Help with a Jensen Fwood furnace

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Old 12-26-09, 06:56 AM
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Help with a Jensen Fwood furnace

Hi all, new here and in need of some direction


We have a Jensen wood/coal furnace installed in our home by the previous owner. We didn't have a manual for it's operation but have managed to get a copy of one. It calls for a flue pipe temp of 300 to 400 d/F and I can't get near that temp without leaving a door open and the damper all the way out.

Only when it's cold (furnace) and the thermostat upstairs calls for heat does the damper fan come on. The owners manual says there is supposed to be a 2 speed blower below this for pushing air around the unit for heat to be blown into the ductwork. It's an oil fired warm air unit it's ducted in to.

From what I see there is no 2 speed fan and no wires coming from what I have determined to be the switches for it's operation......wires go into one side of the switch but the terminal across it is open. The rheostat doesn't seem to control the speed of the damper fan, it'll only turn it on or off when the furnace is cool.

Is this affecting my ability to get the flue temp where it's supposed to be?

Thanks for any help.
 
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Old 12-26-09, 06:00 PM
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Can you briefly describe the layout and joinery shared between the wood stove and oil burner?, and where the damper is situated?

Regarding that damper fan switch?; you say there are (plural wires)?), yet only is hooked to one of the two terminals, with the other terminal being unused? If so, off hand, it sounds like someone is bypassing that fan switch for some reason.

Any chance of contacting the ex-owner over your inquiries?
 
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Old 12-28-09, 05:04 AM
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The hot air from the plenum goes into the cold air intake of the oil burner. The damper fan is located on the back side of the furnace and looks like a hair dryer. It SEEMS there is a fan in the cold air duct to the furnace that is signaled "ON" when the wood furnace gets up to a set temperature and shuts off at a set temp (this I know because when the wood furnace goes out, the damper fan is "ON" (running) and furnace intake fan is "OFF" not running).

My wood should be good, it's dried for 2+ years but a bit damp from snow/rain. All is hardwood taken from my back lot. For whatever reason the flue temp runs consistently aroung 170 d/F. When the damper fan comes on the temp easily reaches 250 d/F before it shuts off, then the flue temp drops. The rheostat switch only turns on/off the damper fan so I'm not sure if it's functioning properly.....I don't want to start swapping things out willy-nilly.

Doing more digging it seems there never was a 2 speed blower fan hooked up or even there, either from the factory or all the wiring/fan box was taken off by the installer.

As for asking the previous owner....I'm not sure I want to ask, it seems all the remodeling work we've done on his handywork has shown numerous shortcuts he's taken that aren't safe or remotely near code....I shudder thinking about the things I haven't gotten to.
 
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Old 12-28-09, 04:45 PM
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If you would, please repost saying whevever a mention is made about a furnace, as to which one it is. I started to read the post and gave up because I had to concentrate too much.
I have to be able to follow posts in seconds in order to post as many answers to people as I do when I am online.


The wood stove dumps it's heat into the cold air of the oil burner? So that means that the oil burner blower is the (only)blower that runs?, in order to make hot air come out the registers? - by sucking hot air out of the wood burner, into the oil burner, and then out the oil burner to your registers? -with no blower in the wood burner?
 
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Old 12-29-09, 03:43 AM
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Originally Posted by ecman51` View Post
If you would, please repost saying whevever a mention is made about a furnace, as to which one it is. I started to read the post and gave up because I had to concentrate too much.
I have to be able to follow posts in seconds in order to post as many answers to people as I do when I am online.


The wood stove dumps it's heat into the cold air of the oil burner? So that means that the oil burner blower is the (only)blower that runs?, in order to make hot air come out the registers? - by sucking hot air out of the wood burner, into the oil burner, and then out the oil burner to your registers? -with no blower in the wood burner?

Seems you concentrated just enough to get it right.....

NO blower fan on the wood furnace to push HOT air
There IS a blower fan for the cold air intake for the OIL furnace
The hot air from the WOOD furnace is pulled into the cold air intake ductwork for the OIL furnace
This is the ONLY fan that forces air through the HOT AIR ductwork
When an increase of temperature is called for only a small damper fan, on the WOOD furnace, turns on until it reaches a set temp then it shuts off
The exit flue of the WOOD furnace is supposed to be 300 to 400 d/F but I can only, on occassion, reach 300 d/F
 
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Old 12-29-09, 05:30 PM
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Originally Posted by TommyD View Post
Seems you concentrated just enough to get it right.....

NO blower fan on the wood furnace to push HOT air
There IS a blower fan for the cold air intake for the OIL furnace
The hot air from the WOOD furnace is pulled into the cold air intake ductwork for the OIL furnace
This is the ONLY fan that forces air through the HOT AIR ductwork.
I envisioned it right then.


