(206) 949-5683, Top Rated Plumber, Seattle
Page 3 of 3 FirstFirst 123
Results 31 to 44 of 44

Thread: Primary Loop on a condensing-style direct vent boiler

  1. #31
    In the trades Dana's Avatar
    Join Date
    Jan 2009
    Location
    01609
    Posts
    2,721

    Default

    Quote Originally Posted by Tom Sawyer View Post
    It could but ain't that just throwing heat out the door?
    That's more like throwing the heat under an asphalt rug, isn't it? :-)

    For the number, length depth & duration of the snow events on L.I. the rationale for a snowmelting system in temperate Long Island is nowhere near what it is in northern New England. That sort of thing might be (very weak, on it's best day) rationale for a boiler that size, but doesn't fix any issues related to it's being so oversized for the space heating loads (which under any circumstances will be the preponderance of the fuel used, unless it's a super-insulated house with miniscule heat load, and it's primarily domestic hot water.)

  2. #32
    In the Trades Tom Sawyer's Avatar
    Join Date
    Nov 2010
    Location
    Maine
    Posts
    2,944

    Default

    I guess that there really isn't a cheap and easy solution to the problem and unfortunately I see this situation time after time. Far too many people don't understand the concept or operational parameters on mod-con boilers and as a result an awful lot of them get a bad reputation when 99% of the time it's installation error, not the boiler. It would be the best option if he can return it and go with something substantially better matched to the radiation but again, assuming the baseboard is copper fin tube, most mod cons are not going to match well. I hate advising less efficient equipment but n this case a gas boiler in the high 80's would most likely perform better and cost about the same to operate. Biase with a Carlin EZ power gas burner would be my choice I think.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  3. #33
    In the trades Dana's Avatar
    Join Date
    Jan 2009
    Location
    01609
    Posts
    2,721

    Default

    I'm not sure how to prescribe a solution without knowing the system or the actual heat load.

    The neighbor's AWOL heat load calculation but it doesn't take a huge amount of information to put an upper bound on the heat load, or the min-temp you'd likely be able to run without short-cycling at min-fire. The notion that the smaller boiler wouldn't cut it is dubious at best- it would even be adequate for most houses in Minnesota, where the design temps are into negative double-digits, even for the same 1950s vintage housing stock so ubiquitous on L.I.. Anything built since 1980 or so usually has even lower heat loads.

    Faith-based sizing leaves too much to be desired though:

    "He has the loss cacl's somewhere, but could find them during our 5 minute talk last night and I don't think I really need them since he already did them and determined the unit to be the correct size. I think I'll be fine with the 110."

    Really? No numbers, no descriptions of construction or size, or the size of the radiation, just an abiding faith in a neighbor? He must be a nice guy and all, but something is really wrong here- most averaged sized houses in ALASKA that would never need the full output of the -110 and could manage just fine with the -60. The true heat loads of most mid-sized houses with OK windows on L.I. pencil out to something a bit shy of 15 BTU/hr per square foot of conditioned space, using reasonable design temps. Even at non-condensing temps the -60 puts out about 54,000 BTU/hr, which would cover a typical sorta-code-min house in the 3500-4000' range, or a tighter-than-average house with better windows in the 5000'+ range. Can't fault the newbie for being easily led down this path by the licensed HVAC guy who should have known better, but oversizing still seems to be the rule rather than the exception in the hydronic heating trades- practically a TRADITION.

    I'm not sure why it's so difficult to convince people that their heat loads are as low as they really are. It may have something to do with the tradition of oversizing cast iron boilers by a minimum of 1.5x. Most I see are around 3x oversized for the actual loads, and 4x isn't rare. While oversizing cast-iron by 1.5x has no real down side, there's an efficiency penalty at 3x. The downsides of oversizing mod-cons by even 1.5x are more dramatic, throwing away the potential efficiency & comfort you might otherwise get out of it, and for no good reason. This forum and others are rife with examples of misbehavin' systems where the boiler is too big to heat the place efficiently, where the contractor or homeowner upsized it a bit "just to be sure". In some cases it's easier to just crank up the temp to make the problems go away, turning a 95% AFUE boiler into an 85% as-used AFUE boiler, but it's a shame when it comes to that, a situation I'm hoping philtrap can avoid with a bit of corrective steering.

