Short Cycling on Oil- an impossible problem?

AJinCT

So I've lived in two houses with oil heat, one that is my parents' house, and one that is a rental house. After dealing with heating problems in both, I've thought a lot about oil fired boilers. I've come to the conclusion that with most typical American heating systems, either fin-tube baseboard or hydro air, there is no way for an oil boiler to function properly. Am I crazy here?

So first of all, the "rule of thumb" seems to be that an oil boiler should cycle on for 10 minutes to get to steady state, and thus run efficiently. The only way I can see this happening is using high-mass cast iron radiators or panel radiators with a high water content, so that there is a lot of mass to heat up, and a lot of mass to retain that heat, avoiding the need for another cycle of the system for some period of time.

If you're using the traditional American fin-tube, the length of a single zone is typically limited to 80 feet, which is about 45k at 180F using Slant/fin 550, or about 40k with 500. The smallest boilers you can buy from Buderus or Burnham are 75k, leaving 35k going into the roughly 8 gallons of water in the boiler, plus the little bit of additional water in the system and thermal mass of the baseboard itself, getting to about a 3 minute cycle time on the burner when one zone is on.

In larger, newer houses that are using hydro air, if the ahus are sized properly, to the load, then the boiler would be sized to the combined size of the ahus, leading to a 3 minute or less cycle time on the burner when one zone is on. If you oversize the radiation, then the zone only stays on for a minute or two, in which case, the boiler still short cycles.

Start oversizing the boiler, and it just gets worse. Add in ODR, and it gets even worse, particularly for fin-tube, which is rated at 180F, versus hydro air, which is rated 140F. Am I missing something here in thinking that oil just doesn't work well in most applications unless you put a buffer tank in? It seems to me that it would only have a prayer of working at near-design temps, whereas a modern gas boiler would be able to match output to load, and run low and slow, and with high TDRs, the exact sizing of the boiler becomes less important.

Thoughts?

SeymourCates

You are exactly correct in all of your analysis.

I have been slightly successful in one nearby building by downfiring a three section Utica so the output is only 71K. It actually needs all of that to warm the CI boiler in a cold crawl space. However, once brought to temperature, the fin tube can in no way accept anything close to 71K. So, it typically cycles until the call ends. Thankfully, this occurs fairly quickly.

I have adapted a set of timer relays that keep the circs running for 15 minutes after the end of the call. This purges the boiler of all that energy and typically raises the room temp by two degrees above setpoint. So, it's a good two hours before the next call and the process is repeated.

As you noted, outdoor reset compounds the problem.

We need a manufacturer to step up and produce a burner that can accept a .45 nozzle coupled with a two section boiler.

Jamie Hall

I've never been particularly fond of the 10 minute notion. While it may take that long for a boiler -- fired by anything, provided it is cast iron and not very light sections -- to reach a steady state temperature, the flame on a properly adjusted oil burner should stabilize in less than a minute, if not much less. After that, the problems with varying draught (which shouldn't happen if the dampers are adjusted properly) and changes in combustion chamber wall temperatures are the same for any fuel.

So... the problem from the combustion standpoint is the compatibility of a high mass boiler vs. a low mass boiler. Fuel choice is not relevant. This can be handled, for hot water work (whether fin tube or hydroair), with properly sized zones and correct control strategies.

Now it is true that a boiler with very little mass can respond much more quickly to flame cycling, which may be advantageous with oil firing, which is difficult -- with presently available equipment -- to modulate. There are some other problems with low mass boilers, though.

The problems to which you refer seem to me to be as much difficulties with zoning and control as they are with boiler stabilization, if not more.

SeymourCates

We did an oil to gas conversion recently.

The house had a five section Weil in it. The boiler would start and run for not more than one minute and shutdown. It was a hot start boiler as it also had a tankless coil for hot water and it lived between 180 and 190F for its entire life.

The heatloss of the house was calculated at 60K BTUH

Design day is -15F.

The degree hours were 132,000.

Therefore the required BTU annually to heat the building should be 99M.

Estimated DHW use consumes another 35M. Call it 135M total. The oil usage was 2000 gallons per year or 280M BTU.

System efficiency: 48%

That is how bad it can get when an oil boiler is short cycled unmercifully.

EBEBRATT-Ed

Last I knew you couldn't get an oil nozzle less than .5 gph which would be 70,000 input (and that's at 100 psi oil pressure)

Making smaller nozzles would help but they are very problematic as far as plugging up is concerned. I would suggest a buffer tank to get some decent run time. Also do not oversize the boiler.

Weil McLain used to make a 2 section boiler oil fired, maybe they dropped it

SeymourCates

@EBEBRATT-Ed

We're running the .55 on the Beckett @140 psi using the DeLavan line filter in addition to the spin-on. We replace them every two years. No issues with plugging in the nozzle. Can't go smaller as the air becomes excessive on the three section.

Paul48

"It was a hot start boiler as it also had a tankless coil for hot water and it lived between 180 and 190F for its entire life".

@SeymourCates ........ Can you elaborate on that statement?

Jamie Hall

Couple of thoughts. First, may I take issue with your comment on gas boilers (or furnaces) not needing maintenance for a decade or so? No major heating appliance -- on any fuel -- should be left for more than a year to a year and a half without a qualified person giving it a good hard look. To suggest otherwise is to encourage potentially dangerous, if not deadly, behavior.

Second, you are basically correct in that if the boiler -- on any fuel (you seem to have a problem with oil, but the problem is actually more general) -- is relatively high mass in relation to the load, it can be difficult to keep it from running short cycles, and your suggested solution, to increase the mass of the load, is the simplest approach. If the boiler or furnace is relatively low mass (the obvious example, of course, is a forced air furnace with primarily sheet metal construction), then the supposed 10 minute time to flame stabilization is not correct, and much shorter cycles are possible without sacrificing efficiency.

I would point out, as a slightly off topic -- but relevant -- point, it is possible to take an aircraft gas turbine (a low mass application) from a dead start to full power in a matter of 30 seconds or so -- including time for instrument checks and stabilization. A typical truck diesel (a high mass application) should reach stable full power operation in less than 5 minutes from a cold start (if yours doesn't, check your engine thermostat!).

STEVEusaPA

AJinCT said:

...I absolutely despise oil in general. It's a dirty, nasty way to heat, and from a Mechanical Engineer's perspective, gas is just so much better of a fuel to provide heat where heat pumps can't or don't. Not only can you modulate it, condense it, exhaust it at low temp, but it burns clean, you don't have to service it every year to clean the gook and goop and glop out of the filter and boiler, but it can also be used for so many other applications like cooking or a generator, where oil can't. From a practical perspective, LPG gives you a smaller boiler, other uses, and doesn't take up so much space in the basement with a giant oil tank and cast iron boiler to burn it. The one application where I just can't think of a good replacement for an oil burner would be steam if it is impractical to convert to hot water.

Although I agree with you about the facts that oil has its limitations (can't modulate, can't get lower firing rates) I disagree with many of the above statements. You thoughts are outdated, and don't reflect what's going on with oil heat in the past 10, even 20 years.

"...It's a dirty, nasty way to heat..."
No it's not. Properly commissioned systems (properly cleaned, tuned and set up), burn very clean and produce less pollution and ozone destroying chemicals than gas.

"...you don't have to service it every year to clean the gook and goop and glop out of the filter and boiler..."

Nonsense if you properly buy, handle, store and treat your fuel using industry standard/acceptable practices.

Solid_Fuel_Man

I agree that oil in today's boilers and burners......Riello.......burns very clean from what was in your father's basement years ago. I've opened up several 3 pass oil boilers and only had about 3 min vacuuming and the combustion numbers were still spot on. And I am NOT IN ANY WAY disagreeing with @Jamie Hall but those boilers could have gone another year and another 1,000 gallons of oil w/o service. But yes those cases are rare, a qualified tech should always be at least inspecting every piece of equipment annually.

That said with proper dual filters and good tuning practices oil is a very viable fuel.

From my engineering standpoint, gas is a good fuel for the small loads of most residential homes, and oil is great for larger loads. But I also believe that biomass is a viable answer to offset much of our oil and gas thirst, but that is a limb which I will not hang on here.....

STEVEusaPA

I don't agree with you that oil is 'pretty dirty and nasty'. I believe it can be, when done wrong, but not when done right. You're experience seems to only be based on heating oil done wrong.

