guess is something happened to the ducting. Maybe it cracked or split open somewhere because of this cold weather, causing hot air to escape into the atmosphere instead of reaching the vents? What's the likelihood of this? If not, what else could it be?

Thanks!
 
How's the filter? A filter that hasn't been changed would restrict airflow. Also it's true, the colder it is, the more btu's it takes to maintain the current temperature. Basically it's the difference between the outside air and inside. It takes a lot more energy to maintain a differential of -20 outside and 70 degrees inside. That's a 90 degree swing and a lot more btus. If it were just 30 and you had it set at 70, then that's just a 40 degree swing.

Also how are the gaps in the bottom of the door? If it's too low and the doors are closed, it's a lot harder to get air to flow. Sorta like a straw, If you block the straw, it's a lot harder to blow through it than when it's open.
 
Originally Posted by Wolf359
How's the filter? A filter that hasn't been changed would restrict airflow.

Good call on the filter. Even though the filter is only about 30 days old and looks clean, it must have been restricting the flow too much. When I took it out, the airflow improved greatly.

Thanks!
 
Depending on the Merv rating on the filter it could look clean but be plugged up enough to restrict air-flow. Try a Merv 8 filter, or a filter that looks like this. These offer the worst filtration but best air-flow:
[Linked Image]




Also if the duct work has dampers in them to balance air-flow and stop air flow and these are loose they could be swinging shut with air flow.

[Linked Image]
 
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We're you using one of those "micro filters" that filter dust and such? If so, those will cause your exact issue even before they get a layer of dust on them.
 
If the filter was not catching the lint, dirt, etc, and there is an air conditioning coil, the AC coil may be restricting the air flow. I once had to clean an AC coil due to the mat of dog hair covering the coil face. House had three german shepherds and the home owner installed a filter that did not fit properly - too small. The hair mat on the AC coil inlet looked like a fur coat ~ 1/2" thick.
 
Originally Posted by StevieC
Try a Merve 8 filter,

Merv8 is what I had in there. I have been using these filters for years and changing them every 90 days, and never had an issue in the past. This is the first time that I noticed such a huge airflow restriction.

Looks like I'm going to have to start using something less restrictive.
 
Check the blower wheel for dirt. If filter maintenance has been lax, dirt can build up in the vanes of the blower wheel, greatly reducing its efficiency.
 
Does the filter look dirty? A perfectly good filter (with high filtration) is going to reduce airflow, and really you shouldn't have enough airflow restriction to notice at 30 days unless you're never vacuuming and always leaving the fan blowing so it has become the whole premises air filtration system in addition to a heater.

Some other things that can reduce flow include a worn out blower motor (bearing shot), or whether the filter was dirty or not (but especially so if it is), gunk buildup on the blower motor squirrel cage, or in very humid environments, if the squirrel cage is metal it may have drastically rusted by now. If it is rusted but not too severely, you can de-rust and prime and paint it, but at this time of year, you might want to just clean it off quick and keep it in service till warmer weather, since you also want warmer weather and fume ventilation for decent long lasting paint. I've used Rustoleum primer and gloss enamel spray.

If there's an A-coil in the stack because it has central A/C too, that might need gunk cleaned out, again at a more frequent interval the faster your filters are getting dirty. If it has not been cleaned recently and your filters are getting clogged at 30 days, you almost certainly need to clean the coil, and probably the blower motor squirrel cage too. If you have the blower motor out to clean the squirrel cage, if you can find a way to service it by oiling the bearings (usually a well with felt in it) that can greatly extend the life of the blower.

In recent decades many blower motor designs are supposedly "maintenance free" with no bearing lube ports but all that really means is they took away the easy way to lube them so they last a fraction as long if you don't lube them, and may need some extent of motor disassembly to lube. Isn't a throwaway society great?

The same is probably true for your exhaust blower motor, that a few minutes and a few cents worth of oil can save hundreds of dollars in the long run. They are at the age where they would benefit from this, before rather than after the bearings start making noise because they're wearing out from lack of lubrication. Considering this is BITOG, there may be much debate about the perfect oil for this application but I've had great results for decades using plain old 5w30 (both synthetic and dino) motor oil. 0W-20 synthetic should work at least as well.
 
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Buy a $10 USB borescope on Amazon (like 15 or 20ft length) and snake it through the vents. Couldn't be easier nowadays with cheap tech!
 
Originally Posted by Dave9
Does the filter look dirty?

Upon further inspection, it does look dirty and plugged up, but very different from how it looked in the past. Normally, I see it turn dark grey over time. This time, it seems to be covered with some white very fine powdery substance. I really have no idea where this came from and what it is, but I think it completely plugged it up.
 
Regarding a borescope, It's very unlikely to be the ducts themselves unless there is some critter in there that has built a nest, but in some tight installation areas it can be difficult to get the stack apart to inspect the A-coil and a borescope can save a lot of time doing that if it turns out to not need cleaning yet.

White powdery that is there now but wasn't before is either dust or mold. The latter can be a serious issue and I'd check the home humidity level at least and a mold test wouldn't hurt either.
 
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How about the house itself? One or two story? Insulation? Air leaks?

It's possible the extreme temperatures are testing your heating environment. It takes a well maintained furnace and a well insulated house together to keep things habitable.

Fireplace? Check your damper.
 
Originally Posted by Quattro Pete
Originally Posted by Dave9
Does the filter look dirty?

Upon further inspection, it does look dirty and plugged up, but very different from how it looked in the past. Normally, I see it turn dark grey over time. This time, it seems to be covered with some white very fine powdery substance. I really have no idea where this came from and what it is, but I think it completely plugged it up.






Sheet rock dust?
 
Originally Posted by Quattro Pete
Originally Posted by Wolf359
How's the filter? A filter that hasn't been changed would restrict airflow.

Good call on the filter. Even though the filter is only about 30 days old and looks clean, it must have been restricting the flow too much. When I took it out, the airflow improved greatly.

Thanks!

Glad you caught it. I once sold a house where the owner didn't know about the filter. They owned it for about 5 years and it was completely black, I was surprised their system even worked.
 
Originally Posted by Quattro Pete
Originally Posted by Dave9
Does the filter look dirty?

Upon further inspection, it does look dirty and plugged up, but very different from how it looked in the past. Normally, I see it turn dark grey over time. This time, it seems to be covered with some white very fine powdery substance. I really have no idea where this came from and what it is, but I think it completely plugged it up.


I'm using Merv 11 (lung problems) and I have enough flow out of the vent in the washroom that it blows the hanging toilet paper end, up the wall when the fan is running and the vent is about 3 diagonal feet away from the toilet paper roll holder just as a comparison for flow. Not scientific measurement but I don't have an an air-flow meter.
grin2.gif
 
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