I’m in the planning stage for a new home and want radiant heating and am looking for the most efficient boiler.  The new modulated gas boilers along the lines of a Munchkin or similar are very intriguing, but here in the Northeast I will be limited to burning propane if I choose to go that way.  My question is how do these boilers stack up to an oil fired boiler and what are the pros and cons to this type of system?   

a modulating/condensing propane boiler will cost a similar amount to run as a well controlled oil boiler here in maine, maybe somewhat more. it certainly is more efficient but propane is significantly more expensive per BTU, so the efficiency difference in the two is simply to get towards "parity".

however it's silent, pretty much odorless, and doesn't need a chimney.

depending on the unit it may require more maintenance, and propane is an explosion hazard where oil is not. Oil is a major environmental hazard if it leaks, though.

Propane burns cleaner with less greenhouse gases.

if you're doing radiant, a mod/con boiler can eliminate the need for a mixing system. it can also handle your hot water far more efficiently than a cast iron beastie.

in the end if economics alone are the only number that matters and you have a chimney or can get one cheap, oil probably wins. But if not, propane mod/cons do have many advantages.

Hope that helps a little at least.

I go for propane and a ModCon high efficiency condensing boiler.

The combination has a 15% smaller carbon footprint of "foreign" oil with virtually no NOx or SOx. Propane is 85% American and nearly 100% North American.

A condensing propane boiler will need less maintenance, burn cleaner and closely matches oil for cost in most markets. Culture rather than good business or good science has more to do with the predominent fuel in your area.

Thanks for the info guys.

Several things to consider.

Propane has 93000 btu/gallon

#2 heating oil = 139,000 btu per gallon

Oil has 49% more btus/gallon

Mod con propane boilers run 5-15 % more efficiently then oil so the net is about 30% more from oil  oil is 2.89 per gallon today in Connecticut so  propane would have to be less then 2.20 per gallon You can do the math for NH. 

Look at http://tonto.eia.doe.gov/oog/info/hopu/hopu.asp for historic price data for heating fuels  and figure out if it is worth it.

First, if you go propane, get a tank big enough to go a year between fills   Then you can buy  gas when it is cheap.   Demand is high in the winter and low in the summer so buy in the summer.  BUY your own tank(Do not rent, at least not in Connecticut).  IF you own the tank you can shop price when it is time to buy.  IF they own the tank you are locked in to one supplier by law and they are going to screw you(at least in this state).  My gas company charges me 38 cents per gallon over the daily wholesale price at the Selkirk pipeline terminal.   Today I would pay $1.88 per gallon, this summer I paid $1.33.  If they owned the tank I might be paying 3$ per gallon average retail in CT this week.  Crazy huh?  Buy the tank. 
They don’t care when I fill up, they make the same profit per gallon.  In fact they prefer people filling in the summer because it evens out demand and they deliver larger loads.  Inground tanks are expensive figure 3-5K for a 1000 gallon one.  I paid 2600 last year for a 500 gallon tank, regulator and the underground line to the house,  My heatload is fairly small so I can easily go a year or two between fillups.

You might as well use propane for the dryer and range and barbeque also.
cheers,
Eric

Incorrect that a mod con runs 5-25% more efficiently. that's the AFUE rating difference, but in real world conditions the differential is more like 15%-30% more efficiently. I believe Dana would attribute part of that to the difference between atmospheric and sealed combustion, which I think I would concur with.

Buderus makes a condensing oil boiler  looks prety efficient to me. I bet it is within 10% of the  mod con  gas one in a house where it is properly sized.  I could be wrong though. Plus it is a pricy beast.

Cheers,
Eric

Sure, if you get the condensing oil beasts, I'd agree... but no one is using those. Yet, anyway. usually the comparison is conventional cast iron oil vs modcon propane. But you're right and I should have specified.

What Rob said.

...and...

It also depends on what your actual design-day & average heat loads are. Standard medium-mass oil boilers don't go much smaller than 75-80KBTU/r, whereas mod-cons can drop below 20KBTU/hr output. If your average heat load is under 30KBTU/hr the cycling losses on the oil boiler inevitably add up. (30K is about my PEAK, not my average. YMMV.)

Standby & operating losses of the oil boiler are also comparatively higher than with propane when you have low-temp radiation. The minimum input temp to an oil boiler is 140F, which is well over the average temperature needs of most radiant systems, let alone their return-temps. If the oil boiler is within conditioned space the loss is somewhat mitigated, but if the boiler room is the warmest room in the house (as it often is), it's far from ideal.

But if your design day heat load is north of 100KBTU/hr, and the system is designed well the differences in operating cost can be less than gia-normous.

I agree  with both of you in the sense that in a small tight house, propane= good oil = bad

With oil you are limited by the nozzle size.  The smallest nozzle is about 1/2 gallon per hour.  Unfortunately #2 fuel oil has a lot of crap in it that clogs small nozzles.  One of my good friends is an hvac installer specializing in oil burner installation and repair.  He said whenever they install oil systems with less than 0.8 gph flow rate they leave extra nozzles and filters with the clients and teach them how to change them out.  He steers people to gas systems if they are smaller than 80 KBTU net output if possible.  

Big old house, lots of heat needed I think oil works out as well or better pluses and minuses.

New construction excellent shell not a mcmansion use propane. 
Build to pasivehouse standard, use a Hairdryer, or 3 dogs.

Eric

At 93% efficiency plus some type of thermal mass or storage to prevent short cycling, it's not clear how one is going to do much better.

http://www.peerless-heater.com/Corporate/News/NewsItem/tabid/74/anid/3/Default.aspx

bad link jon.

I think he's trying to point to a press release about the direct-vent condensing Peerless Pinnacle Oil boilers.  The smallest one is still a 70MBH unit, 2x+ oversized for my loads.

See:

http://peerlessheater.org/DesktopModules/Bring2mind/DMX/Download.aspx?EntryId=8&PortalId=0&DownloadMethod=attachment


Since it's still a bang-bang burner control, you can't get the 91.7% AFUE advertised if your design day heat load is less than 0.6 of the full rated output, or have high mass radiation/buffers to push the knee in the partial-load curve a bit to the left,

If coupled with an indirect and controls to use the indirect as a heat-dump (Energy Kinetics System 2000 style) to lengthen cycles & purge heat it'll do OK, but nothing like it's 93% steady state low-temp operation efficiency.  Figure on 88-90-ish, best case for heat loads like mine (even if I had low enough radiation temps to take full advantage.)

By comparison, a smaller well-designed propane mod-con system with low temp radiation would hit the mid-high 90s, and is probably simpler/cheaper/lower-maintenance than the oil-fired beastie.  Whether it'd be cheaper to run than the condensing-bang-bang oil boiler depends a lot on system design, heat load, and the vagarites of the fuel markets.

If any non-modulating system is over sized for some particular application, sure, you will take some efficiency hit. So a generically valid consideration, but it's not clear that is the case for Kat_man. If you can't use low radiator temps or keep the unit in heated space, *any* system will take a hit. But the AFUE rating already takes into account cycling and lower demand days - don't account for these losses twice. If you have some type of thermal storage (slab, tank, etc), you can avoid some cycling and could exceed the AFUE rating.

I agree that the AFUE rating does not include the benefits of temperature reset and modulating systems would get higher ratings if it did.

AFUE testing assumes oversizing of 1.7x. Oversizing beyond that puts you further down the steep side of the part-load efficiency loss curve-I wasn't counting it twice. AFUE on 'em is ~91.7% (not the steady-state 93% thermal efficiency at low input temps), and it'd be on the order 2.5x oversized for me, not a mere 1.7x, so 90% would be a best-case scenario using most boiler cycling models, 88% more likely, which still isn't terrible, but a closer estimate of real-world performance to expect. I'd be running it at somewhat higher than AFUE-test temps too, but haven't factored that in to come up with those numbers.

I'm sure it'll outperform a cheap propane tankless impressed into use as a boiler, but not a right-sized propane mod-con. If the radiation normally runs at 140F+ both will hit about 86% combustion efficiency, but the mod-con will have fewer cycling losses, but it'll pretty much be all matter of raw $/MMBTU between the two fuels. If the radiation runs much cooler than 140F the mod-con will walk away from it on efficiency, but the $/HDD equation is less linear.

Kat_man lives about 50 crow-miles from me in southern NH, with a ~7000HDD climate. No telling for sure what his real design-day heat load is, but most conventional homes built to code in that neighborhood have design day heat loads less than half the Pinnacle Oil's output, which would be the wrong side of the oversizing assumptions in an AFUE test. Older housing in that region is all over the place though, and I'm sure there are many conventional sized homes where the Pinnacle Oil would be right-sized, and the most appropriate solution. If I had to take a WAG on it base on the minimal information that we have, it's probably oversized, but by the all-critical "how much?", would be too wild a guess even for me. ;-)

Now if I took an even wilder stab at where future energy pricing is going,heating oil is increasingly competing against motor fuel for it's share of the a cracked barrel of oil, which has a long term upward pressure on pricing. While a significant portion of propane is a byproduct oil refining (which is why it's price has generally tracked crude oil prices), another large fraction comes from natural gas. As the Allegheny shales get developed for gas production it will have a moderating effect on propane and NG pricing. If carbon becomes ever more taxed, that too will burden heating oil to a greater degree than propane. While it's been traditionally more expensive than oil per MMBTU, my expectation is for that to flip at some point in the next decade.

All ModCons have outdoor reset which means the operating effiency (not to be confused with the nebulous AFUE) will be lower. Even if matched to fin-tube baseboard, the boiler will condense a good part of the season yielding 88% plus "combustion efficiency". Unless you add-on ODR, oil is the loser. Oil and propane follow a supply/demand curve.

Before you consider a mod/con oil burner attend a training class at Viessmann or Buderus. They both sell mod/cons by the truck load in Europe. But are very reluctant to bring them over.

Primary reason is the quality of fuel. Secondary reason is the diversity of regions. Very cold regions will have troubled with the combustion air freezing, starving the burner and fouling the combustion chamber.

I was sold on the mod/con oil burner because gas is not available in my area. At Viessmann I had a chance to talk to the GenMgr and the instructor at length over lunch. what they told me, in a very polite and diplomatic manner, convinced me not to touch oil mod/con in the US for a very long time.


Enough said, everyone has an opinion. Mine is worth the price paid.