Don't get too hung up on that 95% on gas. It's not like you plug in a 95% gas boiler, and are always (if at all) getting 95% efficiency. And those boilers require annual maintenance or they will plug the heat exchangers and become pretty useless.

As far as environmental impact, please don't try to say that all the methane gas leaking from all the fracking wellheads, as well as all the methane gas leaking from all the 100 year old piping, especially up in New England, and all the methane from burning gas-is less than all the emissions generated from burning heating oil. It's just not true. It's not even less than the impact from burning coal.
The environmental impact alone from fracking is disastrous to the planet, and puts us on an unavoidable, and irreversible path of destroying the planet. Most other countries around the world (those without big gas lobbyist) understand this and refuse to allow fracking in their countries.
Heating oil is big in Europe-better regulated and controlled, better technology. These were mandated by governments who want to do what is best for their citizens and the planet.
Renewables are also big in other countries, with Germany for one taking the lead. If by viable you mean profitable, then no. But without government intervention, which you won't get with this administration, lobbyist will continue to control the money and profit, and the environment will suffer.

I'm just tired of seeing this "...Oil is pretty dirty and nasty...cleaning the boiler and oil filter is rather pungent, and the fuel itself is just nasty..." comment by people who aren't out in the field working on oil burners, and don't understand how to do oil right.
You're entitled to your opinion, I'm just here to provide some facts and experience, so everyone who stumbles on this post gets to hear more than one side.

Jamie Hall

OK @AJinCT ; we'll accept it as read that you simply don't like oil. That's your choice, and you are free to make it. Personal preference, however, is very poor engineering.

B100 is not a drop in replacement; in fact, in most machinery and boilers any of the bio blends (at any percentage) must be evaluated very carefully for compatibility.

You suggest that home heating fuel is less well regulated than diesel. That is so. There are people out there who will happily sell some pretty horrible stuff. The more reliable oil companies, however, sell a fuel which differs from ULSD road diesel in only two ways: it isn't dyed, and it isn't taxed. Otherwise #2 home heating oil and summer ULSD from your local Shell station are the same stuff (winter ULSD has additives to lower the pour point).

I would certainly agree -- I think anyone would -- that cleaning a poorly maintained, poorly adjusted oil fired system is a miserable job. Working with one which has been well maintained, no.

You mention that emissions from oil are higher in CO2 than LP, which is higher than natural gas. This is also true, purely due to the chemistry of the fuels (the ratio of carbon to hydrogen atoms in the fuel molecules). It is not a direct ration, however, as the heat content of oil is also higher, per molecule, than that of the lower molecular weight hydrocarbons.

However, all things considered, and from many years of thought and observation, I would probably have to agree with you that for the average consumer today gas -- either LP or natural -- is the better fuel. Electricity would be even better. Why? Because the average consumer appears to expect something which requires no attention, no thought, and no maintenance, and gets litigious or twittery when their expectations are not met.

STEVEusaPA

AJinCT said:

Aren't there also some detergents or lubricants or something in ULSD that isn't in heating oil? I know heating oil and diesel are, in theory, almost the same thing, but I've heard varying accounts of what is actually different about it.

They are exactly the same. The only difference is when you load heating oil (both ULSD products), they inject red dye to show the fuel was purchased free of any road tax.
You can select additional additives, for a lower pour point, and add different bio blends, but all the same.

The biggest problem with fuel quality is simply storage, especially up in your area. Where I am, in the Philly/metro area, virtually no oil company stores their products, especially bio, in their own tanks. It's proven that without proper due dilligence (testing, additives, etc, i.e $$$) many problems are created. But pulling product from the refinery, and delivering it...not much fuel related problems at all here (we also don't get the harsher winters you get up there). Especially true where proper grade bio is stored separately, kept above freezing, and blended while you load.

Same for gasoline. I always find it funny that people swear this 'brand' or that 'brand' of gasoline is 'better' or 'worse', when all the companies pull the product from 1 of 3 terminals in my area, none of them have their name on them.

The reality is, all fossil fuels are horrible for the environment, and renewables are the best way to go, but we'll never see that here, not in my life time.

psb75

Windhager/Pellergy and Fröling are two other very good Austrian pellet boilers. I suspect Viessmann makes one too but not importable at this time to USA.

Solid_Fuel_Man

Yes, getting a biomass boiler certified for use in the US takes some dollars and a commitment to stay in the US market to recoup that money. That takes a pretty big leap of faith for some companies.

