Converting oil to gas. Have 10 year Weil Mclain. Would appreciate advice and costs.

Discussion in 'Boiler Forum' started by jefferson17, Sep 18, 2013.

  1. jefferson17

    jefferson17 New Member

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    Location:
    Bristol, PA
    Reposting as new thread, instead of on an old one. We're in PA - about 25 miles North of Philly. We've got a 10 year old Weil Mclain boiler that is way oversized - 240K. The crooks who sold/installed it to the previous owner put in a full 2 gallon nozzle! It was there when we bought 4.5 years ago. We can finally get gas now and I've placed the order w/ PECO - finally we'll have a gas cooktop.

    I've done several detailed heat loss analysis workups and I get about 82000, while trying to be at least a bit conservative. I'm not factoring in heating water in this at all - it's strictly a heat loss analysis of the structure (build 1875 - mostly brick, except for an addition put on the back about 40 years ago). We did a lot of air sealing and insulating this year, starting in the spring (we did a full energy audit w/ blower test). This past summer was much more comfortable than prior years. Total sq footage is 2950, 4 levels and 3 zones (zone a is front of house, zone b is middle of house and zone c is rear - only 2 floors not 4). Rear of house also has very new fujitsu split heat pumps, that kept it comfortable solo (that zone was drained out for last 18 months).

    I'm trying to get some quotes from local guys here and would appreciate some basic figures, parts and labor separately - if we go with the following:
    - Carlin EZ conversion
    - Outdoor reset
    - (optional) indirect water heater, perhaps a 40 or 50 Amtrol? They seem to be less expensive and ppl say good things about them (current boiler doesn't seem to have integrated connections for this so if we do go w/ one vs. a standalone gas water heater we'd need a small separate circuit built for that). There is plenty of room next to the boiler.

    Also - does anyone have really good figures on recovery value for an indirect water heater vs a high recovery 50 gallon stand-alone gas water heater? We can get a Rheem 42vr50-40f for under $600 delivered.

    That aside, if we did go with simply "a new gas boiler" that can be directly vented (to avoid lining chimney), any cost estimates? (there is an external wall in basement for direct venting).

    One last thing ... let's say that I kept the boiler as is - and downsized the nozzle to put out say 100K btu (acceptable nozzles are listed on the side of the boiler and this falls into the range) - how much oil might I save if I did NOT mess with anything at all for the boiler?

    Thanks very much in advance, for your assistance!

    Jeff
    Last edited: Sep 18, 2013
  2. Dana

    Dana In the trades

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    Size the indirect for the biggest tub you have to fill. The 40 is probably going to work unless you have a big soaking tub. Recovery performance on indirects is mostly about the burner size of the boiler it's hooked up to, which in your case is more than 2x that of any residential 50 gallon standalone. Hot water performance of indirects is SO good you can usually downsize to 40 gallons from 50 gallon standalone, unless you're hooking it up to a very sub-50K boiler.

    A new boiler + indirect will likely be $8-10K at the very low end for cast iron, no frills or system tweaks, to $12-20K for a right-sized modulating-condensing boiler with the system carefully re-configured to take full advantage of it. A conversion burner, $2-4K in my neighborhood.

    Adding outdoor reset boiler controls only makes sense if the system radiation is sized to actually need 200F+ water on design day. When you've done a bunch of upgrades to bring the load down the water temp requirements for delivering the heat is often even below the safe RETURN water temp for a non-condensing boiler (130F if burning gas, 140F if oil), which means the reset control is always stuck at the low temp end, and the thing just cycles within a narrow temperature range. In those situations you get a lot more out of an Intellicon 3250HW+ or similar heat purging economizer ($200 for the hardware as DIY, $500-700 sourced & installed by a pro.) Rather than keeping the output temperature at particular range, they work by analysing burn times from recent calls for heat to "learn" the system, turning the burner (but not the pump) off prior to the end of a call for heat, dumping the residual heat in the boiler into the zone. If the boiler is above it's programmed low-limit on a new call for heat, it inhibits the burner from firing until the low-limit is reached. By always parking the boiler at a lower temp, the standby losses are reduced, but by allowing the boiler to rise (to 180-220F if need be) during the call for heat, then purging that heat into the zone at the end of the call, the number of cycles and cycling losses go way down too.

    Re-jetting the oil boiler to 100K will likely save ~10-15% if your heat load is truly 82K (I'm skeptical that it's that high, but OK.) If you do that you'll likely have to tweak the plumbing to keep the return water above 140F, and you'll need a stainless flue liner. If it was installed 10 years ago it may already have the liner, and it may be a model tolerant of lower return water temps. If you have the manual , see what it says. If not, what's the model number?

    Either way, if oil stays above $3.50/gallon the conversion burner option pays off in short years, and you can probably get another 15 years or more out of the sucker if it's still in good shape, and revisit the replacement options then- you may have dropped the heat load to under 50KBTU/hr by then. Installing an indirect at the same time as the conversion burner would be another $800-1200 in my neighborhood. YMMV.

    At $3.50 oil heating with the mini-splits costs less than half- comparable to heating with gas in an 80% boiler in most markets. If the older part of the house doesn't have air conditioning and the floor layout fairly open, adding another mini-split and only firing up the oil burner when the heat pump doesn't keep up might be the right thing to do. A 2 ton Fujitsu or Mitsubishi can typically pump out on the order of 30,000BTU/hr @ +15F outdoor temps (the 99% design temp for your area), and may cost less than the total cost of conversion burner + indirect + economizer control. If your peak load for those zones is 50K, a 2-ton ductless would more than cover the average winter load, reducing oil consumption by more than 80%.

    A standalone gas water heater or a better class heat pump water heater like the AirTap or Stiebel-Eltron is dramatically cheaper to run than an indirect on an oil-boiler at current fuel & electricity prices.
  3. jefferson17

    jefferson17 New Member

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    Location:
    Bristol, PA
    Thank you!!!

    Dana,

    Thank you VERY MUCH for your very thoughtful and comprehensive reply. It is the first of it's kind that I've gotten off several boards. Most helpful! I don't suppose that you are anywhere close to us - eastern PA, on the NJ border - 25 miles North of Philly?

    I can readily monitor input temps - I've got a good infrared temp gauge that is quite accurate, to make sure the supply pipe to the boiler stays at or above 140. All the supply valves are wide open currently - so I probably need to experiment with those to reduce flow at least somewhat.

    We've had 3 guys come out to look at things and provide #s to us, for different options. One isn't on our short list - he's from the company that originally put this monster in, and I was hoping he'd slip and indicate how big it is :) I'll be writing them up on the 'net so others know what a bunch of crooks they are.

    One of the guys who came in (a pair of them actually from one company) indicated that if they were to replace the whole thing w/ a gas burner that they'd need to spend some 4-5 hours to count number and size of radiators, length and diameter of pipes, etc - to really figure things out properly. That even a good heat loss analysis on it's own isn't ideal. Do you have any thoughts on that?

    I'm not sure if we have a stainless liner or not. I'm guessing not but it wouldn't be hard for me to pull the flue piece from the chimney and look inside. One guy said it would be about $800 to put one in - another said $1500-2000 (but they didn't do that work). $800 I believe. The other figure sounds outrageously high for a 25' run (or so). I figure $500-600 for materials and 2 guys for 4-5 hours ... That's just how I think of it.

    $800-1200 for an indirect sounds like a VERY good option, provided that I change the boiler to use gas or replace it with a gas boiler. What brands/models do you like in indirect water heaters?

    Apparently, one option for us is to go w/ a new "regular" gas boiler at about 83-84 eff, and vent directly to the rear wall in the basement - instead of lining the adjacent chimney. The one guy who mentioned this option said it would save a bit - like $100 and that then we'd get to keep that flue for the wood-burning fireplace above it (which MIGHT be currently on that chimney or it MIGHT be on it's own side of the double flue inside the chimney). I'd have to check that w/ a flashlight to be sure.

