savings from low mass conversion

Ray_Frechette

I am wondering what sort of savings are typically seen with a conversion to a low mass boiler.



I have 1200 sq ft ranch in Maine 7500 HDD currently consuming 650 gallons # 2 for heat & hot water.



We use an average of 16 cubic feet of hot water per day.



The Heat loss at -2 design is 40,000 BTU.  We have bedrroms and living space zoned off and only heat to 65 in living space from 9:00 A.M. to 6:00 PM with setback to 53 nights.and one bedroom sees 68 days and 65 nights other two bedrooms are 62 degrees nights and 58 days.



Boiler is an old Utica 180,000 BTU boiler from 1967 with a carlin 99 CRD burner on it and a Honeywell AQ 251 series control unit and an indirect 40 gallon heatflow tank.



Looking to replace with a DK2-3 Pensotti this summer.



Any guesses what sort of percentage savings I might see? 



At design temps outside we typically boost up the heat in the house as it is not as comfortable at our normal temps when it is zero outside.  We typically turn up to around 68 all rooms upstairs.  Even there it is not terribly comfortable on a 60HDD day.  Floors are too cold and 36 sq ft picture windows units in dining and living room are big sinks.



At design temps outdoors with lower setback at night we are burning about 30 K of total consumption.  Combustion test shows furnace to be 80 % efficient.  Yes I know combustion test efficiency is not the same as AFUE...



Basement is insulated to R-10  but not heated with a zone.  The zone is there but I am too cheap to turn it on.



On a 30-40 HDD day 65 is plenty fine for my tastes...



Boiler is fired with a  .85 nozzle  More than we need for actual heatloss but needed due to mass of Boiler.  5 Big thick cast iron sections unit is about 4 feet by 3 feet by 2 feet. pin with wet base.



AQ251 purge is active to bring out as much heat as possible after a firing is done.  Have indirect tank on a timer too in order to bring that up to temp first thing in morning right before thermostats call for heat to warm the house back up.  Mostly empty the tank at night before bed too.



So any SWAG'S a(Scientific Wild **** GUess)s to what oil savings might be all other aspects staying the same  IE temps in house day and night??

Jason_13

MPO-IQ

I would consider the MPO-IQ by US Boiler. You can benefit from the pre-purge of the circulator and plug in ODR.

From what you have now I would assume a 30 - 50% fuel savings due to changing from 180k to 84k and ODR. I usually find a 25 - 30% fuel savings with just boiler replacement which the old boiler is much closer in size than you have and no ODR. ODR is usually goos for 10 - 20% dependent on the type of system.

Ray_Frechette

I have Outdoor reset and purge already

The AQ 251 series control panel from Honeywell has outdoor reset.  And it has a purge function.



I couldn't afford doing everything at once so decided in stages.



I bought the control unit to get some savings up front and installed an indirect hot water tank up front.  That eliminated the coils and low limit on boiler a few years ago.  And I added some attic insulation.



All that reduced oil consumption from 1100 gallons per year to current 650 gallons per year.



What I am wondering is what sort of reduction I might see from using the same outdoor reset, and purge on a newer lower mass boiler.  IE What effect justthe mass reduction is likley to have.



I agree the whole package has significant savings,  but I am already enjoying some of the efficiencies withthe indirect tank and the ODS and the Purge feature now that offsets some fo the benefits of a whole package.  Yes it takes a LOG time to heat up that big old boiler I have now,  but by the same token that heat doesn't just flow up the chimney when space heating is satisfied as the purge feature pulls it back down and into building envelope.



  Granted in the summer time more is lost to standby losses,  and granted even in the winter I am seeing more losses than I likely will with a much lower mass boiler,  but the question is , How much?



650 gallons now.  DHW water at 16 cubic feet a day works out to nearly a tank of heating fuel alone per year witha rise from 40-50 incoming to 120 outgoing.  Now I will grant you with shutting tank down early at night and purging the hot water out of it we are not seeing all of those 16 cubic feet at 120 degrees outlet temps...  But by and large I would guestimate 500 gallons for space heating.



My best feel is new boiler should see a reduction of 150-200 gallons per year.  IE reduction of mass alone might account for 15-20% and new Pensotti and Riello has an extra 8-10% combustion efficiency in addition to low mass benefits.,  So maybe in the 20-30% at best range for the final conversion and updating of boiler and controls....

ChasMan

Hard to tell exactly.

