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Boiler replacement plan

gb98501 Member Posts: 4
I am planning to replace an old oil-fired boiler in my house with a natural gas boiler. The house has hot water radiators that operate at about 180 degrees. We use about 350 gallons per year of heating oil. The boiler is probably quite inefficient, so the useful output is probably about 30 million Btu/year. We're in a moderate climate (5500 HDD) with no cooling requirements. I use a gas-fired tankless heater for domestic hot water.

Do these elements of a replacement plan make sense:

1. I should not use a 90+% boiler. My actual efficiency would be less given the requirement for supply temperature. Also, at 30 million Btu/year, the fuel savings compared to an 84% efficient boiler would only be about $30 per year.

2. I should use a boiler with more than one firing rate or stage (example Lochinvar Solution). This will allow the boiler to meet peak heating requirements but operate at the lower, more efficient firing rate most of the time.

3. I should not use an outdoor air temperature reset control if I get a boiler described by points 1 and 2 above.

Thanks in advance for your advice.


  • Thorp Thomas
    Thorp Thomas Member Posts: 23
    edited May 2011
    What's to think about?


    Sounds like you got everything pretty thought out... Given your assessment, you'll never live long enough to see a payback. The number 1 question is: Why make the change?

    There is another book out there you should consider reading: "Brain Surgery" /self taught.

    Of course, I just spoofing with you... But there is a lot more to the story you're not telling us. And there is even more that goes into making the decision on which boiler is right for you. As a heating specialists; it take me an hour to do a thorough evaluation of your present system, then a couple more hours to assimilate the acquired data into a proposal, then two more hours to review it and explain it to you. Then after you had some time to digest it all, I come back get you sign on the dotted line.

    My best advice: call a professional or two and have them come and give you a proposal. But, no more than three as you will become so confused you'll end up doing nothing. It's called, "information overload", I see it all the time.

  • gb98501
    gb98501 Member Posts: 4
    for the energy savings

    Well, sure I'm talking to professionals, and each is giving me his own idea of what to install. Ultimately it's my decision about which of these very different proposals is the best approach.

    Why am I doing it? If I keep my current setup, I'll pay something like $13,000 in fuel costs over the next 15 years. If I install a gas-fired boiler with 84 percent efficiency, I would expect to pay $4,600 in fuel costs over that period. (Both figures are discounted net present value.) I think I can save money with a new system.
  • Thorp Thomas
    Thorp Thomas Member Posts: 23
    Okay, Now that you've suckered me in...

    Here's what I'd do; fuel conversion is a no brainer. You know as well as I do the cost of fuel only has one was to go and that's up. So, if you're planning on spending money on upgrading, go for the most efficient products you can. Skip anything in the mid 80% (that's so yesterday), you'll be owning this next boiler over next 20 years and a lot can and will happen to the economy.


    I would opt for the new HTP Elite boiler at 98%, sidewall vented, integrated outdoor reset control and the SuperStor S/S DHW tank. Actually, who cares who's name is on the boiler, just make sure it has these features. Myself, I'm paschal to HTP because they're made in my back yard (sort-a-speak) and I have been using their products since... I can't remember and they are a great, local, company.


    You only have this one opportunity to make the right choice, make it a good one, one that you'll live with for the next twenty years.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Let's Start

    With a heat loss and emitter measurement along with it's capable output at different water temps. Without either, you have no road map to the best solution.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • gb98501
    gb98501 Member Posts: 4
    edited May 2011
    heat loss and emitters

    Heat loss = 42,000 Btuh

    Emitters are fin tube radiators and cabinet units, 35,133 Btuh @ 180 degrees

    Additional heat source provides 16,000 Btuh output
  • scott markle_2
    scott markle_2 Member Posts: 611
    180 is so yesterday

    Adding up your radiation is not the same thing as doing a heat loss.

    There is a good chance your house has more radiation than it needs (at 180). And it's a for sure that you only need 180 for a very small fraction of the heating season.

    A mod-con achieves better efficiency and heat delivery by virtue of more than just it's ability to condense. The fact that it can condense permits it to provide a wide range of supply temperatures (FULL outdoor reset). Making water "just as hot as it needs to be" confers efficiency gains that extend beyond the boiler. For example less heat wasted in distribution, more stable room temps (when cooler water is circulated for longer periods as opposed to short burst of high temperature operation), less convective air currents, less toasted dust, and other advantages.

    It's really not as simple as just comparing AFUE. Even if the gains are as small as AFUE might indicate you should remember that we are dealing with a finite resource in a growing and energy hungry world, what may seem like a false economy today could seem very prescient tomorrow.

    There are also of course environmental considerations, As individuals we are usually not held accountable for the external effects of our economic decisions, it doesn't cost you to dump NOX and Carbon, nor does your higher consumption effect the scarcity and cost of this resource, But ultimately we all pay for economic choices that are made in self interest alone.

    On a more practical note you will have a problem with the kick space heaters (fans won't come on, or they will blow annoyingly cool air) if you move to a full ODR system.
  • gb98501
    gb98501 Member Posts: 4
    Agreed, that adding up emitters not the same as calculating heat loss

    which would explain why my number for heat loss was different from my number for emitters. I really can't see how my house has more radiation that is required to match the heat loss, given the numbers that I supplied. Nonetheless, I appreciate the generalized statement of support of the mod/con option.
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