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Cost of operation


What you're advocating to do will waste money when compared to an indirect water heater's costs - costs for life cycle, fuel usage and efficiency.

1 - you want more hot water in sufficient volumes to utilize your plumbing.

2 - you noted there are scalding issues

3 - you're wasting fuel

4 - Invest in an indirect, which eliminates problems 1, 2 & 3.

Add an ASSE 1016/1017 certified device & the scalding issue, as remote as it would be with an indirect, goes away.

I've done life cycle calculations for various types of water heaters and an indirect is by far & away the rock-solid winner. Only gets beat by solar.

Once installed, a simple relay control turns the boiler into a heat-on-demand only appliance, which saves fuel. If ME chimes in here, you won't be turning the water heater off, or way down, and an indirect tank looses very little energy in stand-by mode.


  • Charles_8
    Charles_8 Member Posts: 74
    The FIRST question I should have posted about indirect water ;)

    My primary motivation for adding the large indirect tank (with electric backup/supplementation) was to improve my supply of, and steady the temp of, the hot water. Saving money would be nice but not required.

    The parts (electric water heater, circulator, aquastat, various wiring and plumbing parts) will cost about $500 to implement the "hybrid" system we've discussed in several previous posts. It occurs to me that it may actually cost more to run it the way I propose (which is not a big deal but I'm wondering how much).

    I have a 100 year old house in far northern Maine, with foam board+vinyl siding over the original wood with incomplete/settled blown insulation, so not too great wall insulation but 12" thick fiberglass batts in the attic.

    I live there (alone) for three weeks, then take off for three weeks. Thermostat set to 68F during the winter, 60F at night. While away, set to 50F. Non-heating season is about three months long. Still I used over 900 gals of oil in 12 months, expensive at current fuel oil prices!

    With the new system, I would heat water with the tankless coil to the indirect storage tank (the electric elements probably won't even run and could be disabled at the breaker). In the summer I propose to shut the boiler off for three months, and heat my water only with the electric elements.

    During absences the water heater could be turned off completely - the temp in the below-ground basement with the boiler waste heat does not get below freezing, and the tank would sit next to it anyway.

    I'm thinking as I type here. It appears that I am just trading some oil for heating water for some electricity, and a slightly more efficient standby loss (but from a bigger tank), which may be a wash. But if (WHEN) fuel oil prices spike this winter, I'd have the option to heat my water only by electricity (turn the boiler and tank aquastats down, and let the element do the heating).

    SO - any educated guesses? Will my bills (oil + electric) go up, down, or stay the same? Regardless, it will be worth it to have regulated hot water!

  • Charles_8
    Charles_8 Member Posts: 74
    Isn't that what I reinvented?

    ...except with electric backup?

    If I understand you correctly, I should not keep the boiler on "simmer" (180F high limit aquastat setting) in between calls for heat from the thermostat, but instead have it only fire when either house heat (steam) OR hot water to the indirect tank is needed? Not maintaining that hot boiler should indeed save fuel.

    Also, are you recommending I not use the electric elements at all, even in the summer, but just use the boiler on demand for the (indirect) water heat?

    But I am concerned that if I have the boiler on the entire time I am heating water for the storage tank, it might get hot enough to make steam and overheat the house even when the thermostat is not calling? Or will enough heat be diverted by the coil into the storage tank to prevent that from happening by the time the tank aquastat turns the fire off?

    thanks for your patience and help.

  • Darrell
    Darrell Member Posts: 303

    Just keep it simple...

    Add a real indirect fired water heater and run it as a zone of heat just like the rest of the house zones. It will only fire the boiler when it needs to heat the water. They are very efficient, make tons of hot water, and no hocus-pocus is required control wise. Don't keep the old stuff.

    Abandon the onboard coil in place...leave the pipe connections open to atmosphere.

    Change the OEM Triple Aquastat controler, (which maintains a minimum core temperature 24/7/365 whether you need heat or not), to a simple Aquastat controler which will only fire the boiler on call from a heating zone...including the new water heater.

    You will pay for this in a couple of years...almost for certain.

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  • Dave Yates (GrandPAH)_2

    Darrel is right about kicking your coil habit. Take the 'c' off of coil & you'll be kicking that bad habit too! As he noted, you can leave the coil's piping open or cap them off, but add a relief valve if you do.

    Here's the deal: the coil is not a very effective heat-transfer device for feeding an indirect water heater. Would it work? Sure it would, but the slower BTU transfer will keep your energy consumption up while production of domestic hot water will be down.

    How did your boiler manage to stay 'hot' during summer months previously without making steam? You wouldn't be changing that operating characteristic, just altering the manner in which the boiler operates - by not maintaining its temperature 24/7/365. BTW, that change to heat-on-demand only will save fuel all winter long too.

