sizing a new gas boiler and indirect water heater

Discussion in 'Boiler Forum' started by Rozie, May 22, 2013.

  1. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Location:
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    I have a Buderus mod-con. Essentially no maintenance issues. Essentially silent operation if you're at least 3-feet away. Their US headquarters is about 15-miles from me, it got good reviews, and I found a competent installer. SS heat exchanger. Nicely modular, open, easy to work if, should it become necessary. Compact, wall-hung, well engineered.
  2. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
    Sorry Jad,

    We are Buderus/Bosch dealers and they do not make a SS heat exchanger (HX), all are aluminum. Regular maintenance is essential for reliability and efficiency.

    Burnham Alpine and Peerless use helical flat water-tube SS HX, whereas Triangle uses a SS fire-tube HX with more water content and much lower pressure drop.

    Buderus mandates P/S but Alpine and TT let a contractor do the math and use one pumps when he's able.

    It is not the HX or warranty or proximity to the factory that really matters when it comes to a successful boiler installation. It is simply the knowledge of the installer. I will be doing a preventive maintenance call on a Munchkin M140 today for the first time since installation in 2007. First, I will look for the installation manual and then for a start-up sheet. There won't be one.

    You will need a combustion analyser to do a proper start-up. Now that I think of it, it is probably best to use the old-fashioned, inherently inefficient cast iron boiler for DIY if you do not have or cannot afford a professional.

    I don't think dressing up the old cast iron pigs will work for Burnham. I would be more committed to modern boiler technology, but I always have been.
  3. cyruspinkney

    cyruspinkney New Member

    Messages:
    20
    Location:
    new jersey
    moving forward

    Many thanks, all around.

    @Dana
    Sounds like I don't need to upsize my boiler. Wrightsoft was used to calculate the heat loss on the home. The windows on the home are single-pane sliders, the attic has time-compressed fiberglass batt insulation, I think R-8 would be generous at this point. The exterior walls are insulated, but this is based on gutting the bathroom a few months ago, there was fiberglass in the bays. I have every intention of improving the enclosure of the home, mostly with custom storms, blown in cellulose in the attic, insulating the rim boards in the basement, etc. I had been planning on doing a blower door test this week, just haven't had the time. What may be generating the, by your estimation, high heat loss calc may be that a good deal of the home sits over an unconditioned garage (also an area I intend on furring, insulation, etc. down the road).

    We closed on our purchase of the home at the end of January, so we really only spent a month with bitter cold weather--at least for NJ standards--so getting the oil records is something I may try to do. I was under the impression that the heat loss calc would suffice and I could select the boiler directly from that.​

    @Dana
    Thought so, comforting to hear a firm re-assurance. My intentions were to definitely use an IDHW and zoning it priority. We are not the "luxurious" type, so sizing the tank is not a problem. ​

    @Dana
    Sounds like I need to do some more analysis​

    @BadgerBoilerMN

    Not sure if this was directed at me or not, but we'll be using a professional during my install, but a good portion of the work will be done by myself to keep my cost down. I will also be using the professional to fine tune the ODR and other settings. To resign myself to using a less efficient system just because I, myself, am not the professional is a bit ignorant. I am not quite sure I understand your last statement, if you care to elaborate.​

    I have attached a photo of my intended set-up, as the professional I am dealing with had a very similar install and intend to mimic it as closely as I can. The system here was built for a monoflow, 2-zone, with an indirect tank (no pictured), which is exactly my plan. The boiler here is an NTI, but I am not quite sure I want to use them as a manufacturer. I will definitely be using a hydronic separator, regardless if I use an aluminum or ss heat exchanger. I'd like to limit as many possibilities of compromising the HX as possible and hopefully the separator can help with that, even though that upfront cost is more than I had expected. As always, comments are encouraged and welcomed.

    Attached Files:

  4. Dana

    Dana In the trades

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    OK, with R8 in the attic, swaths of single-pane glass, no foundation insulation, and an uninsulated floor over an uninsulated drive-under garage you might be that high.

    Yes, a Wrightsoft heat loss calc is sufficient for sizing the boiler, but only run the numbers on and size the boiler for the "after" picture of what it comes to post-insulation & air sealing upgrades, and be aggressive- don't use a 0F design temp or a 78F indoor temp "just to be sure" or under-rate the actual insulation.