I believe all solid fuel boilers have to be tested to UL391 standard, but may or may not be required to be EPA certified to meet some tax rebate requirements. Then there is ASME if they want to go that far. My wood gasification boiler is UL391 certified by a third party.

In my rural part of northern New England biomass is even used to generate electricity in two local plants, just don't get me going about outdoor smoke-dragons which give us all a cough and biomass a black eye in general. Most don't even know I burn wood.

EBEBRATT-Ed

@AJinCT

I don't know where in CT you are located but Ct has natural gas all over the state. You must be in a Rural area

Jamie Hall

EBEBRATT-Ed said:

@AJinCT

I don't know where in CT you are located but Ct has natural gas all over the state. You must be in a Rural area

It would be nice -- but an awful lot of Connecticut is rural -- or sufficiently so (such as my area) that I'll be long gone before natural gas ever gets this far! Mostly the northeast and northwest corners are without.

Steamhead

STEVEusaPA said:

"...It's a dirty, nasty way to heat..."
No it's not. Properly commissioned systems (properly cleaned, tuned and set up), burn very clean and produce less pollution and ozone destroying chemicals than gas.

"...you don't have to service it every year to clean the gook and goop and glop out of the filter and boiler..."

Nonsense if you properly buy, handle, store and treat your fuel using industry standard/acceptable practices.

This.

@AJinCT , if you have oil-fired equipment and have experiences like that, you need someone who actually knows how to work with oil. Period.

EBEBRATT-Ed

LOL @AJinCT , "What Connecticut are you talking about" Gee, the one 5 miles from my house

you hate oil and don't have gas. Well, I have done some work in Connecticut and there is a lot of gas in CT. I live in MA. Sure the rural areas of both states don't have gas ...unless you count propane. Let's see if I can remember the cities and towns I did gas work in:

Enfield
East Hartford
West Hartford
Hartford
Rocky Hill
Wethersfield
Farmington
Bristol
Stamford
Plainfield
Vernon
Windsor Locks

And those are only the one's I worked on.

Ct Natural gas covers:

Avon
Berlin
Bolton
Canton
E Hampton
Glastonbury
Granby
Greenwich
Hebron
Manchaster
Mansfield
New Britan
Newington
Portland
Simsbury
Unionville



And there are other gas suppliers in CT

Jamie Hall

When you come right down to it, most of the bigger cities an towns in CT have natural gas -- in my area, for instance, Torrington and all the towns down the Naugatuck to Bridgeport. What happens is that you get more than a few miles out from them, and the density of development just isn't enough to support the cost of running a gas line -- they don't come free.

As an aside, that applies to internet service as well -- it's really good in the towns and cities, but somewhere between mediocre and awful away from them -- and the only provider is your friendly cable company, for a price.

An oddly schizophrenic state that way.

Steamhead

Here we go again. Here's @AJinCT 's last rant thread:

https://forum.heatinghelp.com/discussion/157571/why-are-energy-efficiency-standards-so-far-behind-the-technology

For the record, AJ identified himself in that thread as "a Mechanical Engineer, and I work in the defense industry." Not the heating industry.

Just like in that previous thread where AJ condemns steam heating because he lived in a college dorm with a steam system that badly needed work, here he condemns oil because of bad experiences he had in prior residences. News flash, AJ: you were the victim of poor maintenance. That's the fault of the service organizations you dealt with, not that of the oil itself.

I heat with oil, and it works perfectly. No smoke or soot at all. When I open the boiler to service it, there's maybe a little dust in there- no more than that. Our customers' oil-fired boilers run just as well. Some were running very poorly before they had us work on them. The difference now is that we maintain them.

The notion that gas-fired equipment never needs maintenance is completely bogus, though widespread. Every combustion appliance should be checked once a year, including a digital combustion analysis. That's the only way to insure safe operation.

Solid_Fuel_Man

Too add to this fun rant:

It is my conclusion that we don't see more L.P. on smaller accounts is that the price is significantly more money per gallon and therefore substantially more per BTU, as L.P. has about 1/3 fewer BTUs/gallon which we all know.

For the life of me I can't figure out why I can work at an industrial facility with 10,000 gallons of L.P. tanks and they pay less than $1/gal and I can buy the same L.P. from the same supplier for $3+/gal. Don't get me going on tank costs etc, the supplier owns all the tanks. I bought my own!