    Costs according to my calculations for a 34-year life cycle are as follows and include a 5% per year increase in fuel, labor and material costs. Oil will start at $2.25 per gallon, labor will cost $80.00 per hour, you will use 50-gallons of hot water per day with a yearly average rise in temperature of 80F. Given that your oil boiler will be serviced annually, we'll assign a $20.00 value to the technician checking the indirect's operation while they're there. And, I've added in $5.48 to operate the circ with electricity at 10-cents per kWh.

    Indirect water heater with the following conditions: connected to an 83% efficient boiler with a properly sized circulator for efficient transfer of energy. Your first year's oil consumption for hot water will result in a cost of $246.05. Add in a $1,600.00 installation cost (estimated because I can't 'see' your job) and the $20 for main to get a total first year cost of $1866.05. You'll replace this stainless steel indirect approximately 20-years later. 34-years from the installation date (remember - 5% per year increase in all costs), your total costs will have been $29,660.39.

    If you'd bit the bullet and installed a 92% efficient boiler in that first year, your 34-year life cycle costs for hot water (excluding the boiler to keep the picture clearer) would be $23,509.18.

    Now, let's do the same exercise with a less efficient transfer and use the electric water heater while snipping the element wires. We'll be treating this as an indirect water heater. Your fuel costs in the first year (by my calcs) will increase to $383.05. Installation costs (again, I'm estimating, but I'm using the same circumstances & controls as in the first example) will be $1,050.00. As before, we'll toss in anannual maint fee starting at $20.00. First year costs will be $1453.05. You saved almost $500.00 by not installing the more expensive indirect! However, you'll be installing a new electric water heater tank every 13-years and, again, all costs will be increasing by 5% per year. 34-year life cycle costs will be $42,192.17.

    Let's look at that 12K+ difference in the two examples to see if it's worthwhile to install the more expensive indirect. Using the same 5% per year increase, you would start year one gifting yourself $147.31 (34-year increase = an offset of $12,531.21 - just pennies shy of the actual difference for our life cycle cost analysis) on your investment of $550.00 (diff in costs of installation). That's a 26.8% ROI & it's tax free to boot.

    Advice is free, reality is not.
  • Charles_8
    Charles_8 Member Posts: 74
    This is a single-pipe steam system, not BB hot water

    Now I'm really confused. I may have neglected to mention it in this particular thread, but my boiler makes steam for single-pipe radiators. (It's not a baseboard hot water system). The coil *is* the heat transfer device to the storage tank!

    Thanks for the detailed calculation examples, Dave. I plan to own the house for at most five, and more likely two, more years, so upfront costs are more important to me than the long-term payback. Incidentally, oil was FAR above $2.25 last year in northern Maine (it was $2.80 at one point), and it won't be any cheaper this year :(

  • Dave Yates (GrandPAH)_2
    liquid assets!


    Sorry for the confusion.

    All things being equal, the only difference in your operation would be the substitution of an indirect for the coil - your boiler would be clueless regarding the swap. It wouldn't make any more steam in the summer than it does right now. A competent installer can do what's been suggested in their sleep.

    The minimal increase in costs between a Rube Goldberg and the Real Deal can easily be recouped when you sell - liquidate the liquid assets - pun intended. Besides which, an indirect will increase the home's value by far more than $500 or $600 bucks. Meanwhile, your problems would vanish and you'd have the benefits all to yourself - livin large! There's no reason for me to BS you - I'm not selling anything.

    When you have the whole-house inspection prior to the sale, the inspector (if trained properly) will be more likely to approve a legit use than one that's been altered & is being used in an unconventional application.
  • Ken_40
    Ken_40 Member Posts: 1,320

    An indirect is nothing like an electric WH.

    An indirect has an internal heat exchanger! An electric water heater does not it is merely a tank with two elements!

    Electric water heaters are plain steel, glass lined. Most indirects are stainless steel and typically have a lifetime warranty; eletric WH's, 5-10 years tops.

    Right church; wrong pew.

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  • Charles_8
    Charles_8 Member Posts: 74
    Definitions of pews

    Thanks for the clarification. I have apparently been misusing the terms as though "indirect" meant that the heat source is external to the storage tank (which is what I am proposing).

    An indirect heater does have an external heat source in addition to the heat exchanger internal to the tank, of course...

    Anyhow, the 40 gal storage tank should greatly improve the quantity of hot water available. Hopefully I will save some energy too, since the boiler will only come on when heating the storage tank to 130F and won't have to maintain 180 all the time.

    I'm going out of town for a month (so will shut everything down), but when I get it hooked up I'll post on how it's working. I won't know for a few months how much less (or more) oil I'm consuming though...


  • Weezbo
    Weezbo Member Posts: 6,232
    Charles ..in a way i can agree with electric DHW

    i live in Alaska. to day it was 95. yet in the morning i got a call from a friend who had spent the early morning hours working on an underground sewer that had frozen 57 ' ....

    electric for the summer months here is not a bad deal.

    turn the boiler off...use the supply from & through the boiler water maker to feed the electric...a timer on an on demand system is not a great disadvantage either......

    your indirect can do its thing in the winter or should guests stop in to see you during summer......
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