Hydronic baseboard brainstorm

EatenByLimestone Posted By EatenByLimestone, Jun 22, 2017 at 11:43 AM

  1. EatenByLimestone

    EatenByLimestone
    Minister of Fire 2.
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    Jul 12, 2006
    6,030
    704
    Loc:
    Schenectady, NY
    My house has been improved in some way every year I've lived in it. I believe the boiler was oversized when I started caring for this house. Since then, I've insulated and sealed the snot out of it and also finished off the attic adding 400 sq ft to the living area. I think my boiler is at least 50% larger than needed.

    Adding up my baseboard, the bottom floor has 45K btu/hr that can be put out from the amount of baseboards I have at 180F. Upstairs has 19K and change. Neither zone is really stressed so actual heating requirements are much lower.

    I heat my water with my boiler now, and the standby losses are pretty annoying.

    Is there any reason why a tankless water heater, or even 2 of them, couldn't be used to heat the house. It seems like the downfalls of a tankless system would be removed since the output would be connected to the heating system. it really wouldn't matter if the first 30 seconds of water were the input temperature. Since my heating needs are fairly low, 120 degree water, or less, wouldn't be a deal killer going through my pipes.

    Replacement costs for tankless units are much lower than a new boiler.

    What crucial piece of information am I missing? I'm not worried about gas lines. They are easy to run.
     
  2. WoodyIsGoody

    WoodyIsGoody
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    Jan 16, 2017
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    Assuming the current boiler is within the thermal envelope of your house, your standby losses shouldn't be very significant. The only real way to increase efficiency is to send less heat up the chimney. And that can be accomplished with a more efficient boiler. A boiler will likely last longer and require less maintenance/repair than a tankless water heater.

    For some inexplicable reason, residential heating systems in the U.S. are almost always spec'ed with a capacity so large it impacts efficiency. I prefer smaller boilers working closer to capacity a larger percentage of the time. If it takes longer to bring a cold house up to temperature, I'm not too concerned.
     
  3. WoodyIsGoody

    WoodyIsGoody
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    Jan 16, 2017
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    I should add, we turn our boiler off as soon as the house will maintain around 65 degrees.
     
  4. Circus

    Circus
    Feeling the Heat 2.
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    Jan 11, 2013
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    You said everything's over capacity, have you ever tried setting the water temperature down? 160::F vs 180::F would cut standby loss a lot and wouldn't cost a dime.
    My brother had a tankless water heater used for hot water five years ago. When the outdoors dropped to subzero it would freeze solid. About once a year it would flash a trouble code and refuse to work til you spend lots of money. Not a big deal for hot water but a disaster if used for heating. Now it's sitting idle on the wall and he's using a $300 electric water heater. Want a tankless LP water heater cheap? ==c
     
  5. EatenByLimestone

    EatenByLimestone
    Minister of Fire 2.
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    Jul 12, 2006
    6,030
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    Loc:
    Schenectady, NY
    My boiler was converted from oil to ng. I've screwed from the aquastat as much as I can.

    I wouldn't mind turning off the boiler, but right now it heats my indirect water tank. Another option I had considered was running tankless ahead of the indirect tank. The tank has low standby losses so it would only have to absorb the shot of cold water before the heater kicked on.
     
  6. peakbagger

    peakbagger
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    Jul 11, 2008
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    Some folks who do radiant heating systems use tankless units. Generally radiant is set and forget with one constant temp so the constant demand is lower. The reason most home boilers are oversized is they are set up to handle the worse case which is cold house during cold weather where the owner wants to raise the temp. I know it can take a long time to raise my house temp when I am running 15 degrees setback in winter.
     
  7. CaptSpiff

    CaptSpiff
    Feeling the Heat 2.
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    Jan 13, 2014
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    Loc:
    Long Island, NY
    I changed my Oil boiler to NG boiler about in 2001. Had a Utica Compact rated at 150kBTU. At about 30 years old, both it and I were getting tired! I had a 0.75 nozzle, so I figured I was inputting about 105kBTUs. That included the domestic hot water coil which was being replaced by a stand-alone tank.

    Man did I get pushback from my peers when I told them I was getting the smaller 105kBTU input Burnham NG boiler as a replacement. They predicted that it would never turn off, and that I'd be divorced by the Spring. !!!

    In fact I found the new boiler to be excessively cycling (on & off), probably because the water capacity was about 1/3rd, and I had to get a set of new smaller nozzles from Burnham. That reduced the input from 105 to about 95kBTU. I wanted even smaller nozzles, but Burnham refused to send em, despite the fact that I was in the business.

    Looking back, I should have gotten the 90k boiler. It would have come with a 4" flue and I could have insulated the flex liner all the way up the old terracotta chimney. The 5" I got now didn't permit insulation. The new boiler still cycles more than I like, and I lowered the cutout from 180 deg F to 170 deg F with no divorce in site. ;)

    Long story to get to this advise:
    1. don't lower your aquastat too low. You want to avoid starting the fire at a water temp below 130 deg F. I know that's old school thinking, but it will make your boiler last longer. I would never go below 160 set point.
    2. don't fiddle with the Gas Valve pressure setting. Do get some new gas nozzles that are 10% smaller, as a start. The size is stamped on the nozzle. Tell the manufacturer that they got damaged while cleaning.
     
    WoodyIsGoody likes this.
  8. begreen

    begreen
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    Moved to the boiler room for some more experienced user feedback.
     
  9. woodgeek

    woodgeek
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    One of my neighbors was a craftsman, and made some extra cash by fixing up the house he was living in, and flipping it whenever it got nice. IF he had a lot of outside business...that took several years. If business was slow, he flipped every two years or so.

    He swore by radiant and hydronic heating from gas-fired WHs. Not tankless, but small, well insulated HW tank heaters. I know they have some flue losses, but your retrofit boiler could be as bad, I dunno.
     
  10. EatenByLimestone

    EatenByLimestone
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    Jul 12, 2006
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    I've heard of them being used, and it makes sense. If your baseboards can only emit 60k btu in an hour, you don't need a boiler that can supply much more than that.
     
  11. Bob Rohr

    Bob Rohr
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    Jan 9, 2008
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    A few reasons not to use tankless.

    They have small passage ways and usually require a high head circulator to keep them flowing when used in hydronic applications. In some cases you cannot pump them enough to get full burner output.

    In a domestic water heating application you may have 40- 60 psi of water pressure to overcome that pressure drop.In hydronics, a typical circulator, maybe 10- 15 delta P.

    Tankless are are designed for heating a low flow rate at a large delta T. Most tankless are designed for a 70° ∆, heating water from 50- 120° instantly.

    Boilers can run with higher flow rates, and tighter ∆T. Most hydronic systems run 10- 20° delta T.

    Modern mod con boilers can operate with a 10- 1 turndown. So an 80,000 could modulate to 8,000 BTU/ hr output. That should greatly reduce cycling and could be used with outdoor reset control for additional fuel saving, most boilers now include ODR on their control.

    A true boiler will be a listed product with an ASME H stamp, safe and legal for closed loop heating use.

    Now there are some tankless style combi heaters, built and approved for hydronic and DHW from a single unit, that may be a better choice.

    Or a combi boiler like a Lochinvar Nobel, which is a true listed fire tube boiler with a plate heat exchanger for instant DHW production..

    Many have found the cheap front end cost of an import tankless is not worth the problems and headaches they can cause.
     
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  12. tom in maine

    tom in maine
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    Apr 4, 2008
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    We had done a number of systems years ago with tank gas heaters. The efficiency is usually in the low 80% area. Maybe more now.
    They were cheap back up and we used one in a heating system project house we did in Orono, Maine years ago at the University of Maine.
    It was back up to a solar hot water system feeding a radiant slab. No moving parts. It was direct vented and the University had a sweet deal on LPG.
    If it is solely for back up it is a cheap date and simple.

    If it is being used as a boiler, it would require proper low water cutoff.

    We did do some that functioned as a DHW heater with a plate hx. The water heater was used as a DHW heater and the other side of the hx was for the radiant slab. No low water cutoff on that design.

    Again, though, it is for very low heating loads and/or back up.
     
  13. heaterman

    heaterman
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    Oct 16, 2007
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    I'll second everything Bob Rohr said on the tankless unit. They are a less than ideal choice for a heating appliance.
    The main issue is that they are designed to function with a temp rise of 80-90*. A typical baseboard system may operate with a 20* degree split and that is not nearly enough to keep a tankless happy.
     

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