HELP ME CHOOSE AN OIL BOILER. LOW MASS VS MID MASS

ED95Pont

I am an electrician by trade but have spent the past 2 months educating myself in hydronics. I have a full understanding of controls.

I am looking for the system that will use less oil

My Home: 2100 sf colonial built in 1820 in northwest ct. Slant fin heat loss is 68,000 an hour. My home is fairly tight for an old home but I have not done a blower test. Current system is a 144,000 btu GE boiler with a domestic coil. 2 heating zones. First floor zone piping splits off and goes 3 ways and returns back to 1. I have fin tube baseboard. My boiler is located in a below grade basement about 700 sf. The basement is comfortable in the winter. I would assume some of that comfort comes from the loss off my non insulated boiler

I have gotten 5 quotes all different equipment. all 3 pass and indirect with various controls. all the contractors are trying to over size. I am using an interest free loan through our utility to pay for this, only certain contractors are on the list. The contractors I have spoken with are all comfortable with all the choices in equipment other than the b3, they all will not install it. They all think it is not big enough
My Heat loss 68,000
My choices
Buderus 115-3 DOE 85000 Net 74000 8.7 gallons of water
Biasi B3 DOE 67000 Net 58000 3.7 gallons of water
Biasi B4 DOE 97000 Net 84000 4.7 gallons of water
Purepro trio P3 DOE 91000 Net 79000 3.6 gallons off water
My indirect will be between 32 and 40 gallons with priority control.

The best choice that I see based on the heat loss are the buderus with trio next in line. Lets assume that both use the same controls, Tekmar tn2 or honeywell aq251, cold start , otr, purge heat to last zone called, zone sync, Room temp feedback.
My question is with all the above controls what is better the mid mass or the low mass. The buderus has 5 gallons more water in it. I would think it would help with short cycling, but what about the purge to last call. Is the simple fact that it is closer to my correct size all I should consider? None of my contractors can answer that for me.

A step further, can the logomatic be measurably more efficient than the above controls.

Bottom line what will use less oil without sacrificing comfort

Thanks for your time
ED

FranklinD

I will second what Hatteras says about the Slantfin app. I used it extensively when we replaced our boiler. After a winter of spending a considerable amount of time bouncing around the design temp, followed by computing btu/sq ft and actual consumption...the Slantfin app was almost about 25% over. BUT...some of that was my fault, too. And as others have noted, the app doesn't take into account any solar gain situations. I don't have much, but it causes an impact.

kcopp

The Trio and the Biasi are essentially the same boiler.
I agonized w/ my house 12 yrs ago w/ the same thing. I went smaller and then finished the 3rd floor of my house. I opted for a 115-3 Buderus at the time.
These days I have been specifying Trio boilers w/ Carlin burners & Bradford white powerstor indirect WH.

Aaron_in_Maine

I would opt for either of the 3 sections. Make sure your indirect is big enough. I would do at least the 40 gallon run it at 145 degrees and mix it down to 120 to make sure the boiler keeps up. I use a biasi 3 section all the the time on a house your size and it gets a lot colder here.

ED95Pont

Thanks for the explanation of the different boiler ratings, I get it,
I am still not clear on the effects to the system of the 3.6 gallon boilers vs the 8.7 gallon boiler at close to the same btu. If it is negligible then the extra cost of the buderus does not make sense to me.

If I understand correctly I should measure my fin tube length and see if we can get a boiler set to fire less btus than my radiators can deliver. But at what temperature High limit or out door reset corrected temps, or some where in between?

Ed

ED95Pont

I have 122 feet of fin tube first floor zone,79 feet second floor zone 3/4 pipe

Thanks
Ed

kcopp

122' of fin tube.... that must be a split zone. generally 75 feet is the max amt of fin on a 3/4" zone.

ED95Pont

It splits and goes 3 ways then returns to one. It is 1-1/4 pipe from the circulator to the split about 40 feet of 1-1/4

ED95Pont

Thank you,

With the above settings what boiler control would you suggest, The zone sync and purge functions some offer make sense to me on paper but not sure about real world benefit. The Honeywell AQ251 allows me to set the min return water temp?

Thanks Again
Ed

SWEI

Hatterasguy said:

All kinds of fancy controls that vary the water temperatures a couple of degrees here and there. All, in theory, assist in conserving fuel. But, nobody can ever document exactly what they save.

Brookhaven National Lab did some work on this. It's worth a read http://forum.oiltechtalk.com/attachments/fullreportbrookhavenefficiencytest.pdf

Rich_49

I would invest in a larger indirect . Sensor location in the mid tank area can be set , changed to allow boiler to purge into the colder bottom water temp . Purging heat to piping and emitters that are already hot is kind of futile . If you're gonna run a circ to thermally purge a boiler it might as well have an adequate supply of colder water to exchange with . The obvious is that you will lessen DHW calls on average .

The .6 firing rate was mentioned . Will you be direct venting this unit ?

http://www.energykinetics.com/system2000-Brochure.shtml

ED95Pont

I will vent to a center chimney, It will have a new stainless liner installed.

In the study # 3 represents the energy kinetics, What does #5 represent, Buderus 115 or 125.. No 5 is not far off from number3

Rich_49

The main thrust of the System 2000 is the FACT that it is a well designed SYSTEM . Take away any of the components and it is just a boiler . Well , maybe , a boiler with less water capacity that can be purged is gonna be more efficient , it is also gonna get to making Domestic hot water faster . Take into account that every time the boiler runs it purges to the indirect set up , lessening the amount of times the boiler will fire to keep the storage temp where it is set for .

The main reason there is so much debate on fuel usage is because people pick boilers and ignore the rest . You must design and install a system . Maybe not System 2000 but a system none the less .

The Buderus or any 3 pass boiler for that matter is a fine piece of equipment , now figure out the thermal purge to the DHW and you're gonna build a system efficiency . AFUE ratings are severely flawed , hell even EK states that their boiler has an AFUE of 87% but actual is 85% .

Use a good boiler , controls which give a better opportunity for savings , better emitters , ODR , thermal purge to indirect over system , Delta T circs for the system . You'll end up with a better system than is being installed by 97% of the geniuses out there .

Charlie from wmass

I am a fan as of late of the biasi boilers. The mid mass is nice and it has a good simple control
Size and proper installation is key. I also like pairing them with zone valves and the Taco delta Temperature circulator.

Charlie from wmass

I never measured but it appeared to be 2" thick. The difference between 3 and 2 inside the building envelope would not concern me.

Charlie from wmass

You can have too much insulation as the cost and bulk out way the savings.

Charlie from wmass

Btw the insulation is not on the burner end aside from the refractory inside the door.