hi all.  i appologize in advance for my ignorance and asking questions that have probably been asked 100s of times before so feel free to point me to an existing thread that i can read. 

anyway, i'm located in long island NY and i'm looking to change out the 40 year old boiler (originally oil but converted to gas) for an efficient boiler.  i had national grid come by to give an estimate.  The tech recommended the burnham alpine 105 boiler.  he also said that i would need to change out my hot water heater and replace it with a unit that runs off the boiler.  he said thats the best way to improve overall efficiency of the heating/hot water system.  ok so far makes sense.  i was quoted $9500 for the job to change the boiler and water heater.  they would handle everything.  fine. 

i decided to get another installer to come in for a 2nd quote.  on the phone this guy tells me that because my house uses baseboard for heat getting a boiler like the burnham alpine is a waste of money because these high efficiency units are designed to operate in a radiant heat system to achieve the advertised efficiency (in this case 95%).

so here is where i need some help.  doing some quick reading, baseboard leaves the boiler at ~180F and returns at ~160F.  Radiant is significantly cooler something like 80F. 

reading here http://www.aceee.org/energy/state/durkin_ashrae_journal.pdf  its stated that "Operating a condensing boiler (by definition a low-temperature boiler) at an industry standard” 180°F/160°F (82°C/7°C) only will be marginally better than a conventional boiler, and create increased first cost for little operating cost benefit."  this seems to agree with what the 2nd guy told me on the phone. 

However, what i would like to know is this....once an efficient condensing boiler is installed in a 180/160 baseboard system, can the temperature be lowered to increase efficiency, and yet the system still be able to sufficiently heat up my house?  is the 2nd guy just not familiar with the details of how new boilers work?? 

it just seems strange that the gas provider would push these high efficeincy hardware if it doesnt really work in baseboard environments which are quite common...


thanks so much

I'm not sure about the article cited, but my Ultra mod/con at home is measured at 89.9% efficiency on high fire doing high temperature heating (DHW).

that better than the top end for any conventional boiler by at least 5%. but it misses a very important benefit: by modulating, the modulating boiler loses a lot of cycles, and cycles kill your efficiency.

My understanding, observation and belief is that mod/cons almost always make sense. the only time I would say that might not be the case is in systems with lots and lots of mass and high temperatures, where there aren't many cycles and no condensing.

thanks for the reply...

i agree that any mod/con unit would be better then a conventional.  the thing here is the additinal cost to get the hardware thats rated at 95% justified in a system that is inherently not designed to operate in the region of the curve that will allow the boiler to run at 95%. 

it seems that the best i'm gonna be able to see is roughly 86% which is still way better then the junk that i currently use.  just seems like its not worth the extra $.  getting something thats advertised to be 88% in --theory-- sounds like a better approach here...  please set me straight if i'm totally off base here.

thanks

I didn't say 95%. my mod/con, running just like a conventional boiler, runs at 89.9%.

that's at least 5% better than most conventional boilers *at steady state*. on top of that, it will actually *be* in steady state most of the time you are over the minimum modulation rate of the boiler, instead of a much smaller fraction of the time like with a conventional boiler. In other words, it should actually hit its efficiency far more often.

you might get a conventional boiler advertised at 88% but it's unlikely to be there the vast majority of the time, because it can't modulate and can only cycle for shorter and shorter periods as your load drops, with each cycle hitting your efficiency.

secondarily, you might find that your baseboard doesn't actually NEED 180 degree water even on the coldest day of the year: most systems I have run numbers on could be turned down to 160 or 140 *right now* as most systems are over-radiated. plus, with an outdoor sensor, you *will* increase your efficiency for large portions of the winter where you can get below condensing temps. with some experimentation in my leaky old farmhouse, for example, I have found the crappy series baseboard I long to rip out can run at a 145 max. except for a few weeks in january, I'm well over 90%. Plus all my other heating and domestic demands are right there at about 90%.

In short: if it's gas, you should use a mod/con. My only exception would basically be massive standing radiator systems that must operate at high temperatures, which are uncommon.

You might doulble-check the BTU rating, if you have good fuel use data on the old system using the FSA calculator downloadable here:

http://www.nora-oilheat.org/site20/index.mv?screen=home

(This is a pretty good one, based on Brookhaven Nat'l Labs test data for different types of boilers & oversizing.)