  4. #34
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,428

    Default

    FWIW, snow melt under asphalt often doesn't work well...the asphalt (tar) really isn't a solid and it can be problematic...best is concrete. The snow-melting was somewhat of a jest, but for some people, knowing their driveway and potentially sidewalks will be safe to traverse is a major benefit, and priceless. What's the cost of throwing your back out once with the doctors' visits and maybe loss of work time, not counting the discomfort. Or, the heart attack it helps prevent. It is solely self-serving, but it certainly is nice. Depending on where you live, it could cost $100 a pop to clear snow, and a big storm might take a couple of pops to maintain passage. Would not pay for the materials and installation over its life for the average user, but again, it is nice! Depending on your labor costs, it might be a wash once installed, though. It won't go on strike, either!
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #35
    DIY Member philtrap's Avatar
    Join Date
    Jun 2013
    Location
    Long Island, NY
    Posts
    66

    Default

    Thanks folks for all of your input. I'm doing a full heat loss study and will post it soon. I'm paying a guy to do it. I'm still not sure if I'm stuck with this 110...

    FYI - Another guy in my neighborhood with the same house had this heat loss calc done and had an Alpine 080 installed and it works great.

  6. #36
    In the Trades Tom Sawyer's Avatar
    Join Date
    Nov 2010
    Location
    Maine
    Posts
    2,944

    Default

    Quote Originally Posted by Dana View Post
    I'm not sure how to prescribe a solution without knowing the system or the actual heat load.

    The neighbor's AWOL heat load calculation but it doesn't take a huge amount of information to put an upper bound on the heat load, or the min-temp you'd likely be able to run without short-cycling at min-fire. The notion that the smaller boiler wouldn't cut it is dubious at best- it would even be adequate for most houses in Minnesota, where the design temps are into negative double-digits, even for the same 1950s vintage housing stock so ubiquitous on L.I.. Anything built since 1980 or so usually has even lower heat loads.

    Faith-based sizing leaves too much to be desired though:

    "He has the loss cacl's somewhere, but could find them during our 5 minute talk last night and I don't think I really need them since he already did them and determined the unit to be the correct size. I think I'll be fine with the 110."

    Really? No numbers, no descriptions of construction or size, or the size of the radiation, just an abiding faith in a neighbor? He must be a nice guy and all, but something is really wrong here- most averaged sized houses in ALASKA that would never need the full output of the -110 and could manage just fine with the -60. The true heat loads of most mid-sized houses with OK windows on L.I. pencil out to something a bit shy of 15 BTU/hr per square foot of conditioned space, using reasonable design temps. Even at non-condensing temps the -60 puts out about 54,000 BTU/hr, which would cover a typical sorta-code-min house in the 3500-4000' range, or a tighter-than-average house with better windows in the 5000'+ range. Can't fault the newbie for being easily led down this path by the licensed HVAC guy who should have known better, but oversizing still seems to be the rule rather than the exception in the hydronic heating trades- practically a TRADITION.

    I'm not sure why it's so difficult to convince people that their heat loads are as low as they really are. It may have something to do with the tradition of oversizing cast iron boilers by a minimum of 1.5x. Most I see are around 3x oversized for the actual loads, and 4x isn't rare. While oversizing cast-iron by 1.5x has no real down side, there's an efficiency penalty at 3x. The downsides of oversizing mod-cons by even 1.5x are more dramatic, throwing away the potential efficiency & comfort you might otherwise get out of it, and for no good reason. This forum and others are rife with examples of misbehavin' systems where the boiler is too big to heat the place efficiently, where the contractor or homeowner upsized it a bit "just to be sure". In some cases it's easier to just crank up the temp to make the problems go away, turning a 95% AFUE boiler into an 85% as-used AFUE boiler, but it's a shame when it comes to that, a situation I'm hoping philtrap can avoid with a bit of corrective steering.
    You have to remember that before indirect s most boilers had tankless coils in them so everyone oversized for the domestic hot water load.

