Switching from Oil Furnace to Wood Stove -- Relining the chimney?

[Perididdle]

I have poured over these forums all day, and I realized it may just be easier to ask the experts here for their opinion!

We bought a 1950 house in July 2020. The sellers had some chimney work done before we moved in. From the receipt and from speaking with the chimney sweep (Company A) who did the work, we know that the chimney was relined with a 316 5.5'' flexible liner. I was told it was an Olympia brand. I didn't ask him to dig in further, though I'm sure I could.

Today, we had a chimney company (Company B) out to inspect the chimney with a plan to switch from a basement oil furnace to a main floor woodstove as our primary heat. We are hoping to get a medium-ish sized wood stove to heat our 1700 sq feet of living area, without something so big it sweats us out of the living room. We would decommission the oil furnace and use the chimney currently servicing the oil.

Company B they would need to install a new liner, as there were different requirements for wood stoves (creosote build-up) and oil gases. With some more prodding, they said they "don't recommend that type of alloy for wood stoves," and that they would install a rigid liner vs. a flexible one.

The liner is under two years old, and from my understanding, is UL rated for both wood and oil. Company A said he rarely uses rigid liners, and he did not feel like it needed to be re-lined in order to switch to wood.

So, all of that said -- is there a real reason for us to reline the chimney? Is the current liner something of concern, or is this more the Company B suggesting a hardline "best practice" of some kind? We are very safety conscious, and to an extent are happy to do the thing that will cost more now but last longer...but only if it actually has a measurable difference! I don't want to drop $2000 just because, ya know?

Thank you for your advice and help!

 

[begreen]

If the liner is in good condition then it should be ok for wood stove service. 316 is common for wood stove liners and Olympia is a good manufacturer.

 

[gthomas785]

Is the liner insulated?
Flexible liners are used all the time for wood stoves.

 

[Perididdle]

Is the liner insulated?
Flexible liners are used all the time for wood stoves.

Good question! I'll ask and see. Would a liner for an oil furnace typically be insulated?

Company B asked us if it was insulated, too, so that wasn't one of their factors in deciding to suggest a re-line. Would they be able to see that from their inspection, or is it the sort of thing you'd only know if you really get in there?

 

[begreen]

More details on the plan and construction would be helpful. Was the oil furnace in the basement? If yes, does the chimney pass up through the main floor living space in a fashion that it can be tapped into? Is this an interior or exterior chimney? Approximately how tall will the liner be from the 1st floor to the chimney cap? I am assuming that the new furnace will not need any chimney connection, that is a high efficiency unit that vents out the side wall. Is that correct? It can not share the liner with the proposed wood stove.

The furnace liner is most likely not insulated. If the chimney is interior and has 2" clearance from all combustibles, all the way up, then the liner does not need to have insulation for a wood stove. If it's an exterior chimney then the clearance is 1". That said, if it is on the short side then insulation will help improve draft.

 

[bholler]

The type of liner is fine for a wood stove installation. But a 5.5 liner is going to limit your stove choice options. Yes I would typically use a heavier liner for wood not rigid but heavier flex but that doesn't mean light wall won't work.

Now the question of insulation an oil furnace liner doesn't need insulation and probably doesn't have it. A woodstove liner should be insulated.

 

[Perididdle]

More details on the plan and construction would be helpful. Was the oil furnace in the basement? If yes, does the chimney pass up through the main floor living space in a fashion that it can be tapped into? Is this an interior or exterior chimney? Approximately how tall will the liner be from the 1st floor to the chimney cap? I am assuming that the new furnace will not need any chimney connection, that is a high efficiency unit that vents out the side wall. Is that correct? It can not share the liner with the proposed wood stove.

The furnace liner is most likely not lined. If the chimney is interior and has 2" clearance from all combustibles, all the way up, then the liner does not need to have insulation. If it's an exterior chimney then the clearance is 1".

Oil furnace is in the basement, with chimney centered in the house. The chimney goes directly straight up and at least one flat side runs along the living room wall where we would like to tap in.

Fully interior chimney. Height of liner connecting main floor to chimney cap -- rough estimate -- 20'?

We would decommission the oil furnace and use the chimney expressly for the wood stove. Oil is getting too expensive and we live on 48 partially wooded acres, with a roommate who adores chopping wood. With the centralized location, layout of the house, and heat pumps in each bedroom upstairs, we don't anticipate needing a furnace connected to the vents currently used by the oil furnace. Our current heating vent system doesn't even go to the top floor presently.

