In this how to a friend is asking about a problem they are having with their oil heater however the problem is much worse than they really understand. The situation is that they live in a home with Oil Heat and over the past few years the cost of Oil has been astronomical. To the point that some people replace their oil heaters with gas heat if available and others end up replacing older oil heaters that work well with newer ones just to improve the efficiency because the payback time even for 20% efficiency jump or slightly more means a new furnace is worth the cost.
With that condition some people have resorted to other forms of heating their homes. Some people who have fireplaces use them more often than for just decoration and others are installing wood burning stoves to offset or replace their oil heating costs. The price of one load of oil might pay for the wood stove and half a year of wood in some cases.
However in our friends case it seems the previous owner simply tied their wood burning stove into their chimney that is being used by their oil heater.
This is a really bad idea. No other thoughts about this but DO NOT DO THIS. It is just wrong for many reasons but first off what is likely happening when the oil heater is running it is forcing gasses out of the wood burning stove into the house. Secondly you have a $500 wood burning stove and a oil heater worth thousands of dollars and you are filing the oil heater with soot and crap from the wood stove. Really a bad idea. This is just Dangerous and stupid but people do it.
Is it legal for a wood burning stove to share a chimney?
In some states it may be legal to mix both an oil heater and a wood stove but only if they are on the same level of the home and the likelihood that you are placing a wood burning stove in close enough proximity to your oil furnace to share a chimney on the same floor of the home is near to none. Technically some states have not updated their code to protect people and this might maybe still be legal but its really a bad idea even if your situation allows it.
The best situation is to have two separate chimneys for your appliances. There should really be no other consideration because if you mix the two you end up with a soot or carbon monoxide problem at minimum and at worst a flu fire from the wood burning stove could follow down and set your oil heater on fire and maybe the oil tank with 500 gallons of fuel oil. So, don’t do this ever.
The Fix for our friend
The first thing our friend needs to do is call a heating contractor out to their home as fast as they can come. It is the beginning of the heating season so its going to be difficult but maybe they can come out and evaluate the situation. Until they do so they probably should not use either unit. They might have been using one or the other up until now but its a bad idea and unfortunately its getting cold out.
What will the fix be? At the minimum the wood burning stove needs to be disconnected and then the repairs to the chimney made. Most oil heater chimneys are a brick outside with a ceramic inside layer that is made of the same material that clay pots are made of. It is really difficult to deal with ceramic inserts and repairing the insert hole where the wood stove was added may not be possible if it is cracked. At that point a Stainless Steel liner will need to be inserted into the chimney. This might cost a few thousand depending on the contractor and work needed to be done but it can be done in a day once parts are available.
This will get their oil heater up and running after it has been serviced and cleaned. Their wood burning stove will be another matter and it will need its own chimney. For some stoves in a single story home you can go straight through the living room or kitchen roof and install double wall wood stove pipe that will exit the roof and stand up above the roof line of the house.
If the home is a two story building it will have to exit a sidewall of the home and this normally means it will be attached to the outside wall of the home with an offset distance using brackets and then it will extend above the roof line of the home.
Both of these options can be expensive but moving the wood burning stove could mean additional costs.The cost of repairing flooring and whatever else is necessary.
Finally if possible the chimney may be able to hold two different stainless steel inserts to service each unit but don’t hold your breath on that if the original chimney was built for only the oil heater because the chimney will not be large enough.
Final Note
When home owners install products like a wood burning stove it might be legal for them to do this on their own however they must follow specific regulations.
The inspection of the home at the time it was sold to the new owner should have easily caught this problem so the inspector and the realtor may be on the hook along with the previous owner to cover this dangerous situation that obviously was not disclosed.
At the very least this is work that must be performed. It is not an option and it will require professionals to do the repair.