Oil to gas conversion

[RJHNY1]

Those are awesome posts Dana. You're a pretty smart and knowledgeable person and I thank you for taking the time to type all that out.

I actually do have solar on my home, which was installed two years ago.

So, rather than convert from oil to gas, it sounds like you favor the use of heat pumps instead. I really don't know much about it and haven't looked into it.

I spoke to someone at Energy Kinetics and this is what he said: The efficiency of an oil fired System 2000 is 87.6% AFUE and a gas fired is 85% AFUE. You will not notice any difference in the amount of BTU’s (gallons or therms) purchased if you switch fuels. The only difference will be the cost of the fuel which can vary from one year to the next.

While all of you have provided great advice, which I'm very thankful for, I'm feeling overwhelmed with all of the information. I'm not sure how I should proceed or if converting to gas is worth it.

 

[Dana]

I'm feeling overwhelmed with all of the information. I'm not sure how I should proceed or if converting to gas is worth it.

Start by running the (wintertime only) fuel-use based load calculation. If you're willing to share your ZIP code and some December-February fill up exact dates and amounts I'll run them for you. Use the ~88% efficiency of the EK 2000 for that calculation if you like, even though without a freshly tuned burner it's likely to be a percent or two lower than that. Then you would at least have a starting point for thinking about it. If you're on a regular fill-up service that stamps a "K-factor" on the fill up slips, a couple of wintertime K-factors is enough information to get there. (In this context K-factor is base 65F heating degree-days per gallon, the inverse of gallons per heating degree-day,, from which a BTU per degree-hour constant is derived.)

Do you have central air conditioning? If not, would you LIKE central air? That would be driver tipping the scales more toward spending the money on a heat pump solution rather than boiler + AC.

The odds are high that all of the previously quoted replacement equipment are grossly oversized and inappropriate. I haven't looked in to the specifics, but since the EK 2000s are also sold in gas-fired versions, it's highly likely that switching to a gas burner is possible at a fraction of the cost of a full replacement, and with their proprietary heat purging boiler control oversizing that particular boiler isn't always an efficiency disaster. The cost of an appropriately sized retrofit gas burner might even be lower than replacing the failing oil tank.

Once you have a load number, a good place to look for equipment that covers the load is NEEP's online searchable database of cold climate heat pumps. Use the sliders and pull down menus near the top to narrow the selections. The individual short-sheet specs show what the model can deliver at +5F at it's maximum (and minimum) speeds, and again at +17F (an AHRI test temp for HSPF, which is close to your 99% design temp) +47F (the other AHRI test temp for heating) as well as cooling capacity a 82F (the SEER test temp) and 95F (the EER test temp).

For example, say you came up with an fuel use load number of 31,500 BTU/hr and narrowed it down to ducted Carrier heat pump systems that deliver between 30-40,000 BTU/hr @ +5F, one of which is this model. It's probably a bit overkill since at max speed it delivers 50,500 BTU/hr @ +17F, but it would work. This one might be more appropriate, since it delivers 42,500 BTU/hr @ +17F. That's an oversize factor of 42,500/31,500 = 1.35x, pretty close to the ASHRAE recommended 1.4x oversizing, whereas it's big brother is 50,000/31,500= 1.59x. The more important numbers for comfort would be the minimum output rate at +47F, since that will determine whether it's modulating with load most of the season vs. cycling on/off most of the time ( or even short-cycling, if grossly oversized.)

 

[Sponsor]

 

[RJHNY1]

Dana, I will PM you the information that you requested.

Yes, I do have central air. How expensive is it to move over to heat pumps? Would the hot air come out of the same vents as the central air? We have monoflow heating and we hate it.

 

[RJHNY1]

What is model of the boiler? Take few pics of boiler, pumps, water heater and piping around the boiler. What nozzle size does the burner have? Need to know the cost of a gallon oil delivered with tax 140,000 btu's and a therm of gas find the cost.

Hi, sorry I took too long to post this, but here's a picture of my set up:

 

[RJHNY1]

Heating cost calculator
https://c03.apogee.net/mvc/home/hes/land/el?spc=hcc&utilityname=pseg

It seems that I would only save about $300 a year with gas. I'm not sure if that's accurate.

I calculated it this way:

2200 square foot home. I was told the Energy Kinetics has 87% efficiency with oil and 85% efficiency with gas. I keep my home at 68 degrees in the winter. I have no idea my air tightness, so I just slide it between "ok" and "good." I paid $2.23 per gallon of oil this past winter. I would pay $21.66 for the first 3 therms, $1.28 for the next 47 therms, and then .29 cents every therm over 50. This calculator doesn't really account for that, so I just plugged in $1.28 therms.

Using those metrics, it's $1,334 for gas and $1,637 for oil.

I did pay $2,569 for oil in the winter of 2018-2019 and $2,179.39 in the winter of 2019-2020.

 

[Fitter30]

At $1.28 therm ,a gallon of oil 140k btu's. Add 40% to the gas to equal oils btu's $1.79
140k btu @87%= 121800
140k btu @85%= 119000
Saint louis nat gas $1.03 therm all in

 

[RJHNY1]

At $1.28 therm ,a gallon of oil 140k btu's. Add 40% to the gas to equal oils btu's $1.79
140k btu @87%= 121800
140k btu @85%= 119000
Saint louis nat gas $1.03 therm all in

I'm sorry for asking this dumb question, but I'm a novice here. What does that mean?

 

[Fitter30]

Therm of nat gas is 100k btu's @ $1.28
Gallon of oil 140k btu's
to compare cost oil has 40% more btu's than gas. Add 40% to the price of gas to make them equal.
difference in efficiency 87% to 85% is only 2800 btu's
Oil cost $2.23 gas $1.79
$.44 cheaper 20%

 

[RJHNY1]

So in other words, you're saying that a conversion is not worth it. Am I interpreting that correctly?

Thank you.

 

[Fitter30]

Gas is 20% cheaper call the boiler manufacturer see if their gas burner can be retrofitted into your boiler. Like a pic of the main pump and expansion tank. Also the brand and numbers off of the plate heat exchanger for the domestic hot water.

 

[RJHNY1]

The Energy Kinetics System 2000 can be converted into a gas boiler. The manufacturer sells a conversion kit. The problem is, two Energy Kinetics dealers quoted me $8-9K just to convert. The job would entail a chimney liner, running pipe from the meter to boiler, removal of the oil tank, and replacing the burner. It doesn't seem like a good investment for me and would take me years and years to see any payoff from that kind of investment.

Did you want a pic of the main pump and heat exchanger? I'm not sure what you're asking/saying about that.

Thanks again!

 

[Dana]

Dana, I will PM you the information that you requested.

Yes, I do have central air. How expensive is it to move over to heat pumps? Would the hot air come out of the same vents as the central air? We have monoflow heating and we hate it.

If the ducts are sized reasonably and fully inside the home's pressure & insulation boundaries they can probably be used for both heating & cooling. If so, the same registers would be blowing warm (not super hot) air if a heat pump gets swapped in.

What is the model number & /or capacity of the existing air conditioner? The model number of the air handler as well as the condenser would be useful. In an ideal situation (usually only in dreams ) the existing air handler can be used and there would only a swap out of the condenser for a heat pump. That requires a lot of stars to be aligned to work efficiently and well.

Since most existing central air systems in the northeast are grossly oversized for the actual loads (some idiot back in the '90s installed 5 tons of AC for ~2 tons of load in my house- I'm almost hoping it will die so I have a good excuse to replace it) it's possible that the ducts are already nice and fat so that you'd end up with nice low duct velocities (=quieter, and more efficient if they are inside the building's thermal & pressure boundaries) when installing a right-sized system.

Roughly how many square feet of conditioned space do you have currently (not counting the future 500' addition, that is)?

 

[RJHNY1]

My home is 2160 sq feet to be exact. I have 2 zone Trane Ameristar Condensers and Air Handlers. They're 2 Ton, 3 and half Ton 16 SEER. I don't have the model numbers off hand and would have to get it for you. Getting the Model # for the handler is going to be almost impossible b/c it's in the attic and the space up there is tight. The condenser, I can go outside and look tomorrow.

I have to imagine heat pumps are expensive and is probably not an option I'm going to pursue at the moment. As you explained, it seems like too much has to go right for it to work with my current central air.

 

[Dana]

My home is 2160 sq feet to be exact. I have 2 zone Trane Ameristar Condensers and Air Handlers. They're 2 Ton, 3 and half Ton 16 SEER. I don't have the model numbers off hand and would have to get it for you. Getting the Model # for the handler is going to be almost impossible b/c it's in the attic and the space up there is tight. The condenser, I can go outside and look tomorrow.

