Any furnace concerns in extreme cold?

[copyright1997reloaded]

I live in the North East "upstate" where cold weather in winter is the norm. I have an oil burner, and I typically have the house at 58 degrees. I also have a wood stove (insert) which I use to partially heat the house (it isn't enough to keep a 2800+ sq. foot house warm if the temperatures are lower than 25 degrees or so outside).

When the weather is a bit warmer (e.g. 32 or higher), I don't worry so much about things as northing can freeze. But in colder spells and especially if there is some wind involved I will actually raise the central heat (oil) thermostats a bit (e.g. to 62) to prevent any issues involving the edges of the house furthest away from the wood stove. I also have iot tempature sensors in various places to provide a warning if things are getting too cold.

 

[SecondCor521]

of course our annual PM can't prevent all mechanical failures but a yearly inspection can detect issues that may develop into large problems. we were fortunate that one annual PM revealed a leak in the heat exchanger which if undiscovered could have resulted in a significant CO leak. that led to our replacing the furnace.

Cracked heat exchanger scam maybe?

https://johncipollone.com/cracked-heat-exchanger-scam-havertown-pa

 

[Music Lover]

I live on the cold Canadian prairies and have never worried about a furnace overworking in 40 years. I even leave the furnace fan running 24/7 to circulate air and don't give it a second thought.

 

[jazz4cash]

Modern furnaces are engineered to use MERV filters.

What does that mean? What do you consider modern? AFAIK the Minimum Efficiency Reporting Value measures the particle size the filter will capture effectively. If you have problems like excessive dust, smoke, allergies, etc a higher MERV may be helpful but trapping smaller particles means the filter will not last as long. I don’t think this has any impact on the furnace machinery…there are no tiny passages that will plug up with dirt in the furnace. It’s not like a car engine with tight tolerances. The problem if the filter gets plugged is lack of airflow which is uncomfortable in the winter and possibly damaging in AC mode.

 

[Sunset]

What does that mean? What do you consider modern? AFAIK the Minimum Efficiency Reporting Value measures the particle size the filter will capture effectively. If you have problems like excessive dust, smoke, allergies, etc a higher MERV may be helpful but trapping smaller particles means the filter will not last as long. I don’t think this has any impact on the furnace machinery…there are no tiny passages that will plug up with dirt in the furnace. It’s not like a car engine with tight tolerances. The problem if the filter gets plugged is lack of airflow which is uncomfortable in the winter and possibly damaging in AC mode.

I'm no expert.

• I have read and think it makes sense that a plugged up filter will reduce airflow and cause the furnace fan to run more/harder to compensate as the heat is not being raised in the house.
• It could also possibly cause the furnace to overheat and then shutdown temporarily as a lack of airflow will mean no heat is drawn away.

I'd sure like to know if it's true, or there is no concern for even totally plugging up the furnace filter

 

[freedomatlast]

of course our annual PM can't prevent all mechanical failures but a yearly inspection can detect issues that may develop into large problems. we were fortunate that one annual PM revealed a leak in the heat exchanger which if undiscovered could have resulted in a significant CO leak. that led to our replacing the furnace.

CO detectors are designed to detect extremely low levels of CO. If your CO detectors didn't detect it, chances are your heat exchanger wasn't cracked. You do have CO detectors in the house, right? On oil burners they can inject a dye into the combustion chamber that will highlight the crack that you can usually see through the access hole. On gas furnaces it's not as easy to see. After removal, I'd demand to actually see the crack. As noted above, there are many unscrupulous HVAC companies that will stop at nothing to meet their revenue goals.

 

[Winemaker]

During these cold spells it is important to keep an eye on your indoor humidity. In some places the indoor humidity can go below 20%, and when then fan is running, they dry air is pulling moisture from your body and cooling you down. A 40% humidity is more comfortable than 25% at 67degrees. In moister parts of the country, 40 % humidity can mean a big difference in your thermostat settings. I monitor my humidity religiously especially in the basement wine cellar. The humidity during the winter months is very low and because of that, I must put extra moisture in the air so that my aging wine in my 55g barrels doesn't get carried away. Over a 2 years aging period, my 2020 Cab Sauv, lost over 4 gallons to evaporation, and I refill all my barrels on a monthly basis.

Also, be sure to keep your intake and exhaust pipes free and clear of debris, snow and ice. Sometimes these are located in out of sight places or have a bush in front, and you may not notice a snow drift or ice blockage.

 

[COcheesehead]

What does that mean? What do you consider modern? AFAIK the Minimum Efficiency Reporting Value measures the particle size the filter will capture effectively. If you have problems like excessive dust, smoke, allergies, etc a higher MERV may be helpful but trapping smaller particles means the filter will not last as long. I don’t think this has any impact on the furnace machinery…there are no tiny passages that will plug up with dirt in the furnace. It’s not like a car engine with tight tolerances. The problem if the filter gets plugged is lack of airflow which is uncomfortable in the winter and possibly damaging in AC mode.

Someone mentioned to not use a MERV filter. My new furnace came with one, has a compartment that fits a 4” one. I use a MERV 11. I have no problems. So my comment was to the poster who said to not use a MERV.

 

[COcheesehead]

During these cold spells it is important to keep an eye on your indoor humidity. In some places the indoor humidity can go below 20%, and when then fan is running, they dry air is pulling moisture from your body and cooling you down. A 40% humidity is more comfortable than 25% at 67degrees. In moister parts of the country, 40 % humidity can mean a big difference in your thermostat settings. I monitor my humidity religiously especially in the basement wine cellar. The humidity during the winter months is very low and because of that, I must put extra moisture in the air so that my aging wine in my 55g barrels doesn't get carried away. Over a 2 years aging period, my 2020 Cab Sauv, lost over 4 gallons to evaporation, and I refill all my barrels on a monthly basis.

Also, be sure to keep your intake and exhaust pipes free and clear of debris, snow and ice. Sometimes these are located in out of sight places or have a bush in front, and you may not notice a snow drift or ice blockage.

We run our humidifier all winter long. It keeps our hardwood floors from gapping, static out of our clothes and gives the air a soft feel that makes the house more comfortable. You notice the difference as soon as you walk in the door. As soon as it drops below 30%, you can feel it.

 

[wmc1000]

Someone mentioned to not use a MERV filter. My new furnace came with one, has a compartment that fits a 4” one. I use a MERV 11. I have no problems. So my comment was to the poster who said to not use a MERV.

When we moved into our house in 2020 we used MERV 11 filters to "clean up" the air from the previous owners for the first year. There was a significant particle reduction from the first 4" filter that got cleaner as the year progressed. Switched to MERV 8 after that.

 

[Qs Laptop]

I'm no expert.

• I have read and think it makes sense that a plugged up filter will reduce airflow and cause the furnace fan to run more/harder to compensate as the heat is not being raised in the house.
• It could also possibly cause the furnace to overheat and then shutdown temporarily as a lack of airflow will mean no heat is drawn away.

I'd sure like to know if it's true, or there is no concern for even totally plugging up the furnace filter

The techs that replaced the furnace in my son's rental townhouse were astonished that there were zero cold air return ducts throughout the house. (As was I, when it was pointed out.) Instead there were passthrough openings above each bedroom door (think a transom window, but instead it is a permanent opening with grill covers on each side.) There was only one large, approximately 24" X 18", cold air return box mounted directly on the side of the furnace. That box was the cold air return "system." There was also an outside source of fresh combustion air via an 8" diameter "hose".

This is a two story, 2,200 square foot dwelling. No cold air returns.

The techs speculated that the lack of a true cold air return system, the fact that there is only one cold air return mounted on the furnace, and the fact the furnace was in an enclosed closet, contributed to likely overheat the heat exchanger unit over time, and when the extreme cold weather hit, the furnace was working overtime and the heat exchanger cracked. They specifically said with this (dumb) setup the furnace filter should be changed monthly and also said it would be a good idea to leave the closet door open, or at least partially open. If the closet door were to remain closed, then a passthrough opening should be built into the wall above the closet door to increase airflow into the furnace room.

 

[Sunset]

I thought MERV was just a standardized way of describing the filtration ability/level of a filter.

