Indirect water tank or should I....?

Discussion in 'HVAC Heating & Cooling' started by rudebutler, Sep 2, 2007.

  1. rudebutler

    rudebutler New Member

    Sep 1, 2007

    This is my first post on this forum. I've been reading a lot of the posts and I'd just like to say how polite and knowledgeable everyone seems to be.

    I'm considering having an indirect-fired water tank installed. Any thoughts/comments will be greatly appreciated!

    I live in the Hudson Valley in NY. Currently, I have a 2100 sq ft house with hot water heat. The heat and hot tap water are supplied by a Weil-McLean boiler with a tankless coil and a Becket AFG burner. They are about 20 years old but in great shape I am told. There are 4 of us in the house.

    The old part of the house (1901) is on one zone (1200 sq ft) and uses cast iron radiators. The new part of the house (2002) is 2 zone and uses baseboards.

    I have a pellet stove which covers much of the heating duty in the cold months.

    The problem is that since the addition, we don't have enough hot water. The math was done beforehand, but the reality is that in the winter the hot water just runs out. To compensate, we have adjusted the boiler settings to 150 low, 190 high, and 10 diff. This makes for some VERY hot water at first and it just doesn't last. I'd like to install a water tank. I read that an indirect-fired was the most efficient way to go. I got 2 quotes for rather different set-ups and am very confused on which way to go.

    The first was from my plumber. He would disconnect the piping for the hot water coil (?), replace the boiler control, add a Taco circulator, and add a switching relay. He would install a Superstor SSU45 for a total of about $3400. Basically, this set up would only have the burner run when there was a demand-the coil could get completely cold.

    The second quote was from my oil company. Not as detailed, basically add a Peerless Partner and the total would be about $2700. Their thought is to keep the boiler hot (120). I do have to say, one time I went away for a long weekend and shut the boiler down and when I got home there was water all over the floor. So keeping it hot seems like a good maintenance, if not economical, idea.

    I like both outfits a lot, they have been very good to me for many years. Is it worth it to add the tank but keep the controls the same? Is there another option I should be looking into?

    Thanks for reading all that!


    PS-HVAC is not my strong suite. If you need more details, please ask and I will gladly provide!
  2. Furd

    Furd Engineer

    Jul 3, 2007
    Retired energy systems engineer
    Wet side of Washington State
    In my opinion tankless coils are the worst source for hot water one could possibly have.

    Cast iron sectional boiler as a rule do not like heat-up / cool down cycling. Some can take it better than others. Yours has already displayed its dislike of heat up / cool down so I suggest that you do not change the control to what is known as "cold start" but simply dial back the existing control settings.

    You do want a separate circulator pump for the indirect water heater and you may need a priority control that will keep the room heating circulator(s) off while the water heater is recovering. You will most likely never know if this priority is working because indirects heat up pretty fast. The priority controller is an electronic controller for the circulating pumps so it can be installed later if you find you need it without opening any piping.
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Have you had a decent heat load analysis done on the house? Is your boiler oversized, undersized, or about right? Your current HW is probably not working as well because it has a significant calcium or lime buildup, but my experience with them is that they never work great. What I'm leading up to, is you may be a good candidate for a more efficient, modulating, high efficiency boiler. I do think that an indirect water tank is good, but it becomes more efficient if you don't have to maintain a high standby temp in the boiler all summer. This is where the new boilers come into their glory - they adjust themselves so on a mild day, it only runs as low as 20% of max, and can tolerate cold starts.
  5. rudebutler

    rudebutler New Member

    Sep 1, 2007
    Thanks for the quick replies!

    I had a load analysis done before I built the addition. According to the 2 contractors that gave me bids, the unit is adequate for my house. It doesn't seem to run excessively even on the coldest of days, but considering the hot water issue...:confused:

    The coil was serviced when the hot water issue first began. There was no build up in it.

    I completely agree about replacing boiler-would make a lot of sense. But added to the expense of the new tank, how much would I be looking at: $8K-$10K?

    Furd-I will check that the oil company will use a circulator and will see about priority control.

    So, basically, I'm looking at saving a little oil by going this way (lower temp settings) but mostly this will be a "comfort" installation?
  6. Bob NH

    Bob NH In the Trades

    Oct 20, 2005
    New Hampshire
    I have a system that works well with a tankless coil that was not providing enough hot water during winter when the incoming water is about 34 F.

    I installed a 40 gallon electric water heater (gas not available) in series with the tankless coil of the boiler. The feed goes through the boiler whenever hot water is used and is mixed with what is in the electric water heater. I set the water heater temperature at about 130 F so it never comes on when the boiler is in service during the heating season.

    If your tankless system has a tempering valve you should eliminate it or relocate it after the water heater.

    The system completely eliminated the variations in water temperature that made showering uncomfortable in the winter season.

    I considered installing a circulating pump to increase the hot water recovery rate but haven't needed it for two people in the house.

    In the spring I turn the furnace off. I have bypass and isolation valves so I can isolate either the boiler or the water heater but haven't needed them.

    The system was installed for economy reasons when oil prices went above $2.00 per gallon. The boiler was using so much oil to stay hot and ready in the summer that it cost more than electricity for the water heater.

    Total cost of the system ( I installed it myself) was less than $400. for heater, valves, and fittings.

    With four people in the house the economics might be different. What is the cost of fuel that you use during the non-heating season? Much of that heat goes up the stack. That won't change if you use an indirect water heater because the boiler will have to stay hot.

