Switching from oil to gas boiler for the savings, but mod-con not seeing value ?

Dave Carpentier

So we got word that gas is coming this summer, which now means that I dont need to take the intermediate step of propane if I want to move away from oil.

I set up a spreadsheet, into which I put the amount of oil we used this season, and the btu that represents. Then I used 80% eff, which I know is a bit optimistic, to get the btu that the structure required. It was about 60 Million btu (so that could be less).
Then I used that 60M and worked it backwards to figure out how much natgas I would need and used the pricing structure to figure my annual gas bill.

Heres the thing.. if I put 80% for both the oil and gas units, I save about $1200 a year by going gas (conventional). If I put 80% in for the oil and 97% in for the gas (condensing), I save about $1500.
So, it seems like moving to gas is a good plan, but Im not sold on the condensing when you also include the increased maintenance costs and higher initial cost (including new direct vents).
The modulating part of a mod-con could help, as we have variable loads (7 zones in-floor plus an air handler), but could the money be better spent on a large buffer tank ?

pecmsg

I find gas / oil over the years about equal. 

You did calculate the BTU/h difference bea gal of oil and a thermostat of gas?

Hot_water_fan

Oil and gas prices will change constantly so understand that the savings could all disappear, but gas has some other benefits. Is the radiant floor high mass or staple up? If it’s high mass, I’d skip the buffer entirely. 

Tiny heat loss there! 

hot_rod

Anybody guess on where we energy prices prices will go.
In theory we are the largest producer of NG, enough of a glut to export some around the world. So it would be nice to think prices could stabilize? We still import oil  even if we could
produce enough it would still be priced on the global market. Maybe bio oil changes that equation?

Any cooking or cloth drying, outdoor grill that could be gas?

It would be interesting to calculate cycle efficiency on a standard boiler with that many zones, could drive that number into 70,s?

97%would be high for the mod  con if you run above 140 for an air handler?

Hands down a modulating boiler cycles less, so less component wear over a 10 year span.

Ive owned a handful of mod cons and combis. A few went untouched for 5-6 years. As I imagine most do🥴
If they run clean they do not need a yearly service from my experience. If you are at all handy you can open and clean them yourself. Invest in a combustion analyzer.

I believe oil boilers need yearly service and cleaning?  So if you have to hire it out, service costs would be close in price between oil and mod con service 

HomerJSmith

This is my take. You have to decide whether tomorrow is going to be like today. Nat gas is demand service where as oil and propane is stored energy. Propane has twice the kick of Nat gas. Do you believe Nat gas will be endlessly-forever delivered to your house, if so, go Nat gas. Less messy than oil or as unsightly as a propane tank.

Think of Nat gas as money deposited in a bank and oil and propane as money stored in your mattress. When the SHTF, which would you rather have. I go for the mattress. Operating cost are important over the life of the unit. If you are in Minnesota with cold bitter winters, the life expectancy would be shorter for a mod/con. There's a joke about Minnesota, "When the temperature get up to 45 degs, everyone puts on their shorts and goes out for a picnic." "It's true, it's been proved".--Benny Hill.

You might want to have more than one source of heat. I have three sources of heat for heating and cooking-Nat gas, Wood, and Electricity and I don't feel too secure about any of them. I also have stored propane tanks. If they blow up, I'll be posting this from the Moon.

Dave Carpentier

@Hot_water_fan Not sure on the tiny heat loss ? We used 535 gallons of oil.
Its high-mass, 1600 sqft of thicker than normal slab.
My smallest zone is 2000 btu at design, the largest is 27,000.

@pecmsg For the oil I used 138,000 btu per USGallon. For the natgas I used 35915 btu per cubic meter.
(35915 btu is about 0.36 therm ?)

Hot_water_fan

Only 535 gallons is pretty low (still expensive) usage. What area of the country? That’s a heat loss of roughly 40kbtu at 0 degrees! Unless you’re using another fuel too. 

Dave Carpentier

hot_rod said:

Any cooking or cloth drying, outdoor grill that could be gas?

I will likely convert the existing propane dryer to natgas, but it's a small player as we only go thru two 50 pound refills per year

It would be interesting to calculate cycle efficiency on a standard boiler with that many zones, could drive that number into 70,s?

Do you mean the new gas or the existing oil using as a baseline ? The current setup is nearly like clockwork with 7mins on and 10mins off. I suspect a decent amount of heat flys up the stack as it's run as an always-hot boiler. A buffer tank would help the new unit (or this one, for that matter) if it could be run with a large swing.

97%would be high for the mod con if you run above 140 for an air handler?

The circ in the air handler only comes on when its bitterly cold, say about -15 or -20f ? Otherwise, its just the blower running continuously with duct returns only in the main floor rooms, so it kinda turns the air in the house. I would probably have to accept some non-condensing periods in mid-winter. Maybe a 95% average eff would be more realistic ?

Dave Carpentier

Hot_water_fan said:

Only 535 gallons is pretty low (still expensive) usage. What area of the country? That’s a heat loss of roughly 40kbtu at 0 degrees! Unless you’re using another fuel too. 