We had out humidity turned on and it made moisture collect in puddles on the window bottoms so we turned it off. I didn't want mold growing on the window bottoms, and will suffer with low humidity. We do not run the bathroom fan when showering as a way to get some humidity in the house.

 

[Music Lover]

It's good to remember that what may be extreme cold in your area for a short period is just normal temperature every winter in other areas, and in those places furnaces run just fine.

 

[Sunset]

The techs that replaced the furnace in my son's rental townhouse were astonished that there were zero cold air return ducts throughout the house. (As was I, when it was pointed out.) Instead there were passthrough openings above each bedroom door (think a transom window, but instead it is a permanent opening with grill covers on each side.) There was only one large, approximately 24" X 18", cold air return box mounted directly on the side of the furnace. That box was the cold air return "system." There was also an outside source of fresh combustion air via an 8" diameter "hose".

The techs speculated that the lack of a true cold air return system, the fact that there is only one cold air return mounted on the furnace, and the fact the furnace was in an enclosed closet, contributed to likely overheat the heat exchanger unit over time, and when the extreme cold weather hit, the furnace was working overtime and the heat exchanger cracked. They specifically said with this (dumb) setup the furnace filter should be changed monthly and also said it would be a good idea to leave the closet door open, or at least partially open. If the closet door were to remain closed, then a passthrough opening should be built into the wall above the closet door to increase airflow into the furnace room.

Your son's house sounds like the very old houses with the transom's above a door, just "modernized" ?

I've seen vents put in doors when a furnace is in a closet, either way it's going to have to be a large vent (or both).

A very strange and poor heating system setup.

 

[Qs Laptop]

It's good to remember that what may be extreme cold in your area for a short period is just normal temperature every winter in other areas, and in those places furnaces run just fine.

Yes, this is a great point for those that worry about stress on their furnace in "cold" weather yet live in areas where the temperature rarely gets near zero degrees. Your furnace should be just fine the couple times a year it gets down to these temps.

For others, like MusicLover in Canada or me in Minneapolis we just assume our furnaces will run through cold weather, by which I mean multiple days in a row below zero Fahrenheit. Sometimes a week or two in a row with these temps. I do admit to getting stressed lying in bed and not hearing the furnace shut off for hours--this with the thermostat set at 64 degrees for nighttime. Will it keep running?

 

[Music Lover]

The techs that replaced the furnace in my son's rental townhouse were astonished that there were zero cold air return ducts throughout the house. (As was I, when it was pointed out.) Instead there were passthrough openings above each bedroom door (think a transom window, but instead it is a permanent opening with grill covers on each side.) There was only one large, approximately 24" X 18", cold air return box mounted directly on the side of the furnace. That box was the cold air return "system." There was also an outside source of fresh combustion air via an 8" diameter "hose".

Having just one cold air return for a furnace is normal, although it usually has a trunk that draws from several different locations.

The techs speculated that the lack of a true cold air return system, the fact that there is only one cold air return mounted on the furnace, and the fact the furnace was in an enclosed closet, contributed to likely overheat the heat exchanger unit over time, and when the extreme cold weather hit, the furnace was working overtime and the heat exchanger cracked. They specifically said with this (dumb) setup the furnace filter should be changed monthly and also said it would be a good idea to leave the closet door open, or at least partially open. If the closet door were to remain closed, then a passthrough opening should be built into the wall above the closet door to increase airflow into the furnace room.

I agree. The return must be able to draw enough air for the furnace to run efficiently.

 

[Qs Laptop]

Your son's house sounds like the very old houses with the transom's above a door, just "modernized" ?

I've seen vents put in doors when a furnace is in a closet, either way it's going to have to be a large vent (or both).

A very strange and poor heating system setup.

Yes, the techs kept muttering, "I've never seen anything like it."

Twenty-two hundred square feet of area and now consider the main floor has 10 foot ceilings. That's a lot of volume of dead air that is not being returned to the furnace.

 

[Qs Laptop]

Having just one cold air return for a furnace is normal, although it usually has a trunk that draws from several different locations.

Yes, you are correct of course. I should have been more precise in my description.

 

[jazz4cash]

I'm no expert.