    We love our mini splits. Unfortunately, it's not as convenient to add them to any other areas than the back addition. We originally did it to provide AC for these 2 rooms, and found out that they did a great job of heating them also - except when things dropped below about 20-24 F or so. They'd still do ok down to the mid teens but it really doesn't stay that cold here for very long or often. But ... that was before we added closed cell spray foam to these rooms - so I expect they'll do really well this winter. So it seems that keeping that zone closed up is probably in our future.

    Thanks again - we'd very much appreciate any additional info!

    Jeff
  4. Dana

    Dana In the trades

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    Counting the radiation size is important for the system design, but it's not how to size the boiler (only steam boilers are sized that way.) For a replacement burner all you need to know can be gleaned from the current burner-jetting, and firing the system up and monitoring the temperatures. You can definitely run the system at lower temp/lower output with a gas burner, but it'll still have to be a pretty hefty burner.

    You'd only need a stainless liner if you were to run with 130F return water or a gas burner installed in the existing boiler ended up north of 83% combustion efficiency (not likely- 78-80% would be the typical best-case for a dialed-in retrofit gas burner.)

    Going with a side vented mid-efficiency boiler isn't a terrible option, as long as they size it right to the heat load. A modulating condensing boiler would run at higher efficiency though, and would also be side-vented, and they all come with outdoor reset control built in these days, making it possible to tweak in maximum efficiency & comfort. With high-mass radiation single-zoned systems that's pretty easy to do. Where people run into trouble is when trying to run small low-mass fin-tube zones at low water temps, and end up short-cycling the mod-con into low efficiency/early-grave.
  5. Tom Sawyer

    Tom Sawyer In the Trades

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    You will get the most bang for your buck with the carlin EZ conversion and reset controls.
  6. jefferson17

    jefferson17 New Member

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    Location:
    Bristol, PA
    Hi Dana,

    Ah ... I kinda expected that counting radiators, length and diameter of pipe etc seemed kinda like a "story" - at least in terms of sizing a boiler. But it DID make sense to me that the pump valves might well need to be adjusted from full wide open to something slower. If I know what measurements to take that's not hard for me to adjust over time to more-or-less what it should be. Sure I'd take longer doing it than someone who has done it many times but I can't imagine that I'd lose too much money in extra gas bills while I take a week or two making small adjustments and taking measurements.

    When you say "it would still have to be a pretty hefty burner" - were you referring to a conversion burner in the existing 7 stage massive boiler? I think that was your intent but I just want to make sure I'm not confusing things. I've emailed Weil McLain and they say that I can use a conversion burner but it would need to be pretty big since that 10 year old model wasn't designed like newer 2-stages and should not be run at like 100-120K. I don't see why that wouldn't be ok - provided that the flue temps are maintained at 400 or higher. Of course I have no idea what would actually happen if I tried to put a 100K conversion burner at 80 eff in there. And it's hard to know what info to trust - even from Weil McLain.

    None of the 2 guys who were out here on Sat have yet provided a quote. I'm not quite sure what to make of that but I'll see what happens in another 1-2 days.


    It's not that I don't believe this but it does contradict what both local guys are telling me. If I'm understanding you correctly - you are implying that there is no condensation risk in the current chimney using a conversion gas in the current boiler as long as the return temps (i can easily measure this) are say 140 or better. Correct? Would a PA inspector agree with this? Would you happen to have a reference from the national building code? I'd love to be able to validate what is and isn't really needed.