    And DO get rid of the single-pane sliders- fifty square feet of U1.2 air-leaky slider is worth more than 3500 BTU/hr @ +10F all by itself, and the cascade of convecting cold air down the frost encrusted interior on design day is the opposite of "comfort". A U-0.35 or lower replacement with better air sealing would peel more than 2000 BTU/hr off the load and deliver a real uptick in comfort. If it's a west facing slider sans shade-tree a low SGHC glazing is highly recommended to keep the sensible cooling loads bounded. If you have any other single-pane windows, short of an expensive replacement window, tight low-E storm windows (Harveys are the tightest, but the silver or gold series Larsons sold through box stores don't suck), can improve the performance of a single pane to the low U-0.3s at fairly low cost, and is cost effective in short years (quicker than cheaper clear-glass storms) even at buck-a-therm gas.

    An uninsulated foundation wall & band joist is likely to be on the order of 15,000 BTU/hr @ +10F even assuming a chilly 50-55F basement temp. (What did Wrightsoft come up with?) While air-sealing and insulating the band joist & foundation sill is important, don't ignore the elephant in the room. To do it quickly 2" of closed cell polyurethane with an intumescent paint over it for fire-safety works. But in your climate 1.5-2" of unfaced EPS foam-sealed at the edges and trapped in place with a non-structural studwall with UNFACED batts (preferably rock wool) would be higher performance for lower cost (if you discount your DIY labor.) An inch of foam under the stud plate of that studwall is advisable as a capillary & thermal break from the slab moisture/temperature. Either approach is likely to peel more than 10,000 BTU/hr off the heat load, and combined with attic insulation and select window upgrades puts you within the output range of an Burnham ALP80 Triangle Tube Solo-60 or even a Peerless PF-50 or similar. (Smaller=better, almost always.)

    I'm with Morgan (BadgerBoilerMN) on the comparatively DIY un-friendliness of mod-cons relative to cast iron. If you can, tap some shoulders and get in on the factory training (despite being a non-pro) , and let a pro with both the tools & experience do the final commissioning. Paying a real hydronic designer to spec the system is probably worth it too, even if you're the junior-plumber. It's easier and cheaper to do the math and installation right the first time than to be ripping up & replacing to fix a mediocre design/install. It's way more than a simple plumbing exercise, though not impossible for the truly dedicated.

    Otherwise, the mid-efficiency dressed-up cast iron pigs that Morgan detests are more forgiving, and still deliver 85% (but never 95%) true efficiency if dialed in a bit. Of the prettified pigs, the 3-plate Burnham ESC-3 would be the likely candidate, since it can handle low return temps, and has internal hooks for an outdoor reset option to dial in the comfort. With high volume cast iron rads it'll never short cycle. Any new boiler should be sealed combustion/direct vent, if you plan on doing much air sealing (or even if you don't). If you can squeeze the heat load down to a more reasonable 25-30KBTU/hr (not outside the realm of reality) the delta in operating cost between a 2x oversized 85% AFUE boiler and a 2x oversized smallest-in-class mod-con will be pretty negligible until/unless gas prices triple.

    But if you have a competent hydronic designer to tap and are dedicated to the mod-con approach, have at it. But get the heat load down to something reasonable first, eh?
  5. cyruspinkney

    cyruspinkney New Member

    Messages:
    20
    Location:
    new jersey
    cart in front of the horse, but...

    @Dana
    I will admit that I did use the "just to be sure" (I was calling it 'err on the side of caution) method when I was building the Wrightsoft model, so that also may have kicked the heat loss up a bit.

    Great ideas on all fronts for improving the enclosure, most of which have already been put into my longer-term budget. Unfortunately, and I know I am going to get beat up a bit on this forum, I am going to install the boiler before the improvements to the shell. We're a young couple and our budget isn't very forgiving, so I'm going to have to improve the enclosure over a longer period of time. Winter is coming, and I'd really like to NOT have to have another oil delivery.

    After attending Joe Lstiburek's Building Science Summer Camp in MA this and last August, I decided that I am going the route of quality storms instead of replacements. It just makes more financial sense for us (see above). All of the windows in the home, save for a set of double-hung, fixed, double-hung facing east, are original Andersen sliders. The DH-F-DH will eventually be replaced, but I do like the design and character of the sliders, so they'll all probably remain, with the addition of storms...eventually.

    Regarding the basement, I will have to review my model tomorrow for it's breakdown at the basement. The elephant in the room is the room itself, and the assembly(ies) you're recommending are something we've been showing at almost all of our retrofits; while I would love to do the flash & fill, I'll most likely be using the board + batt method. Because of dampness issues on the foundation wall (yea, by this point, you've gathered I bought a bit of a fixer-upper) I thought that XPS would be a better option. The 1" below the stud plate is very interesting and something I will now be adding to my drawings--1" is a hell of a lot better than a roll of sill sealer. The garage, with it's 12'+ of ceiling height should probably get the same treatment, especially considering it's directly below the bedrooms.

