Williams Forsaire Counterflow...Correct behavior?

[Tremelune]

I just moved into a house with one of those tall furnaces that stick out of the wall. It could be 5 years old, it could be 30 years old. I've never seen a heater like this, and I'm trying to figure out if it's behaving as intended...

I'll hear it click on for a minute (warming up?), then the fan will come on and heat will blow out. Early on, the air blows quite hot. Towards the end, it's barely warm at all, as if the hot element the air is blowing over has been "used up".

When it's running "constantly" it runs for a few minutes, then turns off for maybe a minute, then repeats the cycle. During a sunny day it will kick on for a few minutes, then turn off for quite a while until the temp drops again and repeat. Sometimes it will make a rhythmic ping every second for a while...

The thermostat is a White-Rodgers 1F56W-444 mercury unit that appears to be working correctly (turning the furnace on and off to maintain a steady temp), despite being the oldest thing I've ever seen. The pilot/ignition is a Honeywell S8600B.

While it's mostly heating the house adequately, it is definitely struggling at times. More insulation will help, but weather in the teens is common at night for months at a time, so I want to be sure that, if nothing else, the furnace is operating properly. It makes sense that the escaping air would cool down, as it would be less efficient to leave the heat trapped in the element, but...it does seem strange that it runs out of steam, so to speak.

The only reference to thermal control I could find in (what I assume to be) the manual is this bit:

Protection against overheating is provided by means of a limit
switch located near heating elements, which acts to open relay
circuits controlling the heated elements if circulating air volume
is decreased. The limit switch automatically restores operation
when temperatures reach a normal level. As an additional
safeguard, each heating element is equipped with fuse limiters
to protect against excessive and prolonged current surges. If
these protectors open the heating circuit, the heat limiter must
be replaced by your Service Technician who will determine and
correct the cause of failure.

So, am I just eyeballing a perfectly good furnace that is underpowered for the coldest nights of the coldest part of the year in a house that is under insulated, or is there room for improvement by repairing/replacing this furnace?

 

[zmaxmotorsports]

Have you had it serviced/checked lately?

 

[ToecuttersZ1R]

Whats the model and serial #?

 

[Done That]

THE FURNACE WORKS LIKE THIS:
1. The thermostat turns on the control module.
2. Automatic relight system (in the module) opens the gas valve and electronically ignites the pilot. After the pilot flame has been established and proven by the control module, the main gas valve circuit opens and the pilot lights the main burners.
3. Heat builds up in the furnace and starts the fan. The heated air comes out the front bottom louvered panel at floor level.
4. When the thermostat setting is reached, it shuts off the main burner.
5. The fan runs until the heat is removed from the furnace, then it turns off.

That's a snip from a Williams manual. The blower on delay at startup to allow heat exchanger to warm up and purge at shutdown you are talking about appear to be normal operation.

The fact that you mention it only runs for a few minutes when on constantly, then stops and restarts sounds like it could be cycling on an overtemp safety.

 

[Tremelune]

That is very helpful. After leaving it off all day, it has been running steadily, so I'll see how it does over time.

When it has been left off for a long time, the fan howls and squeals for a few minutes, so I guess I gotta oil that sucker up...

I attempted to install a Nest thermostat, and it just doesn't want to kick on. That's a different issue entirely, but man, I wish I could understand why. There's only an R and a W wire, and I'm 99% certain it's a 24V system. Sticking with the ancient mercury thermostat until morning so I don't lose any toes...

 

[zmaxmotorsports]

That is very helpful. After leaving it off all day, it has been running steadily, so I'll see how it does over time.

When it has been left off for a long time, the fan howls and squeals for a few minutes, so I guess I gotta oil that sucker up...

I attempted to install a Nest thermostat, and it just doesn't want to kick on. That's a different issue entirely, but man, I wish I could understand why. There's only an R and a W wire, and I'm 99% certain it's a 24V system. Sticking with the ancient mercury thermostat until morning so I don't lose any toes...

That's a old 2 wire/heat only system. You'll need to run a 4 conductor thermostat wire and run a common back to transformer to make it work.
You won't use the green/fan wire,but if you're going to the trouble to fish a wire through the walls you may as well run the 4 wire for future use.

 

[Tremelune]

Well, I think the fan is controlled by the Honeywell unit in the furnace (at least it's not being controlled by the old White-Rodgers). If I jump the W wire to the R wire, everything works as intended. It makes me think my W connection to the Nest is poor, or maybe I damaged something internally while mucking about.

Seems like the Nest should be smart enough to connect two wires to turn on the heat...