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Indirect efficiency

dh1989
dh1989 Member Posts: 17
I'm trying to determine if I would benefit from an indirect, either a Boilermate/Superstor type tank or a disconnected electric storage tank piped to my tankless coil. My current setup is a Utica Starfire 3 115,000 BTU 81% efficient oil boiler with a tankless coil. I have ran some tests and calculated some numbers to measure hot water BTU usage vs. oil usage as metered on an hour meter (I have a 1 GPM nozzle). My results for hot water only (heat off) have been ~15% efficiency on the coil with the boiler always turned on and ~50% efficiency when I only switch it on as I need hot water. I have seen some indirect numbers thrown out on here claiming 33-40% efficiency, while others claim "highly efficient" without citing a number. I want to see if the cost of adding an indirect would get me over the 50% efficiency I'm at now by just switching the boiler on/off, or if it would be a waste of money.

Comments

  • jumper
    jumper Member Posts: 1,680
    If you have the room for storage you have room for a conventional storage water heater. Saves wear&tear on heating boiler and provides some redundancy. DHW efficiency is a non-issue in America. Pennies per day.
  • BobC
    BobC Member Posts: 5,208
    When I replaced my boiler I looked into adding an indirect but found it just doesn't make sense if you don't use much hot water. It's just me in the house so I stuck with my 40 gal gas hot water heater, it uses 6 or 7 therms a month.

    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • spoon22
    spoon22 Member Posts: 32
    It only makes sense to go with a. Indirect tank. Why would you want to run 2 oil burners when 1 will do the job double the maintenance not to mention the boiler is usually more efficient than the water heater. Also if you let that starfire boiler sit all summer it will shorten the lifespan. an Indirect is the best option . An aqubooster will be cheaper than an indirect but relies on the tank less coil if the coil is questionable it will cut down on efficiency. I would go with an indirect water heater with some sort of outdoor reset control you will have plenty of hot water and save on oil consumption.
  • jonny88
    jonny88 Member Posts: 1,139
    indirects are more sanitary no?who maintains a water heater.Indirect store water at 140 install mixing valve and call it a day.Agree though that the price is a big difference but I have heard on more than one occasion that a water heater is a throw away item.
  • bob eck
    bob eck Member Posts: 927
    I was told that when using a indirect water heater with a oil fired boiler cold start that the home owner can save one tank of oil per year. 150 to 200 gallons savings @ $3 per gallon savings of $450 - $600
    Plus you should never run out of hot water.
    If you have a boiler with a domestic coil and you have hard water and no water softener what does it cost you to heat your domestic hot water as lime hardness builds up on the inside of your domestic coil? Plus what does it cost you to get your domestic coile pumped out (cleaned out) every year or so.
    There are indirect water heaters on the market with 6 to 10 year warranties and some come with a lifetime warranty.
    Water heating for the average home is 14% of the average household expenses.
  • ron
    ron Member Posts: 148
    would you not want to analyze the entire heating system to make this decision? it looks like all he said was he has oil heat, a utica boiler that is 115k btu and a 1 gpm nozzle.
    I assume it's baseboard or radiator hydronic heat to the house?
    If so, I had asked not too long ago here about using an ergomax type hot water heater that is an "inverse indirect" and provides about a 30 gallon buffer of boiler water that would remain hot in that tank... while using a cold start boiler. what are your opinions on that type of setup with the goal being efficiency?
    I am in a similar situation- i have baseboard heat and an oil fired boiler, doing a new boiler soon and hearing that there's not much savings now using an indirect hot water tank versus a new cold start boiler with tankless coil caught my attention.

    The one thing i've heard over the years is maybe the biggest benefit to an indirect tank is a consistent temperature of hot water versus an oil boiler with tankless coil, so you trade efficiency/cost for comfort i guess.
  • ron
    ron Member Posts: 148
    edited May 2015


    There's been a lot of claims of better performance from the reverse indirect. IMHO, I do not see how you can possibly get efficiency out of it when you must maintain the tank at 180° 24/7/365. With the standard indirect, you maintain the tank at 130F-140F.

    i think i am off my reverse indirect kick.
    i threw the "whole system" comment out there because he said 115k btu boiler with 1gpm nozzle and i wondered how over sized it might be and i assume it has a significant size heat exchanger? figuring the primary goal was efficiency and getting all the heat from the oil into your home instead of up the chimney and reducing oil used i wonder if a better solution might be looking at boiler replacement? i know that was not the initial question and probably not what he wanted to hear but if a few grand up front reduces oil used and that cost is recovered with a new boiler in 2, 3, or 4 years....
  • RobinInCali
    RobinInCali Member Posts: 30
    edited May 2015
    I'm not sure we are answering what the OP asked. So I will chime in with my scenario, which I thought, was the OP's.

