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Run new propane heater exhaust inside existing chimney for oil burner?

joea99
joea99 Member Posts: 56
I'm half expecting "are you mad?" replies, but, here goes.

Have existing oil fired hot water baseboard. Domestic HW is already on propane, on demand heater.

Oil burner is in basement/cellar and flue currently ends in the masonry chimney void and makes its way up one floor and an attic space. Maybe 25-30 feet.

Thinking of going to propane due to expected high cost of oil. Would like it to be as close to existing unit as possible to simplify piping.

I would like to keep the oil burner as "backup" and wonder if it is legal/sane to run both exhaust in the same masonry chimney, simply adding appropriate metal flue for the propane?

While just running metal flue for the propane might not be wise, what about also adding metal for the oil burner and both essentially sharing the masonry void as a common "chase"? Would that be OK?

Comments

  • Hot_water_fan
    Hot_water_fan Member Posts: 744
    Both oil and propane will be expensive. If “payback” is the primary consideration, I’d quit now. 
  • pecmsg
    pecmsg Member Posts: 3,087
    You might get a return on investment in 30 - 40 years. 
    As oil goes so does NG and Lp!
  • hot_rod
    hot_rod Member Posts: 16,911
    edited July 30
    Propane nowadays comes mainly from natural gas cracking, and the LP groups claim 90% of the LP is made in the US.
    With a glut of NG, in theory the Lp prices do not necessarily follow the crude oil or fuel oil prices.
    In LP prevalent areas you can buy in off season, or lock in to a pre buy agreement at lower costs.

    But more is involved in a energy decision, like the equipment operating condition and efficiencies. An over sized short cycling oil fired boiler could be running in the 55- 60% range according to Brookhaven Labs testing.  If you can modulate and condense the LP boiler it may run 90%

    So the comparison needs to include more than cost and btu content of the fuels.

    Having a bi or tri fueled system is not a bad approach if it can be done economically. You may notice a lot of fuel oil dealers now offer LP also😉.
    It is quite possible that an electric boiler can be more cost efficient in some areas. Low kWh rates and off peak or time of day rates. 
    20 some states have electric at or below .12, but you need to look at delivered costs, of course.

    And it depends on whos crystal ball you most believe.

    https://coalpail.com/fuel-comparison-calculator-home-heating
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterMan
  • joea99
    joea99 Member Posts: 56
    I've got a locked in price for propane for the next year. Oil only till mid season but I half expect them to try to renege on the oil contract. It's a big outfit, but who knows.

    I know my oil fired unit is oversized and short cycles. It was put in about 10-15 years ago to replace an ancient "tiny" (maybe 85,000 BTU?); Previous owner said it ran almost all the time during cold spells.

    A heat calculation was done and came in at about 105,000 BTU and I was convinced to go larger because "better to have too much than too little on those cold days". Not knowing any better, went along. Been unhappy with the short cycling ever since.

    Even so, something that was overlooked is the house has 4 zones which makes it "Micro Zoned". Anyway getting off track.

    Let's put that aside and get back to the original question, would it be "legal/safe/sane" to put both the oil and the propane vents in one chimney? Or, just pipe the propane and let the oil continue to vent into the chimney as it does now?
  • pecmsg
    pecmsg Member Posts: 3,087
    PVC in the same chimney used to vent oil?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,695
    edited August 1
    As far as venting both LP or Natural Gas into the same chimney as the operating (or able to operate) oil fired unit, I see no problem. There is a correct way to do it, and a wrong way to do it. First thing is you need at least 2 but 3 openings at the chimney base is better. The Natural Gas companies fought hard for this practice top be acceptable. This way an oil heat or coal converted to oil heat customer could add one gas fired appliance when the domestic hot water coil on their oil boiler (heat and hot water from the same appliance. The fuel oil dealers called this a "Summer/Winter hook-up") would fail. The natural gas company could offer to install a stand alone 30 or 40 gallon water heater for a lot less than the oil company repair of replacing the tankless coil. Now that the customer has a gas meter in the home, asking them to convert the heater from oil to gas was a lot easier. "Plan ahead marketing"

    There are still many oil heat customers with gas fired water heaters venting into the same chimney.