    With 4 people in the house you may want to use an 80 gallon water heater.
    Last edited: Sep 3, 2007
  7. rudebutler

    rudebutler New Member

    Sep 1, 2007

    That sounds like a good system. If I understand correctly, the water goes into the electric tank after it's been through the coil before heading to the baseboards and hot tap outlets. So the tank is attached to the hot output of the boiler after the circulator and the output from the tank attaches before the zone valves.

    I don't know if this will work for me since I have to keep my boiler hot. I suppose I could put in the valves you mentioned and not have the water go to the tank in the summer.

    Which would save more energy-running the hot ouput into an electric water tank or just using the indirect all year round? Agreed, the electric tank would cost less, no new circulator or zone control, and prolly less work to install.

    Anybody have any thoughts on this approach?
  8. TMB9862

    TMB9862 New Member

    Nov 12, 2006
    An electric heater doesn't heat very quickly. It's going to be a lot more than what you have now but you basically have what's in the tank and that's it. An indirect fire water heater like a Phase 3 will produce more hot water than an oil fired heater which is pretty high. I forget exact numbers but they're pretty high.
    Also look at what it's going to cost you in electric to run the thing. Is any cheaper then running the boiler all year round? It is better for your boiler to maintain temperature all year round then to allow it to cool off in the winter. I defiantly agree with those who said letting it cold fire every time hot water is called for is very bad for it.
    As far as installation goes it's probably going to be cheaper to install an electric provided you have room in your box for another breaker and you have the correct sized or oversize service.
    What size service do you have and what other large electrical devices do you have (dryer, cooktop, oven, central ac)? If you have a 50 amp service forget about it. I'd want to see a 100amp with only one other 220v appliance before installing an electric water heater. If you two a 150 amp service, three or more, a 200 amp service.
  9. rudebutler

    rudebutler New Member

    Sep 1, 2007

    I have 250 amp service, plenty of space in the panel, and 2 220V appliances (stove, dryer). (When I did the addition we upgraded the panel with room to grow:D ) I think the idea behind Bob's setup is that the tank is filling off the coil so you're not depending on it to heat the water so much as store it during the winter.

    I think the consensus at this point is that I should keep my boiler hot all year. How much would the electric tank turn on? Hard to say. I think the energy savings of an indirect if I'm forced to keep my boiler at 120 all year versus the installation savings of an electric that I turn off in the summer may be negligible. Anyone disagree?
  10. Bob NH

    Bob NH In the Trades

    Oct 20, 2005
    New Hampshire
    The system is not quite as you understand.

    The water that goes through the tankless coil doesn't go through the baseboards.

    The boiler is a closed system. The boiler water is heated in the boiler and that water is circulated through the baseboards when heat is called for.

    The tankless coil is immersed in the hot boiler water but is not connected to the circulating water. The tankless coil is supplied with fresh cold water, and in your current system it goes directly to the appliances that use hot water.

    In my system that line goes to the cold water inlet of the water heater, and the outlet of the water heater goes to the appliances (shower, sinks, . . . ) that use hot water.

    When the boiler is not being used it doesn't have any effect on the hot water stream.
  11. rudebutler

    rudebutler New Member

    Sep 1, 2007

    Thanks for the clarification. I get it now. Hot water from the coil is drawn into the electric water heater when you use it at the tap or for an appliance.

    Unless I have this wrong, I don't think it will help me. Nobody is home during the day, so there is a demand for hot water in the morning and at night. Once the tank fills with hot water in the morning, it would sit all day, cooling, and probably kick on the electric heating element until the evening when there would be use and then the whole cycle would repeat itself0 at night. And I can't shut down the oil burner in the summer. Am I missing something here? Is there a circulator that runs through the electric water tank when the boiler kicks on for house heat?
  12. Bob NH

    Bob NH In the Trades

    Oct 20, 2005
    New Hampshire
    There is not circulator in my system. I bought one but didn't install it because it isn't needed with two people and 40 gallons storage. You could add a very small circulator to use when the boiler is running.

    The water going into the water heater is almost always hotter than the setting of the water heater so the electric units don't come on when the boiler is in service. A well insulated heater will not lose more than about 0.5 F per hour.

    The saving in such a system is the fuel saving resulting from shutting down the boiler in the summer.
  13. vince

    vince New Member

    Nov 16, 2007
    I needed to run my boiler thru the summer for same reasons - for domestic hot-water and to keep the boiler from completely cooling - but at the same time I was hoping to save on oil. What I did was install an X10 outlet (you can find them by searching X10) to power the boiler (controls, pump, circulator etc) and I used an X10 programmable timer to turn the boiler on 5-10 minutes every 1-2 hours during a 24 hour period and also for 2 hours continously in the mornings and evenings. So the boiler/indirect heater operated normally for the 2 hour periods, but the 5-10 minute intervals in-between just allowed the boiler to remain warm - consequently a big saving in oil was realized...
  14. BigLou

    BigLou New Member

    Nov 7, 2007
    If your old boiler is running good I would stay with it. A modulating boiler is nice, I just ordered one! but they are gas only so unless you wanted to convert to gas your not going to get a huge efficiency gain with oil. As far as what inderect to go with, I would ask the oil company for more details the peerless partner is a stainless steel tank just like the super store so I would ask for more info. It seems like they have the better deal.

    Finally letting the boiler cool off is not a problem as long as you allow it to fully come up to temperature and run for a while. short cycling a cold boiler is no good

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