    I have a new mod com boiler for the heating, but I already have a tankless for DHW. I got married last year and we increased our home size by three teenage girls (!). The tankless is a top of the line one and serves us ok, but now we have all the problems a tankless has--cold water sandwich, lowered pressure when two or three appliances/showers are going, etc. I have read interesting posts about adding a cheap electric tank ($300) to the tankless which will fix all the problems. Here is a link to that.

    http://www.houseneeds.com/learning-center/tankless-water-heaters-how-to/takagi-tankless-water-hot-water-high-volume

    So now I'm trying to figure out if it's better to add this cheap electric tank (with the electric removed and a pump running to the tankless. See link.)

    OR if it is time to take advantage of a crazy sale I saw on ecomfort where the Viessman 120 gallon indirect has been marked down to $1,540.

    I would be the one installing either system, so we are basically talking about a savings of about $1,500 for parts (tank, pumps, copper, etc.), and of course, easier labor on the cheap electric one.

    So consistent with the OP, I would ask, which is better? I am sure the indirect would be, if someone else were paying for it. But if my tankless is only a couple years old, why not save some money and just run the cheap electric tank addition to that system instead?

    If I missed the mark on the OP's scenario, I'm sorry, but it seems he/she is asking the same type of question I am.
  • SWEI
    SWEI Member Posts: 7,356
    If you don't have hard water and the tankless coil is in good shape, @icesailor 's repurposed electric tank heater with a pump recipe should be the least expensive solution by far.
    RobG
  • rick in Alaska
    rick in Alaska Member Posts: 1,222
    I have a 120 gallon indirect running a six plex apartment building. Way overkill even with that many girls.
    I would put in the holding tank with circulator to the on demand water heater. Not sure how small of a tank you can get away with, but in my case ,50 gallon water heaters fit the bill and are the cheapest to buy. I have done a couple just recently in restaurant scenarios and it works great. Also a lot cheaper than the new indirect.
    Rick
    RobinInCali
  • SWEI
    SWEI Member Posts: 7,356
    I think he's on oil. Toyotomi?
  • kcopp
    kcopp Member Posts: 3,782

    I'm not sure we are answering what the OP asked. So I will chime in with my scenario, which I thought, was the OP's.

    I have a new mod com boiler for the heating, but I already have a tankless for DHW. I got married last year and we increased our home size by three teenage girls (!). The tankless is a top of the line one and serves us ok, but now we have all the problems a tankless has--cold water sandwich, lowered pressure when two or three appliances/showers are going, etc. I have read interesting posts about adding a cheap electric tank ($300) to the tankless which will fix all the problems. Here is a link to that.

    http://www.houseneeds.com/learning-center/tankless-water-heaters-how-to/takagi-tankless-water-hot-water-high-volume

    So now I'm trying to figure out if it's better to add this cheap electric tank (with the electric removed and a pump running to the tankless. See link.)

    OR if it is time to take advantage of a crazy sale I saw on ecomfort where the Viessman 120 gallon indirect has been marked down to $1,540.

    I would be the one installing either system, so we are basically talking about a savings of about $1,500 for parts (tank, pumps, copper, etc.), and of course, easier labor on the cheap electric one.

    So consistent with the OP, I would ask, which is better? I am sure the indirect would be, if someone else were paying for it. But if my tankless is only a couple years old, why not save some money and just run the cheap electric tank addition to that system instead?

    If I missed the mark on the OP's scenario, I'm sorry, but it seems he/she is asking the same type of question I am.

    This would probably have been better in a separate post, however....
    If the cold sandwich is your only real issue the simplest solution would be to place in line AFTER the tankless water heater a small 120v 4-6 gallon well insulated electric point-of-use water heater that will absorb the cold water slug. Set the temp to the same outlet temp as the tankless and plug it in. No need for a circ/pump.
  • dh1989
    dh1989 Member Posts: 17
    Thanks for the discussion and the info. I think I've decided to hold off on doing anything with the system for now. I do have baseboard hot water heat. Boiler stays off in the warm months until I need hot water. I switch it on and it fires up providing hot enough water for a shower in roughly 5 minutes. I lump shower, dishwasher, laundry all together at the same time each day. Averaging about 7 gal of oil per month. Not sure that I can do much better than that to justify the expense of a storage tank or indirect.
  • BobC
    BobC Member Posts: 5,208
    My consumption has been 6-7 therms a month on a 40 gallon water heater for as long as I can remember (that includes the gas stove). But then it's only me, when I was in the army we used to shower in 4 gallons of water and though I probably use more than that I'll bet it's not much more.

    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • BobC
    BobC Member Posts: 5,208
    I have to say that I only use the stove to make coffee in the morning in the spring summer and fall - cooking is done on the grill. That 6-7 therms a month was true with the old 30 gallon hot water heater as well as the current 40 gallon unit.

    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge