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

  1. #16
    In the Trades Tom Sawyer's Avatar
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    Quote Originally Posted by philtrap View Post
    I would never fire it up without having a licensed installer (my Neighbor) look it over and sign off on it. I'm not that crazy and I don't want any problems or accidents. I'm just trying to save money by doing something I am fully capable to do. It's not rocket science.
    Sign off what? Did you pull a permit? Have you notified the gas company? You do know that the gas company needs to inspect the gas piping yes?

    That you are having to ask questions that are so very basic in nature tells us that you are not fully capable of doing the work. If you were "fully" capable you would already know about primary/secondary piping and you would already know the best practice for venting the unit. Knowing how to solder does not fully capable make. Do you understand that installing a condensing boiler on a system that most likely is fed by copper fin tube baseboard will almost certainly mean that your boiler will never condense and therefore never come close to the efficiencies you think it will. In fact, if the unit doesn't condense your efficiencies will be in the mid 80's But you probably didn't take that into account did you? And if you didn't not only will the unit not run at maximum efficiency, it will also short cycle which will reduce the life of the burner and components and cause you to make a bunch of phone calls to Triangle Tube. There's a reason why we have a license and well,,,,,,as far as I know rocket scientists don't
    Last edited by Tom Sawyer; 06-21-2013 at 07:03 AM.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  2. #17
    In the trades Dana's Avatar
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    Out of curiosity, how did you pick the Solo-110?

    I ask because the min-fire output on that sucker could handle the heat load on my ~2400' not-so-insulated house at Long Island's ~ +15F 99% outside design temp, and would be ridiculously oversized (and short-cycling) on my smaller zones. The -60 is a better match for the loads for the vast majority of existing homes on L.I., and at high fire it could heat my house at 90-100F below zero (!), temps not seen on Long Island since the last ice age.

    Oversizing a mod-con boiler is a common mistake (even from licensed HVAC installers) and leads to paying too much up front, lower average efficiency, and short-cycling the thing to higher maintenance &/or an early grave. Before you get too far along the installation, let's first make sure it's even the right size boiler.

    Now, before you've turned on the power or fired up the burner is the right (and cheapest) time to make any corrections, and I'm telling you straight out, the -110 is too big for almost any average sized house in your area, even oversized for some bigger houses, and if you have it broken up into zones it can be a real PITA to hack the system into working properly with an oversized boiler.

    All good heating system designs start with a careful room-by-room heat load calculation, but unless you're planning on tweaking the radiation, let's simplify it by doing the whole-house load numbers, and the zone-by-zone radiation numbers to see if the -110 would run reasonably, or if you need to down size.

    Start with the approximate size (square footage of conditoined area) of the house, exterior wall area & nsulation type/mounts, attic area and window type/amount, window type & total area, door area, and total square footage of the house.

    Foundation insulation (Y/N)?

    Then how many zones, and how much radiation (and type) per zone?

    If you have a heating fuel use history on the place from a prior boiler, pick a mid-winter bill, note the meter-reading dates, and give us your zip code (for degree-day weather history), and the amount of fuel used in that time period. Then give us the BTU-in and DOE BTU out of the prior boiler. This kind of calculation can be more precise than doing it by the building parameters, or would at least put a realistic hard upper bound on what your whole house heat load is.

  3. #18
    In the Trades Tom Sawyer's Avatar
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    From the pictures on another thread I suspect he is past the point of return. Again and again they come to these sites asking questions when it's already too late to do anything about it. You are correct in surmising that the 110 is too big. I suspect its almost twice as much as needed and I also suspect that the system is 3/4" high temp copper fin tube baseboard that is looking for boiler temps near 200 degrees. So, as I said in the last post, the unit will short cycle and never come close to condensing return temperatures. Essentially, he has spent a whole lot of money and gained nothing but remember, according to him he is more than capable of installing the unit. Primary loop piping won't make a bit of difference and in fact, since the whole system is not matched, primary/secondary is a waste of time and materials. Might as well pipe it straight out and back. A 200 gallon buffer tank might help though but then, you're heating 200 gallons of water for what? Oh yea, to pick up 8 to 10% efficiency....or do the numbers start to run backwards from ther lol scratching head.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  4. #19
    In the trades Dana's Avatar
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    At 200F it doesn't take much fin-tube to cover the +15F heat load of a typical 2500' rancher on Long Island- even 50' would do it for most. Hopefully he has a heluva lot more fin-tube than that, or he's screwed with the -110.

