furnace size

Steve_45

with the actual heatloss for and upstairs and downstairs
appartment at 78000 btu's total, and adding 20% for an amtrol DHW unit (total of 93000 btu)is a boiler rated at 97000 output to close (0 degrees/70 degrees)

Al Letellier

boiler size

Should do the job quite well. If you use a priority control for domestic, you don't need to add in the extra BTU's. You didn't mention what type of boiler you're looking at, but most cast iron oil fired boilers come in three sections, as the smallest size, somewhere around 90-100 MBH, so you're all set with what you have mentioned. (Unless you have a very high DHW demand, then you might look at the next size up boiler

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Ken_15

Careful Al, some here would say go with a smaller boiler and a huge indirect tank!!!! (HA HA HA)

Ken

Steve_45

Thanks Al,

I'm thinking about the Dunkirk 4EW.90Z. I know the Weil-
Mcclain is much more popular, but my father had a problem
with it leaking a number of years back and I'm a little skeptical. The Dunkirk, with the same material push nipples
as the cast iron sections just seems to make sense to me.
And about the 20% added for DHW Amtrol, that's what the supply house recommended. I plan on using a primary/Secondary layout with the Amtrol on it's own loop
(the first off of the primary). I was just concerned that I was cutting it to close. I know the 4EW.90 can be fired
at different rates(Higher if needed) but with all the discussion about firing rates(Maxumim, minumim, etc.) going on here I thought I would ask. It gets a bit confusing.
Thanks,
Steve

Steve_45

Sorry Al.
Amtrol will be 40 gallon.