We're in Canada, north of Minnesota. My design temp is -21f. My heat loss is about 70k, if I used the slant-fin app correctly. Existing oil boiler is 118k doe.
We do tend to insulate a bit more up here, I suppose.

Hot_water_fan

We're in Canada, north of Minnesota. My design temp is -21f. My heat loss is about 70k, if I used the slant-fin app correctly. Existing oil boiler is 118k doe.
We do tend to insulate a bit more up here, I suppose.

535 gallons doesn’t jive with that cold of a climate if the heat loss is 70k and you’re keeping the thermostat somewhat consistent without supplemental heating fuels. Online calculators have many flaws, but I think the biggest is the infiltration values. Without a blower door, that’s a total, impactful guess. 

Regardless, it’s irrelevant- your boiler size options are few for the CI variety, and mod cons fit the heat loss well. We can move on. 

hot_rod

Find this post where I did an example of a cycle efficiency calculation. Just insert your own numbers.

Steamhead

Hot_water_fan said:

....Regardless, it’s irrelevant- your boiler size options are few for the CI variety....... We can move on. 

Au contraire- every major boiler manufacturer has a standard cast-iron gas boiler in the size @DaveCarpentier indicated. As far as I can tell, they all have 2012-compliant controls and their AFUE ratings are around 84%.

Cast-iron boilers have the advantage of being much easier to repair should that be needed, using standard parts, with no long waits for OEM parts as is typical for mod-cons.

Hot_water_fan

@Steamhead that’s what I mean! They make CI boilers that size. The next size down is generally too small and the next size up? Probably what’s already installed. The juice isn’t worth the squeeze. 

Steamhead

That depends on whose model series you look at. Some are closer matches than others. A good installer will have access to several different boiler lines, which would result in better choices.

EdTheHeaterMan

I remember back in the 1960s and 1970s, when everyone was still using older oil heat boilers that were converted from coal to oil. The burners were not very efficient and the boilers were being fired from the ash pit at the bottom of the coal boiler. Not from the upper section of the boiler where the original designer intended the fire to be located. All in all between actual combustion efficiency and thermal transfer efficiency for that antique design, you would expect to get as little as 30% of the actual BTU of the oil to show up inside the home at the radiators. Anyone that switched to natural gas using a smaller mass boiler that was designed to burn natural gas using atmospheric burners at about 78% combustion efficiency was always going to get a lower operating cost. (It has nothing to do with the old boiler being 30% efficient and the new boiler being 60% efficient)

Not understanding the actual thermodynamics of the whole equation, the "Gas Company" used the general population's ignorance to their advantage. Switch to gas and save money on heating your home. Since My father says switching to gas saves money, and we all know that Dad would not lie to us. (Never mind, if you swapped out a coal boiler converted to natural gas at 30% total efficiency, with a new modern Oil Boiler you would get the same result) So, GAS is CHEAPER, is the Gospel Truth no matter how much science and mathematics we apply to the people. We all grew up with the fiction that switching to gas will save you money.

That is the way of the world. and our original poster will save his $1500 this year and when you amortize that over the next 20 years there may even be a pay for itself break even point. To bad the new boiler will only last 15 years. Let the masses go on believing what they want to believe, there is no use in using actual logic at this point.

Just an old man ranting on about stupid stuff

Mr. Ed

Dave Carpentier

Hot_water_fan said:

Without a blower door, that’s a total, impactful guess.

We did have a blower door test back in 2018, as part of a reno rebate thingy.
It was 3.18 ach. We did do a bit more work after that, so it might be a tad lower nowadays.

Hot_water_fan

I’ll run the numbers tomorrow Dave, but 535 gallons isn’t that much for that climate. And small heat loss is good! Lower bills and more comfort. 

MaxMercy

I have oil at home and street gas in my commercial building. Because the two structures are wildly different in construction and size, I won't attempt a comparison of heating cost.

But where I am, I am paying a lot of money for "customer service charge" and "daily demand meter charge" on my gas bill, even when I shut the boiler down from May Through September.

For the year, I'm paying Eversource (CT) about $900 and every year even if I didn't use any gas whatsoever- as long as I have an active account. That kind of money will buy me a full tank of oil and then some. Since I only use three tanks for a full heating season (and hot water) on a 2800sq foot house, the ancillary gas charges makes up a full third of my home heating costs.

So my point is whether you are considering all charges involved in gas usage in making your decision, not just the cost per therm you will use.

Dave Carpentier

I hear ya, Max. The local gas util seems to be fairly straight forward in their billing.
- $24/mo flat rate
- bunch of per cubic meter costs (including the ever rising govt "carbon" fee)
- a project fee per cubic, to lay the main pipe into this neighbourhood. It works out to about 6k for us and is spread out over 15 years.
- taxes

Thats it. The electric util's billing is much more puzzling.

As @HomerJSmith pointed out too, there is an advantage to having the asset at hand, like a tank of oil or propane. Some event at a distance cant suddenly interrupt it, like with natgas or electric.

But as far as future pricing goes, we can only guess at the actual market. However, I think its more likely that the govt will more aggressively greenfee oil/diesel than it will the natgas, due to voter reactions.