I think you might be over optimistic at 200 gal. 100 is a lot too. And that DK2-3 efficiency rating at 88 or whatever, I have my doubts about that. They are running the air gate almost wide open and I bet it will soot in the summer. A few mfgs have done that to lower noise and acheive wild efficiency ratings. I don't think I would buy a boiler that has their burner set up so far away from the burner mfgs standard settings unless it had a combustion chamber or logical statement as to why they need it set that way. Cold start and outdoor reset give you a lot of savings you allready have that. Tripple pass gives you easy cleaning and a wee bit more efficiency but I doubt it is any more than five or ten percent. Low mass vs what? Mid Mass? I doubt that is much at all. If you go from 20 gallons to 5.7 Thats 14 gallons of water you have to heat up over and above the rest of the system which probably has another 10 in it anyways for the tank and piping so in reality you are going from 30 to 16 (50% less water) and with post purge, a lot of that heat ends up in the hot water tank. I do think the fact that you are downsizing the boiler a lot will help. Longer burns for sure. My guess is you save about another 80 gallons. What kind of heat loss and design temperature do you have? 600 gallons doesn't seem like a lot.

Ray_Frechette

I have to think this boiler is more than 20 gallon capacity

I could be wrong.  Problem is there is no way to know what the specs on the boiler are . Utica has no documentation for it.



I do know it takes about 30 minutes firing at .85 to raise temp of boiler to working temps.



New low mass boiler should take roughly 5 minutes at most.



So rather than the Pensotti do you prefer the Biasi 3?

Ray_Frechette

Design heat loss is 40,000 at -2 outside temps

That is guestimating that my air tightness is slightly better than original 1970's construction as I have dealt with several of the easy fixes...  In any event we used to have indoor humidity levels in the low teens with a humidifier going and since tackling the no brainer air infiltration losses to attic we see humidity levels in the 30-40's with no added humidification other than activities of daily living.  With that we do run the two bathroom fans during each shower and for 15 minutes afterwards.



And those numbers reflect an inside air temp of 70.  We never heat the house to 70.



Days hover around 65 nights as low as 53 with setback in living space.  Kids bedrooms are 62 at night and drop during day to 50's.  Master bedroom is kept at 6o nights and 67 days as my wife's office is in there.



Basement is insulated but unheated.  When near zero outside cellar will be near 50.  With outside temps of 30's cellar is near 58.



In any event changeover of the boiler is not solely for efficiency upgrade.  it is tired and time for a change in any event.

Ray_Frechette

Design heat loss is 40,000 at -2 outside temps

That is guestimating that my air tightness is slightly better than original 1970's construction as I have dealt with several of the easy fixes...  In any event we used to have indoor humidity levels in the low teens with a humidifier going and since tackling the no brainer air infiltration losses to attic we see humidity levels in the 30-40's with no added humidification other than activities of daily living.  With that we do run the two bathroom fans during each shower and for 15 minutes afterwards.



And those numbers reflect an inside air temp of 70.  We never heat the house to 70.



Days hover around 65 nights as low as 53 with setback in living space.  Kids bedrooms are 62 at night and drop during day to 50's.  Master bedroom is kept at 6o nights and 67 days as my wife's office is in there.



Basement is insulated but unheated.  When near zero outside cellar will be near 50.  With outside temps of 30's cellar is near 58.



In any event changeover of the boiler is not solely for efficiency upgrade.  it is tired and time for a change in any event.

ChasMan

5 minutes.

5 minutes sounds about right. They do heat up fast. It depends on what zones are calling though. Your boiler sounds like it has a lot more than 20 gallons in it for sure. I have no experience with either the Pensotti or Biasi boilers. I do like the Biasi manual more so than the Pensotti. The firing rates and settings are in line with Reillo specifications and they include a blanket. They also list a lot of approved burners and settings, nice touch. The breech size is at least in the ballpark, The Pensotti has a 6" breech. They both have boiler drain tappings front and rear, The front one could be used as an inspection port if needed, They are one of the few manufacturers that list over fire draft ranging from .01 to .06, that’s kind of wild but I assume that the smaller boilers have lower over fire pressure and the large ones have higher over fire pressure. They do not list the pressure drop for each model and they should. Neither of these boilers have baffles. I find that a bit troubling. Why no baffles? Could it be stack temps are already low? Anyhow. Like I said, I have no experience with either. If it’s not a DIY install, I would find an installer that installs a boatload of them and has references you can check out. If it is a DIY install, make sure your distributor is DIY friendly. You will need a chimney liner for sure with these small boilers.