I was going to start a new thread ,But your thread(Edgeman) is pretty much my same situation.
I actually went out and bought a weil mclain ulta 155 because thats what the HVAC guys said I needed,then while doing research on installing I found out it was way oversized.
I have a 2000sf house in the mid-atlantic(NJ)
Currently have a 100k weil-mclain oil,which when it was put in they oversized it,the one befor that was 80K.
HVAC guys come in look at your heater and say it needs a bigger one
Its a vicous cycle 80k to 100k and almost went to 155K (thank god for the internet)
hotwater baseboard,3 zones includeing the DHW boilermate tank
Heatloss @55k
Ok so Im returning the Ultra155 ,
I was giong to get the 105 Ultra but after reading this thread I'm wondering if the 105 should be knocked down to the Ultra 80,or is that still OVERKILL
I will be adding another 3-400sf within a year or 2
Around here those tanks sell
I just sold one that was 5 yrs old for $250
another older one with surface rust sold for $100
Youd be suprised how many people want or need them

It nerve racking going from 100k to 60-80k