monoflo issues in one zone

Discussion in 'HVAC Heating & Cooling' started by ctreefer, Sep 11, 2012.

  1. ctreefer

    ctreefer New Member

    Messages:
    30
    Location:
    CT
    Hi all,
    It's my first time posting here and hoping I can get some guidance before I start asking local professionals.

    I bought a home in CT 3 years ago and am disappointed with the heating in one zone. The last set of baseboard takes till the end of the boiler’s cycle to get warmed up on one side of the house.
    It’s a hot water boiler hydroponic system with baseboard (fins). There are 4 zones (1 indirect hot water) (3 living areas)
    Boiler is Burnham Oil fired. Main loop in basement starts with 1.5†black pipe into expansion tank down center of basement then splitting off to the multiple loop and mono flo zones. There are some check valves in this area but don’t recall the placement. The primary loops (front ½ of house and back ½ of house have their own loops at the split that return to the boiler) supplying the monoflos is 1†black pipe coming off the 1.5†with multiple mf and regular T’s coming off for each baseboard. The return going into the boiler passes through the circulator pump which is flowing towards the boiler.
    The main living area on the main floor (split level ranch) is a mono flo system. The other two are loops for the bedrooms and downstairs.

    I think they screwed things up when they designed this system because its my understanding you don’t want a long line of radiators on a monoflo system and that last line near the end of the main loop is over 60 of baseboard before it drops back down. (this is the line that is forever cool near the end till the end of the boiler cycle (15 minutes or so).

    There’s part of me that just wants to scrap the whole monoflo system and go with a loop but not sure if it’s a wise decision because one side of the loop (series) is almost double the length of baseboard as the other side.

    I just feel like this is a very inefficient use of heat. The basement is always toasty because of all the heat running through that main loop but the main floor is slow to warm up at the far ends. I’ve bled all the lines till the valves were dripping so I know its not an issue of an airlock. I’ve also checked all the direction of the monoflos to make sure they were installed correctly and they all seem to be right.

    Coming from my old house which was much simpler (1 zone series loop) it always warmed up much quicker and the slantfin was always hot to the touch. This system it seems the heaters just never get that hot.
    Technician during last cleaning changed (increased nozzle size) some nozzles sizes on the injectors thinking this would help for some reason but the only thing it seems to have done is use more fuel (maybe in my head but last year was warmest on record and we used same gallons as previous year.)

    I’ll try and draw up a diagram of the plumbing tonight and post it tomorrow as I’m sure the description above is somewhat confusing.

    To add fuel to the fire, I’m debating on converting to gas from oil soon so will be replacing 25 year old boiler and hot water system. Want to make sure I’m not just wasting $$ on new equipment that runs through a possibly poorly designed heating system.

    Any help would be greatly appreciated. Even if it’s just guidance on what to look for in choosing a professional.

    Thanks
  2. johnjh2o1

    johnjh2o1 Plumbing Contractor for 49 years

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    1,142
    Location:
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    You are correct you can not expect a monoflo tee to supply a loop of baseboard. What should be done is to put the loop on it's own zone.

    John
  3. Dana

    Dana In the trades

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    Just be aware that when breaking out a 60' chunk of low-mass fin-tube baseboard into it's own zone it's micro-zone, prone to short-cycling the boiler. Even with the smallest oil boilers out there running 180F AWT that zone can only emit only about half the boiler's burner output, and at lower temps (or bigger burners) it's even less. If it's cast iron rather than fin-tube it has at least some amount of thermal mass, but whether it's enough depends on the thermal mass in the boiler, the burner size, and the amount of hysteresis in the boiler controls.

    This is also an issue when you swap out the boiler for a gas-fired unit, either modulating-condensing or cast-iron. A mod-con running under outdoor reset control for more condensing efficiency can short-cycle itself into an early grave with low-mass microzones. Whether mod-con or cast iron it's important to pick the very smallest unit that actually meets the design condition load unless you add thermal mass to the system.

    Since you have a history of fuel use on the oil boiler, it's possible to work backward from fuel use and the boiler's steady-state DOE combustion efficiency to put a firm upper bound on the whole house heat load at the 99% outside design temperature. If your oil supplier stamps a "K-factor" on the billing, the K-factor on a mid or late winter bill has all the information we need other than your outside design temp. If you are too far from any of the CT locations in the ACCA Manual-J list (linked to above), it's pretty easy to estimate an outside design temp with a zip code using Weatherspark.com's historical data.