I have to imagine heat pumps are expensive and is probably not an option I'm going to pursue at the moment. As you explained, it seems like too much has to go right for it to work with my current central air.

Five tons of AC for a 2200' house is actually pretty ludicrous, even if this was an uninsulated tarpaper shack with single pane windows in a sticky Louisiana swamp. There is no way the 1% cooling loads are that high, and even if the air handlers are compatible with heat pumps replacing the condensers it's likely to be WAY sub-optimally oversized for comfort or efficiency. If you don't believe me, run some simplified online Manual-J-ish load calculations using aggressive assumptions about air leakage (assume your house & ducts are super air tight, the maximum likely R-values for walls/attic, etc.) . Both of those tools tend to overestimate reality, but when sufficiently aggressive on inputs (per the instructions for Manual-J), they won't overshoot by more than 35-40% (with rare exceptions).

Even a professional Manual-J performed by a competent third party will overshoot reality by 10%, sometimes more, so even undersizing slightly from a DIY CoolCalc or LoadCalc by 10-15% (run them both- use the one that delivers the lowest load number) isn't very risky at all. For a sense of just how much padding there is on these tools, take 11 minutes out of your life to review this guy's measured reality against a WrightSoft (a professional tool) Manual-J using default air leakage loads, or even what it delivers when using his blower-door tested leakage. Real heating and cooling loads are MUCH lower than what most people think, and oversizing creates rather than fixes comfort issues.

So the air handlers are on separate ducts systems (?) the duct sizes are probably on the larger side due to the oversizing. That makes it more likely that if the replacement is right-sized would mean you can probably use right-sized ducted modulating mini-split heat pumps with "compact" air "low static" or "mid static" handlers the size of a large suitcase. A typical 1 to 1.5 ton Fujitsu or Daikin compact duct heat pump in my area would run about $5-7.5K (each) in competitive bidding, and that would include new ducts. The units themselves (no ducts, refrigerant lines or condenser pad) are less than 3 grand, 3/4- 1-tonners are under $2.5K. So if you can re-use the ducts you'd probably be looking at $10-12K, maybe up to $15K at Long Island pricing, but there are probably some NYSERDA and utility rebate incentives due to the much higher air conditioning efficiency compared to typical 13SEER single speed AC.

A 1.5 ton Fujitsu puts out over 21,000 BTU/hr in heating mode at your +15F design temp, a 1.5 ton Daikin puts out over 22K. The Fujitsu's have more flexibility in the installment (they can be mounted vertically like an up-flow air handler, if desired), and a wider modulation range, but they're both pretty good units.

A reasonably tight insulated 2x4 framed 2200' house with clear glass (no low-E) double panes should come in around 30-33,000 BTU/hr @ +15F outdoors, 70F indoors if the foundation walls are insulated, 35-45,000 BTU/hr if the basement or crawlspace are uninsulated and leaky (or worse, vented to the outdoors.)

That's half to 2/3 the WAG heat load numbers I cooked up based on the reported $/year and typical annual HDD, and if your house is REALLY that leaky you're better off spending the money on a serious round of air sealing (blower door and IR camera directed & verified) & fixing any insulation deficiencies. Any known "problem rooms" that run too hot or too cold can get extra scrutiny & treatment (if needed.)

There may be even better incentives for heat pumps coming in a few years due to NY greenhouse gas emissions goals, so it may be better to take a different path. With a retrofit gas burner on a 9 year old System 2000 you can probably expect at least another 15- 20 years out of it before the basic boiler is toast. Energy Kinetics makes oil to gas conversion kits for most of their oil boilers, and it's probably worth getting somebody to quote that as a solution. (Ask about down-firing it with a smaller burner too.) The cost of a conversion should be well under $5K (all-in, gas plumbing included) unless the contractors in your area aren't hungry enough to be bothered.

This summer separately measure the duty cycles of your existing AC units during 1% design-day afternoons to get a firmer grip on the true zone by zone cooling loads (eg, if the 2 ton zone runs a 70% duty cycle on days when it's in the mid to high 80s the real load, including parasitic losses from the air handler & duct design is ~0.7 x 24,000 BTU/hr = 16,800 BTU/hr, and a 1.5 tonner would be appropriate. If it's only a 30% duty cycle the real 1% load is 0.3 x 24,000 BTU/hr= 7,200 BTU/hr, and a 3/4- 1 tonner would work just fine.

Then run a more careful room by room Manual-J load calcs (LoadCalc or CoolCalc are fine), and measure the heat load using the gas-converted System 2K next winter. The fuel used measured load would tell you just how much padding factor there is on the Manual-J, so scaling the Manual-J room by room loads accordingly would give you more precision on what the heating loads are on each zone, so that if a heat pump is eventually installed it's size can be tweaked up a step from the required cooling sizing if needed.

 

[RJHNY1]

Dana, I very much appreciate your detailed post, but I'm afraid much of it goes over my head. I'm not an HVAC technician or a plumber so, while I appreciate how detailed it is, it's like reading a foreign language for me. I hope you can explain a couple of things for me.

Pardon my ignorance, but aren't heat pumps in the wall? You turn it on and it pumps out hot or cold air. I actually have one of those, a Fujitsu, in my basement. How do those units relate to the duct work throughout my house? While heat pumps may be efficient and the wave of the future, I don't think that's the path I would take for my house at this time.

PSEG offers a free home energy assessment, which I plan to take advantage of once they resume them (it's suspended b/c of COVID). That should tell me if air is escaping or coming into the house.

I think a lot of plumbers always oversize. I actually asked the HVAC company I used about sizing it right for the house and they maintained the HVAC was the appropriate size. I don't know enough or understand it enough to challenge them on it. The company did come very highly recommended by many people here in the neighborhood and the owner lives in my town. He's a nice guy, came recommended, and I had trust. For what it's worth, my house was nice and comfortable last summer. I did get new ducts b/c the old ones were bad and I had poor airflow coming to the master bedroom. The HVAC company showed me while they were doing the job how bad the old ducts were and how it was improperly installed in some parts, which was why the air flow to some of the bedrooms were poor.

Regarding converting the EK 2000 from oil to gas, I was quoted by some companies $9-10K. The job entails converting the EK, running a gas pipe from the meter to the boiler, lining the chimney, and removing the oil tank. At that price, I think converting to gas at this time is a poor investment. The EK is extremely efficient and I don't know if there's enough of a difference in savings to be worth it.

 

[Dana]

Dana, I very much appreciate your detailed post, but I'm afraid much of it goes over my head. I'm not an HVAC technician or a plumber so, while I appreciate how detailed it is, it's like reading a foreign language for me. I hope you can explain a couple of things for me.

Pardon my ignorance, but aren't heat pumps in the wall? You turn it on and it pumps out hot or cold air. I actually have one of those, a Fujitsu, in my basement. How do those units relate to the duct work throughout my house? While heat pumps may be efficient and the wave of the future, I don't think that's the path I would take for my house at this time.

Your central AC is a heat pump, but a heat pump that only moves heat in one direction. The primary difference between central air and a heat pump is a reversing valve that changes the direction of refrigerant flow to move heat from the outdoors (even when it's really frigid outside) to the indoors.

There are also ductless heat pump systems that hang on the wall, but that's a whole other story. HVAC contractors screw those up on sizing all the time too (and are able to afford their yacht club dues with the proceeds of "...a ductless head in every room..." approach.) They can be great (and cheap) in open format house plans if done judiciously, but it's a whole other subject.

PSEG offers a free home energy assessment, which I plan to take advantage of once they resume them (it's suspended b/c of COVID). That should tell me if air is escaping or coming into the house.

Most utility programs are ultra-basic. Only rarely (and then only when prompted by the homeowner) will they actually measure the house leakage (with a calibrated blower door test), or the duct leakage (with a calibrated duct blaster.) They also tend to only focus on what services are being subsidized by the utility, not necessarily what makes the most sense or provides the most comfort in the bigger picture. None of those programs in my area will do a blower door test on a house unless it's obvious and egregiously leaky, but it's hard to tell just by looking how leaky a house really is.

I think a lot of plumbers always oversize. I actually asked the HVAC company I used about sizing it right for the house and they maintained the HVAC was the appropriate size. I don't know enough or understand it enough to challenge them on it. The company did come very highly recommended by many people here in the neighborhood and the owner lives in my town. He's a nice guy, came recommended, and I had trust. For what it's worth, my house was nice and comfortable last summer. I did get new ducts b/c the old ones were bad and I had poor airflow coming to the master bedroom. The HVAC company showed me while they were doing the job how bad the old ducts were and how it was improperly installed in some parts, which was why the air flow to some of the bedrooms were poor.

All plumbers oversize- it's only a matter of how much. Even HVAC designers tend to oversize, but the true pros have more appropriate oversize factors, based on measurements rather than rules of thumb or a WAG. Heating design is more than a plumbing job, and specifying heating systems is more than an HVAC installation. Unless they did a formal load calculation (which takes several hours to measure up and assess the house, then enter it all into the appropriate program), and didn't have a thumb on the scale regarding the assumptions AND measured the air leakage with a blower door test, they are mostly just guessing. A lot of the "plummin' an' heetin' "hack contractors in my area just eyeball the house and use an idiot's rule of thumb like "35 BTU per square foot" for older leakier construction, or "25 BTU per foot" for tighter newer construction. Those rules of thumb are guaranteed to be able to heat the place when it's 0F outside, but since it's generally more than 2x or more oversized it will also be able to heat the place when it's -70F or even -100F outside, temperature not seen in my neighborhood since the last ice age. But oversizing "...just to be sure..." the contractor doesn't get the call from an irate customer in the pre-dawn hours of the coldest night of the year is the opposite of comfort.

Heating systems provide the most even-heating and greatest comfort when running long cycles. Sizing it correctly the heating system will run at about a 70% duty cycle when it's +15F, and nearly continuously when it's 0F outside. That means your radiator temperatures would always be at a high but fairly stable temperature during extreme weather, with lower temperature fluctuations during normal cold weather. The same would be true for a single-stage ducted heat pump system. But with a right sized modulating heat pump system (or modulating boiler) the system would be running nearly 100% duty cycles even during normal winter weather, adjusting it's output in response to the rate of the home's heat loss to the outdoors.

Regarding converting the EK 2000 from oil to gas, I was quoted by some companies $9-10K. The job entails converting the EK, running a gas pipe from the meter to the boiler, lining the chimney, and removing the oil tank. At that price, I think converting to gas at this time is a poor investment. The EK is extremely efficient and I don't know if there's enough of a difference in savings to be worth it.

Don't forget that you're going to have to pay for the disposal of the old tank either way, and replacement tanks aren't free. Oil burners need more maintenance and service to maintain efficiency than gas burners too, and that adds up over time.

Did anybody quote just a tank replacement? That's clearly the cheapest thing to do short term.

 

[RJHNY1]

PETRO wanted $3700 for an oil tank replacement. Another guy quoted me $2000 but the tank would have been a smaller size than 275, which is what I have now.

I've done some research and based on my convos with some people, I want to go with a Roth oil tank, if I go that route. It's among the best out there and it will save me space in my utility room that I could put a work bench with the space saved. I haven't gotten quotes from companies that would install a Roth oil tank.

Basically, I'm trying to figure out the savings with a gas conversion versus sticking with my oil boiler and really do good math there before doing a new oil tank.

 

[Dana]

Basically, I'm trying to figure out the savings with a gas conversion versus sticking with my oil boiler and really do good math there before doing a new oil tank.

So, is this what you would pay for gas in your neighborhood? For heating customers it looks like the delivery & service charges are ~$85 for the first 50 therms (which would be most months if heating domestic hot water with gas for a family of 4) plus $0.50 cents per therm for the gas itself. For a low heating shoulder season month that uses 50 therms that's 50 x $0.50 = $25 for the gas, $85 for the delivery, $110 total for 50 therms, or ($110/50=) $2.20/therm.

Using an 82% efficiency gas retrofit burner that delivers a net 0.82 x 100KBTU/therm= 82,000 BTU per therm for ( x 50 =) 4.1 million BTU (MMBTU) net heat into the system for $110, so it's a fairly steep $110/4.1= $26.82/MMBTU or more for low usage months.

For a higher use midwinter months you might be using 300 therms. The first 50 costs $110, but the other 250 therms is costs only $0.29 for delivery, $0.44 for the gas for $0.73/therm, so you'd be looking at a total bill of $110 + (250th x $0.73/th)= ~$293 . That's an average of only $293/300= $0.98/therm, which is less than half the average cost per therm for a low usage month. Normalizing to net $/MMBTU that's 300 therms x 100,000 BTU/therm x 0.82 efficiency = 24.6 MMBTU for $293, or ($293/24.6 MMBTU =) $11.91/MMBTU during the ~3 heaviest heating months (probably ~2/3 the annual usage or more.)

