Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Hot Water heater inline with boiler coil?

farnja Member Posts: 13
Hi Wall!

I have a 1.5g/hour oil boiler that’s going to run all summer keeping my domestic hot water hot via a coil. Last year I spent around $150 to $180 a month just for hot water - I’d like to reduce this. We *do* have natural gas in the house - we added it when we remodeled the kitchen to do a gas range - so I think I have these options:

1. Add a Separate gas hot water tank: Turn on each year for the non-heating season, turn off boiler during non heating season.

2. Add a gas hot water tank in series with the boiler coil. Turn off boiler in summer and let cold water run through coil into gas hot water heater. In winter, hot water from the boiler coil will feed the gas hot water heater.

3. Add an indirect hot water holding tank, let it get heated year round by the oil boiler. This should more energy efficient than the current coil system.

4. Forget about it.

Any advice on the above as far as ongoing cost, installation cost, and simplicity?

One other factor is that my wife would really like to install ductless AC/Heat Pumps at some point, so its I suppose it’s possible that with cases 1 and 2 above I could leave the boiler off except for the coldest days of the year? (This is unlikely today).

Thank you!


    HVACNUT Member Posts: 5,765
    IMO, #3 is your best option.
    Eliminating the coil completely. The fact that there is presently a tankless coil means you have a triple acting aquastat. This will always maintain the 'Lo' setting when there is no space heat demand. With an indirect you can either turn the low as low as it goes, or replace it with a cold start aquastat that will only fire the burner when there is a demand for heat or hot water. The latter will also provide options to use outdoor reset, or boiler reset.
    Can you post some pics of the boiler and controls? Not too close.
  • farnja
    farnja Member Posts: 13
    Thanks for the reply - pictures below.

    You think a separate holding tank would be better than just a separate hot water tank and turning off the boiler in the winter? I think I would agree with you, except that burning gas is a lot cheaper than burning oil so I would think not running the boiler at all would be best?

    Thank you!

  • ScottSecor
    ScottSecor Member Posts: 846
    I suggest one of the following:
    A. If money is a little tight, do away with the tank-less coil. Install an over-sized gas line for a new free standing water heater and a future gas burner. Then have a gas water heater installed and never use the tank-less coil again for dhw,

    B. If you have a medium sized budget, run the over-sized gas line and replace the oil burner with a gas conversion burner. Here in NJ that would reduce your energy use by approximately sixty percent. At the same time have a indirect hot water tank installed.

    C. If you have a large budget, instead of putting money into a roughly twenty year old boiler and burner, consider replacing it with a new gas fired unit. I'd still recommend a indirect hot water tank.

    HVACNUT Member Posts: 5,765
    edited May 2019
    An option not mentioned would be converting to nat gas on the boiler and still do the indirect. A Carlin EZ gas burner goes nice with the Peerless WBV boiler. And as you probably know, unlike a direct fired gas water heater where there is substantial standby heat loss, most indirect water heaters claim a heat loss of .5° per hour or less.
  • bob eck
    bob eck Member Posts: 930
    What about installing a Vaughn indirect water heater with 4500W electric elements.
    You can use the boiler to make domestic hot water during the heating season and if you want you can turn the oil boiler off in the non heating season and use the electric elements to make your domestic hot water.
    In the future you can then install a new boiler when needed going oil or gas when replacing the boiler and you will already have the indirect water heater.

  • farnja
    farnja Member Posts: 13
    Thanks for all of the replies. I’m a little hesitant to do a gas-conversion on an older (2006 installed) boiler and I definitely don’t have the appetite for a new gas unit.

    I think that leaves me between an Indirect Tank running off the old boiler or a separate gas hot water tank. These seem pretty comparable for efficiency - I guess the indirect is little more today but probably would keep using it whenever I replace the boiler and the separate tank is a little less today?
  • hot_rod
    hot_rod Member Posts: 21,898
    Bob's idea of an indirect with electric element may be a good option depending on your cost for KWh. Often called a solar tank, coil at bottom electric element near the middle. Then you have a dual fuel option.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream