boiler sizing

[ssfein]

I have been looking at heat load so bear with me;
I am sizing for a boiler and am trying to decide if I can do with the EKO 25 which is 85000 btu or the Tarm, Biomax, Wood Gun which are in the 130,000 + range. There is a $1000 diff between the EKO and the others, so it is an issue. So her is some figuring I have done.
My fuel usage is:
450 gal #2 average over 10 years
x139000 btu per gal
-------------------
62,550,000 btu used
x .87 eff of my burner --tested yearly by burner tec
------------------------
54,418,500 btu
div. 7500 HDD
------------------------
7255 BTU average per HDD x average # HDD per day in Jan (50) = 362,750 BTU load max
div. 24 hrs.
--------------------------
302 btu loss per hr at HDD
x 80 delta T ( 70 - -10 = 80 )
---------------------------------
24,186 BTU loss max per hour
If this is true then the EKO 25 is enough with 500 to 660 gal storage?
I am also looking hard at flat plate hx and will be interested in how that answer evolves.
Keep up the good work gang
SSfein

 

[Nofossil]

I have been looking at heat load so bear with me;
I am sizing for a boiler and am trying to decide if I can do with the EKO 25 which is 85000 btu or the Tarm, Biomax, Wood Gun which are in the 130,000 + range. There is a $1000 diff between the EKO and the others, so it is an issue. So her is some figuring I have done.
My fuel usage is:
450 gal #2 average over 10 years
x139000 btu per gal
-------------------
62,550,000 btu used
x .87 eff of my burner --tested yearly by burner tec
------------------------
54,418,500 btu
div. 7500 HDD
------------------------
7255 BTU average per HDD x average # HDD per day in Jan (50) = 362,750 BTU load max
div. 24 hrs.
--------------------------
302 btu loss per hr at HDD
x 80 delta T ( 70 - -10 = 80 )
---------------------------------
24,186 BTU loss max per hour
If this is true then the EKO 25 is enough with 500 to 660 gal storage?
I am also looking hard at flat plate hx and will be interested in how that answer evolves.
Keep up the good work gang
SSfein

Always good to do the math. My numbers are quite similar. When I heated with oil, I burned 600 gallons per year during the heating season, and my peak load is about 30,000 BTU per hour. I bought the EKO 25. While it's rated at 85,000 BTU/hr, its probably better to think of it as delivering a sustained 60,000 BTU/hr.

Amazingly, I average about 11 or 12 hours per day burn time during the coldest week of the year - just what the numbers predict.

I have 880 gallons storage. I would rate that as adequate but not generous for my situation. I'm adding a radiant zone to let me get more usable heat out of my storage.

In your case, I wouldn't consider the larger unit unless you could do a lot more storage to use its capacity. I think the 25 will do fine.