Twin Furnace Troubleshooting

[littldo]

Hi, In the fall of '02 I purchased a 100+ year old 2story farmhouse (< 2000sq ft) for weekends that had been mostly rehab'd. The house has 2 newer high-eff (York PD2* Diamond furnaces and questionable insulation(different issue).

Last winter we didn't have any problems, but a few weeks ago we had to replace the hot surface igniter in 1 furnace. The technician remarked about excessive condensation and thought it was the cause.

Now, this weekend we can only keep 1 furnace running at a time. Turn them both on, the both blow cool air, turn furnace A off, the other works fine. Turn it off and the other works fine. Being these are newer furnaces we suspect electronic controls and numerous safety sensors.- potentially a flu pressure sensor.

The chimney runs thru the house off-center from cellar to the attic where it angles to exit the center ridge of the roof. It’s probably a run of about 40-50'. There is no chimney cap, but we know it's needed. The furnaces are on separate thermostats (1st floor & 2nd floor), but vent to the same chimney.

We are wondering if it’s possible that a clogged/dirty chimney could cause enough back pressure to cause a switch off(if there is a switch).

Any thoughts or guidance would be helpful.
Thanks



Cheers!
Doug

[16x80]

littldo

Welcome to the Home Repair Forums

I will try and help here.

It is possible that what you fear is the cause, You can do some investigating work yourself to help determine the issue. Remove both vents and use a mirror and a flash light to look inside the chimneys for any type of blockage, You would have to look from the top side also because of the bend. You could also jumper out the sensor on one or both furnaces to see if it is the culprit! (I do not recommend running your furnace in such a manner, Jumping out safety's is only for [u]testing purposes only</u>)

As for your venting they are both running metal pipe to the chimneys? The condensation would be from the moist hot air being put off by the furnaces "raining" in your chimney!

"raining" Where the moist hot air from the furnace does not make it to the out side air but instead condensates and rains back down the chimney!

"raining" in the chimney can cause a multitude of problems to include Rotting out the mortar and brick which would cause unsafe erosion to the chimney!

16x80