Jamie Hall

Couple of thoughts. First, putting a natural gas line to somewhere isn't free, and someone has to pay the cost. If not the individual customer, then all the customers. It's unlikely that folks would be really happy with that.

Second, wood heat is all very fine in some respects. However, unless the logging is done very carefully (disclaimer -- we offer that service with out team for small lots -- up to say 100 acres, and on large scale projects (say 500 to 1,000 acres), it can pay to bring in the specialized non-damaging equipment) the environmental damage is somewhere between considerable and catastrophic. Not to mention the air pollution from all but the very best gasification boilers.

I quite agree that a heat pump for a new system is close to ideal -- provided you have a backup heat source for those cold days. Today, for example, Cedric will run close to 16 hours -- and burn close to 50 gallons of oil in the process. A heat pump just wouldn't do anything at all today; it would have to be oil or LP or electric.

And one other thing... a truly well insulated and designed new house in New England can be heated entirely with solar. How do I know? I've built them, and the occupants are happy.

Steamhead

AJ, when you figure in the shorter service life of many mod-cons, their efficiency doesn't look so good. Some of the early Giannoni-based mod-cons started leaking after five years. That might be replacement time in Germany, but not here.

Many of our parents and grandparents lived through the Great Depression- the 1929 one, not the 2007 one- when, if you had to buy something, it better last a while because you couldn't afford to replace it again any time soon. It's hard to see how you can achieve a net savings if you have to replace the unit two or three times more often as you would a cast-iron boiler.

Then there's the fact that a wet-base power-gas-burner steam boiler is some 6% more efficient than the typical atmospheric gas steamer. This is due to better control over combustion air and the greater amount of available heat-transfer surface. Our customers love these units.

At the moment, it's 22° F in Baltimore, going down to about 16° tonight, and we can expect the same over the next week or so. As @Jamie Hall says, a heat pump just won't handle this weather without some sort of backup. In most cases that's electric resistance, which will be minting money for BG&E. You can keep your heat pump- I'm quite happy (and so is my bank account) with my oil-fired radiators, and so are my customers with theirs.

Solid_Fuel_Man

Ok ok ok, a few words on the ever elusive mini-split, for all the flack mod/cons get for their short expected life span, mini-splits in my expierence will not last more that 10 years. I have worked on a lot of conventional and mini split refrigeration systems. Mostly large commercial systems and compressors simply don't last that long. Especially when they're asked to work 24/7. Running on an inverter at 4 to 6000 RPM. I personally have installed over a hundred of them, and the AC and shoulder season heat is all I would care to use them.

EBEBRATT-Ed

I hope no one is comparing LP versus oil based on gallons. If you are you don't know what you are doing

oil is 140,000 btu/gallon
LP is 91,000/gallon

Steamhead

In Hartford, CT right now, it's 10° F right now and will be in single digits tonight. There just isn't enough heat in that frigid outside air for a heat pump to work without backup.

It's 23° F in Baltimore, going down in the teens tonight. We're working a boiler replacement on a Trane Vapor system this week. The house also has Mitsubishi mini-splits and they can only maintain about 55° F inside. That should be enough to keep the pipes from freezing, but is totally insufficient for comfort.

The new boiler is a wet-base/power burner unit, and when we get it running that house will be warm. The Vapor State rules.

We don't do refrigeration, but @Solid_Fuel_Man 's experience seems to put these mini-splits in the same category as mod-cons: shorter service life.

In this weather, steam is king.

Jamie Hall

@Steamhead -- you are so right! As I type this, at the principal place I care for, it is -10 and windy and going down to I don't know what. The house -- throughout -- is a nice comfortable 68. Cedric is close to what he can handle, but not quite there yet (cycling on pressure a wee bit -- at the very tag end of a run (say 45 minutes) he will shut off at 6 ounces for the length of the post/pre purges and then come right back on for 10 minutes or so. Can't complain -- @Charlie from wmass has him dialed in pretty close).

The other place we care for is hot water -- and my daughter is camped out over there to keep an eye on it to make sure it doesn't freeze up. It's closed for the winter, but the owner won't drain the pipes and won't put glycol in. Grrrrrrrr....

Steam Rules!