# Share Flu with propane furnace?



## eladdvf (Jan 15, 2015)

Greetings,


I have a 100 yr old 2-story farm house which is currently heated with propane (hot water radiators). We also have a propane fireplace that vents out the side (better than nothing when the power goes out, but not much more).  We also have ducts for central air (the air handler is in the same basement room as the propane boiler/furnace. I had insulation blown into the siding years ago and also blew insulation under the attic floor. The windows were replaced with triple-glass years ago. Even with those efforts its still an old leaky house by nature. I was able to reduce my annual propane bill from $3K to about $2K with a better furnace 2 years ago (and by reducing the thermostats to 66 as well (no one is happy with my cost-saving  efforts though).


My main goal is to reduce my propane bill. I am  considering  using an add-on wood furnace (either something to tie into my existing A/C duct system ... or maybe it would be wiser to buy an add on wood boiler instead?). Except for an intermittent cord of wood every now and then (when neighbor clears ditch next to farm), I would need to purchase wood.  

1.  If I purchase a wood burning add-on furnace or boiler, is it possible for me to share the same flu with the propane furnace (given that they would not be running at the same time). I am sure that adding a 2nd flu from my basement would cost a small fortune. I'd probably have to run it outside from the basement all the way up which would also look terrible.

2.  Which do you think would make more sense:  a wood boiler system to tie into my radiators or simply use my A/C ducts with forced air?  

3.  Would I still get some passive benefit from a wood burner in my basement (given a power outage situation)?

4.  I'm concerned about extended power outages (uncertain future looming IMHO)  …  wondering which system would lend itself better for  solar back-up power (may not be practical for either system… just a thought). A traditional wood burner would work for that of course, but my wife wants the mess in the basement (a dungeon in reality) which is why I'm looking at furnace add-ons.


Many Thanks !


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## 1970roadrunner (Jan 15, 2015)

1. Are you asking to use the same flue, or chimney?  You're calling it a flue, but you describe something that is actually a chimney (aka: running it outside from the basement all the way up).  No matter what is physically possible, for safety I would recommend getting a professional to inspect what you have to give you your options.  For safety and insurance coverage sake, you need to make sure everything is 100% to code for your area.  

2. Both can work, and they both make sense.  

3. You get some benefit, but its not a lot.  You have to limit your fire size in an add-on during a power outage since the unit can't shed extra heat by using the blower.  If you really want to prep for doomsday, set yourself up with a small generator that can provide enough power for your furnace blower. 

4. See above-I prefer to rely on a generator as a back-up.


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## eladdvf (Jan 15, 2015)

Thanks for the reply. You are correct that I hope to share the very same chimney if that is possible (as opposed to running a second one up the side of the house on the outside... the place that installed my propane furnace said there was not room for 2 liners in the chimney). I know they added a new liner when they  installed the propane furnace a couple of years ago too, though that may not be suitable for a wood furnace (as you said... I should get a pro to assess). I was just wondering in general if was possible for a propane gas furnace to share the same chimney liner  with an add-on wood furnace since they are not simultaneously used.

Thanks for mentioning the need to limit the fire size during an outage (wouldn't have considered that...have lots to learn).

Also... presuming you are referring to a gasoline powered generator for use with intermittent outages. Wish there was more of an off-grid power solution for longer periods ... don't have place to store a lot of gasoline currently (solar would no doubt be very expensive solution to achieve this... enough to run the radiator pumps, a well pump, and a couple of lights). A traditional wood stove in the living area is still the easiest way to go for that kind of concern

Thanks again


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## bholler (Jan 16, 2015)

If you cant run 2 liners you cant do it it would be unsafe and never pass any inspection.   With your concerns i would recommend a regular wood burner somewhere


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## F4jock (Jan 16, 2015)

No. You can't share a flue. Against every code I know of.

If you have to buy wood go pellets. Less work, lower maintainance. No matter what you choose I'd go with a boiler. Hot air heat basically sucks.


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## maple1 (Jan 16, 2015)

Can you direct-vent the propane unit?


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## Bad LP (Jan 16, 2015)

As the other wrote NO, you can't run it in the same chimney chase but if you can get two flue pipes in the opening your GTG.


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## Eric Johnson (Jan 16, 2015)

maple1 said:


> Can you direct-vent the propane unit?



This.

The reason it's against code is that any creosote deposited by the wood side has the potential of blocking the chimney when using the propane, resulting in a dangerous carbon monoxide situation. A related danger is that a chimney fire would be difficult to control if there's another source of air, i.e., the propane appliance.

All that said, I've done it, but only after physically disconnecting one or the other and thoroughly cleaning the chimney.

Ironically, it's not against code to connect a combination oil/wood boiler or furnace to a common chimney.

But, don't do it.


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## eladdvf (Jan 16, 2015)

Eric Johnson said:


> This.
> 
> The reason it's against code is that any creosote deposited by the wood side has the potential of blocking the chimney when using the propane, resulting in a dangerous carbon monoxide situation. A related danger is that a chimney fire would be difficult to control if there's another source of air, i.e., the propane appliance.
> 
> ...





bholler said:


> If you cant run 2 liners you cant do it it would be unsafe and never pass any inspection.   With your concerns i would recommend a regular wood burner somewhere


Thanks... I am back to considering a wood burner too.


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## eladdvf (Jan 16, 2015)

I cannot direct-vent the propane furnace that I know of  unfortunately (what a shame I didn't go with the super high efficiency furnace a couple of years ago as my chimney would be available if I had done that). It sounds like I should have a pro assess my set-up to confirm again whether or not I can run 2 pipes up the chimney, etc.,  and if the code in my area permits this, etc.. Otherwise, I may have to consider using a traditional wood burner. I did price that out 1st before I started exploring furnace add-ons with a local dealer in Toledo (I liked the large Summit wood burner). He wanted $1776 for the pipe materials alone + $1250 for pipe installation... then add the large PE Summit stove (it was either $3300 or 3,500) and a beautiful but overpriced one-piece hearth (and then tax), which put the final price tag over $7200. (hope I can live long enough to get that back given that I will likely be purchasing my wood most of the time). We have another dealer in town (Lopi) that I'll need to check out too if I'm back to considering a more traditional wood burner. Having never owned one my wife is concerned that the house will smell like a wood burner, that our clothes will smell like a campfire, and that the house in general will become more dirty and require more effort to maintain (cannot counter this since I have no experience with this stuff).. Thanks again for your comments... very helpful!


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## Eric Johnson (Jan 16, 2015)

I wouldn't be so quick to assume you can't direct vent your existing rig. My mom has a cheap propane boiler in her basement for a backup, and it vents right out the basement window with standard 3" galvanized stove pipe. It was installed by the local gas company that sold her the boiler, so I know it's up to code. Unlike oil, there's very little smoke and no resulting soot on the siding above the outlet. Unless you've got a long run to the foundation, you should be able to do something similar and free up your chimney in the process. I think my neighbor does the same thing with a natural gas furnace.


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## bholler (Jan 16, 2015)

Eric Johnson said:


> It was installed by the local gas company that sold her the boiler, so I know it's up to code.


Just because some gas guys did it doesnt mean it is up to code.  To my knowledge there is no appliance that can be vented through a wall with single wall galvanized pipe.  I could be wrong but i have never seen one.  For the op a power venter might be an option


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## Eric Johnson (Jan 16, 2015)

bholler said:


> Just because some gas guys did it doesnt mean it is up to code.  To my knowledge there is no appliance that can be vented through a wall with single wall galvanized pipe.  I could be wrong but i have never seen one.  For the op a power venter might be an option



Good point about the code. And I should clarify, the part going through the wall is insulated stainless steel pipe. Everything else is galv. My bad.


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## bholler (Jan 16, 2015)

Eric Johnson said:


> Good point. And I should clarify, the part going through the wall is insulated stainless steel pipe. Everything else is galv. My bad.


ok then that could be to code then possibly but the boiler needs to be able to be direct vented not all can be


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## eladdvf (Jan 16, 2015)

Good points.... I'll be sure to find out what is possible for me here.


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## peakbagger (Jan 16, 2015)

There are multifuel boilers that use one flue and use two fuels so sharing a flue is technically possible but it would need to be an appliance rated for this service. I know several folks with Tarm units that were code legal when installed (not sure now) and they work well.


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## Bad LP (Jan 16, 2015)

Single wall galvy is OK only if that's what's called for in the instruction manual. At the end of the day the manual (UL listed) overrules all codes and common sense.