    If your toasty basement is currently uninsulated, the heat loss out the basement could easily account for 25-30% of your total fuel use, so don't be afraid to undershoot a boiler sizing number derived from a fuel-use analysis. (And if it's mostly unfinished, even with condensing-gas it's cost effective to insulate the basement. Check other threads here on how that's best done without creating mold problems, or start a new thread under "remodeling" or something.) In many cases it's cheaper to insulate the basement than to rip up an existing hydronic heating system and start over. If the basement still overheats you can insulate the pipes too, but the better bang/buck on fuel use is to start by insulating the foundation walls along with insulating/sealing the foundation sills & band joists first.
  4. ctreefer

    ctreefer New Member

    Messages:
    30
    Location:
    CT
    thanks for the info. Hadn't thought about insulating the walls. The basement is prone to water issues which I am still tackling. (long story and getting longer but there is hope still.) Anyway, the walls are cinderblock and I've painted them with the water proofing. I'll search out the links for insulating them so again thanks.

    Question though, if I insulate the basement and it's already warm won't it just get warmer? I understand that I'm getting heat loss through the walls but how does that affect the upstairs if the basement is sealed off other than warming the floorboards?

    First time posting a pic here but hopefully it works. That's the layout for my current setup. You can see that long 60'+ section which is slantfin. Not sure if that whole system can be converted to a loop in series.

    Attached Files:

  5. Dana

    Dana In the trades

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    If you insulate the basement and seal/insulate the band joists the heating system will run less often- it may be somewhat warmer or somewhat cooler, but you'll be burning a LOT less fuel. Warmer floors on the first floor lower the amount of heat that needs to be delivered by the radiators & baseboards, so it's something of a balancing act.

    When I sealed & insulated the basement walls to ~R18 in my Worcester, MA house the average mid-winter temp in the basement bumped up from ~65F to ~68F, but the shoulder-seasons the basement dropped a bit under 65F due to the lower duty cycle of the heating system. Previously it would be warmer than 65F in the mid-fall or mid-spring seasons, cooler mid-winter due to the higher heat loss, a fraction of which was air leakage at the band-joist/foundation sill & elsewhere. Now the biggest heat loss out of the basement is through the slab to the ground, but that's WAY below what the wall + leakage loss had been. YMMV, but for most 1 or 1.5 story houses in this region foundation wall losses & leakage are more than 15% of the heat loss, and if your basement is running in the mid-70s during the heating season it would be almost surely be more than 20%, probably more than 25% of the total heat loss/fuel-use.

    Deal with the bulk water issues first, but there are good/better/best ways of dealing with wall insulation, all involving at least some amount of foam (rigid &/or sprayed.) Exterior sloping & drainage are job-1, and it may take a buried skirt of roofing-membrane attached to the foundation sloping away to redirect surface water sufficiently far away from the foundation:

    [​IMG]

    Sometimes it's necessary to jackhammer out an interior perimeter drain sloping to a sump to bail. If the basement has a history of flooding it doesn't mean you can't insulate, but it does affect your options.

    Converting to a series loop may end up with even worse balance problems than you have now, and should only be done after a thorough analysis by a competent hydronic designer. (I'm pretty good at hackin' with the napkin-math on hydronic systems, but I'd probably hire this one out rather than guestimating and hacking it into balance.) If it's just the fin-tube zone that's out of balance, treating that and that alone is probably do-able. If it's possible to cut in a ball valve on the parallel section of the main loop between tees to/from the fin tube you could force more flow in the fin-tube, at the expense of lower flow elsewhere. It may work fine that way, but that's strictly in the nature of a hack, not a well-designed solution.

    Cutting the fin-tube free and capping the Tees, and putting the fin-tube on it's own circulator as a micro-zone would surely work from a heating point of view. You'd need to deal with the short-cycle aspects, but that's a tractable design problem.

    Part of the reason the baseboard section stays cool until the end is that while radiators put out heat in proportion to their temp- even when they're only 90F and rising it's radiating, whereas fin-tube falls off pretty sharply below 110F or so since nearly all of the heat transfer is via convection, which requires bigger delta-T between room & water temp. North of 120F it's pretty similar to other types of heat emitters in terms of linearly increasing output with temperature. If it were cast-iron baseboard it would do better, but that's not to say it would still be well balanced with the rest of the zone. (Replacing it with brand new cast-iron baseboard would run at least a couple of grand, but probably less than a grand if you went with reclaimed goods. But that's still not likely to be enough on it's own.)
  6. johnjh2o1

    johnjh2o1 Plumbing Contractor for 49 years

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    Boy are your posts long boring.

    John
  7. ctreefer

    ctreefer New Member

    Messages:
    30
    Location:
    CT
    Dana,
    Unfortunately mine isn't an issue of surface water but rather ground water. House was built 60 years ago on top of a stream bed they diverted but the ground water is still there. Footing drain was root bound so replaced that. Issue with backup from street storm drain (am installing a backwater valve in basement at footing drain. Already existing sump so I'm good there and the only thing left is to build up the apron at the end of our driveway to prevent water from entering towards the house. (almost there.....)

    Briefly did some checks on insulating with insulation board. I don't plan on ever finishing the basement so it looks like my best option is to get one of the non flammable types (Thermax or Tuff-R). Just measured and looks like I have about $750 for a cost of 1.375" foam so not too bad. Will consider for this heating season but still want to investigate the change of the current setup. Going to start looking for local companies to come in and give me some quotes. I'd do it all myself but I need the right design.

    thanks again
  8. Dana

    Dana In the trades

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    Location:
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    The issue with Thermax and other fire-rated iso is that the polyisicyanurate is hygroscopic, and will take on water if submerged, and will even (very slowly) wick water. If you go that route, stop with the iso several inches above the high-tide mark. Also, 1.375" goods are only about R8-R9, and at the price of oil going R12+ would still be cost-effetive long term. It's also important to air-seal & insulate the foundation sill to the top of the iso after the fact. A pro would run you ~$2.50 per square foot for 2" (R12) of closed cell polyurethane, maybe even more/sq.ft. if it's a tiny job, but it's also not rocket science as a DIY for small jobs using a 600 board-foot 2-part foam kit (Fomo-foam, TigerFoam, etc.), which works out to about $2.50/sq.ft for 2" as well, but you can do it on your schedule.

    Some good tips for DIY installation of fire-rated iso on foundations can be found on this blog:


    http://blog.energysmiths.com/2011/08/basement-insulation-part-3.html


    with some editing & repeats here, and here.

    If you went with EPS (expanded polystyrene beads) or XPS (extruded expanded polystyrene) the tolerance to liquid water is 1000x better, but it would require an ignition barrier (half-inch gypsum or half inch OSB/plywood) to meet code.

    There are multiple sources in southern New England for reclaimed roofing iso at a fraction of the cost of virgin stock, (eg: http://boston.craigslist.org/gbs/mat/3242658674.html or http://providence.craigslist.org/mat/3234444099.html or http://newhaven.craigslist.org/mat/3229579666.html Insulation Depot in Framingham MA, but that too would require an ignition barrier. I too have groundwater issues with the slab at below the local water table during the spring snowmelt, with an underground stream/spring flowing along the north edge of the house.

    I went with 3" reclaimed roofing iso (R18) at $20/sheet for 4' x 8' (I've seen it as low as $15). I mounted it with 1x furring through-screwed to the foundation with 5" TapCons, and put up half-inch gypsum as the ignition barrier. The insulation and gypsum both stop ~8" from the floor (more than 4" above the highest ever mark), and put in 10" PVC-composite kickboards at the bottom. It's more labor, but significantly less cash outlay than fire-rated iso using the Hilti plastic fasteners the way Marc Rosenbaum (the blog guy) did it.
  9. Dana

    Dana In the trades

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    Thank you for that insight! :rolleyes:

    ...as long & boring as yours are short & content-free, mayhaps? :)
  10. ctreefer

    ctreefer New Member

    Messages:
    30
    Location:
    CT
    Thanks again for the info. Just sent an inquiry to the New Haven Craigslist listing. As you can imagine I've been prowling all over looking for board and was a little deterred by the price. I didn't realize the thermax would absorb water. Don't want to go that route. I may end up with the EPS or XPS and just deal with framing it out and throwing sheetrock over it. I don't have any good feelings about using Tapcons through the block. I've seen some holes in this block that have dripped water when it's really wet in the spring and would prefer not to test fate. I may just frame to ceiling and down to floor using pressure treated for the bottom plate. Good idea on the PVC trim although since I won't finish the basement I may just have a wallboard seam 8" above the floor so if things got bad I could just replace the wet area. Who knows, if my fixes to the basement water system hold up I may end up finishing part of the basement anyways.

    thanks again!
  11. Dana

    Dana In the trades

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    Thermax will only absorb water if the bottom edge is submerged or resting on a constantly wet surface. The absorption rate is quite low, but so is the drying rate.

