Thread: Wood & Oil Furnace in same flue

Are there any instances that you are allowed an oil furnace adjacent to a wood furnace and the to vent in the same flue?
I am thinking no way but found a diagram that suggests it may be allowed in some areas as long as the units are on the same floor and the wood flue is connected below the oil???
Looks very fishy.. and there is a humidistat connected to the the wood burning duct that has melted..

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Looks like an older Thermo-Pride oil furnace with what they called companion units. They came as wood or coal fired systems that came with controls to tell the burner to come in when the fire was no longer warm enough to heat the space. The vent pipe seems to be correct.

I'd definitely call for a full servicing of the system by an HVAC pro. There's a lot of staining on the wall beneath the flue pipe. Heat discoloration on the cabinet above the flue pipe. And why does that barometric damper door have a chain attached to it keeping it open? The melted humidistat you already covered.

A 'companion' unit is not the same as a 'combination' unit. You cannot common vent solid fuel with other fuel fired appliances.

The common vent would have to be capable of handling both units, which oversizes it.

The chimney should have a level II inspection, which would most likely incidcate the need to reline.

There is no visible requisite cleanout

The woodstove cannot use galvanized steel smoke pipe

The barometric damper needs to be at least 2 duct diameters from that elbow and not modified but properly leveled and adjusted with a draft gauge. I couldn't see a test hole but if there is one there, it is in the wrong place.

Combination units otherwise known as "dual fuel" should be tested as listed as such. Most have very, very specific venting requirements.

HTH,
Bob

And they still build them. I tell homeowners that 'technically' it's not allowed, however the intent is to have a backup. If you primarily burn oil and the power goes out, it doesn't really hurt to light some logs until the power comes back on. But, if you primarily burn wood and decide to switch back to oil - have the chimney cleaned first to avoid a chimney fire.

True but if the power goes out, forced air isn't going to work anyway so it seemed that the intent is to use wood whenever possible and the oil will work when nobody is home.

If they had an additional flue for one of them, I could see it working but there is no room for an additional flue.

I'm thinking that the oil system needs a very good service, the flue needs a level II and wood unit should be taken out of service.

I haven't even performed the inspection yet, I was only setting a radon test.

Is there anything else I should look for? I have never had this type of setup to inspect before.

I had one of these years ago. Fan center is not needed - gravity and convection takes over. You'd be surprised. Hot air rising and cold air falling will actually create a draw in the cold air return.

In order to melt that control, you need a lot of heat. Having that much heat in a warm air plenum is scary. Could be the HX is gone. That amt. of heat in a warm air duct is a fire hazard, in addition to the CO risk.

The smokepipe does not appear to have any screws attaching it to the appliance or subsequent joints. The pipe itself appears rusted out and in need of replacement.

If you have return duct leaks, you can either backdraft the appliances or retard the draft sufficiently to cause overheating.

There is inadequate space btw appliances for inspection and service.

Usually, wood boilers require their own barometric dampers just like oil fired appliances do.

The safety that prevents the oil burner from firing concurrently with the wood would need to be tested regularly. If they fire coincidentally, it could certainly overheat both appliances. You can shut down an oil burner with a high limit but you can't with wood--it has to consume the load in the combustion chamber. These installations need their venting inspected MONTHY for creosote build up and sweeping as needed. I'm not sure if a chimney fire would have enough impact on that plenum to melt that stat but any such signs of heat stress warrant further inspection. Note the heat stress at the appliance connection. A partially plugged flue from a chimney fire will raise temps back at the appliances but will also cause backdrafting.

I think I see a combustion test hole right in the elbow where it usually is. Wrong placement but that's where 95% of the techs put it. You need 1.5-2.0 duct diameters of straight pipe to allow for proper mixing of flue gases. Samples in elbows are notoriously unreliable.

There are enough problems here to warrant a comphrehensive inspection of the chimney with reference to the appliance manuals AND inspection & service by a qualified HVAC tech, who also has access to the manuals. For one, one or the other will need to conduct a worst case draft interference test and seal duct leaks. The baro. dampes should have spill switches. The house needs low level CO protection.

Bob

It will be interesting what I find here when I'm actually at the inspection tomorrow.

Either way, they still can not combine the wood and oil flue right??

So they have no other option but to abandon the wood unit without adding a new chimney..

Jon, I recommend you locate the manuals to BOTH appliances. If it shows where those exact models are tested and listed as a SYSTEM, then the AHJ would have reasonable grounds to sign off on it. Otherwise, there's not much ground to stand on.

A mfr. may design and "approve" of a certain installation iteration but until it has been tested by a recognized testing lab to a recognized std., passed and is listed by that agency, you don't have much to hang your hat on. Most codes now require any combustion appliance to be "listed". That does not mean you can use a toaster oven in place of a chimney termination just because it carries a listing label--the listing must apply to the application[thanks to Dale Feb for that analogy].

Please try to get more pics including rating plate.

I went onto the TP website and did not see a woodburner listed. Can anyone provide a link to a TP woodburner furnace's installation instructions and possibly a brochure? --TIA
HTH Jon,
Bob

This particular unit is most probably from the early 1980s so you may not be able to find much on it. Think Reaganomics and oil embargos.

I did find an ad in an old newspaper for one tho.



Lundington Daily News - Google News Archive Search

Originally Posted by David Bell

I did find an ad in an old newspaper for one tho.



Lundington Daily News - Google News Archive Search

and the Chippiwas won the title!

i gotta learn how you looked this up and how u made a link right to it

Here is the manual for the unit.
The model # is WC-27

Here are some better pictures of this system.

What might the cause of scorching at the front of the oil unit be?
I'm still waiting to hear from the mfr about the utilization of the same flue.

holy crap ... the flue pipe for the wood burning side seems to have alot of black tar or something inside that pipe.. looks like cresote ?

The signs of heat damage at the front of the oil burner suggests either a problem with the venting, clogged heat exchanger or burner. Regardless, it must be followed up by a qualified professional. There's the rub: show me an oil tech who is certified by some agency for woodburning OR vice versa. Maybe up in Canada you'll find oil techs who are also WETT certified but it would be very rare indeed to find one in the States.

This is a great example why the listed instructions MUST be kept at the appliance. Can you imagine a tech trying to figure out that damper linkage?

The chimney connector for the oil flue cannot be galvanized steel--it will burn off as shown releasing toxic zinc vapor. The pipe should run up vertically first then slop towards the chimney at 1/4" per foot unless the mfr. has other specs. The oil burner should have its own barometric damper unless expressly prohibited by the appliance listed instructions. I don't see any screws in those pipe joints. The pipe is not supported.

I don't see a chimney liner---what's the flue look like?

I still think this setup is an abortion.