When an increase of temperature is called for only a small damper fan, on the WOOD furnace, turns on until it reaches a set temp then it shuts off
What does the damper fan do? Is it for fresh air intake? - or control of flue gases? - or some inline 'circulation air' damper? Where is it exactly?

The exit flue of the WOOD furnace is supposed to be 300 to 400 d/F but I can only, on occassion, reach 300 d/F
Is this the job of the damper - that it is a flue gas damper that is thermostatically controlled, where it opens more with a roaring inferno, ands closes some with a lesser fire, and other temp scenarios that are inbetween? IF so, is that damper adjustable in any way? Is the damper a factory mounted item or to factory specs in regard to it's location? What I am getting at is - if someone retrofit it, and it was too far up the flue, or too low, it might give wrong readings.
 
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Old 01-01-10, 03:54 AM
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Originally Posted by ecman51` View Post
I envisioned it right then.




What does the damper fan do? Is it for fresh air intake? - or control of flue gases? - or some inline 'circulation air' damper? Where is it exactly?



Is this the job of the damper - that it is a flue gas damper that is thermostatically controlled, where it opens more with a roaring inferno, ands closes some with a lesser fire, and other temp scenarios that are inbetween? IF so, is that damper adjustable in any way? Is the damper a factory mounted item or to factory specs in regard to it's location? What I am getting at is - if someone retrofit it, and it was too far up the flue, or too low, it might give wrong readings.

As far as I see the damper fan provides fresh air to the fire only. The resulting stoking of the coals/wood causes an increase in temp that travels (through a hand op'd flue damper) out the smokestack. This increase in temp causes my temp gauge needle (on the flue pipe) to move up TOWARDS 300 d/. The fire reaches a temperature of ?? and the fresh air blower shuts off.....and my flue temp gauge needle stops moving, drops and finally settles and stays, to around 160-170 d/F.

I already have the damper cover off so the blower gets all the air it can push.

All ducting SEEMS to be proper.

I'm gonna visit the place that probably sold the unit and see if I can pick their brains a bit. They sell but do NOT install....

This is what/why I'm asking...Is this thing set up properly. I am NOT a HVAC guy. The one I had here this Summer ( C air went out) says the unit the last service company installed was a bit too small for the house. Stuff here is FUBAR......and service calls are a luxury not in the budget
 
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Old 01-01-10, 03:19 PM
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Have you tried to verify that the temp on the gauge is reading correctly? You could shoot an infrared thermometer at it, or place the probe of a metal probe meat thermometer against the flue, and insulate around the probe.

It sounds like the fresh air damper may be doing what it is intended to do, to make sure the temp does not get too roaring hot. And so now it is a matter of if the damper is not set to the right temp., lost it's calibration, or is inaccurate.

I had a wood stove once that got over stroked, and it became a runaway fire. And the stove became cherry red and started to become almost translucent (even though it was opaque black), and you could hear the fire up in the flue. Very scary. It sounds like with your setup that you have a safeguard against this.
 
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Old 01-01-10, 04:04 PM
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Your damper you are talking about is a forced draft fan. Set to operate when your thermostat drops, calling for heat it will energize the fan. The forced draft fan should be through your limit control, shutting off if it hits too high of temps. Your woodfurnace should not go into the return of the oil furnace. Its a nice way to get things too hot and cause damage to the oil furnace. As far as your flue temps go, if you are taking a reading at the surface, double that and you will have a rough internal flue temp. Your low flue temps are about right on a standard woodfurnace. They will operate at lower temperatures because they don't have any sort of secondary combustion. Just keep an eye on the flue of the furnace and the chimney, sweep if needed. One way to tell if your burning properly is look at the chimney, you should have light to no smoke. That will give you an idea on how to burn properly. I have installed a few woodfurnaces, both in series and parallel and recently updated to a EPA certified model which burns clean and uses less wood. So I would say your furnace is not set up properly. The air from the top of the woodfurnace should go into the plenum of the gas furnace. The gas furnace should then have a backflow damper so air won't back feed. This is if you have a blower on the unit now. If your flue temperature gets too low, then open the air some.
 
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Old 01-04-10, 01:32 PM
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Thanks for the reply laynes

I didn't think the ducting was quite right......I went to the place that most likely sold the unit to the original owner and the salesman I talked to acted like I was a bother to him.

First he said it's wet wood....it's dried outside for 2 years in log diameter but fireplace length

Then he said that my new s/s liner is broken.....kinda doubt that

Clueless about ducting and controls

THEN he recommends that I scrap out my unit and purchase a NEW one...NOT gonna happen

We're looking for a new oil/service provider that may have an idea about this thing, if not I'll just contact a HVAC guy and swallow hard when I get the bill
 
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