Adding Hydronic Baseboard to Basement

Discussion in 'HVAC Heating & Cooling' started by jtforester, Feb 24, 2021.

  1. jtforester

    jtforester New Member

    Joined:
    Jan 5, 2021
    Location:
    Massachusetts
    Hello,

    I'm adding a heat zone to my existing boiler to include my basement. The space is 24ft x 30ft with a garage on one 24ft side, one 30ft side above ground (mostly), one 30ft side underground and the utility room adjacent to the last 24ft side. I've used the Slatfin app to calculate the heat load which came out to about 15,500 btu/h (Eastern MA). I'm planning on installing Runtal UF baseboard units and currently have a couple of outstanding items to figure out.
    1. The partially above-grade Wall is 30ft, has 2 windows and sits on top of about a 14" foundation sill. See attached picture. The foundation is not insulated (1974 construction).
      1. Will the baseboard better serve me closer to the floor and attached to the foundation versus attached to the wall under the window or does this not really matter? Floor is not insulated, just floating vinyl plank with vapor barrier.
      2. Can the heat output from two 8ft units (UF-3 @770 btu/ft) on this wall effectively heat the full 24ft width of the open basement? I'm also planning for a 6ft unit on the adjacent garage wall (far side). Will I have a coldspot in the far corner with no baseboard?
    2. I'm considering a monoflo type install since there is "extra" capacity one side. The thought is to be able to "fine-tune" the output. Is this overkill?
    The Runtal units cost adds up when looking at all of the "accessories" that are needed and I'm trying to balance cost and comfort.

    Thanks for any experience-based feedback.
     

    Attached Files:

  2. fitter30

    fitter30 Well-Known Member

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    Feb 2, 2020
    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    Put fin tube under windows to offset heat loss attach to the block because sill looks like it sticks out 5" or 6". Use taco e series pump.
     
    Last edited: Feb 24, 2021
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  4. jtforester

    jtforester New Member

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    Jan 5, 2021
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    Massachusetts
    Thanks fitter. When you sat attach to the block, do you mean the top (horizontal) pert or the vertical surface closest to the floor?

    What's your thought on running 3/4 (or 5/8) pex vs. 1/2 inch pex? Would I benefit from a monoflo setup here?
     
  5. fitter30

    fitter30 Well-Known Member

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    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
  6. Dana

    Dana In the trades

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    Jan 14, 2009
    Location:
    01609
    The Slantfin app is almost always 35%+ higher than reality. For a basement zone adjacent to a drive-under garage to have a design load as high as 15.5K in eastern MA you have to either leave a window open, even with NO wall insulation. (Current code-min in MA is R15 continuous insulation, or equivalent.)

    It's far better for both comfort and efficiency to air-seal and insulate the basement walls to the current code min, and insulate the partition wall to the garage (if it isn't already) before actively heating it with pretty and pricey radiation like Runtal UF baseboard. Even leaving it unheated it's likely to stay 60F or higher in winter. This can be done fairly inexpensively using reclaimed roofing foam from places like Nationwide Foam/Insulation Depot on Waverly Street in Framingham, or Green Insulation Group in Worcester. That would bring the load down to something like 2000-4000BTU/hr (depending on air leakage and the size/type of windows.) The floor losses are quite modest compared to wall losses, particularly the above-grade portions of the walls.

    I've covered the details of alternative methods of insulating basement walls on multiple threads on this site, but if you're interested I could go into it more here.

    Without insulated walls it will be difficult to heat the space evenly, but once insulated a much smaller panel rad (than a pair of 8' UF-3s) below the window will keep room temps fairly even across the entire space.

    FIWI: I have about 1600' of mostly below grade not directly heated basement in Worcester, with an average above grade exposure of ~25-30" on a very odd footprint. After putting 2" of reclaimed roofing polyiso (~R17) on the basement walls the entire heating bill dropped by a bit more than 15%, and the basement stays at about 65F pretty much year-round. The air sealed and insulated walls also reduced the amount of summertime dehumidification needed to keep the "musty basement smell" at bay by a bit more than half, despite being a 1920s antique with a 2" rat slab for a floor that is sometimes below the water table level after spring rains (4 sump pumps in different locations keep it from flooding).
     
  7. jtforester

    jtforester New Member

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    Jan 5, 2021
    Location:
    Massachusetts
    Hi Dana,

    Thanks for your insight and experiences. I did update the above grade 2x4 walls (66" tall) with R15 batt after using a can of spray foam on areas I believed to be leaky. The below grade wall got R10 Foamular (in between an old 2x3 stud wall directly touching the painted concrete). I haven't touched the garage wall yet. Pretty sure it's 1974 R11 batt like the rest of the house. The bays in-between the floor joists aren't yet insulated but got the same spray foam treatment as the rest of the wall. There is 9/16" shiplap on 3 of the 4 walls with the garage wall gypsum on both sides.

    The basement doesn't drop below about 60-62 now. I do have a young family and this is going to be a play/TV space for the next 12 years at least.

    So if I stick with the reverse return piping, do you recommend one 8ft UF-3 under the window and one 6 ft UF-3 on the far half of the garage wall? This woud give me about 10.8 kbtu.

    John

    On a side note, I can't seem to find a HVAC pipe fitter to reconfigure my boiler headers to change my pumps from the return side to the supply side and add room for the additional zone for less than $4-5k. I understand it's a couple of days to do the job but the parts are only about $600, with a new SR-506 (2 spare zones for future radiant retrofit). I may wait til summer and tackle it myself. I value the experience and expertise of folks who are good at this work but I seem to be charged a premium for my zip code.
     
  8. fitter30

    fitter30 Well-Known Member

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    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    Fin tube in basement what is the rest of the house using? What is water temperature your running?
     
  9. jtforester

    jtforester New Member

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    Jan 5, 2021
    Location:
    Massachusetts
    Rest of the house has fin tube. Burnham boiler set at 190F. No AC currently. Attached some pics.
     

    Attached Files:

  10. Dana

    Dana In the trades

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    Jan 14, 2009
    Location:
    01609
    If the 2" of XPS (R8.4 when fully derated for age) were continuous, and extended to all exterior walls you'd be in great shape. You currently have it cut'n'cobbled between studs(?), which would undercut it's performance to about R6 due to the thermal bridging, R7 tops, less than half the current code minimum.

    If all exterior walls are insulated even to half code-min there is no WAY the 99% heat load is as high as 15K.

    Insulating basement ceiling between the first floor joists would be a waste of money, and possibly even a move in the wrong direction. If it's conditioned space both above and below, the temperature difference is small, and the insulation doesn't change the heat load.

    Shiplap on the inside of a batt insulated wall is fairly risky. Shiplap leaks a ton of air, and even if the R15s have facers they are nothing like a true air barrier. A continuous layer of air tight gypsum board under the ship lap can work, but without the interior side air barrier the sheathing is loading up with excess moisture every year from slow convection of indoor air through the batts. It will usually survive years without falling apart, but there will be high mold-spore counts in the basement every spring, and eventually rot will get going in the exterior structural sheathing.

    The fact that it doesn't drop below 60F is further indication that the heat load can't be anywhere near 15K. With at least some insulation on all walls and storm windows over single-panes (or 70s vintage double panes) you're looking at less than half that, and a single radiator under the window would keep temps reasonably even, assuming it's all one big open space, no doors or partition walls breaking it up.

    The boiler pics look like a P208 or P209 plate Burnham(?), either of which would CRAZY oversized for heating any normal sized house, even an air leaky 70s vintage R11 type house, or even a pretty big house. That's something north of BTU/hr for a DOE output, serving a much lower load, so the duty cycle on the burner is small even at design condition. If the radiation is similarly oversized (probably is) you would likely be able to heat the place with 120F water on design day, no point in setting the high-limit to 190F. At 190F the standby losses are a significant fraction of the total (an other serious reason not to insulate between the basement & first floor), and may be part of why it's staying so warm down there. If you're on one of the major utilities in MA there are good rebate incentives through MassSave for installing right-sized condensing equipment, and probably well worth doing if your plan is to stay another decade or more.

    To get a handle on your actual oversize factor, run this math, using base 65F degree-day data on your December & January fuel use. Fuel use load calculations automatically includes the standby & distribution losses (indeed, it can't be separated out). There is some error in that type of analysis from solar gains, but those are minimal in December & January, and it's offset by the error introduced by domestic hot water. In unusual cases (like "mid century modern" houses with huge expanses of glass) the errors might be as high as 25%, but not much more. For most houses it's within the noise error of infiltration & ventilation losses.
     
  11. jtforester

    jtforester New Member

    Joined:
    Jan 5, 2021
    Location:
    Massachusetts
    Hi Dana,

    My boiler is the P207 and yes, I believe it's grossly oversized. It's only 13 years old and replacing it at this point is premature.

    The lack of insulation between the joists I mentioned is just the perimeter rim band. I have no intention of insulating between the floors. The R15 has a facing and I know this isn't "text book." I took down a plywood panel wall and the faced R11 and there was sign of air infiltration but no suspect mold growth or rot after 45 years exposure to leaky sheathing and clapboard.

    On the 2x3 wall, I took down fiberboard paneling and there was no insulation. The non-continuous R10 is an improvement over prior status without rebuilding walls.

    I also sprayed the floor with radonseal plus to limit moisture vapors and use a dehumidifier in the moist seasons. A Robert's vapor barrier is going under a waterproof floating floor.

    There is additional work planned for the house over the next few years. The basement was moved to the front of the line to give my kids a place to play and call their own in the midst of the Covid-19 distancing.

    The room above the garage is pretty cold with the hearth that is exterior to the house at least 30F below the room temperature during the winter and single pane windows creating constant convection of cold air. The series baseboard in that room are at the end of the run for the zone. Some of this baseboard will be lost during a planned renovation. Our plan is to retrofit with radiant (and replace windows) at that time.

    I've used Cool Calc to estimate loads and, depending on inputs, get anywhere from 64 kbtu/h to 73 kbtu/h for peak heating load with the basement right around 4500 btu. I have less confidence in the input methods of the cool calc app than the Slatfin app but the discrepancy between the two is quite large.

    I can turn down the supply temperature and see how that affects comfort. Having the basement as it's own zone with such a small load is certainly going to short cycle that boiler.
     
  12. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    Though it's not perfect, and lacks some of the features of pro-tools, it is a real Manual-J methods tool. Even though it usually overestimates, it's still a much more accurate and useful tool to work with than the SlantFin app. Run a fuel-use load calculation and eyeball the difference between that measured reality and the 64-73K CoolCalc is coming up with.

    If CoolCalc is calling out 4500BTU/hr, reality is likely to be less than 4K, but it wouldn't be insane to install radiation good for 4500 BTU/hr. With that much (little) radiation the duty cycle will still be reasonably high when it's cold out, high enough to be comfortable. But it WOULD be insane to install 15,500 BTU/hr of radiation, which would be able to heat up the place quickly, but would have less than a 30% duty cycle even at design condition, maybe even less than 25%. That would lead to pulses of warmth between long enough stretches for the baseboards to cool almost to room temp, and it would incur a slow draft of cool air below the window pooling on the floor. With right-sized radiation it will say on most of the time when it's cold out creating a nearly constant updraft in front of the window mixing with & counteracting that cool draft.

    With a tiny load and tiny radiation the boiler's burn times would be short when serving just that zone, but there would only be 1-2 burns per hour. The P207 is good for about 160-165KBTU/hr, but has enough stored heat in thermal mass of it's water volume & cast iron that the burner wouldn't necessarily fire on calls for heat from a tiny zone if set up with heat purging boiler controls. The P207 has ~5olbs of water and another ~50lbs of "water equivalent" in cast iron thermal mass for a total of about 100lbs. With a difference of 20F between the high and low limits it would then deliver 20F x 100lbs= 2000 BTU per burn.

    Even at design condition that's only 2 (short) burns per hour, but at design condition it's unlikely that the basement would be the only zone calling for heat. One or two short cycles per hour isn't going to substantially impact the lifecycle or average efficiency of the boiler the way 10 short cycles per hour would.
     
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