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Thread: monoflo issues in one zone

  1. #16
    In the Trades Tom Sawyer's Avatar
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    Water will always flow to the path of least resistance. Running too much baseboard off a monoflow tee does not work because the resistance through the loop is greater than the resistance through the main. If you have the money the best thing to do is to pull the main monoflow feed and return altogether and run individual pipes ( I like 5/8" heat pex ) to each convector or radiator and then bring them back to manifolds at the boiler. A single circulator can be used with balancing valves or a single circ with thermostatic valves at the radiators. The baseboard loops get brought back to their own circulators and their own thermostats or they can be grouped as separate loops with theri own thermostat(s)
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  2. #17

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    Tom, that is what I am hoping would work. I've revised the drawing from earlier and wonder if this might not work out. I think if I were to break up the two main loops differently as shown I can get a closer to even flow restriction on both sides of the loop thereby limiting issues with the circulator drawing more from one side than the other.

    thin green and blue line represent your recommended 5/8 pex creating new series loop and thick blue line is main supply feed coming off boiler.
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  3. #18
    In the trades Dana's Avatar
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    Quote Originally Posted by ctreefer View Post
    Dana, any chance you got to see the post above from 9/14? I'm wondering if this would work and if the foam shown on Craigslist is good at 2" thickness.

    thanks

    vince
    At 2" polyiso is good for ~R12. (R6/inch).

    If you compressed low density R11 batts in 1.75" framing the compressed R value would be ~R7, and with the thermal bridging of the framing that layer averages ~ R5+, but with the R12 iso that's still R17 or so, which is pretty good- better than a typical 2x6 framed wall with R19 batts.

    If you went with 2x3s and R11s it would be R9 center cavity, ~R7 average after thermal bridging. For compressed batt values at standard lumber depths, see: http://numsum.com/spreadsheet/show/21111

  4. #19

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    Quote Originally Posted by Dana View Post
    At 2" polyiso is good for ~R12. (R6/inch).

    If you compressed low density R11 batts in 1.75" framing the compressed R value would be ~R7, and with the thermal bridging of the framing that layer averages ~ R5+, but with the R12 iso that's still R17 or so, which is pretty good- better than a typical 2x6 framed wall with R19 batts.

    If you went with 2x3s and R11s it would be R9 center cavity, ~R7 average after thermal bridging. For compressed batt values at standard lumber depths, see: http://numsum.com/spreadsheet/show/21111
    thanks again, I'm down to a couple last questions.

    1. I've been searching some sites online that mention the same method of insulating a basement but I don't see anything regarding what to do around a boiler flue that exits on the outside wall. The boiler right now is 17" from the wall and the flue obviously runs into the wall. What would you suggest for this area?

    2. One wall faces an attached garage but its a split level so half the wall faces the garage and the other half is below grade. Should I just insulate the whole thing?
    3. Regarding insulating above the foundation: my gap between the inside foundation wall and sill plate is only about 1-1.5 inches. Should I fill that with foam or bring the foam up 2" and fill the gap? also since I don't plan on finishing the basement what should I do regarding the foam I shove into the space above the wall against the outside surface so its not a fire hazard?

    thanks again for all your help.

  5. #20
    In the trades Dana's Avatar
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    You can use an R13 rock wool batt wrap around flues to provide the necessary clearances from flues to combustibles. Rock wool is spun slag from steel making- about the only way the flue can reach the ignition temp of rock wool is if you're too close to a nuclear explosion. The combustion temp of iso is pretty high compared to other foam insulation, but once you light it off it does sustain a flame. Most fire codes require 3" to combustibles, from B-vent, and a 3.5" thick non-combustible batt gets you there. If it's a single-wall flue it needs to be at least a double-wrap. (Roxul has pretty good distribution in New England- the big blue home center stocks it near me, don't know about Thermafiber, but both have a wide range of rock wool product.) If the installation manual for the boiler specifies 18" clearance from the flue in any direction, use rock-wool only for the wall insulation (no foam) and steel studs in that area, and use fiber-cement board (Hardie-backer or similar) rather than gypsum.

    The minimum side/back clearances to combustible walls for most modern (post 1980) oil boilers is less than 1' but look up the installation manual for yours to verify side clearances. I don't know of any that require 17" or anything like it, but some are pretty close to a foot. Front-side clearances are usually higher (2' is typical) due to the potential blow-back via combustion-air paths.

    Go ahead and insulate the whole thing- a garage isn't exactly "outdoors", but it's average winter temp may be less than the subsoil temp (~50F), and it's still worth putting at least R8 between basement & subsoil when it can be done cheaply.

    Cut in the 2" thick block a the top of the foundation and foam-seal it, or use 2" of spray foam.

    The code on thermal barriers for foam is usually relaxed and/or commonly ignored for band-joist/foundation-sill apps. When it's iso the threat is even lower than with other types of foam. There are paint-on fire-retardents that would usually meet code in places where code demands it, but I wouldn't bother until/unless somebody makes an issue of it. DO take care to air-seal around the foam in a cut'n'cobble on band-joists- you don't want a convection loop depositing moisture on the now-much-colder band joist all winter. If you want to you could trim & stuff rest of the rock-wool batts to add R to the interior side of the band-joist foam too, but don't stuff just batts with no foam or you would run some risk of moisture/mold issues over time.

    On the studwall, put an inch of EPS or XPS (and NOT iso, which would absorb moisture) between the bottom plate & slab as a moisture & thermal break and TapCon the plate to the slab. Give the edge of the iso itself at least an inch of clearance &/or EPS/XPS to the slab too, to prevent long term wicking of moisture from the slab into the iso. Polyisocyanurate wicks, absorbs, & retains moisture where polystyrene does not, but it dries just fine through unfaced batts + gypsum wallboard (even with a coupled coats of latex on it.) Avoid kraft-facers on any batts you use. (Unfaced R13s & R11s are usually marketed as acoustic abatement batts, and are widely available.)

  6. #21

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    thanks again!

    Ahhh, Poly Iso is Polyisocyanurate. I didn't reason that one out.

    Just out of curiosity. I follow the rock wool notes but I'm wondering.... The current boiler runs year round (indirect hot water). I wonder if I just left an 18" space (no insulation or framing) around the flue if that would be OK. Since it's year round operation the block in that area is always "warmed" by the flue so there shouldn't be any issues with condensation and heat loss would be minimal if its just 18" square.

    I say this because I'd like to upgrade to a gas boiler (high efficiency likely) so my not need the flue in the near future anyways. This way once it's gone I can just seal it up the way the rest of the walls are.

  7. #22
    In the trades Dana's Avatar
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    That 18" + flue-radius CIRCLE are the lossiest square footage in your house, since it's the highest-temperature interior wall with the least amount of insulation!

    Since it's going into (moisture tolerant) masonry or concrete it wouldn't matter if there were a wintertime moisture drive or not, but assuming an average wall temp within the circel of about 100F (it might be higher- you'd have to measure it with a IR thermometer), with ~R2 of concrete &/or brick that section is losing 35BTU/square foot per hour at an average outdoor temp of 30F (about your three month winter average temp).

    For 100 days of winter that's 2400 hours x 35BTU/hr= 84,000 BTU/ per square foot of loss, add in your shoulder season losses and its about a gallon or more of fuel use per square foot of near-flue wall.

    Insulate with R13 batts in steel studs you cut loss that by about 75%

    Assuming an 8" flue with an 18" clearance that's a 22" radius circle, which is about 10 square feet, or on the order of 10 gallons/year. That could be cut to 2.5 gallons/year with less than $50 worth of material. At $4/gallon you'd be paid for the material in under 2 seasons, maybe only one. That's a better payback rate than the rest of it.

  8. #23

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    Well, it was a long weekend but my monoflo system is no more. Lot's of planning for rerouting lines to balance the system. Ended up going with the same 3/4" copper instead of Pex. My skinny fore arms are sore from all the cleaning of fittings and pipe. In between fingers I've got a nice little rash from the flux. (not to mention I can't seem to get all the black out of my hands.) I was using gloves for the most part....

    Glad to say the heat now works on both sides of the house. It's awesome to get "real" heat coming out of those last baseboards at the end of the one 60' loop that never got hot before.

    Only bummer was Sunday morning realizing that my pressure/temp gauge on my boiler wasn't working (no change in pressure readings). I seem to recall now the last time it was serviced the guy telling me that. Would have been good to have one on hand to replace while the system was down.

    Thanks for all the input. Now on to trying to get more insulation in the house....

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