    I THINK that I may be following you but ... not entirely sure. When you reference "small low-mass fin-tube zones" I think you are referring to the radiators throughout the house? The zones currently active are 100% big heavy old cast iron radiators. Some are smaller than others but all are the big solid kind. The drained out zone 3 section in the back is the newer small baseboard type - with what I would think of as "low mass fin tube" design. I wasn't planning to use that zone, and keep using the heat pumps there - unless it makes sense to do so (or if it gets really cold and then use it for a month or so and then drain it out again).

    Am I picking up what you are putting down?

    Thanks!

    Jeff
  7. Dana

    Dana In the trades

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    "When you say "it would still have to be a pretty hefty burner" - were you referring to a conversion burner in the existing 7 stage massive boiler?"

    You can only undersize the burner so much for the size of the heat exchangers in the boiler without ending up with insufficient turbulence on the fire side for efficient heat exchange, and high potential for destructive condensation in the boiler itself. If the thing is design for optimal heat exchange with 240-250KBTU/hr of input, you can't just drop a 100K burner on it without a big hit in efficiency or other problems. You may be able to derate it to 200K, but not much lower. It's probably a 7-8 plate boiler- got a model number?

    "It's not that I don't believe this but it does contradict what both local guys are telling me. If I'm understanding you correctly - you are implying that there is no condensation risk in the current chimney using a conversion gas in the current boiler as long as the return temps (i can easily measure this) are say 140 or better. Correct?"

    Oil exhaust is FAR more corrosive than gas exhaust, and has a higher dew point than natural gas exhaust. With oil it would be condensing inside the boiler with ~135F return water, and you may have flue condensation problems with 140F returns. With natural gas you won't get condensation in the boiler until that return water is under 125F, but you would likely still have some flue condensation at 130F. The exact numbers are somewhat boiler & burner dependent, but condensing boiler manufactures struggle to eke out even the slightest amount of condensing efficiency above 125F return water which takes sophisticated mixture controls, and even then the highest I've seen to date is a claim of condensation starting at 127F (which I would only believe in the lab bench-test after tweaking by the engineers, not in the field.) With cast iron boilers forget about it- an 86% efficiency tuned up burner on a cast iron boiler would start condensing around 122-123F. As long as it's set up at 83% combustion efficiency or lower the risk of condensation even in the flue is near-zero until the return water is 130F or lower, and with most conversion burner's it's difficult or impossible to hit even that number on an oil boiler.

    It's possible that the existing oil boiler was installed without a stainless flue liner. (That would have been a code violation in my neighborhood even 10 years ago, but not everywhere.) If so, it's also possible that the tile or masonry flue liner is oversized for the BTU input, and would require a narrowing liner on those grounds. It's still legal in most places (including my neighborhood) to install an 83% efficiency gas boiler on a terra cotta lined flue, as long as the flue is sized correctly to the burner, even places where stainless liner is mandatory for 85% oil. I have no insight as to local codes on this in PA.

    "I THINK that I may be following you but ... not entirely sure. When you reference "small low-mass fin-tube zones" I think you are referring to the radiators throughout the house? The zones currently active are 100% big heavy old cast iron radiators. Some are smaller than others but all are the big solid kind. The drained out zone 3 section in the back is the newer small baseboard type - with what I would think of as "low mass fin tube" design."

    The specific heat of water is 1 BTU/lb-F, and radiators contain a lot of pounds. The specific heat of cast iron is much lower at 0.11 BTU/lb-F, but cast iron radiators have a lot of that too. Add it all up (including the water & iron thermal mass in the boiler itself) and even at 200-250BTU/hr boiler output it takes several minutes to slew the 15-25F from the boiler's low-limit temp to it's high-limit.

    The specific heat of the copper is even lower, ~0.09BTU/lb-F, and fin tube doesn't contain very much of it, and not much water mass either. On zone that has only fin-tube the temperature slew rate is an order of magnitude faster, reducing what might be 10-15 minute guaranteed minimum burn time to the sub-100 second range, which causes an order of magnitude more ignition cycles (& flue purges, with mod-cons). At high water temperatures the BTU output rate is pretty good, and as long as it's a large fraction the boiler output the burn lenghts are long enough the it runs efficiently, and it's not problem. But at 140F the fin tube is putting out only half what it delivers at 180F, and at 120F condensing temps it's putting out about a third, leaving 2/3 of the boiler output with nowhere to go to heating up the water in the loop. Most mod-cons only run a 5-7 differential around the outdoor reset (with some it's a programmable setting, but it usually tops out at 15-20F differential), so even at the minimum modulated fire they often run into short-cycling issues on fin-tube.

    If you're required to put in a new stainless liner for any reason go to with the conversion burner, it may be cheaper to go with a smaller right-sized direct-vented cast iron beastie like a Burnham ESC series vented out the side. A liner + burner + heat-purge control all adds up- find out the number. The ESC series already has the smart controls, and self-protects even with 110F return water, and has the hooks for adding an internal outdoor reset control, which may work out pretty well for you with all of your cast iron radiation. But sizing it for the actual heat load would be important. If you have a mid to late winter oil bill with a "K-factor" stamped on it, assuming you weren't using overnight setbacks below 60F or running a wood stove or some other auxilliary heat regularly, that would be sufficient information for right-sizing a smaller cast iron boiler. If the radiation is SO massive that it delivers design-day heat at 120F you may have to design in more cool-return protection into the near-boiler plumbing. I suspect you'll probably end up with something between the ESC4 to ESC6 (4 thru 6 plates), the internet-retail cost of those units are all under $3K. It's hard to say with any accuracy what the installed cost would be from a competent contractor, but $10K is a likely upper bound, but probably not less than $6K. If the bids for conversion burner + liner + heat purge controls come in north of $5K, it's worth finding out what a right-sized smart-controlled direct-vent cast iron piglet would be.

    But if they'll do the conversion burner for something like $3-4K with an Intellicon 3250 HW+ or similar heat-purge control added, its worth using up the next 10-20 years of boiler life you probably have left in the oversized beast.
  8. jefferson17

    jefferson17 New Member

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    Location:
    Bristol, PA
    You are correct - our current Weil Mclain is a 7 section. So I COULD convert it but then I would have to use a BIG gas burner like 200K. And THANK YOU for your very detailed explanation of WHY this actually is!

    So, so clearly it makes more sense to do this right - and get a right-sized new gas boiler, which can be installed at the rear of the basement and directly vented out the rear or side wall - and not worry about the chimney at all (I suspect that it's not lined - and it MIGHT also be the same flue that a wood burning stove is currently sharing (though not connected).

    Maybe I can get a bit of money from selling my current oil boiler? I'm guessing $500-1000? Any ideas?

    Oh! And my existing oil tank. I'm wondering if I would "have to" remove it or not. It's 100% above ground - a 225 gallon unit. I ran it dead empty at the end of last year. It's located in an unheated area outside the main basement, under an unheated vestibule area outside the 1st floor living room. The only way to take this thing out would be to take apart the side stairs ... that wouldn't be fun.

    GOT IT! I actually followed MOST of that :) Ok so now I REALLY need to validate my proper Heat Loss #s and then figure out whether it makes more sense to buy a "good standard mid efficiency gas boiler" or "high efficiency mod/con".

    http://www.pexsupply.com/Boilers-449000 has a bunch of stuff. And that is ONLY the Burham models - they have all sorts of gear. So do other places. It's so much to choose from for a layman! From a shear $s standpoint, it looks like a good mid efficiency boiler for say $2000-2200 is a really good pick. Maybe something like a http://www.pexsupply.com/Burnham-ES2-4-ES2-4-105000-BTU-High-Efficiency-Cast-Iron-Boiler???

    Honestly, I'm a bit anxious about the mod/cons. I've been reading a lot and they seem to require some care/feeding/maintenance? If I'd really need to spend say $100 a year to keep tuning them up - I would think that would make any additional savings of say 90-95 vs 84 or so a moot point, right? Assuming the mid-efficiency units are more carefree? A lot of folks seem to have issues with these mod/cons. Maybe they were badly installed or tuned? I really don't know. There are a lot of pretty bad reviews against nearly all manufacturers on http://www.furnacecompare.com. But I can't believe that all these manufacturers make so many bad models. I can only GUESS that there are a lot of bad installers out there.

    For us I don't have to worry about saving every single dollar in gas vs gas. We want something that we put in, and it just does it's job without too much maintenance - except maybe simple things I can do myself like changing filters and such - whatever is called for. Ideally I don't want to buy something that requires annual pro maintainence, if I can help it.

    Since we'll definitely want water heat too ... I wonder if some of these mid-efficiency or high mod/con units are designed exactly with that in mind? Kinda like an integrated unlimited tankless system built into the boiler? Seems like someone would have thought that up, right?

    Thanks!

    Jeff
  9. Tom Sawyer

    Tom Sawyer In the Trades

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    You can remove sections from the boiler.
  10. Dana

    Dana In the trades

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    Jeff- the ES2 series boilers are atmospheric drafted, which WOULD require you to use a chimney with a flue liner. The ESC series is power vented (and can be direct-vented, drawing it's combustion air from outdoors- highly recommended.) They are the same boilers underneath, and mostly the same boiler, controls, but the installed cost of the ES2s would probably be comparable or even higher due to the flue-liner cost. Both series come with heat purge boiler controls to maximize efficiency, with hooks for outdoor reset if desired.

    Mod cons are great if sized correctly & installed competently, but unfortunately that's not always the case.

    All cast iron boilers can be set up with indirect hot water tanks. Size the tank to the biggest tub you need to fill (got any 150 gallon spa tubs?) Embedded hot water coils require you to keep the boiler at a much higher standby temp, which is takes a serious toll on operating efficiency. While there are a few highly-insulated European boilers out there that would have standby losses as low as an indirect tank, most boilers that you're likely to find at a reasonable price & local support will do considerably better with an indirect. And the smaller you go on the boiler burner, the more important having the thermal buffering of a tank becomes. To take a steady 2 gpm shower with a 65F temperature rise (40F in, 105F out) takes 65,000 BTU of boiler output, which is 76,000 BTU input with an 85% boiler. That's no big deal for a 240,000BTU boiler, but if your true heat load comes out under 100,000 BTU/hr the sheer hot water peformance takes such a hit with an embedded coil that it's just not worth going that route.

    Oil boilers are showing up on the "free- if you can take it out of my house safely" listings on Craigslist these days.

    Tom is correct- you can remove sections from boiler to down-size it, but that too comes a financial cost. First and most important is to figure out what your true heat load is. If your true heat load at the 99% design temp actually over 80KBTU/hr you can leave it intact, install a ~200K conversion burner plus heat-purge controls and end up in the ~78-80% AFUE range if you can tweak the raw combustion efficiency into the 82-83% range (maybe possible, maybe not.) If you cut the boiler down to 4 plates and install heat purge controls it would deliver an AFUE comparable to whatever raw combustion efficiency you can get out of it.

    Got a K-factor with which to sanity-check your calculated heat load numbers? Using fuel use against heating degree days is a valid way to get to the whole-system peak load numbers. If you want to refine it for oversizing factors on your behemoth, the NORA oil heat organazation has a handy (but buggy- it crashes sometimes) calculator downloadable from their web site, based on boiler models developed by Thomas Butcher's testing at the Brookhaven National Labs.
  11. Tom Sawyer

    Tom Sawyer In the Trades

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    Removing sections isnt that big a deal. Weil McLain used rubber seals between sections so its just a matter of stripping the boiler down and unbolting 4 cinch rods then re-installing the rear section. New seals would be a good idea however, If its 10 years old its most likely a Weil McLain Gold series and its a single pass, cast iron design thats 60 years old pretty much. Its a shame that it was installed in the first place.
  12. Dana

    Dana In the trades

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    Unbolting the plates is only part of it- to de-rate a 7-plate 240BTU/hr beast down to where he needs to be requires the tin governing the venting parts to be appropriately scaled too- it's basically a complete boiler-rebuild.

    If popping only one or two plates out, maybe not, but IIRC his calculated heat load was well under 100K, and reality is likely to be under 75K. He'd have to take at least 3 plates out to get it down to "merely" 2x oversizing, rather than the current 3x, at which point with a heat-purge controller the as-used AFUE might begin to resemble the steady state efficiency. The efficiency difference between heat-purged on the boiler as-is vs. de-plated would likely never pay off within remaining lifecycle of the boiler.

    His boiler as-is has roughly the same efficiency at 3x oversizing factors of boiler #1 (detailed in Appendix 1 starting on page 17, .pdf pagination.) According to table 3 on p.14 that pretty-good oil boiler with the embedded coil for hot water ran at about 75% efficiency at 3x oversizing, 78% at 2x oversizing. If you look at the regression curve Figure A1-2 on p.19, assuming the average load is about half the peak load, and thus in the 17-25% of full capacity, you see that both at 2x or 3x oversizing are operating most of the time near the knee of the curve but still on the flatter part, and well over the cliff during the shoulder seasons.

    But with heat purge and an indirect HW heater the knee in the curve moves do the left, making it similar to that of the heat-purged steel boiler, the regression curve of which is on p.25. where the curve is VERY flat all the way down to about the 10% point, which means the horrific efficiency hit during the shoulder seasons is much mitigated with either, and the net efficiency difference between 2x and 3x oversizing is now less than 1%. (See boiler #3's 2x and 3x oversizing efficiency numbers in Table 3.)

    It's worth buying an Intellicon heat purge control to recover most of that 3% delta from oversizing, but I'm not so sure it's worth the cost & risk of pulling half the plates and re-cobbling the tin to gain back the next 0.5%.
  13. Tom Sawyer

    Tom Sawyer In the Trades

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    He can keep the tins and stuff the space with more insulation LOL. I was being facetious in the earlier post. Though removing sections is possible, it would cost more in labor than it would be worth especially considering that even if it were originally a 3 section boiler, it would still be crap efficiency wise. I don't recall the original post and don't feel like going back to read it but the best and most cost efficient thing to do here is get an accurate heat loss and then tailor the boiler and radiation to the load.
  14. jefferson17

    jefferson17 New Member

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    Gosh I'm glad that you are joking - I'd never consider that vs just getting a new proper gas boiler.
  15. Dana

    Dana In the trades

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    Tom: On his other thread the lipstick-on-mirror math on his fuel-use implies a heat load under 35K at the 99.5% design temp.

    A mis-match that large means it's time to scrap the behemoth-boiler rather than invest in a conversion burner, since on even on design-day he's a bit to the left of the 15% point on the regression curves, and most of the time it's under the 10% point. It would take the more serious math and model to come up with the true heat load, given that it's ~6x oversized for the load, and delivering nowhere near 85% AFUE as-used. He didn't have very precise fuel use numbers, but even worst casing it for all possible errors the heat load is under 55K, unless he's outright lying or totally confused about the fuel use numbers. As-used it's most likely averaging under 70% efficiency, maybe in the low 60s, and it won't do any better with a conversion burner. A right-sized 85% AFUE cast iron with purge control will likely cut his heating bill by 2/3 or more, whereas a conversion burner cuts it by about half.
  16. Tom Sawyer

    Tom Sawyer In the Trades

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    Ok so I took the time to read through the thread and I concur with your assessment. This thread is very close to another on the same subject so it gets confusing but yes, the old 7 section has to go.
  17. jefferson17

    jefferson17 New Member

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    Hi Tom,

    I would greatly appreciate it if you share your thoughts on a few subjects here - would you mind?