FWIW my garage heater failed final inspection because we used B vent versus galvy. I'm looking at replacing it for the 3rd time and most likely will do what should have been passed in the first place.


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## STIHLY DAN (Jan 16, 2015)

Power venter's are around $500. Then use the chimney for the add on.


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## bholler (Jan 16, 2015)

Bad LP said:


> Single wall galvy is OK only if that's what's called for in the instruction manual. At the end of the day the manual (UL listed) overrules all codes and common sense.
> FWIW my garage heater failed final inspection because we used B vent versus galvy. I'm looking at replacing it for the 3rd time and most likely will do what should have been passed in the first place.


Are you saying that they want you to use single wall galvanized through a wall?  Yes the manufacturers instructions over ride code but i would be amazed if any manufacturers call for stove pipe to be used to pass through a wall.


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## eladdvf (Jan 17, 2015)

I like the idea of using a power vent and didn't know that was possible (learning so much here). I plan on visiting a local chimney/stove shop this morning that specializes in chimney work. I'll find out what my options are given my furnace model and local code requirements.  I really like the idea of freeing up that chimney. I may even ask my wife to reconsider a traditional wood burner (if we can really free up that chimney). We have a perfect spot for one in a central location next to the chimney wall (I ruled this out knowing the chimney was not available to us). 

Also, I'll need to find out more about what life is like with a wood burner though. She believes that anyone who walks in the house will immediately know we are heating with wood (smell) and fears it will make our house and clothes smell like we just came from a campfire. She also worries that in general the house will require more cleaning and fears that wood burners are just too dirty, etc. (neither of us have any experience whatsoever with them).  I'll pose this question as a new thread to see what the experience of having a modern wood burner is like.  Many thanks for all of your input!


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## bholler (Jan 17, 2015)

ou may need to go to a furnace guy not a chimney guy about the power venter.  I know we dont do them and in our area most of the furnace guys do


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## Bad LP (Jan 17, 2015)

bholler said:


> Are you saying that they want you to use single wall galvanized through a wall?  Yes the manufacturers instructions over ride code but i would be amazed if any manufacturers call for stove pipe to be used to pass through a wall.


 

Thru the wall using a thimble but the pipe itself is single wall galvy. Rusts out easily


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## Eric Johnson (Jan 17, 2015)

eladdvf said:


> Also, I'll need to find out more about what life is like with a wood burner though. She believes that anyone who walks in the house will immediately know we are heating with wood (smell) and fears it will make our house and clothes smell like we just came from a campfire. She also worries that in general the house will require more cleaning and fears that wood burners are just too dirty, etc. (neither of us have any experience whatsoever with them).  I'll pose this question as a new thread to see what the experience of having a modern wood burner is like.  Many thanks for all of your input!



It depends on how it's installed and operated. If done right, your house won't smell like smoke and neither will you. At least not most of the time.


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## bholler (Jan 17, 2015)

Bad LP said:


> Thru the wall using a thimble but the pipe itself is single wall galvy. Rusts out easily


It is galvanized outside and that is what the manual calls for?  What model is it?


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## brenndatomu (Jan 18, 2015)

eladdvf said:


> Also, I'll need to find out more about what life is like with a wood burner though.


Do you have basement access without traipsing wood and ashes through the house? That will help alleviate a lot of mess.
As far as the smoke smell, a good chimney will go a long way toward preventing any smell. Heating from the basement helps too because that usually means a tall chimney which normally equals a strong draft.
Also, some boilers/furnaces are better than others at preventing smoke rollout on reloading (thats usually where the smoky "cabin" smell comes from) but if you have a good chimney (1. tall 2. lined 3. insulated (liner) 4. an-internal-to-the-house chimney is the best (not that you can change that) you won't have to deal with smoke in the house much, if any at all.
Burning well seasoned DRY wood (cut/split/stacked a couple years, three is even better depending on species) and burning in complete cycles (reloading only when the last load is down to a few red hot coals) will help a lot with smoke in the house too.
The last item that would/could be an issue with the lil lady would be the "extra" dust. A good furnace air filter will catch most of the dust if you have a forced air system, that and be real careful to not stir things up too much when emptying out the ashes. A lot of furnaces have an ash pan that can be taken out to dump, that helps.

We heat 99.9% with wood and the house is not dusty, and I have asked people when they come over if the house smells like smoke, they said not at all.