    If you frame out an interior-side studwall to trap the foam, put an inch of XPS or EPS between the bottom plate of the stud framing & slab and TapCon it to the slab. The foam keeps water from wicking into the wood, and it keeps the temperature of the bottom plate above the summertime dew point (or at least close to the room temp), to limit mold & rot potential. Reclaimed & surplus EPS is dirt cheap, and going with at least 3" (~R12) is recommended, 4" (R16) if you have the space. ($4/gallon oil makes even 5" cost effective, but that's probably hard to retrofit.)

    Seal the seams of the foam with duct-mastic or expanding 1-part foam (eg. Great Stuff)- tapes & caulks don't stick well enough. At 4-5" it's still vapor-permeable enough that the block can still dry toward the interior, but since the masonry is fairly moisture tolerant it does'nt need to ever dry super fast. Some people tack dimple-board type vapor barrier underlayment between the foam and the foundation wall, but if the studwall has no cavity insulation and no interior side vapor barrier, the studs will track the humidity of the basement, not the foundation.

    If the basement never floods you could go with 2" of EPS and put UNFACED batts in the studwall, which would end up at about R18 (after the thermal bridging of the studs is factored in.) If EPS, don't go less than 2" with a batt-insulated studwall, since at 2" or less its fairly vapor permeable, and the stud edges would be cold enough in winter that the wood would collect moisture when the foundation is wet.
  12. ctreefer

    ctreefer New Member

    Messages:
    30
    Location:
    CT
    Dana,
    Not sure regarding materials. The link you sent for craigslist insulation says that it's Poly ISO. would that be EPS or XPS? 2" or more? I'd prefer to not encroach too much into the space so would prefer 2".

    Here's my thought and you tell me if this is bad. Was thinking after placing 2" foam against foundation and taping all edges with recommended materials use 2x4 ripped in half as stripping then using R11 in the cavity and cover with drywall. Otherwise maybe 2x3 with R13. This way I'm only coming in 2+1.75+.5.

    Another question: I haven't found a lot of info as to what to do around the boiler in the basement. How do I insulate the wall where the vent goes out to the chimney on that exterior wall?

    I'm on the shoreline in CT so it doesn't get too bad down here temperature wise in the winter.
  13. hj

    hj Moderator & Master Plumber Staff Member

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    Location:
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    I can see several possible issues with the MonoFlo system, which are installation errors.
    1. MonoFlow systems depend on the "flow resistance" between the tees be almost equal to the pressure drop through the radiation. You have several areas where the tees appear to be almost adjacent to each other. If they had to be that close together they should have either placed an elbow between them or used two MonoFlow tees to increase the flow resistance.
    2.This requirement appears to be exacerbated by connecting a "loop" to the MonoFlo system.
    3. Regardless of how you pipe the system, if there is not enough heat in the water to last till it flows through the final radiation, it will not heat. The water has to flow faster and/or start out hotter so it lasts till the end of the system.
    4. Those two "center sections" which tee off on the right hand piping, but connect back AFTER other connections, especially the one having the problem, are starving those areas, because a MonoFlow system DEPENDS on the diverted water returning to the main BEFORE it encounters another MonoFlo tee.In other words, you cannot "stack" the feed tees and then connect them back further down the line.

    5.what is the temperature of the water when it returns to the boiler, compared to what it starts out into the system?
    Last edited: Sep 15, 2012
  14. ctreefer

    ctreefer New Member

    Messages:
    30
    Location:
    CT
    hj,
    I can't measure the temp currently since "fortunately" heating season hasn't started yet. By memory I can say that the main basement loop supply the monoflo T's is hot till right before the last T that brings the largest loop back into the system (right before the circulator.) On the boiler side of the T it stays cold for most of the boiler cycle. Only near the very end does it start to heat up into the boiler. The loop on the other side of the house gets hot pretty fast as it gets to the circulator.

    I was puzzled as I mapped out the multiple lines criss crossing the loops. It took a while to see where everything was going. I'm amazed that everything other than that last bottom largest loop works as they do. Just wish they would get hotter.
  15. ctreefer

    ctreefer New Member

    Messages:
    30
    Location:
    CT
    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
  16. Tom Sawyer

    Tom Sawyer In the Trades

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    Location:
    Maine
    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)
  17. ctreefer

    ctreefer New Member

    Messages:
    30
    Location:
    CT
    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.

    Attached Files:

  18. Dana

    Dana In the trades

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    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
  19. ctreefer

    ctreefer New Member

    Messages:
    30
    Location:
    CT
    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.
  20. Dana

    Dana In the trades

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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.)
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