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Sizing help for replacement gas boiler

djackman
djackman Member Posts: 12
Starting to plan for a correctly sized boiler to replace the current oversized 80's vintage Hydrotherm HC-145 (116k net / 100k IBR) gas boiler. 1200sq/ft quasi-split ranch, two baseboard zones 52' and 58', each has a toekick heater also. DHW is a 50gal gas HWH that eventually will be replaced with an indirect. Basement is unfinished and not heated, no plans to finish.

Slant/fin app shows ~25k. We've done a lot of improvements - new windows, replaced acoustic tile ceilings with sheetrock, attic and exterior wall insulation (fiberglass), significant air sealing.

Was looking to stay with a CI boiler for cost and simplicity. So far only one I found that comes close is a Burhnam 202 (30k net) but would that be enough to handle an indirect HWH?

Comments

  • bob eck
    bob eck Member Posts: 930
    I would use a tank type gas water heater 40, 50 or 75 gallon depending on how many showers and how many people.

    30,000 BTU going into an indirect water heater will not be a lot of BTU.
    You can get a Vaughn indirect water heater with electric elements to back up the coil being heated by the boiler.
    You can install a bigger indirect water heater and recover it slowly.
    How many showers and how many people?
  • djackman
    djackman Member Posts: 12
    DHW load is 2 adults, no jacuzzi tubs or teenagers. With electric pushing $0.25/kwh here I'd upsize and/or up the storage temp then mix down before adding electric.

  • Jamie Hall
    Jamie Hall Member Posts: 23,169
    If you really want an indirect, you have a problem: nowhere near satisfactory recovery from the small boiler. Go to an independent 30 or 40 gallon gas replacement -- you and the people using the showers will be a lot happier.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,453
    I would use an indirect and hook it up for DHW priority and you will be fine. Most gas fired water heaters are only 40K input (32k net maybe) for a 40 gallon tank. With a 30 k boiler and only two people a 40 or 50 gallon indirect will be fine. A 50 will give you 40 gallons of hot H20
    (80% of the tank is considered available the remaining 10 gallons of hot H20 is considered cooled by the incoming cold water)

    Not a Burnham fan but that's just me. Weil McLain has the CGA & CGI which are about 37knet
    Gordy
  • Gordy
    Gordy Member Posts: 9,546
    edited January 2019
    I would use an indirect also. A 40 gal conventional tanks burner is mid 30k. No big DHW loads you are golden. The only thing is an indirect would be higher cost, but will usually out last a conventional which is not maintained.

  • djackman
    djackman Member Posts: 12
    Just checked and the current HWH is 38k input, sounds like it would be about an even swap. Looking to an indirect to get rid of the standby losses up the chimney and hopefully better quality.


    Not a Burnham fan but that's just me. Weil McLain has the CGA & CGI which are about 37knet

    Thanks that gives a few more options.