    Thanks in advance for your generous time. If people like you and Dana weren't so very helpful, it would be difficult to get really good info - even from all the hours that I spend reading articles and web forums on these subjects. Like you both I "give back" as well - and am a top-rated expert on ********** for computer networking. It feels good to help people out!

    RE: gas conversion of my old unit. I'm not sad that it doesn't make sense. It is just too bad that it was sized so crazy high to start with. Weil Mclain could have been much nicer and more descriptive with their version of "can't undersize it much". You and Dana really helped me understand WHY it can't be - and I'm so grateful!

    I'd appreciate it if you would chime in with specific thoughts for a new boiler. Are there brands/models that you like? If you don't like some brands/models then I'd appreciate knowing that too.

    Thanks to you two - a Direct Vent Boiler is clearly the best solution. We can use the rear basement wall or side basement wall - about 10' further back than the existing boiler location.

    Would you mind outlining your thoughts on "mod/con vs medium eff boiler"? It doesn't SEEM like the mod/cons would actually save us much - or maybe nothing if they need any yearly pro maintenance. What are your favorite gas boiler brands and models? Are there ones that you don't like? It's always useful to know what to avoid!

    And what about maintenance costs for mid vs mod/con? I have read a LOT of articles and threads all over the place but I can't seem to find too much about yearly maintenance costs for gas boilers and gas mod/cons.

    Lastly - let's say that I'm really interested in an indirect water heater. Does that modify your boiler recommendation? Our water use isn't excessive. 5 people, and 4 showers - no baths. 1.85 gpm showerheads.

    THANKS!!!
  18. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,183
    Location:
    New England
    No, unless you were running something like a spa or a Laundromat where you needed hot water constantly all throughout the day, do not upsize the boiler for water heating. The key, though, is to size the tank for your simultaneous uses.. It typically gets plumbed as a priority zone, so when it does need reheating, it gets the full priority of the boiler. This normally doesn't take all that long, and you shouldn't notice - the thermal mass of the house is typically way more than the short time the house heating is disabled to reheat water in the indirect.
  19. jefferson17

    jefferson17 New Member

    Messages:
    34
    Location:
    Bristol, PA
    Hi Jim,

    Thanks for chiming in. Yes I do understand that the boiler sizing isn't affected by an indirect water heater. We are JUST 4 showers - and 2 of them are for only Amy and I. One of the heating guys who was here claimed we'd need to add 40K for an indirect. It's very nice to know he is either ignorant or intentionally lying.

    My question at the end RE: indirect was whether this Use Case would change a recommendation at all via "med eff gas boiler" vs "mod/con". Or if it would perhaps affect the recommendation of any particular make/model boiler selections. I was thinking that some makes/models might be especially good choices if I were to also add an indirect water heater - perhaps they are already set-up for this and I wouldn't need to buy extra valves/pumps. That was my thought process for this question. I can see where my intentions could be easily misconstrued - and thank you for getting me to clarify it.
  20. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,236
    Location:
    Maine
    Never add anything for the indirect load. It is an intermittant load and oversizing the boiler by say 40K for what amounts to probably less than an hour of run time daily makes no sense and is wasteful. Boiler controls like the Taco SR and ZR series relays provide for hot water priority which in essense switches all power to the indirect when it calls. A nice feature and it is switchable, honestly I rarely use the feature. A 40 gallon indirect will give you all the hot water you need. As far as boilers go a lot depends on what is available in your area. You want equipment that you can easily get parts for should it break down and while I am a fan of Buderus and Lochnivar if you don't have a local supplier you should probably go with what is available. Condensing versus non? well a lot of that depends on how much radiation you have. If you dont have enough radiation a condensing boiler will rarely if ever actually condense and give you those high efficiency numbers. Most, if not condensing will run between 87 and maybe 92% plus or minus and you are paying a premium for equipment that never reaches its potential. The truth is that unless money is no object you have to trade off between best efficiency and most cost effective.

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