Author Topic: Gas Furnace Maintenance  (Read 909 times)

DrumAllDay

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Gas Furnace Maintenance
« on: October 02, 2018, 02:24:34 PM »
Does anyone here do there own yearly maintenance on a gas furnace and have any good resources or advice for doing this?

I want to keep my older furnace running for as long as possible and I want to see if I can perform some simple maintenance on it without paying a $100-$150 service call.

wheezle

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Re: Gas Furnace Maintenance
« Reply #1 on: October 02, 2018, 03:07:38 PM »
Also interested. Just got a new one and was just thinking about this. It's a high-efficiency furnace, to boot, which makes me more worried about its service life and my ability to maintain it.

sol

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Re: Gas Furnace Maintenance
« Reply #2 on: October 02, 2018, 03:17:04 PM »
Replace your filters if they're paper, or wash if they're electrostatic.  Every six months.  That's the thing that most commonly causes furnace failures.  Ask this landlord how he knows that.

When the filter clogs, they will overheat and either melt the control board ($600) or you'll toast the blower ($200).  Some furnace systems have multiple filters, so check both on the intake vent on the wall and inside the furnace unit itself where the air return enters.

Gas furnaces are pretty mechanically reliable devices.  They're just jets and a sparker and a big fan.  The sparkers and jets don't seem to break, but I have seen malfunctions related to 20 year old thermostat wiring jiggling loose.  You should be able to visually confirm that all of the gas jets are lit, just by looking in there while it's running.

If you have one of the newer high-efficiency units, then you probably have a plastic (rather than metal) vent pipe coming out of the top, and it produces condensation.  That moisture has to be removed, and depending on the geometry of your unit you might have a gravity drain line that drips it out under your house, or a pump system that uses an electric pump to remove it.  Those electric pumps are intermittent and will typically fail years and years before the gas furnace does, which can cause all kinds of problems.  I'd find your condensate line and figure out where it goes, because that's probably the second most common failure point after the air intake clogging.

If you have a heat pump instead of a gas furnace, then you have ten other failure points to worry about.  I'd call a professional.

wheezle

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Re: Gas Furnace Maintenance
« Reply #3 on: October 02, 2018, 03:24:54 PM »
When the filter clogs, they will overheat and either melt the control board ($600) or you'll toast the blower ($200).  Some furnace systems have multiple filters, so check both on the intake vent on the wall and inside the furnace unit itself where the air return enters.

...

Those electric pumps are intermittent and will typically fail years and years before the gas furnace does, which can cause all kinds of problems.  I'd find your condensate line and figure out where it goes, because that's probably the second most common failure point after the air intake clogging.
Excellent, thank you! I just opted to drain the condensation without a pump, and I'm even happier about that decision now -- it seemed like a likely and expensive failure point.

Wouldn't have thought of the filter. I do it on a window A/C all the time, but I don't yet understand the way my furnace works. I'll get there.

sol

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Re: Gas Furnace Maintenance
« Reply #4 on: October 02, 2018, 03:35:52 PM »
Wouldn't have thought of the filter. I do it on a window A/C all the time, but I don't yet understand the way my furnace works. I'll get there.

Your furnace is a lot more simple than your window AC unit.  It has a big fan that sucks air from inside your house into the furnace unit.  In there, it burns natural gas in a big flame to make heat, and then it blows that hot air back into your house through your ductwork.  There is no thermodynamic compression cycle, no phase changing fluids, no pressurized fluids that can leak or condensers that can crack.  It's literally just a burner and a fan, and some electronics to tell it when to burn and when to blow.

But if that air intake gets clogged, you can still break it.  I've done it twice, once when a long term tenant never cleaned the electronic air cleaner as instructed, and once when a furnace had a second hidden paper media filter inside the furnace unit.

wheezle

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Re: Gas Furnace Maintenance
« Reply #5 on: October 02, 2018, 08:00:46 PM »
But if that air intake gets clogged, you can still break it.
Is it because not enough air can get in? Or does the fan try to overcompensate with higher RPM? Makes perfect sense either way.

sol

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Re: Gas Furnace Maintenance
« Reply #6 on: October 02, 2018, 08:08:07 PM »
But if that air intake gets clogged, you can still break it.
Is it because not enough air can get in? Or does the fan try to overcompensate with higher RPM? Makes perfect sense either way.

Not enough air gets in, or out.  The burners keep pumping heat into a closed metal box with no airflow.  Eventually something melts, usually something electronic and delicate and expensive.

wheezle

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Re: Gas Furnace Maintenance
« Reply #7 on: October 02, 2018, 08:10:18 PM »
Not enough air gets in, or out.  The burners keep pumping heat into a closed metal box with no airflow.  Eventually something melts, usually something electronic and delicate and expensive.
Got it. Makes perfect sense. I'll keep an eye on those filters.

acepedro45

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Re: Gas Furnace Maintenance
« Reply #8 on: November 24, 2018, 12:57:06 PM »
I know I'm posting this way too late for DrumAllDay, but here are the notes I took during a professional cleaning of the gas furnace at my new house (subsequent cleanings will be non-professional).

Our boiler is a Well-McLain gas boiler similar to the ones pictured here:

https://www.weil-mclain.com/products/eg-gas-boiler

1. Vacuum beneath furnace thoroughly to avoid sucking up any debris as air flows to feed the fire. Avoiding debris is 90% of preventative maintenance.

2. Disassemble pipes and clean each pipe with a light sandpapering.  Tap to get any internal stuff out.

3. Inspect and clean Thermocoupler on middle pipe. Replace as needed (5+ years). The thermocoupler is very important safety-wise as it shuts off the gas feed if the pilot light is somehow extinguished accidentally. You can prolong thermocoupler life by shutting down your boiler completely in the summer months as opposed to idling it with just the pilot light (plus a save a little money on using less gas). 

4. Visual inspection of boiler underside.

5. Test for gas leaks at all supply line junctions using soap and water

6. Light Boiler following printed instructions. Verify damper is functioning and boiler is firing. Verify automatic water feed functioning.


topshot

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Re: Gas Furnace Maintenance
« Reply #9 on: December 03, 2018, 02:50:59 PM »
Replace your filters if they're paper, or wash if they're electrostatic.  Every six months.
I'd do it every month personally. Your system will run more efficiently. If you have a particularly clean house and outdoor environment then may every quarter.

EricEng

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Re: Gas Furnace Maintenance
« Reply #10 on: December 03, 2018, 03:02:14 PM »
Replace your filters if they're paper, or wash if they're electrostatic.  Every six months.
I'd do it every month personally. Your system will run more efficiently. If you have a particularly clean house and outdoor environment then may every quarter.
Every month?  That is exceedingly expensive.  Those filters can run $5-15 each unless you get the spun fiberglass ones that do almost nothing.

Rufus.T.Firefly

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Re: Gas Furnace Maintenance
« Reply #11 on: December 03, 2018, 03:48:30 PM »
Replace your filters if they're paper, or wash if they're electrostatic.  Every six months.
I'd do it every month personally. Your system will run more efficiently. If you have a particularly clean house and outdoor environment then may every quarter.
Every month?  That is exceedingly expensive.  Those filters can run $5-15 each unless you get the spun fiberglass ones that do almost nothing.

For paper filters, the cheapest, thinnest filters are best. They promote air-flow better than the expensive ones because they have less material the air must pass through and thereby tax the overall HVAC system less than the thicker filters. And they should be changed every month due to their thinness.

source: father-in-law who is in the HVAC business for 30 years

topshot

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Re: Gas Furnace Maintenance
« Reply #12 on: December 03, 2018, 08:30:57 PM »
For paper filters, the cheapest, thinnest filters are best. They promote air-flow better than the expensive ones because they have less material the air must pass through and thereby tax the overall HVAC system less than the thicker filters. And they should be changed every month due to their thinness.

source: father-in-law who is in the HVAC business for 30 years
+1. But I do have an electrostatic filter so no need to replace, just clean it.

EricEng

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Re: Gas Furnace Maintenance
« Reply #13 on: December 04, 2018, 10:29:12 AM »
I really wish they would switch home filter slots to allow 3-6inch deep filters.  These do such a better job and have 10+ times the surface area so they don't impact air flow.  We use these for industrial scale and don't have to change them near as often.

toganet

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Re: Gas Furnace Maintenance
« Reply #14 on: December 04, 2018, 10:30:19 AM »
Another complexity with forced-air furnaces are the sensors that the electronics rely on to tell it when to burn & when not to.  I've specifically had issues with the exhaust sensor (it checks to ensure the exhaust gases are venting properly).  If the system thinks the exhaust is not venting it won't light the burners, in order to prevent Carbon Monoxide, etc., from venting into the living space.

After paying for an emergency visit from the HVAC guy, I learned to check the tiny tube between the sensor and the exhaust pipe -- it can clog, leading to a faulty reading.

Also, if your furnace vents through an actual chimney, make sure it has a cap that will prevent critters from entering.  On two occasions (once while I was ~2000 miles away) I had birds fly down and get lodged in the exhaust fan, leading to the same effect as above.

Jon Bon

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Re: Gas Furnace Maintenance
« Reply #15 on: December 04, 2018, 11:32:54 AM »
Another complexity with forced-air furnaces are the sensors that the electronics rely on to tell it when to burn & when not to.  I've specifically had issues with the exhaust sensor (it checks to ensure the exhaust gases are venting properly).  If the system thinks the exhaust is not venting it won't light the burners, in order to prevent Carbon Monoxide, etc., from venting into the living space.

After paying for an emergency visit from the HVAC guy, I learned to check the tiny tube between the sensor and the exhaust pipe -- it can clog, leading to a faulty reading.

Also, if your furnace vents through an actual chimney, make sure it has a cap that will prevent critters from entering.  On two occasions (once while I was ~2000 miles away) I had birds fly down and get lodged in the exhaust fan, leading to the same effect as above.

+1000 pressure switches! That is what those tiny tubes are for. I'd say their false alarm reading is 99.9%!

This is also very common after doing something very dusty (drywall/demolition, hardwood floor refinishing) no matter how much you try to keep the dust out it will eventually get sucked in and can end up in those 1/16 inch tubes. So if you do a major Reno and the furnace wont start gentry pry those little rubber tubes off and clean them out if needed.

But yeah stay on top of furnace filters as well. The one time I melted a mother board was there was an old filter jammed in there that was black as night with dust. SO no matter how clean I kept my new ones the old one was a major air constriction and fried my electronics.

toganet

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Re: Gas Furnace Maintenance
« Reply #16 on: December 04, 2018, 12:01:40 PM »
I really wish they would switch home filter slots to allow 3-6inch deep filters.  These do such a better job and have 10+ times the surface area so they don't impact air flow.  We use these for industrial scale and don't have to change them near as often.

I lucked out with the current house and the furnace takes 4" wide filters.  They're are a little more pricey but they seem to last ~6 months and provide good airflow.

DrumAllDay

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Re: Gas Furnace Maintenance
« Reply #17 on: December 06, 2018, 06:23:50 AM »
Replace your filters if they're paper, or wash if they're electrostatic.  Every six months.
I'd do it every month personally. Your system will run more efficiently. If you have a particularly clean house and outdoor environment then may every quarter.
Every month?  That is exceedingly expensive.  Those filters can run $5-15 each unless you get the spun fiberglass ones that do almost nothing.

For paper filters, the cheapest, thinnest filters are best. They promote air-flow better than the expensive ones because they have less material the air must pass through and thereby tax the overall HVAC system less than the thicker filters. And they should be changed every month due to their thinness.

source: father-in-law who is in the HVAC business for 30 years

So my furnace filter cartridge has a specific model it recommends. It's about $25 or so and it says it will last a year. I have heard other people say they just put a bunch of the cheap thin ones but I am weary of going against the recommended type.