    A point I failed to mention is the relocation of these mechanics, from one end of the basement. The current, original boiler is tied into the masonry chimney, but it creates an uncomfortable floor plan, so the desire is to move the new boiler to a more logistically (at least for future use of the basement) reasonable location on the other side of the basement. The relocation all but forces me to vent with PVC, 1) because of it's lack of a chimney, 2) because I don't have the space to run a chase chimney for a b-vent. Thus, I am a bit limited to what boiler I can install. Other than a mod/con, I have only found the WM GV+ series that allows for PVC venting. I have not dismissed the idea of the GV+, although, after @Dana's suggestion, I will most certainly be going with a GV+ 3 instead of the 4.

    I am willing to "overwork" a smaller (undersized for current conditions) mod/con (or the GV) for one winter, while I go about improving the enclosure/reduce the heat load, than have an oversized boiler for the future 20+ years. Anything is better than the original American Standard oil-sucking beast I have now which can't be operating at much more than 60%.

    While I don't know if I could ever get the home down to 25-30K (come onnnnnn MegaMillions), what are the thoughts about installing @Dana's recommended "smaller" boiler to satisfy future considerations, although it may be taxed this winter.
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,129
    Location:
    New England
    Keep in mind that you likely only need the full output of the boiler (if it's sized properly) on the coldest design day and also consider that that usually only occurs just before dawn, then it warms up. Plus, the house doesn't magically become an icebox - it would fairly gradually cool off if it can't keep up until the outside conditions moderate. It may mean that instead of keeping it 73-degrees, it can only keep it 72 or 71, depending. If you rerun the calcs using more 'normal' temps, you'd get a better idea of what to expect.
  7. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
    The NTI pictured is appears to be enormously over-engineered, over-pumped for sure. It is rare when we use P/S, the bulk of our business being mod/con boilers; case in point we will be installing an NTI TFT250 condensing boiler for a Class II snow/ice melting system next week. One pump , no "hydraulic" separator, all the math done up front. We could design a system for you for less than the seldom needed hydraulic separator (an appliance that inevitably raises the return water temperature) will cost installed.

    We use Wrightsoft to design everything and recommend sizing to the final building envelope. The layman and professional often have an irrational fear of under-sizing equipment. The professional because he does not explain the benefits and detriments of this practice and doesn't want the angry phone call, and the layman who doesn't know that under-sizing a boiler will lead to lower-than-design temperatures in the house lasting a week or so. Typically this amounts to a room reaching 66°F instead of 70°. If it is a transitional situation a sweater or temp heater would be in order.

    Here is a recent fully automatic Class II snow/ice melting system in Prior Lake, MN, using a an NTI, TFT 175. Note the single circulator...

    Attached Files:

  8. Dana

    Dana In the trades

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    It doesn't take megamillions to get the heat load of a 1700' house down to 30K, but it's dead-easy to get it under 50K when you're starting out with essentially no insulation in the attic and glaring single-pane glass loads. And the true heat loads are lower than Manual-J's imply by a good 15-25%, even when you think you've been pretty meticulous about subtracting off all of the internal sources like sleeping humans, refrigerators, etc.

    Whose shoulders do you have to tap to get an invite to Joe L.'s party? :) (I'd probably fit right in with the gaggle of energy nerds there in Westford.)

    XPS is more vapor retardent than EPS, but EPS is more moisture tolerant over the long term, and it's cheaper.

    And the R-value at the end of 50 years after 90% of the HFC134a has leaked out of the XPS to add to the global warming is barely better than EPS at the same density & thickness. (I've been designing XPS out wherever possible on lifecycle greenhouse gas grounds.)

    If you went with something like a Solo-60 and your heat load at +10F really WAS something like 65K (unlikely, but OK just sayin') you'd be about 10KBTU/hr short of boiler out at 70F indoor temps but only 5K short at 65F, and fully covered for 60F indoors. In the unlikely event that it stayed 10F or lower for most of the day you could make up the 100% of the shortfall with a couple of 1500W oil-filled radiator type space heaters at $50/per. If you're planning to have air conditioning (I would, in a place as sticky as NJ in summer) a 3/4 ton mini-split in heating mode would also be able to more than make up the shortfall.

    No matter what it's better to right-size the boiler for the load you anticipate over the lifecycle of the boiler than to start out oversized to only end up RIDICULOUSLY oversized. Sight unseen I'd almost be willing to bet that with your air-sealing and attic & basement insulation upgrades you'd really be in the sub-50K range.