    Being capable of doing the plumbing isn't the same as being able to assess the system design. I s'pose that what the neighbor-buddy was going to be doing for him(?), but if that's the case, I'd hazard he didn't even do the crayon-on-napkin math, unless this is a 4500' uninsulated barn with single-pane glass (with some panes broken), in which case the money would have been far better spent tightening up the place.

    [edited to add]

    philtrap: Before finishing off the plumbing take the time to figure out the answers to the questions on my prior post. Any fixes in the design should rightly be done BEFORE you throw the switch, whether you keep the Solo-110 or not, rather than having to hack into the system when it starts misbehaving. You'll probably want it fully vetted, tested, & tweaked before the heating season begins. If you are going to need to buffer it to kill off the short cycling, making the buffer tank your hydraulic separator may be better than whatever primary/secondary scheme you're currently working on.

    At min-mod on the Solo-110 and an 8F of hyseresis (I'd have to look up whether that's even programmable with the Solo series) you can get better than 3 minutes min-burn out of a 25-30 gallon high-mass hydraulic separator which would at least save the boiler from early death. It won't modulate the way you'd LIKE to be able to do with a mod-con when appropriately sized, but it won't burn out by doing 100,000 ignition cycles a season. If you're radiation-limited or have only fin-tube for heat emitters you would always be putting out at least 120F water into the radiation independent of load, and there are versions of massive hydraulic separator/buffers out there with internal heat exchangers for potable domestic hot water. (eg, ErgoMax E23). There's some crayon-math required to determine whether that's an appropriate solution here though- need to know the real heat load, and the real heat emitters, etc. and there'd be some tweaking of the outdoor reset curve limits and the aquastat on the tank to keep it all within the delta-T limits of the boiler a any season, yet still give good hot water performance, during the summer, etc.

    But I'm getting ahead of myself here- let's pencil out the true heat load and radiation conditions first, and figure out if it's too late to pack the boiler back up once we determine in black & white what we're all feeling gut-wise, that a smaller boiler would be more appropriate for your actual loads & radiation.
    Last edited by Dana; 06-21-2013 at 11:37 AM.

  5. #20
    In the Trades Tom Sawyer's Avatar
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    He's going to ignore us and go elsewhere or tell you to Die too. Lol
    Not what you want to hear after you've shelled out a couple grand on boiler and materials.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  6. #21
    DIY Member philtrap's Avatar
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    Thanks for your time Dana - I have a graduation this weekend and will have to get back to you on the heat loss numbers. My neighbor sized it up and has them and he is using the same unit and has a very similar home.

  7. #22
    DIY Member philtrap's Avatar
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    Thanks Dana - Don't worry, I won't tell you to Die. You have been very helpful, unlike Tom who has been nothing but condescending from my first post.

    I spoke to my neighbor very shortly last night a our daughters graduation and he said the 110 was not oversized for our homes. He has the same unit and that's why I bought it. As I noted before, his home is very similar to mine, with the exception that I added a one room extension, so my home is a little bigger. Both homes were built by the same builder in the same year. They are much more larger than what you quoted as average for Long Island.

    Anyway, he did the heat loss calculations when he installed his unit (I think it was 2 years ago) and he recommended that I get the same unit since it works great for him and that's why I bought it (actually thru his heating supply Co.). 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

    I do plan on installing a water heater to it, but not right away since the one I have works and is fairly new.