• I have read and think it makes sense that a plugged up filter will reduce airflow and cause the furnace fan to run more/harder to compensate as the heat is not being raised in the house.
  
• It could also possibly cause the furnace to overheat and then shutdown temporarily as a lack of airflow will mean no heat is drawn away.
  

I'd sure like to know if it's true, or there is no concern for even totally plugging up the furnace filter

I agree with all your comments and I think they are not inconsistent with my post.

 

[COcheesehead]

I thought MERV was just a standardized way of describing the filtration ability/level of a filter.

We had out humidity turned on and it made moisture collect in puddles on the window bottoms so we turned it off. I didn't want mold growing on the window bottoms, and will suffer with low humidity. We do not run the bathroom fan when showering as a way to get some humidity in the house.

If you have condensation, your humidity is too high for the temp outside. Turn the humidity down and the condensation will dissipate. The colder it is, the lower the humidity should be set.
As to MERV concerns…change the filter if it’s dirty.

 

[ERD50]

The techs that replaced the furnace in my son's rental townhouse were astonished that there were zero cold air return ducts throughout the house. (As was I, when it was pointed out.) Instead there were passthrough openings above each bedroom door (think a transom window, but instead it is a permanent opening with grill covers on each side.) There was only one large, approximately 24" X 18", cold air return box mounted directly on the side of the furnace. That box was the cold air return "system." There was also an outside source of fresh combustion air via an 8" diameter "hose".

This is a two story, 2,200 square foot dwelling. No cold air returns.

The techs speculated that the lack of a true cold air return system, the fact that there is only one cold air return mounted on the furnace, and the fact the furnace was in an enclosed closet, ....

That sure doesn't sound up to code. The 8" supply for outside air helps, but still not a good setup. More than just efficiency concerns, that is a recipe for "back-draft" - the cold air return right in the closet is sucking a lot of air. It can suck the flame right out of the furnace and start a house fire. There is an over temperature cut-out for that but you don't want to rely on that.

Having those air vents in above the doors to those rooms in place of separate returns isn't so bad, I've seen that before - that air will flow out (pushed by the supply air), but there should be a main air return in a hallway, not right in the closet itself.

Here is something that might be easy, and it would help. As mentioned, add a large grill to that closet, but run the furnace air return directly to it, sealed, without any openings to the closet. That way, it would be sucking air from the rooms (balancing the air it is pushing out the supply ducts). The 8" outside air duct would feed the furnace and not get mingled with the room air. So it would also improve efficiency.

If a tech just replaced a furnace with that same setup, they should lose their license. It should be brought up to code. I'm not sure what the codes are exactly for bringing fresh air in through a duct, but that's how the sealed systems work, with just 3" or 4" (IIRC) PVC. So an 8" duct should be enough, if you know it is clear and not restricted.

This kind of stuff shouldn't be left to chance. Get it done right. Threaten to report the landlord if it isn't fixed. In the meantime, get several smoke/CO detectors.

-ERD50

 

[ERD50]

...

I've seen vents put in doors when a furnace is in a closet, either way it's going to have to be a large vent (or both). ....

Yes, that's fine (and common) for drawing combustion air to the furnace. But it should not be drawing return air for there as well.

I remember researching the code, I was wondering if I should have return ducts in the finished basement to help circulate the A/C in summer, to help reduce humidity. There were a lot of warnings about air returns in a basement, that it could cause a back-draft for the furnace.

Having that air return in the same closet is 1000x worse. As I said, the 8" outside air alleviates that somewhat, but it is still a really bad setup, and likely not to code.


-ERD50

 

[RobbieB]

My 80,000 BTU/hr is in a closet now. Combustion air coming from attic on open ceiling.

Return air from (2) 12" x 24" intakes below the furnace. Very efficient.

 

[ERD50]

My 80,000 BTU/hr is in a closet now. Combustion air coming from attic on open ceiling.

Return air from (2) 12" x 24" intakes below the furnace. Very efficient.

Where do those (2) 12" x 24" intakes below the furnace go to?

-ERD50

 

[RobbieB]

The space under the furnace. The furnace sits on a "filter box" that is not a part of the furnace and holds a 4"x20"x25" pleated filter. The house slab is the floor of the space.