Alternative option would be to use an exterior wall in the living room and vent directly out up to the ridgeline. This would mean keeping the oil heat as a back-up back-up, but since we anticipate rarely using it (if ever), it feels like a waste. We also have somewhat limited layout options, so this would require considerable reworking of the space.

When you say chimney has clearance, I assume you mean the outer wall of the chimney, not the distance between the liner and the interior walls of the chimney? This I'm not sure of, I'll have to poke around.

Thank you for your patient sharing of knowledge!

 

[Perididdle]

The type of liner is fine for a wood stove installation. But a 5.5 liner is going to limit your stove choice options. Yes I would typically use a heavier liner for wood not rigid but heavier flex but that doesn't mean light wall won't work.

Now the question of insulation an oil furnace liner doesn't need insulation and probably doesn't have it. A woodstove liner should be insulated.

Is it sketchy to, say, fit a 6'' stove to a 5.5'' liner? I honestly don't know. And is 316 definitely a light wall, or does that vary depending the specs of the specific liner that was installed? I can see about more info from Company A.

Is insulation the sort of thing that would require a re-lining, or can it be done on top of what's already there? Or perhaps retrofitted -- pull out the liner, insulate, re-insert? I have a very fuzzy knowledge of what insulation entails.

 

[stoveliker]

@begreen
@Perididdle
"...with a plan to switch from a basement oil furnace to a main floor woodstove as our primary heat. We are hoping to get a medium-ish sized furnace to heat our 1700 sq feet of living area"

I understood there is an oil furnace now, and there will only be a woodstove later (no new furnace)?
Or is the current furnace going to be replaced by a new furnace AND a woodstove?

 

[Perididdle]

@begreen
"...with a plan to switch from a basement oil furnace to a main floor woodstove as our primary heat. We are hoping to get a medium-ish sized furnace to heat our 1700 sq feet of living area"

I understood there is an oil furnace now, and there will only be a woodstove later (no new furnace)?

Correct! Apologies, I just saw that brain fart. Yes, we will *only* have the woodstove and no new furnace. I will change "medium-ish sized furnace" to "woodstove" for clarity.

 

[bholler]

Is it sketchy to, say, fit a 6'' stove to a 5.5'' liner? I honestly don't know. And is 316 definitely a light wall, or does that vary depending the specs of the specific liner that was installed? I can see about more info from Company A.

Is insulation the sort of thing that would require a re-lining, or can it be done on top of what's already there? Or perhaps retrofitted -- pull out the liner, insulate, re-insert? I have a very fuzzy knowledge of what insulation entails.

Yes you could insulate your current liner it would probably mean pulling the liner. Removing the old clay liners insulating the liner then reinstalling.

Honestly I would not eliminate the oil furnace as a backup. The difference between heating with wood almost exclusively with a central backup. And heating with only wood no backup at all is a very big difference. No backup can mean issues with homeowners insurance. It means having someone come over to load the stove if you want to go away. It means you need to get a stove large enough to handle the most extreme temps possible with no help etc.

 

[stoveliker]

Yes, what happens if you leave one week in winter ..

Another backup could be suitable too. But any other than the current furnace will be significant extra $$..

 

[brenndatomu]

Yes, we will *only* have the woodstove and no new furnace. I will change "medium-ish sized furnace" to "woodstove" for clarity.

I'd leave that furnace be...your bank requires insurance and the ins co requires "automatic" primary heat.
Adding a chimney out through the wall likely won't cost any more than making the existing liner correct...and I'm saying since they used the oddball 5.5" size, there is probably not enough room for a 6" liner, let alone adding the insulation needed for a wood burner.

 

[Perididdle]

That's a valid concern, but I'll tell you that the herd of horses, handful of goats, gobs of chickens, and four dogs will complain about being left alone for a week well before the heating system. 😁 So that is not as big of a concern for us. We also have heat pumps serving all bedrooms and the two main rooms downstairs.

The wood stove is about 50% aesthetics, and 50% supplementing the electric for deep winter in Vermont. That said, I can still see an argument for keeping the oil back up because insurance tends to be funny about not having a centralized heating system. Hmmmm...

 

[Perididdle]

I'd leave that furnace be...your bank requires insurance and the ins co requires "automatic" primary heat.
Adding a chimney out through the wall likely won't cost any more than making the existing liner correct...and I'm saying since they used the oddball 5.5" size, there is probably not enough room for a 6" liner, let alone adding the insulation needed for a wood burner.