    Thanks again Dana

  8. #23
    In the Trades Tom Sawyer's Avatar
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    I may be condescending but I'm also right which is what really pisses you off. Your house would either have to be a mansion or have next to no insulation in it to need a boiler that big. Even getting your hot water off it using an indirect is not going to correct your and your neighbors mistakes. Anyway, I'll be helpful for a minute. Walk around your house and add up the total amount of fin tube. Multiply that by 590 and with an expected water temperature of 180 degrees, that will tell you how much heat your radiation is capable of delivering. Now figure out if you can get return water temperatures near or below 135(delta t) I'm betting you can't possibly accomplish anywhere near that without dropping the output temperature which of course delivers less heat and less output to the baseboard. Most folks ( and I guess some heat guys) don't understand that copper fin tube baseboard needs relatively high water temperatures because its not radiant, it's convective but, your neighbor the heat guy knows this right? Understand that if you can't get return temps low the unit will not condense and it will short cycle. All of which basically means that you have thrown a wad of cash out the window mistakenly believing that you have bought high efficiency equipment. If as I suspect, your radiation is fin tube, you would have been better off with a cast iron low mass boiler like maybe a Biase with a gas power burner. It would have run at the same or better efficiencies and it wouldn't short cycle.

    More help. You should have done the heat loss before you bought the equipment but even at that it still comes back around to the radiation. At this point a heat loss is only going to hammer the nail home.
    Last edited by Tom Sawyer; 06-22-2013 at 05:38 AM.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  9. #24
    DIY Member philtrap's Avatar
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    Thanks Tom - I'll take my own measurements... It will take some time since I'm having and going to many graduation parties this weekend.

    But, let's say you and Dana are right and my neighbor is wrong and the 110 is oversized (even though his doesn't short cycle). I can try to return it, but I'm not sure I will be able to since it's been unpacked and hung on the wall. The only connections made are the two 3" PVC vent. The box it came in is crushed. I won't know until Monday if they can swap it. The price difference between the two is only like $300.

    If I can't return it an am stuck with it, I'm asking, can I hook it up as designed, let it short cycle and maybe die in a few years and then replace it with the PT60 since all the fittings are the same? I know that's a waste, but if you guys are right it may be the only option at this point. Or is there something I can do to help it not short cycle, like add heating zone in my basement or screened in porch and make it 3 seasoned? I Know your going to say you need the heat loss info, but I'm just thinking out loud while trying to get thru this. You also said something about hooking it up like a regular boiler without a Primary Loop. Maybe that's an option.

    It's a tough situation because I'm getting different advise. My neighbor is saying it's OK and will be fine and you guys are saying it's way oversizes...

    Thanks,

  10. #25
    In the Trades Tom Sawyer's Avatar
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    There are several options but they are only band aids. I'm boarding a plane for Kansas City so I'm not going to be able to post for a few hrs. Maybe Dana will chime in
    Last edited by Tom Sawyer; 06-22-2013 at 09:36 AM.

  11. #26
    DIY Member philtrap's Avatar
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    Thanks Tom - I'm fine with band aids. As long as it works, I'm OK. I'm even OK with buying a replacement in 4-5 years, so whatever works to make it run properly (if they won't take it back) I'm fine with that. Even if I have to place a zone that runs all the time facing the exterior of the house to heat a shed or even the yard, I'll do it I just want it to work and condense as designed.

    I'm now in a rock and a hard place with my neighbor for this, but I'll take the lumps and pay for whatever extras I need.

