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Indirect vs Direct Fire

honda99ex Member Posts: 2
edited April 2018 in Domestic Hot Water
Took bids on oil to gas conversion.
1450 sq ft house, unfinished basement Long Island NY. Think the estimate was 67k BTUs to heat the house. Don't have many simultaneous draws, maybe a laundry load will go at the same time as a shower. Otherwise max 2 back to back showers or a bath would be the biggest continuous load. DIshwasher goes on before we go to bed. Only caveat is that we travel and sometimes no hot water draws for weeks. Thinking I can just lower the temp setting on HW Heater???

2 bids were for ~105k BTU and stand alone 45-50 gallon hot water heater. I'm not a fan of stand alone heaters from reliability standpoint. But they were priced $1100 less than any indirect option.
The others were for indirect fires coupled with higher BTU boilers. The one that caught my eye was a TurboMax 23 from a price point of view. I don't have hard water which I think fouls these things up but otherwise hard to find recent info on these. The guy did say that I didn't need to upgrade the boilers to more BTUs to run the indirect which doesn't make a whole lot of sense to me? He proposed 105k BTU boiler with net at 77k BTU. That leaves me with a 10k BTU excess outside of the heating. Is that enough? Should I "upgrade" to the TurboMax or just pocket the $1100 and use the conventional gas fired 50 gallon Bradford White?



  • PhilDavid
    PhilDavid Member Posts: 68
    Most indirects are stainless steel tanks and will outlive and out perform stand alones. An indirect water heater will almost always have a priority option on the boiler or system control. If priority is enabled all other heating zones are temporarily turned off until the tank is heated or a predetermined time limit on the control has been reached, typically an hour. Should never take an hour for a water heater to recover especially in your application.
    That being said you would be using your heating system 365 days out of the year. Some think this is good and others not so much. But personally I would go with the indirect if you are installing a high efficiency condensing boiler. If you decide to install a low efficiency cast iron boiler then do a stand alone water heater.
  • honda99ex
    honda99ex Member Posts: 2
    PhilDavid - Thanks.

    Definitely all bids were using cast iron boilers in the 83-85% range, not high efficiency condensing boilers. So I shouldn't consider the TurboMax or any indirect then using such a boiler? Because those were the contractor's suggested combinations not mine..

    I guess when I leave for any extended period I could just drop the water temp on the stand alone heater or turn it off??? Or is that not recommended?
  • bob eck
    bob eck Member Posts: 929
    Weil McLain has their GV90+ 90% AFUE cast iron gas boiler. This boiler can be vented sidewall with PVC pipe or polybutylene pipe. There are polybutylene plastic chimney liner kits available to vent vertically up the old chimney. With this boiler you could use an indirect water heater. If turning the IDWH off when away I would store the water at 160F degrees and use a mixing valve with 120F degrees water temp going out to the faucets.
    I am no expert but turning the water off in an IDWH and not draining that tank could that lead to legionella bacteria growing in the tank while that water is not being used and once you start using that water could it lead to legionnaires disease?
    This type of job might be good for a combi boiler. Heating and domestic hot water on demand no storage tank needed.
    Or cast iron boiler with tankless gas water heater. Tankless gas water heater would need to be sidewall Vented.
    A good heating contractor can address you needs and concerns.
  • gennady
    gennady Member Posts: 836
    Turbomax usually inverted indirect water heater, you can keep it at high temperature and store boiler water there. You can use taco i-series valve with outdoor reset and heat house off this indirect. Install DHW mixing valve as well.
  • lchmb
    lchmb Member Posts: 2,997
    size your boiler to your heat load (output). Put an indirect on priority with a mixing valve. your only talking one or two cycles a day for hw. Even a cast iron boiler (im a fan of the GV90 btw) will have no issue keeping up. I like to stay with one system for 2 reasons..it will run all year round and you only have one set of controls..one gas valve... less parts less maintenance
  • PhilDavid
    PhilDavid Member Posts: 68
    Whether you go with an indirect or a stand alone you can turn them down or off. There is a minuscule probability that Legionella bacteria will grow and contaminate your tank. Usually this is an issue in commercial or industrial hot water tanks that are extremely large. All current residential hot water heaters have a minimum standby heat loss of 1/2 degree an hour if you do decide not to turn it off or down.
    @bobeck is spot on with the combi set up. That would be a high efficiency boiler with tankless hot water. No worries about unnecessarily heating domestic hot water while away.
  • Condoman
    Condoman Member Posts: 86
    I like my system runs year round even if I am away. It keeps critters out of the chimney and when home I can hear it fire, a reminder that all is well.