Oil burned at 88% efficiency in a Sys-2K delivers a net (0.88 x 138,000 BTU/gallon =) 121,440 BTU/gallon, so it's (1,000,000/121,440 =) 8.23 gallons/MMBTU. At the previously stated contract price of $2.33/gallon that would be $19.18 MMBTU, with all months being roughly the same cost.

If you're spending a couple grand per year that's $2000/$2.33= 858 gallons/year or (0.82 x 138,000 x 858 gallons =) 97.1 MMBTU/annum. Something like 3/4 of that during the coldest three months, or ~73 MMBTU, which costs (73 MMBTU x $19.18/MMBTU= ) ~$1400.

To deliver the same amount of heat with gas during that season costs only (73 MMBTU x $11.91/MMBTU=) $870, a $530 savings for the heating season.

Assuming all of the other (97 MMBTU - 73MMBTU = ) 24 MMBTU per year is at the higher $26.82/MMBTU low monthly usage price point the remainder of the year costs another (24 MMBTU x $26.82/MMBTU = ) ~$644.

But with oil the rest of the year would only cost (24 MMBTU x $19.18/MMBTU= ) $460, which is $184 less than with gas.

The net annual savings with gas vs. oil at those prices would be ($530 - $184 =) ~$350/year.

Assuming the Sys- 2K has another 10 years of life in it (which is all but assured) the remaining lifecycle savings would still be only $3500, if 15 years (there's still pretty good chance it'll go that long) it's about a 5 grand savings. But since the gas plumbing is already installed you'd then be able to replace the system with an even higher efficiency condensing boiler (if that's still even legal in 15 years, depending on state & federal policy changes) without a lot of extra expense. But even at the end of 15 years it will not have "paid back" even in simple terms if the conversion cost is $9-10K and just replacing the tank is $2k -$3.7K.

Of course this all presumes that pricing per MMBTU for gas relative to oil will always be in lock step, which it sort-of is most of the time, but not always.

If the long term goal for this house is to get off fossil fuels it's better to save the conversion money up front, and in the nearer term spend the difference on fixing the air leakage & insulation deficiencies of the house to increase the house efficiency & comfort, which would also lower the annual operating cost. Then when either the central air or boiler craps out (one or the other probably will fail to the point of not being worth fixing within 15 years), replace the AC with a right-sized heat pump solution.

If local, state & federal policy makers make it worthwhile with big subsidy or carbon tax incentives it may become reasonable to retire the existing heating & cooling systems even before end of the anticipated service life, but no matter how you're heating and cooling the place, fixing up the thermal performance of the HOUSE is the necessary prerequisite for making the place truly comfortable. Even with the oversized systems comfort will increase with a tighter, better insulated house, but when the systems are replaced with right-sized equipment for the (now lower) design loads the comfort levels would then soar.

 

[RJHNY1]

So, is this what you would pay for gas in your neighborhood? For heating customers it looks like the delivery & service charges are ~$85 for the first 50 therms (which would be most months if heating domestic hot water with gas for a family of 4) plus $0.50 cents per therm for the gas itself. For a low heating shoulder season month that uses 50 therms that's 50 x $0.50 = $25 for the gas, $85 for the delivery, $110 total for 50 therms, or ($110/50=) $2.20/therm.

Using an 82% efficiency gas retrofit burner that delivers a net 0.82 x 100KBTU/therm= 82,000 BTU per therm for ( x 50 =) 4.1 million BTU (MMBTU) net heat into the system for $110, so it's a fairly steep $110/4.1= $26.82/MMBTU or more for low usage months.

For a higher use midwinter months you might be using 300 therms. The first 50 costs $110, but the other 250 therms is costs only $0.29 for delivery, $0.44 for the gas for $0.73/therm, so you'd be looking at a total bill of $110 + (250th x $0.73/th)= ~$293 . That's an average of only $293/300= $0.98/therm, which is less than half the average cost per therm for a low usage month. Normalizing to net $/MMBTU that's 300 therms x 100,000 BTU/therm x 0.82 efficiency = 24.6 MMBTU for $293, or ($293/24.6 MMBTU =) $11.91/MMBTU during the ~3 heaviest heating months (probably ~2/3 the annual usage or more.)

Oil burned at 88% efficiency in a Sys-2K delivers a net (0.88 x 138,000 BTU/gallon =) 121,440 BTU/gallon, so it's (1,000,000/121,440 =) 8.23 gallons/MMBTU. At the previously stated contract price of $2.33/gallon that would be $19.18 MMBTU, with all months being roughly the same cost.