  12. #27
    Retired Defense Industry Engineer jadnashua's Avatar
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    How about running snow-melting for the sidewalk and/or driveway! You'd probably want to use a heat exchanger so you wouldn't need antifreeze in the whole system. In reality, on a cold day, your house probably only requires maybe 30-40KBTU. On an absolute coldest day, a bit more. The only way to tell for sure would be to run a decent load analysis. Unless you're running a spa where your hot water usage is constant, you do not take the IWH in as part of the system load, since first, it stores some energy, and you typically have some time to reheat the tank after usage. To get condensing, you need cool return, and that's limited by how much heat you can radiate, and by how much you are putting into it at the beginning. As stated, the type of heating devices can dictate your input temps to the system - some can handle lower temperatures, but some just don't work well unless it is higher - higher means less likely to return cool enough to condense. On an average day, I doubt you'll get much condensation. For decent efficiency, you want relatively long burn cycles, and when the boiler is way bigger than needed, that just can't happen unless you bandaide the thing, maybe a buffer tank. As a result, you won't be reaching expected efficiency levels. Each start cycle takes a hit on efficiency, and you also lose some when it shuts down. Ideally, it could just run for a long period, just meeting your needs, and adjust as those needs varied. Can't happen when it's too big.
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  13. #28
    In the trades Dana's Avatar
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    Until you divulge the information necessary to make the heat load calculations and the zone radiation information we're kinda stuck here. So far we don't even know how big your house is, the number of zones, and the amount of radiation per zone (or whole-house.) Got a zip code, with a winter gas bill that includes the meter reading dates & fuel use?

    I'm sure you can make the think work without short-cycling at a non-condensing temperature, but that's not why you would ever buy a condensing boiler. With a condensing boiler you'd like to be able to set it up so that it can run nearly-continuous burns at a temperature low enough to get 95%+ efficiency whenever it's kinda-cold outside, say 35F, and only run at a higher non-condensing temp (if ever) when it's at or below your 99% outside design temp.

    Adding zones won't stop it from short cycling, nor will adding a snow melting zone. It's condensing boiler's 101:

    The min-fire in on the thing is about 30KBTU/hr- the size of the radiation of the SMALLEST zone relative to that 30KBTU/hr that will determine the lowest temperature you can run without it short-cycling. The min-fire input of the Solo 60 is about 16KBTU/hr. The lower you can run the system temperature, the more condensing you can get out of it, but in general you won't get ANY condensing performance until your average water temps are below 130-135F, a temperature at which fin-tube baseboard can only deliver ~300 BTU/hr per foot. At 30,000BTU/hr and 95% efficiency the boiler's dumping 28,500 BTU/hr into the system, so at the beginning of condensing temps the smallest zone needs to be able to deliver that heat to the room without heating up or it'll quickly go over the reset curve temp and turn off, making a short cycle. So at 300BTU per hour per foot that means your shortest baseboard zone needs to be at least a large fraction of (28,500/300=) 95 feet long.

    With the -60 at 95% efficiency the output is about 0.95 x 16,000= 15,200 BTU/hr, and the smallest zone only needs to be a large fraction of (15,200/300=) 51 feet long.

    If your smallest zone is actually 15' long, you'll have to bandaid something even with the -60, but you'd be totally screwed with the -110. Most bandaids involve adding thermal mass to the system in an appropriate way to stretch out the minimum burn times, or adding radiation, reducing the number of zones by tying them together, etc. But you can't cheat the basic physics- it needs to run at low temp to get condensing efficiency, and it needs to at least approximately balance the BTU-in with the BTU-out, even at those lower operating temperatures.

    But so far you've given us nothing to work with to figure any of this out- you haven't even shared your neighbor's heat load numbers (and at what outside design temp he used), nothing about hour house design/construction, square feet of window, etc.

    Using a standard indirect for hot water won't fix any of these problems, but using a "reverse indirect" can make a real difference in burn-times, since it's not a separate zone, but rather a massive hydraulic separator for the heating system.

  14. #29
    Retired Defense Industry Engineer jadnashua's Avatar
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    Humm, snow-melting a 300' driveway could make a difference, but as said, it depends on your smallest zone and the lowest output available...it's unlikely the 110 can go low enough and the only time it would likely ever go to max would be on maybe reheating the indirect, should you have one.
    Jim DeBruycker
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  15. #30
    In the Trades Tom Sawyer's Avatar
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    It could but ain't that just throwing heat out the door?
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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