If you oversize the boiler for the load, it won't generally meet it's efficiency ratings. Even modulating boilers only go to ~25% of full out at their lowest modulation, and if 25% of the output is 75% of your coldest-day-of-the year heat load you'll be losing efficiency in cycling, putting unnecessary wear on the equipment in the process.

If you use the outdoor reset controls that come with the boiler, no matter WHAT radiation you have it'll be condensing or near-condensing for much of the season. With baseboard you're unlikely to hit/beat 95%, but low 90s is common enough. If you added 50% more baseboard to each room you'd be able to run it at least 15-20F cooler for more condensing performance. (If you have the space for it, more baseboard is pretty cheap stuff. If it buys you 5-10% more in seasonal efficiency it's quite the bargain!)

If you use a non-modulating mid-efficiency boiler it might have tested at 86% in an AFUE test, but if it's 3x oversized for the load it'll average under 80% as-installed. You can buy-back most of that efficiency derating using a buffer tank and some smart controls, but it's best if you get it as close to "right sized" for the heating load as you can. Most cast iron boilers in the NE aren't running anywhere near their AFUE performance: 3-4x oversized is VERY common, under 2x oversized is rare. AFUE presumes 1.7x oversizing, and if you have low enough temp radiation you can meet/beat that performance with retrofit outdoor-reset controls. Not shown in an AFUE test, a direct-vent/sealed-combustion unit will save you several percent in fuel over something that draws it's combustion air from conditioned or semi-conditioned indoor air. All mod-cons are direct vent, but mid-efficiency boilers are available both ways, and a perfectly sized 86% AFUE non-direct-vent unit will use at least 10% more fuel than a direct-vent mod con running at 90%, not 4-5% more.

FWIW: The Alpine 105's min output is 21KBTU/H, which is in fact ~70-75% of my design-day heat load in a ~2000' house in central MA, much cooler than L.I. Unless your place is unusually leaky or a lot larger the 105 is probably oversized for you too, even with the indirect HW factor thrown in. But the FSA calculator should give you a pretty good idea how much boiler you really need.

Whether higher efficiency burners are worth the money requires some calculation. If you're only burning $500-700/year in fuel, saving 15-20% with high efficiency goods is still under $150/year. If you're burning $2000+/year the math becomes more favorable. If there are large subsidies available, that too can be a factor.

Last,(maybe least, maybe not)- if you're primarily a showering family with no huge spas to fill, a drainwater heat recovery system installed at the same time as the indirect delivers/recovers ~30kbtu/h to the hot water during showers (but not tub-filling), and you need not oversize the boiler just to handle the hot water heating load, as is commonly done. It'll save only ~50-75 therms/year directly, but if it keeps you from oversizing the boiler it saves you more due to improved shoulder-season efficiency from the boiler. It'll cost a large fraction of a grand up front, but some of that is paid back immediately in the lower cost of a downsized boiler. (People who heat water with electricity get a rebate on L.I. for drainwater heat recovery, but not those who heat water with gas.) If you go that route, price out the models that beat 50% in the NRCan independently tested performance ratings:

http://oee.nrcan.gc.ca/residential/personal/retrofit-homes/questions-answers.cfm#q45

(Note, some of the 3" drain versions in that performance range are pretty tall- if you don't have the headroom, there are plenty of 4" versions that may fit better.)

Dana1, thanks for a detailed reply.

i did heat loss calculations and i get roughly 38000btu/hr heatloss. given that number, what would be the ballpark btu that i should shoot for when selecting a boiler? i'm also looking to use the boiler to drive and indirect heat system like the weil ultra 40. both guys that came to give me a quote said ~100000btu. seems overkill to me... i'm figuring something that puts out 80000btu should be sufficient, so something like alpine 80 perhaps which is the smallest they burnham makes. unless i'm missing something

get whatever you can with the lowest minimum modulation rate (Prestige Solo 60, Ultra 80, Munchkin T50/T80, etc).

then, size an indirect for your needs with that boiler. that is the road to optimum boiler sizing.

What Rob said.

The minimum-modulation of the Alpine 80 is 16KBTU/H, same as the Solo 60, a bit lower than the Peerless Pinnacle T50's 18K, etc., and lower than the Alpine 105.

If your design-day heat load is under 40K, you still have 40K of burner to spare for the Ultra 40 using the Alpine 80 should you need gobs of water at 5AM on the coldest night of the year. This is as much burner as a typical (lower efficiency burner) standalone 40 gallon tank has going for it. If your contractor is happiest supporting Burnham, the Alpine 80 sounds like your boiler.