I see a lot of folks around the internet mentioning they have 5.5 liners. Are they really that odd? Is it not advised to attach most wood stoves rated for 6 in to one of these?

 

[bholler]

I see a lot of folks around the internet mentioning they have 5.5 liners. Are they really that odd? Is it not advised to attach most wood stoves rated for 6 in to one of these?

The majority of stove manufacturers will tell you absolutely don't do it. Regency is ok with it on all their 6" stoves. But you will still need to pull the liner remove the clay insulated the liner.cut a new crock etc. It certainly can be done but after all that work why not put in a proper 6" liner.

 

[begreen]

Yes you could insulate your current liner it would probably mean pulling the liner. Removing the old clay liners insulating the liner then reinstalling.

Honestly I would not eliminate the oil furnace as a backup. The difference between heating with wood almost exclusively with a central backup. And heating with only wood no backup at all is a very big difference. No backup can mean issues with homeowners insurance. It means having someone come over to load the stove if you want to go away. It means you need to get a stove large enough to handle the most extreme temps possible with no help etc.

It also means no heat in the basement which could end up freezing plumbing during a bad cold snap. It's also a risk if the furnace remains, but is not allowed to occasionally cycle during a bad cold snap. This could be worked around with an electric space heater in the basement.

Do you know what size the clay tile liner is? That may explain why they went with the 5.5" ss liner. If it is 7x11 then that may explain company B's response. They may want to replace it with Duraliner insulated, oval, rigid pipe which would avoid having to break out the liner.

 

[Perididdle]

It also means no heat in the basement which could end up freezing plumbing during a bad cold snap. It's also a risk if the furnace remains, but is not allowed to occasionally cycle during a bad cold snap. This could be worked around with an electric space heater in the basement.

Do you know what size the clay tile liner is? That may explain why they went with the 5.5" ss liner. If it is 7x11 then that may explain company B's response. They may want to replace it with Duraliner insulated, oval, rigid pipe which would avoid having to break out the liner.

I don't know about the clay tile liner -- time to ask!

Would any of this (replacing the tile, or replacing with an oval pipe) make more sense than doing the exterior wall pipe instead? It was suggested this was prohibitively expensive due to material costs, but if we think about keeping the furnace as an "in case", it's sort of six of one, half a dozen of another since we can't plug two sources into the same chimney.

 

[begreen]

Yes, keeping the flue system in the house is a good idea. It will keep the flue gases warmer for better draft and a cleaner liner as long as dry wood is burned. It also is a much cleaner look.

How old is the furnace? If it's very old then replacing it with a modern high-efficiency unit is one option. In some cases, it may be possible to power vent it out the side of the building.

 

[Perididdle]

Yes, keeping the flue system in the house is a good idea. It will keep the flue gases warmer for better draft and a cleaner liner as long as dry wood is burned. It also is a much cleaner look.

How old is the furnace? If it's very old then replacing it with a modern high-efficiency unit is one option. In some cases, it may be possible to power vent it out the side of the building.

So, if we keep the furnace, we'll not touch it. We'll probably just let it be! It got a clean bill of health on inspection and it surprisingly efficient for being a few decades old.

But to add a stove, we will need to decommission the furnace *or* vent the wood stove out an exterior wall. All whole-house logistics aside, just thinking wood stove here, does it make financial sense to get the chimney relined and use it instead of installing a secondary Class A chimney that goes up 2 floors?

 

[stoveliker]

removing clay tile is indeed costly.
If you have room for a chase with Class A above the floor (and stove pipe from stove until the first ceiling), that may be cheaper if you want a stove and keep the chimney for the furnace.

 

[begreen]

Keeping the oil furnace, for now, is a good plan if it is in good operating condition. It's important to have a primary system for resale of the home and insurance and it's fine to operate it as a backup to stop pipes from freezing or for when you are away.

The two choices for a wood stove installation are running the chimney up through the house or exiting out a wall and then going up the side of the house with an exterior chimney. Going straight up is preferred and with careful placement and measuring it might be able to be chased (enclosed) in a closet on the second floor. Going through an exterior wall can be done, but it may require cutting an eave or soffit and is often more expensive for parts and labor depending on the complexity of the installation.

 

[kborndale]

Having the oil furnace for backup is also good for if an unforseen injury makes you unable to use the wood stove

 

[clancey]

I would listen to Kborndale for he warned me about a expensive home check for energy and I wasted a lot of money and he was "right"....clancey