The places that I have been in that stink usually have a stove on the ground floor with a short chimney and burn wet wood. So it is all up to you, installing a proper system, and develop good wood burning habits.


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## Bad LP (Jan 19, 2015)

bholler said:


> It is galvanized outside and that is what the manual calls for?  What model is it?


 Sterling ceiling mounted 74KBTU sealed combustion


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## eladdvf (Jan 19, 2015)

Many thanks for the great responses. Love this forum


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## cspalding0926@gmailcom (Mar 29, 2015)

eladdvf said:


> Many thanks for the great responses. Love this forum[/quot
> Better late than never, your gas furnace can vent through sidewall using a power vent. Your liner is probably not approved for woodstove venting. Just because its ss doesnt mean its made to handle wood temps and it needs insulated to keep creosote at a minimum. Im not sure what region you are in but maybe add a heat pump to gas furnace to achieve hybrid heat. We install them all the time, it generally cuts lp bills by 2/3. We usually set the balance temp at 20-25 degrees. I am located about 150 miles west of DC.


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## jdogg (Mar 29, 2015)

You can run more than one in a chimney, they did it all the time in the old days prob had a stove on every floor. But nowdays to be up to code you can't. It would prob be cheaper to run the LP furnace through something else IMO. It's like this you could prob do it (run with just one chimney) but if doing so causes the house to burn down your prob not covered. Although I don't see how doing so would cause more or greater chimney fires. The real danger is a plugged chimney by wood furnace then the LP kicks in cause say your out of wood CO2 rises and kills someone.


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## Owen1508 (Mar 31, 2015)

eladdvf said:


> 3.  Would I still get some passive benefit from a wood burner in my basement (given a power outage situation)?



Addtionally to what Roadrunner stated if you remove the blowers and rehook up the return air duct you will get a slight increase in benefit.  All in all not much but it will help the air flow.,   again small fires and keep an eye on the fire box temps.


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## jdogg (Apr 1, 2015)

Owen1508 said:


> Addtionally to what Roadrunner stated if you remove the blowers and rehook up the return air duct you will get a slight increase in benefit.  All in all not much but it will help the air flow.,   again small fires and keep an eye on the fire box temps.


I think mine said pull thermocouple (thing that looks like a finger, going next to firebox) out if power fails and your burning a fire. I think it also said you could unbolt and open one side of the furnace jacket. And yes of course you get heat from a furnace with no power enough to say keep the pipes from freezing. Would prob have to sleep in the basement after the first night though.


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## bholler (Apr 7, 2015)

jdogg said:


> You can run more than one in a chimney, they did it all the time in the old days prob had a stove on every floor. But nowdays to be up to code you can't. It would prob be cheaper to run the LP furnace through something else IMO. It's like this you could prob do it (run with just one chimney) but if doing so causes the house to burn down your prob not covered. Although I don't see how doing so would cause more or greater chimney fires. The real danger is a plugged chimney by wood furnace then the LP kicks in cause say your out of wood CO2 rises and kills someone.


It causes problems because you get allot of dilution air from the furnace which causes creosote and then if it does catch you have a good supply of air you cannot shut down coming through the furnace.  Not to mention the draft issues with both running and allot of other potential problems.  The codes are there for a good reason follow them


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## kennyp2339 (Apr 7, 2015)

To the OP - 2 story farm house, what type of square footages are we talking about, is there a open floor plan for atleast the popular rooms ie: living room, den, kitchen, dinning room? (you may or may not have these rooms) I'm have a raised ranch total square feet about 2,200 give or take. I use to have the stove in my main living area (living room) but I moved it to my semi unfinished basement this past fall because I was literally baking us out of the living room, dinning room. kitchen; kind of thinking about it even the bedrooms were to warm. Anyway the stove is in the basement, I leave the door open to the top stairs and cut a return hole in the one closet above the stairs. I use a blower (came with the stove, and usually on medium setting) I am able through nature air movement keep the popular rooms upstairs in the low 70's in the coldest of weather, my house is insulated but not tight by any means. I give you an example of my place because when it comes to free standing units the possibilities are endless, I also installed my own 6" all fuel stainless triple wall chimney, all in all its about 22ft from stove collar to chimney cap and it really wasn't that much $$ considering the savings from not heating with oil or electric.


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