Basement heating?

Discussion in 'HVAC Heating & Cooling' started by moreira85, Dec 19, 2013.

  1. moreira85

    moreira85 New Member

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    About ready to drywall the basement. I'm starting to think about heating options. The temp is always pretty comfortable down there. I was thinking about electric baseboard. The house has forced hot water Weil McLain (5 years old) 2 zone set up. Wondering how difficult it would be to have a plumber see if it can be run as a 3 zone?
  2. Dana

    Dana In the trades

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    Model number on that Weil McLain is...? And fuel type?

    Heat loads in basements are pretty tiny, especially if insulated the basement properly (?) as part of finishing it off.

    When you have a boiler serving a tiny heat load you often have to up-size the radiation to keep it from short-cycling the boiler, but given the MA prices for natural gas vs. electricity it's still worth it to go with the hydronic solution.

    But let's have the particulars first.

    Fuel type

    Boiler model/make size

    Insulation & window details on the basement to estimate the load.
  3. moreira85

    moreira85 New Member

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    I'll have to get the model number when I get home.
    Runs off gas. 3 windows in the basement. 2 full size windows (walk out basement) and one of those little basement windows. The basement exterior walls are all insulated.
  4. Dana

    Dana In the trades

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    How is the foundation insulated? (Hopefully not just a studwall up against the concrete with kraft-faced R13s, unless you were planning on getting into the mold farming biz.)

    Window glazing type, and sizes?

    Depending on how the whole thing is insulated, the U-factor of the walls will be somewhere between 0.07 and 0.12 BTU per square foot per degree-F. For a rough order of magnitude number, just assume a U-factor 0.1. If the walk-out wall is a 2x6 R19 wall, call that wall U0.07

    Add up all of the non-window above-grade square footage, and multiply:

    sq. ft x U0.1 x 65F= xxxx

    If the windows are all clear glass double panes, not low-E, not gas-filled, call it U0.5. (If single pane, call it U 1.0 ). Then multiply:

    sq ft x 0.5 x 65F= yyyy

    Any 2" solid wood doors are also about U 0.5, measure it up, multiply that out.

    Add it all up, and you'll have a pretty good rough idea of the heat load when there is a 65F delta-T, say when the interior is 70F, exterior is +5F (the 99% outside design temp for Worcester).

    Then you'll be pretty close to the real heat load number- we can add fudge factors for air infiltration and the below grade losses to that for good measure, but most insulated walk-out basements will be well under 10,000 BTU/hr, and very likely will run in the sub-5K range. But run the numbers to see where yours lives.

    With a zip code (for a more precise outside design temp and delta-T) and better wall stackup/insulation details we can refine it a bit, but it won't change a huge amount from the crude load numbers. If the boiler and hot water heater are in the basement, their standby losses can be subtracted off the heat load directly, but again, it's not going to change substantially. The issue in 99% of the cases is to provide enough radiation or thermal mass to keep the boiler from short-cycling. The "right" hydronic solution will be a function of both the boiler output and the heat load. When the zone load is tiny relative to the boiler output you have to play some games, but there is always some sort of solution.
  5. moreira85

    moreira85 New Member

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    Thanks. That's way over my head. I'll just call the plumber I know and have him take a look.
    No it's not studs up against concrete. They are studs spaced 4.5 to 5 inches off the wall. It's a walkout and not a damp basement.
  6. moreira85

    moreira85 New Member

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  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    FWIW, lots of hvac guys are great and know their stuff, but there's also a bunch out there that, while they may be good mechanics, have no clue on how to size and optimize what they put in...it's best to run some numbers for yourself, then compare with what they suggest...the two may be worlds apart.
  8. Dana

    Dana In the trades

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    If you have batts without an exterior side air-barrier into that 4.5-5" gap it will dramatically underperform at the cold temperature extremes due to convective air transfer between the cavity space and the fiber. (An R13 may operate at R8-9 when the cavity area is 25F or lower.)

    If the batts have a vapor barrier on the conditioned space side, the framing wood will run at very high humidity levels unless that gap is fully vented to the exterior. It doesn't have to be a "damp basement" for this to be the case- all below grade-walls/slabs have ~100% relative humidity dirt on one side, and vapor diffusion alone will raise the humidity level in the space to nearly the same level over time, if the wall can't dry toward the interior. If your foundation sill & band joist leak enough air that may save you from the mold issue, but that's also a large heat leak.

    If you can slip in 2" of rigid EPS foam and glue it to the concrete with foam-board construction adhesive, and can-foam/or Froth-pack seal the EPS to the foundation sill, as well as sealing all seams of the foam board itself, and seal the band joist at the same time, you'll then have a wall that out-performs the fiberglass-in-studs all by itself. In that stackup you'd then be able to use kraft-faced R19 compressed up to the foam and have something that meets/beats current code min for MA basements. IRC 2012 code min for a climate zone 5 MA location is R15 if continuous like the foam, R19 if in a studwall, but R19 in a studwall runs in to wintertime condensation vs. ground moisture accumulation problems. At 2" the EPS is about R8, with compressed R19s you would more than double it but if you left the ~2" gap between foam & R13 you'd add about an other R10 with the R13s. With the foam in place a kraft facer would be sufficiently vapor permeable to manage the ground moisture loads, but unfaced goods would be better.

    The more expensive alternative would be to spray 2" of closed cell foam on foundation conrete from the slab right up to and including the foundation sill and band joist, but at $2 per square foot it adds up fast. R8 EPS runs about 75 cents a square foot, 25 cents/foot if you buy reclaimed roofing foam from folks like the Insulation Depot in Framingham- there are others in MA dealing in reclaimed foam too- cheaper than batts sometimes.

    Plumbers aren't usually hydronic heating designers, they don't calculate heat loads, and they know damned little about keeping boilers from short-cycling. The CGI-4 has an output of 85,000 BTU/hr. To balance that perfectly using fin tube at 180F output calls for about 140' of baseboard, and it can probably get away with 80-100' if you bump the high-limit on the boiler to 210F or something. But that is a RIDICULOUS amount of oversizing of the radiation to serving the basement zone that has a max load in the 2-5000 BTU/hr.

    What probably makes the most sense is to run the heat load calculation for the basement and put in a generous amount for the space, but use a parallel branch from the first-floor zone, with a zone valve controlled by the basement thermostat for the basement branch. The heat loss characterisics of basements (even walk-outs) don't match upper floor zones well, but any time there is a significant heat load on the basement there would usually be an even more significant load on the first floor, so by oversizing the radiation for the basement and piggy-backing on the first floor zone, but limiting the basement temp with it's own zone valve & thermostat you can probably get decent comfort there without short-cycling the boiler or oversizing the radiation by 10x.

    How much radiation is there on the other zones (broken down by zone)?
    Last edited: Dec 20, 2013
  9. moreira85

    moreira85 New Member

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    image.jpg image.jpg image.jpg image.jpg

    So I have continued to research and take some measurements. In the basement I have about 600 sq feet. You can see the windows there are 2 34x38 windows as well as the door and the little window. The long wall with the windows is above grade and about 32 ft long by 7.5 feet tall. It stays very comfortable in the basement around 65 maybe even when it's freezing out. I want to install the baseboard now so I can boost the temp a little. Currently in the house we have 112ft of baseboard being run on two zones. I was estimating maybe 14000 btu for the basement since it is well insulated? House is 6 yrs old.
    Last edited: Dec 23, 2013
  10. moreira85

    moreira85 New Member

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    A few more pics

    image.jpg image.jpg image.jpg image.jpg
  11. Tom Sawyer

    Tom Sawyer In the Trades

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    A gross over complication of a simple problem. Stick 20' of baseboard down there on its own thermostat and zone valve and forget about it. Some of these guys want to make a science project out of everything. You don't need to do a heat loss.
  12. kcodyjr

    kcodyjr New Member

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    Tending to like Tom Sawyer's keep-it-simple-stupid approach, but make sure you leave yourself a way to add more baseboard later if 20' turns out to not be enough. The trouble with shooting from the hip is the chance of missing the target. The heat loss calculation tries to take the guesswork out of it.
  13. Dana

    Dana In the trades

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    What kcodyjr said but for different reasons. A zone with only 20' of baseboard is guaranteed to short-cycle that boiler. Baseboard is cheap- 50' still wouldn't balance but would be more likely to run long enough to overlap with a call for heat from another zone, all of which are apparently under 60' anyway. At 162' total it still comes in at 524 BTU/ft with all three zones calling for heat, so it won't require any tweaking of the near-boiler plumbing to protect against return water that is too cool.

    As configured any single zone can only emit about a third of the boiler output, which isn't the greatest way to run the boiler. With three zones of 50-60 feet it pretty much balances when all zones are calling for heat. But a 20' zone can't even emit 1/5th of the boiler output, and will cycle quite a bit when it's the only zone calling for heat.

    There seems to be a lot of gaps & compressions on the above-grade fiberglass, which is going to cut into it's performance fairly severely. Tuck them in at the corners & edges, then tug gently until it's just proud of the stud edges so you get a complete fill- it' makes a difference.

    And lose the poly sheeting. The ubiquitous use of 6-mil poly has been the cause of more problems than it ever solved in a MA US climate-zone 5 location. Air-tightness is more critical than vapor-tightness for controlling wintertime moisture adsorption at the sheathing, and if you seal the wallboard carefully (foam the back side of any electrical outlets with can-foam, and caulk the front side to the wallboard, and caulk the wall board edges to the framing), you won't have a significant mold risk at the sheathing even running with no interior side vapor retarder. If you have vinyl siding you can call it "done", and be fully code-compliant, since vinyl siding is inherently back vented, and the sheathing passes through at least some of the winter moisture load during the winter, and dries quickly when it warms up. With vinyl siding it meets the "Vented cladding over wood structural panels" prescriptive for [URL="http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_7_sec002_par025.htm" US climate zone 5[/URL] (which is all of MA), and that allows you use standard latex paint as the interior vapor retarder (3-5 perms), which has significant drying capacity for purging any moisture that finds it's way into the assembly, making it far more resilient to moisture drives from either the interior or exterior.

    If you have a less-vented siding type, to meet the full letter of code you can paint the wallboard with a "vapor barrier" latex, which is about 0.4-0.5 perms, which is about the same permeance of the kraft facers, and is the middle range of a Class-II vapor retardency, yet still provides an order of magnitude faster drying rate than 6 mil polyethylene. (What takes a full season to dry through poly can pass in a week with vapor-barrier latex.) Only if you lived in northern Quebec or the cooler parts of the Canadian midwest would poly vapor retarders be of more help more than harm.

    On the below grade lower-wall section you'd be better off with the kraft facers on the cool side of the assembly since as-installed they impeded the drying of ground moisture into the room, trapping the framing in the damp. If you slip in an inch or two of foil or vinyl faced rigid foam between the concrete and studs and re-install the batts with the fiberglass in contact with the rigid foam the kraft facers will be OK. If you go with unfaced EPS, unfaced batts thick enough to contact both the foam and the wallboard in a compression fit would be much better. (Unfaced type-II EPS is about 1.5 perms at 2".)

    Hopefully you stuffed some backer-rod in around the window framing gaps and sealed it with a low-expansion foam before stuffing the fiberglass in? Here too a full cavity fill is important to limit the thermal bridging. With the exterior side foam-sealed stuffing those skinny cavities with fiberglass completely with a compression fit. You want to stuff it until it's about as springy as an R13 batt or a little bit denser- nowhere near as loose as an uncompressed R19. When you compress it a bit tighter than an 13 it's R value rises to about R4 per inch, whereas with gaps and low density you'd be lucky to see R2/inch.
  14. Tom Sawyer

    Tom Sawyer In the Trades

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    It's a 20 year old cast iron, fairly high mass and water content boiler. It might short cycle a little bit but probably not all that much.
  15. Dana

    Dana In the trades

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    A simple napkin math calculation that guarantees this boiler will short cycle on a 20' stick, if/when that's the only radiation. The boiler has about 2.1 gallons of water in it (x 8.34= 17.5lbs) and about 225lbs of cast iron (x 0.11= 25lbs of water-equivalent mass). Assuming another gallon, call it two for the radiation loop we're still talking maybe 60lbs of water-mass equivalent. Assuming 20F of differential between the high and low, it takes (60lb x 20F =) 1200 BTU to swing between the high and low limit. Assuming and an emittance of 15,000BTU/hr (750 BTU/foot of baseboard, which it might deliver at 200F) you have about 70,000BTU/hr of boiler excess going into that mass, or about 1200 BTU/minute.

    So realistically we are talking one-minute chirps here to feed a 20' zone, on a boiler that is best run at ~10 minutes per burn to hit it's full steady state efficiency. At a load of say 15,000 BTU/hr that's more than 10 short cycles per hour, which is two levels deep into efficiency hell, unless it overlaps calls for heat from the other zones to lengthen the burns.

    Even with 50' of fin-tube it's still a sub-3 minute burn unless it overlaps a call from another zone, which is still far from ideal, but not any worse than the existing zones.

    The only unknowns are the actual heat loads, which will determine whether a short zone would generate enough short-cycles to be an efficiency/longevity issue.

    The ~$250 for the "extra" 30' of fin tube at box store pricing to ensure that it's burn cycles are at least as long as on the other zones doesn't really much of a cost-adder, and guaranteed to be more than sufficient radiation for any realistic WAG on the basement's actual heat load for those who can't stand doing math.
  16. moreira85

    moreira85 New Member

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    Appreciate the help. I like Tom Sawyers approach definitely over complicated. I had a plumber check it out and he agreed the temp down there is very comfortable. He said a 16 ft run on the long wall where the windows are will be plenty. I was going back and forth between just putting a pellet stove or doing the baseboard. I'm just waiting on the estimate.
    I estimated the parts $150 for baseboards, $130 for zone valve, $75 for pex pipe, $50 for thermostat and wire run and then any little misc copper Ts to tie it in. It'll be interesting what the labor amounts to rough it, drain the boiler and tie it in to existing system. The estimate I get will decide if end up abandoning ship and throwing in the stove or rough the pex myself and tie it in down the road.
  17. kcodyjr

    kcodyjr New Member

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    I'm going to side with Dana on this one. 16' is definitely way too short, since the math says that 50' itself is already too short.

    Unless, of course, your goal is to fry your boiler and get the insurance company to pay for a new one. YMMV.

    If we're settled that extreme short cycling is something to avoid, I see three viable options:

    1. Run the basement baseboards off the same zone as the 1st floor. I'd put it in series, after the 1st floor, so the basement "sees" slightly cooler water. This will still almost certainly overheat the basement, but warm air rises and you'll get most of that back. Could make the basement uncomfortable, though. Alternately, you could plumb it in parallel and put a gate valve onto it to restrict flow, thus manually tweaking the balance.

    2. Put 50' or so of baseboards in so that the basement zone is more like the others. Ideally, you should probably downsize the boiler next time you replace it, or maybe run an indirect water heater off it as well to make use of its excess capacity. The more perfectly the boiler is matched to the radiant (and indirect) load, the more time it will spend in its steady-state efficiency zone. The idea here is to make it run in short normal cycles, rather than short-cycling. The difference is in whether the room thermostat or the boiler's internal thermostat is making the shutoff decision.

    3. Hang it all and just put independent electric baseboards down there.

    For what it's worth, I don't see an overly warm basement as an entirely bad thing. It reduces the heat load above, and buys time when the power goes out before your pipes are at risk of freezing. Just so it's not so hot you can't go down there.
  18. Tom Sawyer

    Tom Sawyer In the Trades

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    The math is going to cost him a couple grand that he doesn't need to spend. He said its always pretty comfortable down there without any heat at all. His existing heat pipes, domestic hot water pipes, washer and dryer all add heat to the zone. 20' of base will bump it up the few degrees he wants and I'll bet a whole lot that the cycle times are not materially different than he is already seeing on the rest of the house. I see this as the difference between engineers that spend their days at a computer and someone that has done so many similar installations that I can't even begin to count them. If he had a mod con down there I would probably side with you guys but not here. You are all over thinking this thing.
  19. Dana

    Dana In the trades

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    That's exactly why you DON'T just let a plumber be your hydronic heating designer!

    If you run a parallel branch off the first floor zone and put a tweakable ball valve adjust the proportional flows between first floor/basment you can probably just drop in the 16-25' or whatever and get reasonable temperature without a zone valve and without a basement thermostat. It'll also lengthen the burn times on the first floor zone calls, which will improve the net efficiency slightly.

    The napkin-math says even a 50' zone will be a comparative short-cycle at a 20F differential on the boiler controls. It's probably worth installing a heat purge economizer control (eg Becket AquaSmart, Intellicon 3250 HW+, Hydrstat 3200, all sub-$200 at internet pricing) to "exercise" the thermal mass of the system, maxing out the burn lengths, parking the boiler at a much lower temp during idle for lower standby loss. With sub-2 minute burns the thing is probably running about 75% efficiency instead of it's nameplate ~84% AFUE, but with a heat purging economizer control it can be pulled back north of 80%, saving maybe 10% on the overall fuel use.

    Try turning down the thermostat by 5F on the existing zone with the greatest amount of baseboard, and bumping up the thermostat on the shorter baseboard zone by 5F, then time and count the burns for an hour. If the aquastat controls can be set up for a differential greater than 20F between the high and low limits, max it out, whatever it is (keep the low-limit above 130F though.)

    Electric baseboard cost about 3x to heat with than 80% gas.

    The output of even the smallest pellet stove will be RIDICULOUSLY oversized for the basement heat load- don't go there!

    A pretty-good 3/4 ton mini-split (eg: Fujitsu AOU-9RLS2, Mitsubishi MSZ-FE09NA) would have an installed cost comparable to the pellet stove, and would be more appropriately sized, and it will modulate with load. It would cost about as much to operate as heating with 80% gas, and would be cheaper to run than a pellet stove. As a mostly-DIY you can get out for under 2 grand. Wth a pellet stove
  20. Dana

    Dana In the trades

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    If the math is going to cost a couple grand, I'm clearly in the wrong business, or not charging enough! :)

    As a mostly DIY site, if you give them enough of napkin level math, they can usually hit it close enough.
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