If you're spending a couple grand per year that's $2000/$2.33= 858 gallons/year or (0.82 x 138,000 x 858 gallons =) 97.1 MMBTU/annum. Something like 3/4 of that during the coldest three months, or ~73 MMBTU, which costs (73 MMBTU x $19.18/MMBTU= ) ~$1400.

To deliver the same amount of heat with gas during that season costs only (73 MMBTU x $11.91/MMBTU=) $870, a $530 savings for the heating season.

Assuming all of the other (97 MMBTU - 73MMBTU = ) 24 MMBTU per year is at the higher $26.82/MMBTU low monthly usage price point the remainder of the year costs another (24 MMBTU x $26.82/MMBTU = ) ~$644.

But with oil the rest of the year would only cost (24 MMBTU x $19.18/MMBTU= ) $460, which is $184 less than with gas.

The net annual savings with gas vs. oil at those prices would be ($530 - $184 =) ~$350/year.

Assuming the Sys- 2K has another 10 years of life in it (which is all but assured) the remaining lifecycle savings would still be only $3500, if 15 years (there's still pretty good chance it'll go that long) it's about a 5 grand savings. But since the gas plumbing is already installed you'd then be able to replace the system with an even higher efficiency condensing boiler (if that's still even legal in 15 years, depending on state & federal policy changes) without a lot of extra expense. But even at the end of 15 years it will not have "paid back" even in simple terms if the conversion cost is $9-10K and just replacing the tank is $2k -$3.7K.

Of course this all presumes that pricing per MMBTU for gas relative to oil will always be in lock step, which it sort-of is most of the time, but not always.

If the long term goal for this house is to get off fossil fuels it's better to save the conversion money up front, and in the nearer term spend the difference on fixing the air leakage & insulation deficiencies of the house to increase the house efficiency & comfort, which would also lower the annual operating cost. Then when either the central air or boiler craps out (one or the other probably will fail to the point of not being worth fixing within 15 years), replace the AC with a right-sized heat pump solution.

If local, state & federal policy makers make it worthwhile with big subsidy or carbon tax incentives it may become reasonable to retire the existing heating & cooling systems even before end of the anticipated service life, but no matter how you're heating and cooling the place, fixing up the thermal performance of the HOUSE is the necessary prerequisite for making the place truly comfortable. Even with the oversized systems comfort will increase with a tighter, better insulated house, but when the systems are replaced with right-sized equipment for the (now lower) design loads the comfort levels would then soar.

Fantastic post, thank you very much. So because of how efficient the EK is with oil, it makes zero sense to convert to gas. EK told me that the life expectancy of the boiler is 30 years. I'm 9 years in, so maybe I'll even have 20-22 years left on it!

FYI, I was told that if I converted the EK to gas, it would retain an 85% efficiency. Where did you get the 82% number? Even then, that wouldn't change your calculation much in that I would not save money converting to gas over the long term.

 

[Dana]

FYI, I was told that if I converted the EK to gas, it would retain an 85% efficiency. Where did you get the 82% number? Even then, that wouldn't change your calculation much in that I would not save money converting to gas over the long term.

The minimum legal efficiency is 82%. While many gas-burners will hit 85% efficiency, with time and de-tuning (how often do gas valves in boilers actually get re-adjusted?), the 3x+ oversize factor (even with the Sys 2K it loses a percent or two) and the age degradation of the heat exchanger, 80-82% as-used efficiency is going to be about right for a 9 year old boiler with a mid-80s efficiency burner.

The biggest risk factor with oil heating is price volatility. Natural gas pricing is regulated by state utility regulators and long term contracts between utilities & suppliers. With oil it hardly matters that the US is net self sufficient on oil- the price of oil is determined by the international markets. At times when the Saudis &.0r Russians are in a price war to take more market share (or to put more US frackers out of business) the world price and local US price crashes. When regional conflicts or hurricanes take production off line the price rises. So $2.33/gallon for #2 oil, delivered might be your short term contract price, but there are many ways it can go higher.

Even contracts with local oil delivery companies can go south when the international markets see abrupt rises. During the intense crude price runup in 2007-2008 several #2 oil suppliers near me went bankrupt, unable to absorb the extreme price difference between their rapidly increasing price from their suppliers and the quoted seasonal contract prices to their customers. Seasonal fixed price contracts with their customers during the early autumn 2007 season did not anticipate the wholesale price more than doubling by December.