Will buy a new gas furnace

Help Support House Repair Talk:

Guzzle

Well-Known Member
Joined
Nov 24, 2021
Messages
549
Reaction score
183
Location
Maryland
in the spring or summer, about 50k or 60k input btuh.

Our present 169k unit is 40 years old & I'm getting a bit nervous, I'm not fond of gas explosions.

I prefer 82% efficient because the highly efficient are supposed to be touchy.
I prefer relay logic [no solid-state computer] so I can fix it myself but that may not be available.

What should I avoid?
If I get a Factory Service Manual will it be useful to me? Apparently Factory Service Manuals for cars are now useless to the DIYer.

TIA.
 
Last edited:

Steve123

Well-Known Member
Joined
Jul 5, 2017
Messages
291
Reaction score
122
I would avoid any furnace that is not at least 95% efficient, and didn't have a variable speed blower.
 

Guzzle

Well-Known Member
Joined
Nov 24, 2021
Messages
549
Reaction score
183
Location
Maryland
Thanks for your comments.
At present I seem to want to trade high efficiency & low fuel bills for a simpler furnace. This furnace has never annoyed me with false alarms & only once was I compelled to call the HVAC guy to replace the gas valve. It failed by not opening rather than by not closing.

I have all the documentation for our furnace & I realize what I should do now is to introduce a fault to test it.

For the house to blow up, the gas would have to fail to be ignited & the device that checks for this would also have to fail.

If the furnace passes my self-induced fault I should run this test probably once/month or sooner until I replace the furnace.
If it fails my test I should replace the checking device immediately.
I'll do this when my wife is elsewhere.

"Gas explosions in the U.S. kill approximately 65 people annually" about the same as lightning strikes or shark attacks.
With these odds I don't much care, but for sure my wife should not be injured as a result of my negligence or incompetence.
 
Last edited:

Guzzle

Well-Known Member
Joined
Nov 24, 2021
Messages
549
Reaction score
183
Location
Maryland
An HVAC guy came by, seemed to recommend 90 K input BTU/hr, I'll wait for his bid.
He agreed I would not be able to fix the control board & he did not give me a price for that board.
Our dishwasher board is $100 & is probably more complex than a furnace controller.
I don't know if I should have played dumb, I'll try that with the next bidder.

Maybe this week I'll risk simulating a failure to check the backup devices.
 

maxdad118

JOAMOS
Joined
Jan 25, 2017
Messages
311
Reaction score
56
Location
Northern California, bay area
Do you have any pics of the unit? Is your local gas company a service company as well? I do safety inspections on gas appliances and even some older units have limit switches and safeties. While not as efficient the older ones can still be perfectly fine depending on the maintenance that’s been done. Is it so old that it has a standing pilot?
 

Guzzle

Well-Known Member
Joined
Nov 24, 2021
Messages
549
Reaction score
183
Location
Maryland
Can't do pics.

Our GaCo tried to entrap me into defrauding them because I had "dirt" on them.

It has a spark that lights a pilot. The gas valve has 3 internal coils which I want to fully understand before I start disconnecting things. That explanation is probably on the net if I happen upon the right search terms, e.g. "pick coil".

Maintenance has been a new gas valve years ago, a blower motor, an inducer motor, the control board for that motor, and cuts & jumpers on the main control board to bypass relay contacts that were flaky. It just happened to have spare contacts that I wired in.

Water had dropped on the board edge connector & tarnished them, giving me the most confusing symptoms. A connector pin was acting like a 60 megohm resistor, I had 3vac across the connection.

I did all except the gas valve.

If I do nothing the odds are probably with us but I'd like to tip those odds even more until we get a new furnace.
 

Guzzle

Well-Known Member
Joined
Nov 24, 2021
Messages
549
Reaction score
183
Location
Maryland
Sounds like a 3 wire flame switch style? Green, yellow and white wire along with an orange electrode cable?
So it seems there's a wiring color code for the furnace gizzards.
I'll check that, thanks for your help.

Edit:
Bingo on the colors going to the pilot flame sensing switch assembly & the spark wire.
This Bryant is 397haw060140acba.

The HVAC guy didn't seem too concerned about an explosion.
Today or tomorrow I'll start messing with the wires.
 
Last edited:

Guzzle

Well-Known Member
Joined
Nov 24, 2021
Messages
549
Reaction score
183
Location
Maryland
There is non-destructive testing & destructive testing.

I could disable the spark gen & jumper the flame sensor [assumed bimetallic] switch but this is more like sabotage.

I’m not going to do this test.

Bryant could rightly argue that no bimetallic switch has ever closed unless it was heated.

IOW, when this place
"Hel, in Norse mythology. . ."
freezes over.

Thanks for your help, anyway. Me knowing gas furnaces down to the molecular level can't hurt.
 

