Gas conversion burner for Weil Mclain WGO-5 oil boiler

jesmed1

I do maintenance for a 4-unit condo building. We have 2 Weil Mclain WGO-5 oil boilers and burn about 1200 gallons of oil a year total. Am looking into changing over to a Beckett or a Carlin conversion natural gas burner to save $$. I've looked at natural gas prices vs heating oil over a 10-year period here in the Boston area, and figure natural gas would have saved 25%-30% in fuel costs over the last 10 years or so. I have figured materials costs for 2 burners, 2 gas dampers, and 2 vent safety switches. Chimney is already lined. And we have a gas line right near the boilers, so the gas hookup will be easy. I've asked our oil company to give us a quote on doing the conversion and haven't got a number from them yet. Wondering if anyone has experience with these conversion burners and any words of wisdom.

EBEBRATT-Ed

I would use the Carlin. It will work well in that boiler.

But please remove your pricing we cannot discus pricing on this forum

jesmed1

Thanks, Ed. I forgot to mention that these boilers are probably about 25 yrs old. Still in good condition, but I saw a statement somewhere that the gas conversion burners should only be used in "newer" boilers, like 10 yrs old and newer. Is there any truth in that? I don't really see the logic. Newer Weil-McLain boilers are designed just like the older ones, and we have new combustion chambers and the pins are in good shape. We could get another 5-10 years out of these boilers, and when they go, we would just get another pair of Weil-McLains and keep using the gas conversion burners. (PS--I removed my cost estimates as you requested.)

EBEBRATT-Ed

@jesmed1

No reason not to convert. Some might balk at putting the conversion cost into a 25 year old boiler but you seem to have a handle on that.

mattmia2

That is true for warm air furnaces, the metal in the hx doesn't like being heated in a new pattern and can crack, with a boiler because it is water filled it doesn't get as hot so it is not a common problem.

Steamhead

We do this all the time. The burner to use is the Carlin EZ-Gas.

HVACNUT

I would think 1,200 gallons a year isn't too shabby for a 4 unit condo near Boston.
What provides domestic hot water? And can you explain the math on 25-30% fuel savings? There's more to it than just cost differential.

Mad Dog_2

They are all Good..Beckett, Carlin & Rialto (finicky but excellent). Carlin is my first choice.   Two things..order spare HSIs (hot 🔥 surface ignitors aka Glow plugs) and do a very thorough cleaning of the boiler and sections.  Have a Pro With a Combustion analyzer set them up.  Mad Dog 🐕 

pecmsg

Steamhead said:

We do this all the time. The burner to use is the Carlin EZ-Gas.

and do you see a 25 - 30% savings?

jesmed1

Thanks, everyone. HVACNut, domestic hot water is from a gas fired water heater next to the boilers. That's why it should be easy to run gas over to the boilers. The math on the 25-30% fuel savings is based on comparing gas vs. oil historical prices for the last 8 years in my area, taking one data point from a day in December on each of those years. Yes, one day in December is not an average over the entire heating season, so it's only a snapshot in time, but the results were remarkably consistent. On a random day in December for the last 8 years, natural gas was consistently 25%-35% less expensive on a per-BTU basis than oil in my area.

Mad Dog, yes, I would hire our HVAC contractor to do the setup with the combustion analyzer. They do a good job on our oil burners each year. We typically get 84%-86% efficiency on the WGO-5's running Beckett AFG burners.

pecmsg

Isn’t gas 15 or 20% less in BTU output over oil?

jesmed1

@pecmsg, the way to compare oil vs. natural gas is to compare the cost on a per-BTU basis. A BTU is purely a measure of thermal energy, just like a food calorie is a measure of thermal energy. One calorie of sugar has the same energy as one calorie of maple syrup, but the quantities of those substances will be different to get that one calorie.

