There is a LOT of misinformation out there regarding residential heating systems, particularly when it comes to comparisons of natural gas and oil. Much of the pro-oil data is propagated by industry groups representing the oil dealers.∗ That is not to say that natural gas systems are better – they have their marketers, too – only that this is a subject that requires a little extra effort to counter the spin.
Environmental Impact
We originally had this section at the bottom but realized we were burying the lead. It’s important to keep in mind, when discussing the relative merits of gas and oil systems, that they are both dirty, polluting, and inefficient (in most situations) and should be prioritized behind insulation and air sealing, and should be compared against heat pumps when you’re actually contemplating a retrofit. We are cooking our planet and our built environment is a big source of inefficiencies, causing enormous amounts of greenhouse gasses to be spilled int the atmosphere unnecessarily. Read this article, enjoy, but before you make decisions about central heat work with a pro to tighten up your home and consider heat pump technology paired with renewable energy.
Okay, maybe you’re still in the market for a boiler or furnace. I don’t blame you. So, what are the relative environmental impacts of heating oil and natural gas? Pretty darn hard to compare, actually.
Burning oil does release about 38% more CO2 during combustion, but natural gas has a fracking problem. There are big issues with fugitive methane emissions (a stronger greenhouse gas) and with water – both its overuse and contamination. Check out the EPA’s review of fracking for an overview: https://www.epa.gov/sites/production/files/2016-12/documents/hfdwa_executive_summary.pdf.
There is also delivery to consider. The two fuels are vary different in regards to how they get to their final destination. Oil can be transported great distances by ship and/or pipeline, before being transferred to trucks for delivery. This presents opportunities for spills and requires significant energy.
Natural gas is transported mostly via pipeline, a system which has had a good track record, but which has recently come under scrutiny. Depending on where you are, a significant amount of natural gas may be leaking from the network of pipes that provide your building.
A final note about environmental impact, you’ll see claims from the pro-oil groups that, since oil burners can use quite a bit of biodiesel and some heating oil has some biodiesel content already, that oil is some sort of semi-renewable resource. This is hogwash. ASTM standards allow for up to 5% biodiesel in anything being sold as heating oil, and most of it has less or none. And as we turn away from biofuel subsidies nationally, there will be less and less mixing. Although, it is true most burners can deal with up to 20% biodiesel, so if you have your own source, go for it!
Heat Content and Unit Cost
An oil dealer service tech once told my parents, “Gas has less Btus than oil so you’re going to have to turn your thermostat up if you switch to gas.” Lots of things are troubling about that statement. Giving him the benefit of the doubt, he was probably thinking about the heat content of propane. I don’t know what he was thinking of with the t-stat setpoints.
Anyway, natural gas is very energy-rich, as is heating oil. The prices of both go up and down and all around but here’s a little breakdown; you can plug in your own unit costs when you read this:
1 ccf natural gas = 103,000 Btu
1 gallon heating oil = 140,000 Btu
If gas is $1.41/ccf, than 1 MBtu natural gas costs $1.41 X (100,000/103,000) or $1.37.
If oil is $2.80/gallon, than 1 MBtu heating oil costs $2.80 X (100,000/140,000) or $2.
The fuels are close in unit price, but it’s been a while since you could definitively say that oil is cheaper. Note, this has nothing to do with efficiency of the available systems or environmental impact.
Maintenance Cost and Lifetimes
I went looking for hard numbers on maintenance costs and lifetimes for gas and oil boilers and found a lot of estimates, guesses, and anecdotes.
The national Renewable Energy Laboratory’s measures database lists the lifetimes as 24 years for both types of systems. They don’t get into heat exchanger material and other detail. Considering peer reviewed literature, I didn’t find any direct studies but found multiple articles that use lifetimes for purposes of lifecycle analysis. In some of those, cat-iron boilers do get a longer life – up to 35 years versus about 20 for gas systems – which fits with what you read on the trade blogs. All in all I would say the heaviest oil boilers probably are going to live longer, on average.
Maintenance costs are going to be about the same. Annual cleaning/tune-ups are recommended by all major manufacturers for both fuel types. In my area (the only data I have), the technicians charge the same.
Do not believe the garbage floating around the internet about parts being harder to find for efficient gas systems like the Bosch/Buderus series. To me, this sounds like either xenophobia or people conflating the desire to support U.S. manufacturers with wanting prompt and inexpensive service. Also, Bosch employs tens of thousands of people in the U.S. and efficient gas-fired boilers have been around for a long time.
Efficiency
In terms of AFUE, which is a measure of heat output to fuel energy input, oil boilers currently top out at 92% while gas boilers can hit 97%. Those represent the bleeding edge and are very expensive. Among the more typical high-end products the efficiency gap is wider; there are a number of 95% AFUE gas boilers widely available but if you go looking for efficient oil systems you will typically end up with an 86% AFUE unit.
Many other factors go into annual energy consumption for heat and, with combi systems, domestic hot water. Using variable-speed ECM circulator pumps makes a world of difference. And, if your hot water pipes are outside of conditioned space, good quality insulation is well worth it. These factors apply equally to oil and gas systems.
Which do I buy?
After you’ve
- Improved the thermal efficiency and leakiness of your building’s envelope; and
- Investigated heat pumps and renewables; then
decided you need a new boiler, do you buy an oil or gas system?
If you’re an HVAC pro, you probably had your answer before you started reading. Building professionals tend to have there favorites, based on experience, and they stick with them.
If you’re a DIYer, this is one of those times you really should consider getting pro advice. HVAC design is extremely difficult to do well. Especially if you are looking for a system to provide heat and domestic hot water (“combi”) or have an unusual load profile (e.g., you’re a snow-bird), it’s important that you find someone with experience and training who can look at your situation and use good judgement and good software to design a best-fit system.
Good luck!
∗ Why are we even talking about oil? And what’s the deal with this “misinformation” we mentioned?
In the Northeast and parts of Michigan, we have lots of oil boilers in houses. This has been the case for a long time and they continue to be prevalent in new construction. Oil makes its way to our homes on trucks, an amazing number of which are owned by independent dealers. [It’s really quite amazing so many interchangeable, competing firms can coexist.] Industry groups have emerged to protect the oil delivery/service firms that employ a great many people. These industry groups have developed some slick websites and social media profiles that are very misleading. Gas utilities have committed their own sins, but the economics are such that capturing consumers is not as high a priority for them; they are more interested in convincing politicians to build pipelines.