BuzzLOL

Well-Known Member
Joined
Oct 26, 2015
Messages
436
Reaction score
203
I bought 2 Whirlpool 90+% furnaces about 35 years ago, a 100K and 75K BTUs, and they've been totally reliable... I bought them under TempStar name... also sold under Heil, Dayton, and Sears Best names and several others... they look about like the previous 1950's furnaces, but probably about 3 times better actual efficiency... the old furnaces were rated 80% efficient but that was before the Govt. actually tested to make sure the claimed efficiency rating was real...
80% is probably fine if live in an area where just need 'touch up' heat occasionally... I live in N.W. Ohio where sometimes -20 F...
 

Hamberg

Supporting Member
Joined
Mar 3, 2021
Messages
118
Reaction score
60
Location
Horsham PA
Our present 169k unit is 40 years old & I'm getting a bit nervous, I'm not fond of gas explosions.

I prefer 82% efficient because the highly efficient are supposed to be touchy. I prefer relay logic [no solid-state computer] so I can fix it myself but that may not be available.
Certainly not an HVAC tech but (IMO) the new units are way super easy to service and short of changing the filter, require no maintenance.

Granted they've had motherboard LEDs for 25+ years but the new units are mostly self-diagnosing. Electronics are encapsulated on 3 or fewer boards and the boards themselves are plug-n-play - unscrew the old one, insert new.

Just replace our 22 YO unit with a Coleman 2-stage, 96% efficient unit. Literally, removed the old spit, unboxed and positioned the new - was 1.5" taller so had to cut some sheet metal, reattached the gas, (direct vent) reattached the vents, plugged it in, sealed it and had our HVAC guy charge it - took all of about 4 hours (and 3 beers).

Wife does the bills but she says we are about $70ish a month less in our gas usage with the new unit. Think the temps have been pretty close to last year.

Here is a good site to check on (potential) savings based on the old/new units: www.seerenergysavings.com/afue-savings-calculator
 

Guzzle

Well-Known Member
Joined
Nov 24, 2021
Messages
549
Reaction score
183
Location
Maryland
If we saved $70/mon with a new four kilobuck furnace that actually does 82% eff. like our old furnace once did, the breakeven point would be 5 years.

By next Feb we might be able to see the savings if next winter is reasonably cold. I'd have to correct for the Heating Degree Days.

My spreadsheet offers a "paired t-test" for finding these kinds of small differences. Never did one.

I could have done one for the new windows we got ten years ago but I didn't save the gas bills going back that far & the gas company ignored my request for those bills. :(
 

BuzzLOL

Well-Known Member
Joined
Oct 26, 2015
Messages
436
Reaction score
203
Here is a good site to check on (potential) savings based on the old/new units: www.seerenergysavings.com/afue-savings-calculator

Granted they've had motherboard LEDs for 25+ years...
Too bad they don't use same AFUE and yearly cost ratings for gas , electric, wood, steam, hot water, and heat pump furnaces so that they can be compared simply... but the manufacturers would raise a quick big stink...

The furnaces after mine used a 'smart gas valve' with a printed circuit board on top of it... condensation dripped on that board and ruined it...

My furnaces have some sort of computer (no LED lights) but they've never given any problem... the controls are all easily found to buy and replace Honeywell brand rather than proprietary units that can only be bought from the original factory (if still in business)... that was a good selling point, but I haven't had to replace any...
 
Last edited:

Hamberg

Supporting Member
Joined
Mar 3, 2021
Messages
118
Reaction score
60
Location
Horsham PA
Too bad they don't use same AFUE and yearly cost ratings for gas , electric, wood, steam, hot water, and heat pump furnaces so that they can be compared simply... but the manufacturers would raise a quick big stink...
Think you can choose which type of heating (at least most??) you are changing from.

1642111508884.png
 

Steve123

Well-Known Member
Joined
Jul 5, 2017
Messages
291
Reaction score
122
@Steve123 , why is that? I’m perfectly happy with my 80% that I installed 10 years ago. Yeah, maybe a little less efficient but I’m near the Bay Area, CA so it’s not a killer
A high efficiency furnace will source combustion air from outdoors. An 80% furnace will source combustion air from indoors -- and for every cubic foot of air that you exhaust, you will suck in a cubic foot of cold, dry air from the great outdoors, into your house.

The variable speed motor allows running the fan 24/7 at a very low speed (when not in heat mode). I leave the fan on full time to get air circulation and more constant temperature through the house. The blower fan on my old Rheem ran so slow and silent you would hardly know it was on. However, on the Armstrong at the new house, the continuous speed on the blower is somewhat higher and not really adjustable.

But I agree than in San Fran, furnace efficiency is not really an issue.
 

BuzzLOL

Well-Known Member
Joined
Oct 26, 2015
Messages
436
Reaction score
203
A high efficiency furnace will source combustion air from outdoors. An 80% furnace will source combustion air from indoors -- and for every cubic foot of air that you exhaust, you will suck in a cubic foot of cold, dry air from the great outdoors, into your house.
My earlier 90+ efficiency furnaces use indoor air for combustion and I like the idea that it slowly removes the bacteria/virus laden air from the house and replaces it with fresh air drawn in from outside. If it didn't do that and I had the double piped furnace, I would add a heat exchanger to change the stale air with fresh air without losing much heat. And creating a healthy house in place of a 'sick house'.
 

Latest posts

Top