    For reference, when I moved into my current 1923 vintage home in central MA, the where-is-as-is heat load on the ~1900' house with 1200' of uninsulated basement was in the neighborhood of 50KBTU/hr @ +5F as measured by HDD against fuel use, with double-hungs and clear-glass storms, no foundation insulation, a leaky and barely insulated (mostly cathedral ceiling & kneewalls) attic. After an addition was added it become 2400' plus 1500' of basement, with air sealing, a modest amount of attic insulation,fixing some (not all) of the wall insulation gaps and putting 3" rigid foam on the foundation walls the heat load is now under 35K, and there are still HUGE gaps in the insulation, with only the foundation insulation meeting current code. At the 130F max water temp I'm running the current heating system I'm radiation limited to ~42-44kBTU/hr, and this place has sailed through -8F weather just fine without losing ground.

    Different heat load tools have posited heat loads between 39-45K @ +5F for this house, but for that to be the case I'd have to have a magic 10K burner hiding somewhere in the house. At the site shading factors it SURE isn't solar gain skewing the fuel use numbers, and at the rate my kid goes through hot water if it's skewed, it's the other direction. By rights should have been uncomfortably cold on those 99.97% bin nights, but strangely the system keeps up. I won't bump up the water temp just 'cuz the load tool and radiation specs says it needs it- I'll only bump it if my wife says it needs it. :)
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,129
    Location:
    New England
    It's pretty cheap to seal penetrations into the attic, then pick up a bunch of blown in insulation. Most places will loan you the blowing machine for free with purchase of enough insulation, and really, it took maybe 30-minutes for me with a helper filling the machine, to blow in 20 bags into my attic. You probably could use more, but you get the idea time wise and improvement in comfort was immediate - the second story bedrooms were immediately more comfortable and, quieter.
  10. cyruspinkney

    cyruspinkney New Member

    Messages:
    20
    Location:
    new jersey
    much appreciated, now who wants to help?

    @BadgerBoilerMN

    I haven't done much research on the separator, but my mechanical consultant (who speaks broken english, so I gather he meant to say "hydraulic" not "hydronic) suggested it to reduce the floating particles from my cast iron rads clogging the HX. Is this the intention for the separator or am I losing something in translation? If I don't need it, I'd love to trim off the $400+ that I see them going for online. In any case, I think I do need some help sizing my system and components. Any takers?! ​

    I will re-run my calcs with my intended envelope. I admittedly have the fear of under-sizing the equipment, mostly because it seems like some of the old-school plumbers (I know, I know) are so against it and general, uneducated consensus has suggested much larger boilers. I thought I would play it safe and split the difference in my sizing, but I now have every intention in sizing the boiler for the life of it. I'd rather not install the new system and embarrassingly still need the sweater or temp heater, but if I have to do it for a few days during the coldest parts of ONE winter, I can live with it.​

    @Dana

    Breaking the numbers down that way, especially considering the limited time that the conditions are as noted, I feel more comfortable with the smaller boiler. Also, I have thought about mini-splits, but the designer in me, and the complainer in my fiance, doesn't want to be adding any "furniture" to the walls, although I probably will put a small one in the basement, more for cooling than for heating.

    Interesting about your home and encouraging to know getting towards 35K is something I can legitimately strive for, especially considering your colder winters in MA than mine in NJ. My home being a raised ranch with a fair amount of roof, I'm kinda banking on the solar heat gain for this winter, even though convection won't work in my favor :mad:

    @jadnashua

    I have every intention of renting an AttiCat (or whatever the big box rent), especially after $320+ cooling bills this summer with being very conservative with our old, but kicking central air. The blown-in is a guarantee and probably will get done this winter Maybe it'll be nice and toasty in the attic while my new boiler fills the house with heat. :D


    I am now much more comfortable with properly sizing the boiler itself, but am a bit hesitant on the sizing of the other components. I have a friend who works at a plumbing supply and has been asking me to get him a list of what I'll need, but so far I know is a whole lot of copper, a 30-40g indirect hot water tank, and (1) boiler.

    If anyone wants to take a look at my layout, I'd be more than appreciative. For clarity, here's a link where the image quality isn't reduce if you're so inclined: http://db.tt/RK79aYjn (I apologize if you've seen this before)

    Thank you anyone and everyone in advance!

    Attached Files:

    Last edited: Aug 30, 2013
  11. Dana

    Dana In the trades

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    Basement cooling loads are a tiny fraction of the cooling of the upper floors, since they typically have limited window area, and ~75F conditioned space above it rather than a 130F attic. But if you DO put a single-head mini-split in the basement, the 3/4 ton Daikin Quaternity is probably the best choice, since it has independently settable relative humidity & temperature setpoints, and can dehumidify in either heating or cooling mode (without any sensible heating or cooling if the temperature setpoint has already been met.) It's considerably more expensive than a standard name-brand 3/4 mini-split, but since the primary cooling load of the basement is latent-load, it's the right mini-split for the load.

