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Burner running too much?


I had a new boiler installed about 6 weeks ago to replace an old, rusted 45 year-old unit. It’s the first winter in this house, so I don’t have a lot to compare. I’ve had hot water in apt. buildings, but not a boiler one floor down right in my basement. More specs below the story.

We set it at 67 overnight, then up to 69 during waking time. The unit can take 60-90 minutes of continuous burner run to bring everything up to temp. Although, often, the thermostat will hit the set temp but it will keep running for up to that average 60-90 min. time. The pump seems to run that entire time with the burner.

Then, the unit cycles roughly 10 on, 10 off (which matches the set cycle specification of the thermostat—3/hr) to keep the thermostat set temp. These timings can vary based on outside temp, of course. (Sometimes it will obviously cycle less on warmer days.)

Both the installer (who was highly rated) and the manufacturer (in a roundabout way) said this was normal operation for a modern boiler. The installer said we should just let it run. My quandary is: I want to trust the pros, but also it seems strange for a 96K burner to run so much and for so long to bump 2 degrees.

Or is it? (Questions that come to mind: Is it undersized, maybe it's the thermostat, etc.?)

In an effort to be reasonable but educated about expectations: I’m seeking opinions to help me determine if I should ask the installer for a follow-up system check. Or, should I not worry and just let it run?


96K BTU input, forced hot water

House built 1923, stucco

Not zoned

2000 sq. ft.

Don’t know about wall insulation, but probably not much

New double-pane windows throughout (2013)

9 cast-iron radiators


Don’t have enough gas consumption data to make a good comparison yet



  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    We set it at 67 overnight, then up to 69 during waking time.

    This could be perfectly OK, depending on what you have. A couple of days ago it got pretty cold outside and my boiler ran 12 hours straight. But it depends on what you have.

    For one thing, I do not do setbacks because most of my house is on a radiant slab and it takes 24 hours to deal with setback I also have a modulating-condensing boiler with outdoor reset and the game with that is to have it fire as low as possible so as to deliver only as much heat as is needed to overcome the heat loss. I got it to run 18 hours straight one time, but that is not usual. So if you have a system like mine, I suggest you not bother with setback because the mod-con will not supply enough heat to recover from setback unless you run it too hot for best efficiency.

    As far as running after the thermostat attains the desired temperature, it depends on your thermostat. Mine will do that but not for very long. It has a zone that is about 1 degree F, and if I set it at 69F, it will call for heat until it gets up to about 69.5F as measured on a Kodak mercury process thermometer that can be read to about 1/4 degree. and when the house cools down, it will not turn on the heat until it gets down to about 68 1/2. Or so. I have seen it get up to 71F once in a while when the outdoor temperature drops suddenly for a while (overnight) and the boiler tries to keep up with that by raising the water temperature. That heats up the slab and then the outside temperature goes up a lot, and the slab is too hot for that, so I get out of range. Outdoor reset keeps these swings from becoming uncomfortable.

    In other words, it could be working just fine.
  • Steamfitter66
    Steamfitter66 Member Posts: 117
    Boiler model #

    would tell us the rest of the story
  • Running
    Running Member Posts: 4

    Bryant BWB AA 96

    Per the previous response, I've wondered if it's actually less efficient to use the setback. Is it actually more efficient to maintain the water temp within a closer range?


    (When I called Bryant, by the way, they were actually quite helpful--by "roundabout" I meant the usual it's hard to know without actually being there.)
  • Zman
    Zman Member Posts: 7,543
    Model Number

    Can't find anything for that model number.

    Double check?

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • GusHerb
    GusHerb Member Posts: 91

    In Chicago, it's been a very cold December this year (more like January). Without knowing specifics of the system operation it's unsurprising your boiler is taking awhile to recover. Best off setting it and forgetting it. I'm heating 2,400 Sqft with a 140k (input) boiler, used to do 67 at night 70 in the day and it took a long time to recover. After deciding to keep it at 70 24/7 the gas bills actually went down a small amount.

    What model thermostat are you using? Most Honeywell models round up to whatever the set point is so it could be reading 69 when it's in fact still 67 in the house. Also may wanna bump the CPH setting down to 2 CPH. Each home is different so experimenting for awhile is a good idea before settling in on a certain pattern/settings, especially with hydronics.
  • Running
    Running Member Posts: 4
    Model # again

    Here's the full #

    The full model number: BWBAAN000096AA

    Makes sense about the recovery and whatnot. That's one of those things that defies logic on the one hand, but makes perfect sense on the other. Thanks.

    We got multiple quotes on this, and everyone was all over the map on sizing the BTUs and their rationale. We went with the one right in the middle, which checked out on a couple web site computation formulas (mainly owing to the updated windows. On our list for the future is a general insulation upgrade where we can. Don't know if you can pump cavity insulation with stucco, but we plan to find out).
  • Zman
    Zman Member Posts: 7,543

    A boiler running constantly during a cold spell is a sign that the boiler is sized correctly.

    I can't find any info on your boiler. If it is a high efficiency modulating boiler, I would expect it to run most of the time. This type of boiler will modulate down to match the load.

    If a single stage boiler is running constantly, it would make me take a second look.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Running
    Running Member Posts: 4
    BW Series + General Efficiency Question

    I think it's part of the BW "Legacy Series," for which there seems to be either a letter or a number after the BW. It has the "CAC/BDP" marking on it, which I understand is the Bryant parent company. It doesn't seem to come up exactly on the Bryant site, but this may be similar:


    It's not a high efficiency model, just what seems to be the standard 82% efficient. I don't know if that's single stage or modulating, though.

    When you say modulating, do you mean that the burner doesn't fire at full strength due to the current water temp or something? Or that it fires at various rates based on need so that it's not always "full blast?"

    The Honeywell thermostat does seem to round itself up liberally, by the way, to respond to an earlier question.

    I stopped the set back and it's actually been cycling without a long 60-90 min. burn since doing that. It's a bit warmer out the last couple days, but even still there was obviously no need for a long recovery between set points.

    So then, generally, is using the setback not a good idea with hot water? Is the general consensus that it might even be less efficient to get a large volume of water (at least 6-7+ gallons, right?) up to a high enough temp to move the dial than to just maintain an even rate?

    Thanks for everyone's input on this, by the way. Not the most exciting issue on the board, I'm sure, but I like to know how stuff works and I appreciate the info.
  • Steamfitter66
    Steamfitter66 Member Posts: 117
    If it kept your house warm when

    it was below zero the other day then not to worry. More contractors are properly sizing equipment which means it runs longer because its closer in size to the actual heat loss of the building. Like a smaller car driving down the freeway vs a suv in town.
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