To compare oil and gas, I convert total oil gallons used in a season to BTU's by multiplying by 140,000 BTU per gallon of oil. Then I have a total BTU's burned per heating season using oil. Then I find the equivalent amount of natural gas by dividing by 1050 BTU's per cubic foot of natural gas. That gives me the equivalent cubic feet of natural gas. Then multiply by the price of gas per cubic foot, and that's the equivalent cost of natural gas for a heating season.

jringel

Just keep in mind that just because the gas lines for the hot water are close to the boiler doesn't mean you can use them. You will have to make sure that the piping can supply the necessary BTU'S for both of those boilers and the water heater.

jesmed1

Thanks, John, good point about the pipe size. I have checked a natural gas pipe sizing chart, and I think the boilers are close enough to the meter that the existing 3/4" pipe will be sufficient.

Steamhead

pecmsg said:

and do you see a 25 - 30% savings?

Depends on how dirty the fire-side is. If it's like this:

https://forum.heatinghelp.com/discussion/188633/soot-vac-was-heavy-when-i-finished-this-one

or this:

https://forum.heatinghelp.com/discussion/184249/you-can-tell-how-long-ago-this-was-serviced

the savings will be substantial. BTW, both pictured boilers were "serviced" every year.

If it's relatively clean inside, no. But, by switching to gas, the owner gets rid of the oil tank (or should, we sometimes still find abandoned tanks in basements) and sidesteps the chance that they'll run out of oil.

If I find a boiler in the neglected condition pictured, and there is natural gas to the house, the conversion sells itself.

jesmed1

By the way, on the subject of cost comparisons, I just did a more detailed historical cost comparison between natural gas and heating oil in the Boston area where I live. Over the last 9 heating seasons, we would have saved an average 34% if we had used natural gas instead of oil. The potential savings dropped significantly in the 2020/21 and 2021/2022 heating seasons because of the Russian invasion of Ukraine that caused a spike in natural gas prices. But natural gas prices dropped sharply earlier this year, and the price differential is likely to be significant again this winter, which is why we're looking at converting.

mattmia2

If it is extremely close to the service regulator and there is a separate 3/4" pipe for each water heater so the combined load in the pipe is only about 200,000 btu/hr, maybe. If there is only one 3/4" pipe then there is no way it can supply around 400,000 btu/hr, at least in a conventional 6" wc system.

jesmed1

Thanks, Matt. We only need 100,000 BTU max supplied to both boilers (50kBTU each). The WGO-5's are way oversized for our actual heating needs. Eventually when we get around to replacing the boilers, we'll probably downsize to WGO-2's.

mattmia2

You can't just downfire the burner ~50%. There won't be enough energy in the flue gasses for it to draft right and it likely won't get the cast iron hot enough to keep it from condensing.

mattmia2

It would make more sense to only convert one boiler and abandon the other and connect all the loads to one boiler if it really is that oversized.

Steamhead

jesmed1 said:

Thanks, Matt. We only need 100,000 BTU max supplied to both boilers (50kBTU each). The WGO-5's are way oversized for our actual heating needs. Eventually when we get around to replacing the boilers, we'll probably downsize to WGO-2's.

mattmia2 said:

You can't just downfire the burner ~50%. There won't be enough energy in the flue gasses for it to draft right and it likely won't get the cast iron hot enough to keep it from condensing.

mattmia2 said:

It would make more sense to only convert one boiler and abandon the other and connect all the loads to one boiler if it really is that oversized.

I agree. Downfiring those boilers 50% is not a good idea. If the heat in that building is not separately metered, set them up so either can handle the whole building but only one can run at a time. The other boiler would then be a spare, and you could switch over immediately if the active boiler goes down. Most larger buildings I've worked in are set up this way.

jesmed1

OK, thanks for the input about downfiring rates. Then maybe we run each boiler at 75kBTU, since the lowest nominal firing rate of the Carlin EZGas is 75kBTU. So maybe we have a max demand of 150kBTU on the gas pipes, and we'll re-check the pipe sizing and upsize if needed.

Unfortunately we can't switch to one large boiler for all 4 units in the building, because the way the building is zoned. The building has a partition wall down the middle. One side of the building has one boiler for two floors, and the other side has one boiler for two floors. Each side of the building has different heat loss rates because one side is in the sun, the other in the shade. So each side of the building has to be heated independently, and as it's set up now, the system works quite well.

I know in theory we could run all the piping to one boiler and install zone valves, but I'm afraid of upsetting the balance of water flows. There's only one thermostat for each boiler, installed on the first floor unit above the boiler, and no thermostats on the second floor, and no zone controls. That means the pipe sizes and flow rates had to be calculated so that the upper floor would get the right amount of heat, even though it has no thermostat and no zone control. The piping runs in the basement look like total spaghetti, but somehow the old timers who set this system up (in a 100 year old house) got the pipe sizing exactly right so that the upstairs and the downstairs units stay comfortable at all times in winter, even though the upstairs units have no physical connection with the downstairs units. And I'm afraid that any change to the heating plumbing would mess up that delicate balance.

Steamhead

Would both boilers be on the same gas meter?

mattmia2

If it is only 2 large zones you could easily zone it with circulators. Someone had to rebalance it when it was switched from gravity to pumped. If the emitters are sized correctly then the flow should be less important in balancing the system.

jesmed1

Yes, both boilers on the same meter, so the pipe would need to accommodate the firing rate of both boilers at the same time. I took another look at the natural gas pipe chart, and we might need to go up to 1" or 1-1/4" pipe. There's a 75kBTU water heater, and if both boilers are running at 75kBTU, that's 225kBTU. Then there's a gas dryer at 20kBTU. So the entire draw at the meter is maybe 250kBTU.

jesmed1

Matt, I guess we could zone it with circulators. But we have limited capital, and I'm trying to minimize outlay for maximum payback, and right now it looks like converting the existing system to natural gas with the absolute minimum expenditure is our best option. We just don't have the $$ for a lot of replumbing. I just want to plug in some Carlin EZGas burners as cheaply as possible. Then 5-10 years down the road when the boilers crap out and need to be replaced, we can consider further replumbing.

mattmia2

You can run a separate line from the meter just for the boilers (or 2 separate lines if the location of the boilers makes that easier), you don't have to upsize the existing piping other than the common piping by the meter.

jesmed1

That's true, I think we could run 1" pipe from the meter to the boilers, and just tee the existing 3/4" for the water heater and dryer into that.

pecmsg

Can your meter handle the extra capacity?

jesmed1

Steamhead said:

pecmsg said:

and do you see a 25 - 30% savings?

Depends on how dirty the fire-side is. If it's like this:

https://forum.heatinghelp.com/discussion/188633/soot-vac-was-heavy-when-i-finished-this-one

or this:

https://forum.heatinghelp.com/discussion/184249/you-can-tell-how-long-ago-this-was-serviced

the savings will be substantial. BTW, both pictured boilers were "serviced" every year.

If it's relatively clean inside, no. But, by switching to gas, the owner gets rid of the oil tank (or should, we sometimes still find abandoned tanks in basements) and sidesteps the chance that they'll run out of oil.

If I find a boiler in the neglected condition pictured, and there is natural gas to the house, the conversion sells itself.

Just to be clear, we're talking apples and oranges here. The 25-30% potential savings I cited for us switching to gas is based on the observed history of gas vs. oil prices here in Boston. I looked up historical price data and calculated that over the past 9 heating seasons, if we had been using gas instead of oil, on a cost-per-BTU basis, we would have saved about 34% in fuel costs. That's the "25-30% savings" that pecmsg was asking about.

Then there's the question of boiler efficiency, which as you observed, decreases severely when the heat exchanger is full of crap. I'm ignoring the efficiency issues in my case, because our boilers get cleaned every year and are well adjusted to run at 84-86% efficiency (with oil), and (I'm assuming) we'll get roughly the same efficiency if/when we convert to gas burners in those same boilers.