    A ceiling or mini-ducted cassette or two on the main floor could probably work out fairly well for both heating and cooling if you wanted to. A single mini-ducted cassette with split output in the top of the closet could probably serve both the office and bedroom. The big open dining/living room area could be served with a ceiling cassette. But that's a bigger investment than a cheap minimum efficiency no-name 1-ton with a wall-wart blob. A small 1.5-2-ton ducted split system would likely be the cheaper option for cooling-only, and would be small enough to provide reasonable latent cooling comfort (which is likely to be at least half your average load.) Like heating systems, most cooling systems are way oversized in the northeast, and while there's less of an efficiency hit to oversized air conditioning, you pay a penalty in humidity-comfort with oversizing. Mini-splits modulate with the load, and will usually provide higher comfort (and lower noise.)

    Most raised ranches have a gross thermal bridge and air leak point at the cantilevered overhangs. Dense-packing that with cellulose or a full cavity fill of open cell foam on those overhangs can help both aspects a lot. If there is room to add 2" of rigid EPS as a thermal break (EPS only, lest you create a moisture trap) for the cantilevered joists that's worth it in the long term, but not the highest priority. Stopping the air leakage at the cantilever is far more important- many were (wrongly) built with a ventilation gap between the sub-floor and batts (if insulated at all), and have no real air-barrier where the joist-bays cross the foundation.

    A hydraulic separator would make for an awfully expensive junk filter if it's not really needed from a flow-isolation point of view. The primary purpose for hydraulic separation is to be able to set the radiation flows and boiler flows separately. The radiation in the system design will have a range of flows at which it will work well, the boiler has a hard minimum flow, but also a max delta-T at which it can be operated, and over pumping the boiler leads to erosion on the internal plumbing. It's not uncommon to find a satisfactory flow rate at which both are happy, but this is best left up to a competent hydronic designer who will stand behind the design rather than a taking web-forum napkin-math stab at playing Jr. Hydronic Engineer.

    You don't necessarily need a $400 system component for the hydraulic separator though- when the flow requirements are modest it's possible to cobble up an acceptable hydraulic separator out of 2"-3" fittings with reducing tees- there's no real magic to it (but you still need to do the math.)

    BTW: While our average winter temps are more severe in central MA than the interior northern NJ, the design temps are not dramatically different. My 99% design temp is +5F, only 5F cooler than the +10F 99% design temp for Patterson or New Brunswick, whereas the binned hourly average winter temps are about 8-10F cooler.
  12. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
    It is a three day course, but you can do the math if the manufacturer will let you. It is certainly much easier to add a pump and go home...well, add a couple hours and a couple hundred dollars and a couple thousand in operating costs for the redundant pump..if it doesn't fail before it wears out, in which case you will have proved the probability of doubling the chance of a pump failure, since your beloved P/S system will not run without at least two pumps!

    P/S is not religion.
  13. cyruspinkney

    cyruspinkney New Member

    Messages:
    20
    Location:
    new jersey
    appreciative

    @Dana

    Thanks for the suggestion. Humidity is already an issue down there, so I think I will look into that model, regardless of the price.​

    Well it's apparent that I got some bad information, as it was explained to me the sole purpose for the hydraulic separator was to be a filter, with no mention of it's true purpose. I think I'll avoid that and go with the reducing tee setup if necessary.

    I guess I'm going to have to reach out to some of our contacts from the office and see if we don't have a competent hydronic engineer we can dial up​

    @BadgerBoilerMN

    Once again, I'm not sure if your'e directing this at me specifically or you're just making general points. I don't recall claiming anything about P/S rather just questioning if that is a possible setup for my condition. What I am trying to do, however, is further educate myself on some of the finer points of hydronics for both my personal gain and my occupational benefit. I was under the impression that this forum was to share our experiences and help one another. If you were not directing it at me, I apologize, and let's just chalk it up to the lack of emotional clarity via the interwebs.

    If no one is comfortable taking a stab at helping me size the system, I totally understand, it's not your responsibility, I was just putting it out there. However, is there any other resource I can find online that I might be able to help me in my quest? I have no problem hiring someone to do the calcs, but feel it may be something I can look into myself. My architecture licensing doesn't involve this type of engineering (at least at this extent), but I do think i might enjoy checking the math out for my own peace of mind. This is not to say an experienced engineer wouldn't have better and more accurate information, but a little insight into that world is something I am interested myself.
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