    I think I would rather go with an AFUE 87 than short cycle a mod con or run it constantly at very high temperatures. The 87% stuff is built to take the constant temps.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  7. #37
    DIY Member philtrap's Avatar
    Join Date
    Jun 2013
    Location
    Long Island, NY
    Posts
    66

    Default

    All right folks... So here is the deal....

    I'm still waiting for my heat loss data which I'll get to you as soon as I get it, but I'm pretty sure (maybe 99.999%) that you guys are correct and my neighbor is totally wrong and the -110 is oversized. I probably should have bought the -60 from the start. Now here is my dilemma...

    The supply house won't take it back since I don't have all the packing. I'm OK with this. I have 2 options:

    1) buy the -60 and sell the -110 for a loss of +/- $1,000 (which I'm OK with)

    2) use the -110 and let it short cycle and not be efficient a die in a few years and then replace it then. Both units are the same size and have the same connections so it would be an easy swap.

    Bottom line is I got screwed by trusting someone and now I'm in a jam. I'm still going to save money in the long run by doing it myself even if I throw away the -110.

    Thanks again and please make your answers and thoughts quick and to the point (i.e don't lecture me... It's bad enough you already have and I could have left this forum, walked away and no one else could learn from this mistake).

  8. #38
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,428

    Default

    You'll be more comfortable and save money with the smaller unit. You may not lose as much as you think on the one you have, but that's a crap shoot, especially if you need to move it quickly. While maybe illogical, a lot of people don't think about replacing a boiler until fall when they need to turn it back on, and it doesn't work. Then, you have the conscious thing regarding selling it to someone where it will probably be oversized. Call the manufacturer and ask if the one you have can be converted and what it costs...it may work out that it can be derated to provide the same functionality of the 60 by just changing a few parts, and the cost won't be as bad as losing the money on the one you have and replacing it. For optimum operation, you should have someone with a combustion analyzer come in to check and tweak (if necessary) the burner, especially if you can derate it, which changes parts.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  9. #39
    DIY Member philtrap's Avatar
    Join Date
    Jun 2013
    Location
    Long Island, NY
    Posts
    66

    Default

    Quote Originally Posted by jadnashua View Post
    Call the manufacturer and ask if the one you have can be converted and what it costs...
    They said they don't recommend it. The Tech said I may be better off by getting a 50 Gallon buffer tank. I know it's still too early until I get the heat loss numbers, but he was confident that I would be able to make it work. I did call the supplier again and asked if they would take it back as an "opened box" item at half the price I paid. I think that's fair and may solve the problems...

    I wonder if there is a buffer tank the can be used for hot water...

  10. #40
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,428

    Default

    YEs, there are buffer tanks that also produce potable hot water.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  11. #41
    In the trades Dana's Avatar
    Join Date
    Jan 2009
    Location
    01609
    Posts
    2,721

    Default

    Like the Ergomax E23 I mentioned several posts back:



    They run about a grand at full retail, and won't give you anything like the full water heating performance you'd get out of a standard indirect. The aquastat on it has about 7F of hysteresis, and if you set it to ~130F and use it as the priority zone on the zone controller it'll do OK as a water heater with the -110 behind it, but would be pretty marginal with the -60.

    When the other zones are calling for heat you can let the boiler output track an outdoor reset curve (at temps above 130F anyway), and the ~215 lbs of water in the E23 gives it a minimum burn time no matter how many zones are (or aren't) calling for heat. I suspect with the curves dialed in, most of the time you'd be looking at 130-135F water out, 115-120F water back from radiation, which would still be into the 90s for AFUE. When only the ErgoMax is calling for heat it'll be condensing whenever there's actual water being drawn, but at the end of the burn you'd be running 85-88% thermal efficiency.