So, my understanding is that, assuming we're using the same clean boilers well adjusted for maximum efficiency, the only real "savings" we'll see is from the price difference between gas and oil. The efficiency of the boiler with either fuel should be more or less the same, within a few percent.

Steamhead

@jesmed1 , how did you determine that you only need 100,000 BTU per hour to heat the building?

Did someone do a heat-loss calculation? If so, what design temperatures were used- for example, 70°F inside and 0°F outside?

jesmed1

I'm a mechanical engineer and have done heat loss calcs using 4 different methods. All come up with a range of 80kBTU/hr to 100kBTU/hr. The method I trust most is observed run times on the boilers during a zero-degree day last year. I put a data logger on the boilers for 24 hours during a zero-degree day and calculated total run time over that 24 hours. The boilers ran roughly half the time, with Tstats set at 68. Which means the boilers are massively oversized for 99% of the winter. And I also know the nozzle size and pump pressure, so I know the oil gph input, and thus the BTU input. I also know the boiler is running at 84% efficiency from the stack results. Based on those combined numbers, I know exactly how many BTU were input and output from the boilers on that zero degree day, based on observed run time. Those are the numbers I trust most, because they're real. But surprisingly, the other heat loss methods I used got within 20% of that number.

jesmed1

But to be safe on the natural gas burner, I would probably set up for 125kBTU/hr input. The WGO-5 is rated for 200kBTU/input, so 125/200 gives a ratio of 0.625. Al Letellier said on another thread that Weil-McLains can be downfired to around 65% without losing efficiency, and a 125kBTU input from a gas burner would put us right in that ballpark. It's still way more heat than we need in the building, because we have 2 boilers, giving us a total of 250kBTU input from 2 Carlin burners running at 125kBTU each, but it sounds like maybe the minimum we can run the WGO-5's at without worrying about condensing and losing efficiency.

jesmed1

pecmsg said:

Can your meter handle the extra capacity?

Good question. The rating plate on the meter says "250 cu ft/hr @ 1/2" which I assume is the max flow rate. Since one cubic foot has roughly 1000 BTU, that's around 250,000 BTU/hr. If we have 2 gas burners at 125kBTU each, plus a 75kBTU water heater, plus a 20 kBTU gas dryer, that's 350kBTU/hr if all are running at the same time. So our meter may not be big enough.

pecmsg

jesmed1 said:

I'm a mechanical engineer and have done heat loss calcs using 4 different methods. All come up with a range of 80kBTU/hr to 100kBTU/hr. The method I trust most is observed run times on the boilers during a zero-degree day last year. I put a data logger on the boilers for 24 hours during a zero-degree day and calculated total run time over that 24 hours. The boilers ran roughly half the time, with Tstats set at 68. Which means the boilers are massively oversized for 99% of the winter. And I also know the nozzle size and pump pressure, so I know the oil gph input, and thus the BTU input. I also know the boiler is running at 84% efficiency from the stack results. Based on those combined numbers, I know exactly how many BTU were input and output from the boilers on that zero degree day, based on observed run time. Those are the numbers I trust most, because they're real. But surprisingly, the other heat loss methods I used got within 20% of that number.

If your calculations are correct than change the entire boiler for a proper size.

Personally, in a condo I would size for 2 boilers. Each 75% of the total. Now there's a backup for when somethings wrong and its sized closer to reality!

jesmed1

pecmsg said:

If your calculations are correct than change the entire boiler for a proper size.

!

I will, eventually. But the first step is to change the burners from oil to gas. That alone is going to cost us around $5k, but will start saving us $1k-$2k per heating season. Then when the boilers fail eventually, I'll get much smaller boilers to replace them, and we'll already have the new gas burners set up for them.

We don't have the budget to make many expensive changes all at once. We have to do things incrementally, and we can't afford to buy a new boiler unless it's absolutely necessary.