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Community and Q&A

Lochinvar Boiler Sizing?

db_neuhaus | Posted in General Questions on

Zone 4 (York, PA) 
Finish carpenter currently working on updating our personal home, this is our first winter here and the gas bills are as bad as I expected.  I ran the calcs from Dana Dorsett’s (thanks!) article on actual fuel usage for the month of December.  I realize December isn’t the ideal month to use for accurate design temp purposes but I think it should get me in the ball park?  Also I haven’t completed our energy updates.  New fiberglass casements are in, but zero window treatments or trim.  Some air sealing is complete in the attic but it currently only has sparse r30 batts  and I have r-60+ cellulose scheduled in a week.  The wall system is r13 batts, 1 1/4 continuous poly iso sheathing and brick. 

The fuel usage calcs came out to 37,100 btu/hr.  I also ran the projected updated construction numbers through the betterbuiltnw hvac sizing tool tool and came up with 29k btu/hr.  The current system is a 4 zone baseboard heat with a boiler rated at 175k output!  Its a weil mclain cga 83% and only 10 years old. I’ve timed it multiple times and when only 1 zone calls for heat the boiler only fires for 45-50 seconds.  It’s short cycling constantly.  

A great friend runs a plumbing and heating business and has recommended a Lochinvar Knight fire tube replacement.  I’ve researched the specs and reviews and it seems like a great option.  The floor model option will make replacement very easy as well.  His supplier for the 69k output model is currently out of stock and he is suggesting installing the 89k output model.   I realize the 69K is already over the 1.4x recommended oversize but with the 10:1 turndown would I have major issues with the 89k output model?   It’s available now and actually a couple hundred bucks cheaper for some reason.  
Thanks so much.  

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  1. paul_wiedefeld | | #1

    The larger boiler is fine - the smallest mod con output is around 8,000 btus, for whatever reason, they haven’t been able to offer lower minimum outputs. You can electronically limit the boiler size to your heat loss in the set up process.

  2. pico_project | | #2

    Is this a combi boiler or just a boiler?

  3. db_neuhaus | | #3

    Stand alone boiler. Currently have a separate 10 year old gas water heater. I'm going to switch that to a heat pump water heater for a few reasons. I'd rather not run a combi boiler at all during cooling months. I plan to duct the cooler air into a finished section of the basement during the summer. And the $500 instant rebate makes the hpwh more attractive.

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