    You'll need to watch the max delta-T on the boiler when you set up the system design and flows with one of these. If you set the output of the boiler to 180F for the "priority" call from the E23, and it's average temp is about 125F, the bottom of the tank could be under 120F. I'm not sure what the max delta is on the TT Solo is, but I suspect it's not rated for 60F+. Whatever that is, respect it, assume that under heavy DHW draws the water entering the boiler will be 10-15F below the aquastat setpoint, so if the spec is 40F max, and the E23 is set to 130F, program the boiler to deliver no more than 155F water, and design the flow rate on the loop to ~3-4gpm. At 3 gpm on the loop with a 40F delta it can deliver the full ~60,000BTU/hr, and you can take reasonably long 2 gpm showers despite the fact that it's only a 26 gallon tank, but you might bust over the max delta-T on high-rate tub fills. It's not ideal by any means.

    Like I said, there's a lot of crayon-on-napkin math to designing the system, and it may be easier to just use a bargain-basement $200 40 gallon electric hot water heater (not wired up) as a buffering hydraulic separator, and set up the boiler flows to run at pretty much a minimum-modulation, unless it's not keeping up with the heating loads. You can then just run it under outdoor reset control with the floor at about 120F (below which the heat output of fin-tube is pretty non-linear), with little risk of stressing the boiler with excessive delta-T the way it's technically possible with "reverse indirects" like the E23.

    There's lots of tweaking and dialing-in to be done to max out the efficiency once it's installed, no matter how it's configured.

    And you're still better off running all of the numbers a couple of times before doing any more plumbing on the system or buying any more hardware. This includes developing realistic whole-house heat load calculations, and measuring the radiation per-zone. That will all be necessary for figuring out a reasonable starting point on the reset curves, and will tell us whether even the smaller boiler would need to be buffered.
    Last edited by Dana; 06-26-2013 at 01:54 PM.

  12. #42
    DIY Member philtrap's Avatar
    Join Date
    Jun 2013
    Location
    Long Island, NY
    Posts
    66

    Default

    Thanks Dana

    The buffer takes place of the closely spaced tees so the drawing below is wrong...
    Attached Images Attached Images  
    Last edited by philtrap; 07-03-2013 at 02:44 PM. Reason: made a call to TT support

  13. #43
    DIY Member philtrap's Avatar
    Join Date
    Jun 2013
    Location
    Long Island, NY
    Posts
    66

    Default

    OK - I have the heat lost done and the following are the results:

    Zone 1 upstairs = 20,057 Btuh
    Zone 2 down stairs - 31,055 Btuh

    Total = 51,112 Btuh

    Local Outdoor +15 degrees F

    Remember, I'm stuck with the 110. I think using a buffer tank may help, but by how much if I use a 40 gallon?

  14. #44
    DIY Member philtrap's Avatar
    Join Date
    Jun 2013
    Location
    Long Island, NY
    Posts
    66

    Default

    Folks - Do you think I need to install a Differential Pressure By-Pass Valves? See the attachment 2 posts ago. The diagram calls for one after the two zone valves and before the returns in the primary loop. I have seen a few installations and none of them have this valve.

    Thanks

Similar Threads

  1. Do I need a primary loop? (Lochinvar Knight)
    By dwassner in forum Boiler Forum
    Replies: 7
    Last Post: 04-27-2013, 05:26 AM
  2. Direct vent boiler connected to chimney
    By lurch in forum Boiler Forum
    Replies: 0
    Last Post: 06-08-2009, 02:15 PM
  3. Direct Vent Boiler Into A Standard Flue?
    By plunger76 in forum HVAC Heating & Cooling
    Replies: 2
    Last Post: 10-05-2008, 07:21 AM
  4. Selecting a condensing gas boiler
    By BrooklynJon in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 7
    Last Post: 11-01-2007, 01:36 PM
  5. odor from direct vent Buderus boiler
    By marsol in forum HVAC Heating & Cooling
    Replies: 1
    Last Post: 06-11-2007, 06:46 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •