Basement heating?

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

  1. Tom Sawyer

    Tom Sawyer In the Trades

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    3,261
    Location:
    Maine
    I'm not trying to slam anyone here and I'm just a guilty of overselling myself but sometimes a little light comes on and I stand back and look at the bigger picture. Sure, putting 20 feet of base is not the optimal thing to do but then again, his boiler is 20 plus years old and I'd bet money that the other zones are less than optimal in length too. It probably will short cycle a bit but no more than it probably already cycles.
  2. Dana

    Dana In the trades

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    2,974
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    01609
    It's all true!

    He says has 112' of baseboard cut up into 2 zones, so at least one of those zones is going to be pretty damned stubby for 85K of output, so if he is averaging better than 3 minutes of burn out of it I'd be surprised.

    Which is why piggybacking the basement onto the first-floor zone by whatever means necessary is a marginal improvement, and a 20' stick by itself takes yet another step down the efficiency scale.

    Definitely a candidate for a retrofit heat-purge control. If he can combine the basement & first floor with reasonable temperature balance and heat-purge the boiler at the beginning/end of calls for heat it'll cut down the number of cycles, lengthen the average burn, and crawl at least a bit out of the efficiency hole it's in.

    At 85,000BTU/hr it's delivering about 200% of the actual 99% outside design heat load for the average MA house (according to utility site surveys) and about 300% the heat load of post-1980 2x6/R19 houses in MA. With the info at hand it's hard to say for sure what the whole house heat load is, but it isn't likely to be anywhere near 85,000 BTU/hr. He could probably heat his place just fine at 140F AWT, a temp at which the 112' of fin-tube is putting out ~35-36,000BTU/hr., and a boiler that delivers 40-50K would still have plenty of margin. But even a 40K output boiler will short-cycle on a 16-20' baseboard zone, yet would operate just fine on a 50' zone. Whatever he replaces it with should be right-sized for the heat load, but sizing the radiation on a new zone so that it will always short-cycle even with a right-sized boiler seems short-sighted.

    A 20 year old short-cycling boiler is very likely to be replaced in under a decade. A $200 heat purge controller will likely pay off within 2 years. Spending the "extra" couple hundred in additional baseboard to ensure the next boiler doesn't get short-cycled seems "worth it" to me. YMMV.
  3. moreira85

    moreira85 New Member

    Messages:
    56
    Location:
    Massachusetts
    It's 20 degrees out. My basement is 68 degrees without any heat.
  4. kcodyjr

    kcodyjr New Member

    Messages:
    103
    Location:
    Chelmsford, MA
    That'll change when you replace that boiler with a newer high efficiency unit after it croaks from all the short cycling.

    Really, no amount of insulation is *that* awesome, even at R9999999ZOMG999, heat leaks, albeit slowly. Obviously something is adding heat to the space, and if there's no deliberate radiation, what's left. The boiler, the water heater, and the pipes.

    I'm thinking, if you're looking for simple, make the basement zone about the same size as the others, but then don't actually make it a zone. Either connect it in series with the 1st floor so the basement gets the "used" water from above that's cooled some or put a tweakable valve on it. Then, when you finally do replace the boiler, replumb the basement near-boiler piping to be its own zone.

    Otherwise, set aside some extra $$ for adding more fin tube at the same time as the eventual boiler replacement.
  5. moreira85

    moreira85 New Member

    Messages:
    56
    Location:
    Massachusetts
    How about some comments on roughing the pex tubing? If I have an 8 ft run of baseboard where would I want the beginning and end of the tubing to be roughed out of the drywall. If I also have 2 8 footers that I will have put together where should I start and end the pex out of the drywall?
  6. kcodyjr

    kcodyjr New Member

    Messages:
    103
    Location:
    Chelmsford, MA
    That's really dependent on the particulars of the hardware you've got and how exactly they bolt to the wall and/or each other.

    Just think of it as a jigsaw puzzle with the picture missing from the box.
  7. Dana

    Dana In the trades

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    Location:
    01609
    That's due to the ridiculously high standby losses of your oversized boiler- it's like having an uncontrolled radiator parked in the corner of the basement.

    If you ever replace it with something right-sized or more efficient you'll need enough intentional radiation to cover the load.
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