    Enough of the history lesson. The right way to add a gas (LP or Natural) to an existing oil heat chimney is to:
    1. See that the chimney can handle all the appliances that can operate at the same time. (if the oil heat will never operate when the oil heater is operating, then you must install a lockout relay in order to prevent both burners form operating at once unless the chimney can handle both (all) loads at once.
    2. Have the masonry chimney lined with stainless steel chimney liner material. (this will reduce the inner dimension of the chimney and the BTU capacity of the chimney, so repeat step one
    3. Have at least 2 tee fittings at the chimney base, one just above the other. This is because oil fired appliances will accumulate more solid debris at the chimney base.
    4. Connect the oil fired appliance a the lower connection. If the lower vent connector somehow fills up with debris, the oil fired appliance will probably cause odors and visible soot damage before the Carbon Monoxide (CO) gets to a deadly level in your home. (oil is more likely to be the problem and more likely to be discovered early)
    5. The upper flue connector is for connecting the gas appliance. Since LP and Natural gas can make CO at dangerous quantities with much less odor and soot, you don't want the oil heater to operate properly while the gas vent is blocked allowing odorless colorless CO escape into your home.

    I'm not saying this is the best reasoning because an oil fired appliance can let dangerous CO levels escape in to your home of the vent is partially clogged, or if there is a momentary downdraft or other venting issue. I'm just telling you how it was explained to me many years ago, when Oil Burners were much less efficient.

    Ideally you would vent every appliance in a separate chimney. but building a masonry chimney for every wood stove, kitchen stove, oil burner, water heater, coal heater fireplace, and trash incinerator back in the day was quite expensive. So the fire inspector(s) and insurance inspectors would create and update the code based on what happened at that last fire and how can we prevent it from happening again.

    I believe the dual fuel in the sale chimney is still ok for Gas and OIL. Never put a hand fired appliance (Wood, Coal, Pellet) into an automatic fired appliance (Gas or Oil) in the same chimney. That is what I was taught and I have stuck with that my entire professional career.

    Mr. Ed
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org

    jasonmm
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,695
    edited July 31
    Here are the 3 openings recommended. T
    The bottom is for maintenance

    Also I assumed you were talking about a cast iron old style heater. The kind that will last forever and has a metal vent connector to a chimney...
    SO! WHAT HE SAID!
    pecmsg said:

    PVC in the same chimney used to vent oil?

    Don't vent a condensing boiler into a chimney. Follow the manufacturer's venting instructions on any vented appliance. You usually cant go wrong if you understand and follow the instructions.

    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org

  • Labenaqui
    Labenaqui Member Posts: 59
    May I suggest a new/used IWH (Superstor) for your DHW? Upgrade your current oil boiler aquastat to a Hydrolevel 3250-Plus Hydrostat (if necessary), zone in your IWH with Cold Start/Economizer Operation. Our customers are also in a Fuel Co-Op (NH) yielding 10-40% savings, depending upon the market. Note: Propane is locally a 62% premium per our calculations.

    jasonmm
  • joea99
    joea99 Member Posts: 56

    Here are the 3 openings recommended. T
    The bottom is for maintenance

    Also I assumed you were talking about a cast iron old style heater. The kind that will last forever and has a metal vent connector to a chimney...
    SO! WHAT HE SAID!

    pecmsg said:

    PVC in the same chimney used to vent oil?

    Don't vent a condensing boiler into a chimney. Follow the manufacturer's venting instructions on any vented appliance. You usually cant go wrong if you understand and follow the instructions.

    The oil fired unit is cast iron, a Burnham V-something, 8 I believe. It vents directly to the chimney via single wall pipe, 6 or 8 inches.

    I would definitely NOT vent any gas unit directly to the same space, but am asking about it being OK to run the appropriate vent pipe in the same space. PVC would seem to mean also altering the oil fired exhaust to be piped all the way up as well. The flue gas temp of the oil unit would likely not be good for the PVC.
  • joea99
    joea99 Member Posts: 56
    Labenaqui said:

    May I suggest a new/used IWH (Superstor) for your DHW? Upgrade your current oil boiler aquastat to a Hydrolevel 3250-Plus Hydrostat (if necessary), zone in your IWH with Cold Start/Economizer Operation. Our customers are also in a Fuel Co-Op (NH) yielding 10-40% savings, depending upon the market. Note: Propane is locally a 62% premium per our calculations.

    I already have an indirect unit, not a SuperStore, but that type. I got tired of buying oil year round (last time it got outrageously expensive) and having a hot basement in the summer, so went for an on demand Tagaki. I have them plumbed in "parallel" with the indirect as a backup. I also once had the idea of using the indirect to supply a radiant system for an addition that is, still, in the day dream stage.

    I use propane also for cooking and for a backup generator. Here in the burbs and woods, we lose power way too often to go without. Right now, I'm locked in a little over $3.00 for propane and little more for oil. But I expect to hear some loud noises when delivery resumes this fall.
  • Hot_water_fan
    Hot_water_fan Member Posts: 744
    edited July 31
    $3 for propane is about $4.5 for oil. Is there another motivation beyond payback here? How much savings are realistic? 
  • Bob Harper
    Bob Harper Member Posts: 932
    You can common vent oil and LP (or NG) into the same flue IF: There is sufficient capacity, both appliances have "primary safety controls" and it works.
    The chimney must have a Level II inspection per NFPA 211. This will undoubtedly call for a liner. However, you cannot run one liner inside an active flue. You could run co-axial (side by side liners) much akin to a double-barreled shotgun. However, if there is sufficient room, why not just size one liner for both? You can configure the connections as shown in Ed's fine drawing.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,695
    edited August 1
    I seem to think that @joea99 did not understand my first comment that says the gas and oil appliance CAN be vented into a common chimney.
    joea99 said:


    I would definitely NOT vent any gas unit directly to the same space, but am asking about it being OK to run the appropriate vent pipe in the same space. PVC would seem to mean also altering the oil fired exhaust to be piped all the way up as well. The flue gas temp of the oil unit would likely not be good for the PVC.

    So I guess your question should read "Can I use an existing Masonry chimney as a chase for venting 2 separate boilers that are burning 2 different fuels, OIL and LP Gas?"

    If this is your query, then the answer is YES, if there is enough room to get 2 separate vent pipes to the top. This seems unlikely though, since the chimney is probably not large enough to have a 8" pipe and a second smaller pipe for the gas appliance within the confined of that space. If you have a gas boiler that is vented with metal stove pipe, then why not just put them in the same opening as I suggested in my previous comment https://forum.heatinghelp.com/discussion/comment/1706478#Comment_1706478
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org

  • joea99
    joea99 Member Posts: 56

    $3 for propane is about $4.5 for oil. Is there another motivation beyond payback here? How much savings are realistic? 

    Current COD price for oil around here is almost $6.00.

    The motivators are: Less messy maintenance; greater inherent efficiency of the gas fired unit; better fuel usage by properly sizing this unit, Oil burner short cycles and apparently is only effectively 50-60% efficient. It is only 78% at best according to the label.
    Hot_water_fan
  • joea99
    joea99 Member Posts: 56

    You can common vent oil and LP (or NG) into the same flue IF: There is sufficient capacity, both appliances have "primary safety controls" and it works.
    The chimney must have a Level II inspection per NFPA 211. This will undoubtedly call for a liner. However, you cannot run one liner inside an active flue. You could run co-axial (side by side liners) much akin to a double-barreled shotgun. However, if there is sufficient room, why not just size one liner for both? You can configure the connections as shown in Ed's fine drawing.

    Thanks. I'm looking to be educated on the issues. I was under the impression that a gas flue would need to be 3-4 inches, depending on unit, while the oil fired needs to be 6-8 inches. Also thought I had read somewhere that one could not mix dissimilar fuels into one flue.
  • joea99
    joea99 Member Posts: 56

    I seem to think that @joea99 did not understand my first comment that says the gas and oil appliance CAN be vented into a common chimney.

    joea99 said:


    I would definitely NOT vent any gas unit directly to the same space, but am asking about it being OK to run the appropriate vent pipe in the same space. PVC would seem to mean also altering the oil fired exhaust to be piped all the way up as well. The flue gas temp of the oil unit would likely not be good for the PVC.

    So I guess your question should read "Can I use an existing Masonry chimney as a chase for venting 2 separate boilers that are burning 2 different fuels, OIL and LP Gas?"

    If this is your query, then the answer is YES, if there is enough room to get 2 separate vent pipes to the top. This seems unlikely though, since the chimney is probably not large enough to have a 8" pipe and a second smaller pipe for the gas appliance within the confined of that space. If you have a gas boiler that is vented with metal stove pipe, then why not just put them in the same opening as I suggested in my previous comment https://forum.heatinghelp.com/discussion/comment/1706478#Comment_1706478
    Yes, that is an accurate phrasing of my original question. Seems there are a number of options, so I can start looking at units knowing a bit more that I did.

    I first looked a year or so ago, and got the impression they wanted dedicated piping all the way to ultimate exit point.

    The gas unit I have is a Takagi TK-3, which has a short stainless concentric intake/exhaust directly through a side wall.
  • Hot_water_fan
    Hot_water_fan Member Posts: 744
    @joea99 you’re using around 1000 oil gallons per year? 
  • pecmsg
    pecmsg Member Posts: 3,087
    joea99 said:

    $3 for propane is about $4.5 for oil. Is there another motivation beyond payback here? How much savings are realistic? 

    Current COD price for oil around here is almost $6.00.

    The motivators are: Less messy maintenance; greater inherent efficiency of the gas fired unit; better fuel usage by properly sizing this unit, Oil burner short cycles and apparently is only effectively 50-60% efficient. It is only 78% at best according to the label.
    Dont forget to add in the extra cost of maintaining that gas fired heater along with all the bells and whistles that can and will fail. There not cheap and at times unavailable.

    As oil goes so does NG, LP and Electric!

    I also question 1000 gals oil. Somethings not right.
  • joea99
    joea99 Member Posts: 56
    edited August 1

    @joea99 you’re using around 1000 oil gallons per year? 

    Don't think I said I used 1000 gallons. More like 500-700. While I feel even that is too much, when I signed up with a supplier last winter, they seemed to think that was typical usage. They did not seem to think "short cycling" was unusual either, so apparently there have been a lot of over sized units installed over the years in this area.
    Hot_water_fan
  • pecmsg
    pecmsg Member Posts: 3,087
    One issue with using a oil supplier is Their business is to sell oil!
    MikeAmann
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,695
    edited August 1
    joea99 said:

    I seem to think that @joea99 did not understand my first comment that says the gas and oil appliance CAN be vented into a common chimney.

    So I guess your question should read "Can I use an existing Masonry chimney as a chase for venting 2 separate boilers that are burning 2 different fuels, OIL and LP Gas?"

    If this is your query, then the answer is YES, if there is enough room to get 2 separate vent pipes to the top. This seems unlikely though, since the chimney is probably not large enough to have a 8" pipe and a second smaller pipe for the gas appliance within the confined of that space. If you have a gas boiler that is vented with metal stove pipe, then why not just put them in the same opening as I suggested in my previous comment https://forum.heatinghelp.com/discussion/comment/1706478#Comment_1706478
    Yes, that is an accurate phrasing of my original question. Seems there are a number of options, so I can start looking at units knowing a bit more that I did.

    The gas unit I have is a Takagi TK-3, which has a short stainless concentric intake/exhaust directly through a side wall.


    This Takagi is already operating, Correct?
    It is currently vented according to the manuf. instructions Correct?
    So this is not the LP Gas appliance that you are proposing for space heating, Correct?

    Based on the model of the proposed LP heater, you may be able to vent into the same chimney as the operating oil heater chimney. You need to select the appliance before you determine the venting options. There are basically 4 different venting categories when it comes to appliance venting.

    Category I is an appliance where the flue gas temperature is high enough to prevent condensation of the flue gas inside the flue pipe and chimney AND the flue gas pressure inside the pipe is lower than atmospheric pressure around the pipe. also called natural draft. If there is a leak or opening in the vent pipe, room air will leak into the vent pipe so no gasket or sealant is required. Your oil burner is vented this way. An old school lowest cost steel or cast iron gas boiler or furnace with a draft hood would be a Category I vent appliance. Both the oil and gas appliance of this Category can be in the same chimney.

    Category II venting is an appliance that has a flue temperature that is lower that a Category I, so condensation of the flue gas will occur and therefore requires special venting material that will hold up against the corrosive nature of that condensate. The Category II is also at a lower pressure inside the pipe than outside the pipe. This is a rare venting design. This can not be vented in the same chimney with the oil burner.

    Category III is a high temperature vent with a positive pressure inside the pipe usually as a result of a combustion fan of some type. There will be no condensation of flue gas. Since the exhaust gas is under pressure, the piping must be sealed at every joint and seam to prevent flue gas from leaning out of the pipe into the living space. Your Takagi is a Category III. This can not be vented in the same chimney as the oil burner

    Category IV appliance is very common. This is low temperature venting and under pressure. There is usually a fan that forces or draws the combustion gasses thru the appliance. The fan creates a positive pressure in the vent pipe. Often this appliance is vented with plastic vent pipe like PVC. This can not be vented in the same chimney as the oil burner.

    The Category I appliances are usually the simplest design with few moving parts. This makes them the lower cost option for purchase and for maintenance and repair. Their top efficiency is about 80 to 85% AFUE. The Category IV appliances are always over 89% AFUE and often reach 96% AFUE. The energy savings of the high efficiency appliance is often offset by the cost of maintenance and repair. So make your appliance choice based on installation cost, operating cost and future repair and maintenance cost.
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org

    MikeAmann
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,695
    Labenaqui said:

    May I suggest a new/used IWH (Superstor) for your DHW? Upgrade your current oil boiler aquastat to a Hydrolevel 3250-Plus Hydrostat (if necessary), zone in your IWH with Cold Start/Economizer Operation. Our customers are also in a Fuel Co-Op (NH) yielding 10-40% savings, depending upon the market. Note: Propane is locally a 62% premium per our calculations.

    You may always suggest a Superstore @Labenaqui, It is highly unlikely that @joea99 will follow your suggestion as he already owns a Takagi tankless.

    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org

  • Hot_water_fan
    Hot_water_fan Member Posts: 744
    Don't think I said I used 1000 gallons. More like 500-700. While I feel even that is too much, when I signed up with a supplier last winter, they seemed to think that was typical usage. They did not seem to think "short cycling" was unusual either, so apparently there have been a lot of over sized units installed over the years in this area.


    Thanks for the clarification. What state are you in? What I'm getting at is that using 500-700 gallons per year is not very much for a home with a heat loss of 105,000 btu. So if the previous owner was correct that the 85kbtu boiler ran nearly non-stop during cold spells, that puts your heat loss probably in the 70kbtu range, which is good news! It also means there's limited savings opportunities, but obviously the switch would get rid of the mess. The sizing concerns are unrelated to fuel source (at this heat loss, it changes for lower heat loss houses).
  • joea99
    joea99 Member Posts: 56

    Don't think I said I used 1000 gallons. More like 500-700. While I feel even that is too much, when I signed up with a supplier last winter, they seemed to think that was typical usage. They did not seem to think "short cycling" was unusual either, so apparently there have been a lot of over sized units installed over the years in this area.


    Thanks for the clarification. What state are you in? What I'm getting at is that using 500-700 gallons per year is not very much for a home with a heat loss of 105,000 btu. So if the previous owner was correct that the 85kbtu boiler ran nearly non-stop during cold spells, that puts your heat loss probably in the 70kbtu range, which is good news! It also means there's limited savings opportunities, but obviously the switch would get rid of the mess. The sizing concerns are unrelated to fuel source (at this heat loss, it changes for lower heat loss houses).
    I'm in New York, Mid Hudson valley area. I guess if I felt the Burnham was not short cycling, with the implied lower efficiency, I might not be so eager to change. But I already have it down fired to .85 GPM, which is the lowest they spec for this unit. I suppose I could go lower still, but I should probably try to contact Burnham for confirmation. Though last time I tried I was told they only provided support to "Professionals". Honesty is not always the best policy I guess. BTW, I do have a Bacarach combustion test kit for oil burners. Got it on Ebay years ago when it became clear the service groups here did "eyeball and sniff" tests when servicing.
    MikeAmann
  • joea99
    joea99 Member Posts: 56



    The gas unit I have is a Takagi TK-3, which has a short stainless concentric intake/exhaust directly through a side wall.


    This Takagi is already operating, Correct?
    It is currently vented according to the manuf. instructions Correct?
    So this is not the LP Gas appliance that you are proposing for space heating, Correct?

    The TK-3 has been in operation for years and is only used for Domestic Hot water and uses their approved concentric intake/exhaust fittings.

    Anything for the baseboard hot water would be an additional unit. I have heard of people claiming they use on demand domestic hot water units for baseboard heat. But I wonder about the wisdom of that approach.

    Thanks for the description of the various categories.

  • Hot_water_fan
    Hot_water_fan Member Posts: 744
    I'm in New York, Mid Hudson valley area. I guess if I felt the Burnham was not short cycling, with the implied lower efficiency, I might not be so eager to change. But I already have it down fired to .85 GPM, which is the lowest they spec for this unit. I suppose I could go lower still, but I should probably try to contact Burnham for confirmation. Though last time I tried I was told they only provided support to "Professionals". Honesty is not always the best policy I guess. BTW, I do have a Bacarach combustion test kit for oil burners. Got it on Ebay years ago when it became clear the service groups here did "eyeball and sniff" tests when servicing.


    Give this a shot: https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

    That's a pretty cold climate and not very much oil usage. Getting the specific fill up dates and exact heating degree days will help with sizing. Unless you're going on long winter vacations, your heat loss is much lower than you think. Even with the decreased efficiency, you're probably talking a ratio of 10-20x the installation cost to the best case fuel savings, which is a lot of risk to take on. Plus there's an alternative way: wait to see if the oil supplier breaks the contract before spending on a replacement.
  • joea99
    joea99 Member Posts: 56

    I'm in New York, Mid Hudson valley area. I guess if I felt the Burnham was not short cycling, with the implied lower efficiency, I might not be so eager to change. But I already have it down fired to .85 GPM, which is the lowest they spec for this unit. I suppose I could go lower still, but I should probably try to contact Burnham for confirmation. Though last time I tried I was told they only provided support to "Professionals". Honesty is not always the best policy I guess. BTW, I do have a Bacarach combustion test kit for oil burners. Got it on Ebay years ago when it became clear the service groups here did "eyeball and sniff" tests when servicing.


    Give this a shot: https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

    That's a pretty cold climate and not very much oil usage. Getting the specific fill up dates and exact heating degree days will help with sizing. Unless you're going on long winter vacations, your heat loss is much lower than you think. Even with the decreased efficiency, you're probably talking a ratio of 10-20x the installation cost to the best case fuel savings, which is a lot of risk to take on. Plus there's an alternative way: wait to see if the oil supplier breaks the contract before spending on a replacement.
    Wow, that article has a lot to digest.

    One thing that did hit me right off is his contention that "short cycling" is not really a big hit, if any, on efficiency, it is more one of annoyance and potential faster wear out of components.

    I still feel I'm using "too much oil", but that may just be my wallet pinching my back end.

    Not sure I can use the suggested method of measuring oil usage to determine heat load, as I do have a wood stove and mini splits. Aging brain being what it is, I cannot be sure how often I used either. So, I may do one of the other calculations again as an exercise.
    Hot_water_fan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,695
    edited August 1
    joea99 said:


    The TK-3 has been in operation for years and is only used for Domestic Hot water and uses their approved concentric intake/exhaust fittings.

    Anything for the baseboard hot water would be an additional unit. I have heard of people claiming they use on demand domestic hot water units for baseboard heat. But I wonder about the wisdom of that approach.

    Thanks for the description of the various categories.

    Good that you wonder about the wisdom of using a DHW appliance for space heating. If you search enough on this and other forums, you will see that this mismatch is nothing but problems.

    As far as selecting a new LP Gas appliance, you can select one that is very close to the 99% design temperature load calculation in that article from @Hot_water_fan. Since your intention is to keep the existing oil heat in place, If you ever get to a condition where you need 78° and the outdoor temperature is below the design temperature, all you need to do is crank up the oil boiler.

    Or the wood stove, or any of the other heaters you mentioned.

    Once you select the replacement boiler, then you can decide on the venting design, after that you will want an efficient way to keep the gas heat from being wasted into the non-operating oil heater. You can manually valve it off or you can do it with innovative piping design like Primary/Secondary. That is a whole different discussion on the best way to connect both boilers to heat the same radiators... but only one at a time.

    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org

  • Hot_water_fan
    Hot_water_fan Member Posts: 744
    One thing that did hit me right off is his contention that "short cycling" is not really a big hit, if any, on efficiency, it is more one of annoyance and potential faster wear out of components.


    It depends - for furnaces, probably minor efficiency hit because they’re physically lighter. More so for boilers, but you can get one with a “thermal purge” which dumps the residual heat into the house. It may be annoying and will wear more, but maybe not at a meaningful rate.
  • Bob Harper
    Bob Harper Member Posts: 932
    Just to reiterate: The code DOES allow you to common vent liquid and gaseous fuels as I stated above with the 3 requirements. You don't have to run them into separate liners unless you want to. However, liners must be supported at the top with their listed top support plate, which is not going to accommodate co-linear (side by side) liners in the same flue. No liners are listed for use co-linear I'm aware of except for gas inserts (intake and exhaust). You could run type L vent side by side if its a straight up chimney but the sulphur from the oil will eat up the outer jacket.
    If you want to power vent an appliance into a chimney, it cannot be common vented with a CAT I or II appliance and should not be common vented with anything, even though some mfrs. condone the practice. Any venting under positive vent pressure must by listed, which precludes PVC in the US. You can use polypro flexible liners listed to UL 1738 for CAT IV.