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Thread: Who makes modulating non-Condensing Boilers

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  1. #1

    Default Who makes modulating non-Condensing Boilers

    Am planning a conversion from oil to N.gas. Have a 6" SS lined chimney in the Northeast and finned element radiators. At the current gas price, I'd only be savings less than a hundred dollars a year with condensing efficiencies (even if they could be achieved, without adding 70% more radiator length to accept 130F water temps). So, I'm looking at heat only non-condensing gas boilers.

    I've only found one manufacturer of a modulating non-condensing gas boiler so far. Space heat loss is 70k BTU/h and already have a 41 gal. indirect tank heater and my shower useage at only 2GPM (hot only) would indicate DHW load of at least 100k-120k output needed. That's the boiler output I have now and the DHW is acceptable. Unfortunately the two smallest of three space zones are BOTH only 14k each. Without a modulating firing rate, a typical 130k output boiler would be short cycling a lot delivering only 14k.

    What other brands are out there that installers like installing.

    Thanks, Ted

  2. #2
    In the trades Dana's Avatar
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    Jan 2009


    Glorified-tankless combi-heaters pretty much fill that bill.

    The RayPak XPak 85 is a finned water-tube boiler, 68,000BTU/hr out at max fire with a 4:1 turndown rato. With 17K at min-fire you'd be counting on it's hysteresis or bumping the temp up a bit to keep it from cycling on zone calls. It can run in condensing mode, but doesn't have to.

    The Rinnai E75C combi unit is pretty similar, 69K out max, 17K-in min.

    The Navien CH-180ASME also modulates down to 17K-in, with a much bigger 150K max, but the reputation & technical support for Navien in N.America is less than stellar. Web-forum complaints abound, but more often the not the issues are related to incompetent installation. Some folks do just fine with them for years, others... It's attractively cheap though ~$2K USD at internet pricing.

    These finned heat exchanger water tube boilers all have condensing potential, but only test out in the low-90s range on AFUE type testing, and are $500-1000 cheaper than most small mod-cons. (The Rinnai might be a bit higher than the others.)

    At 2gpm it only takes about 70KBTU to heat water from 35F to 105F (showering temp), so you'd be able to take endless showers even running it in combi-mode, but with the indirect operated as a priority zone you could even do higher GPM for reasonable amounts of time. I don't quite get how you think it'll need 100-120K to support your DHW loads WITH the indirect. Most homes do just fine with 40 gallon indirects and a 50K boiler, unless they have an oversized tub to fill.

    A 6" flue is kinda overkill for any of these, and even though they're forced draft you'd may run into issues if you have lateral runs more than a few feet with such an ovesized flue. Even active flue purges aren't guaranteed to be effective if the flue's total volume is way oversized for the BTU rate of the equipment.

    Which non-condensing modulating boiler did you come up with?

  3. #3


    Thanks very much for the alternatives. I'll look them up, but let me first respond to your questions.

    Baxi and Laars Endurance EPD110 are mod non-con's. And I already have a 41 gal BoilerMate on priority so getting a combi seemed like paying for something I didn't need. My current boiler puts out about 110m BTU/h output (1.0 GPH rate) and I can only get about a 30 minute shower before it starts to cool. I like even longer. The Boilermate ratings are a mystery to me but they suggest a much bigger output for good recovery. And wouldn't I have to heat the DHW to more like 125F so I wasn't using just the hot tap in the shower?

    Thanks very much

  4. #4
    In the trades Dana's Avatar
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    Jan 2009


    The EPD110 is another finned water tube boiler, but with a copper rather than stainless heat exchanger- same basic techology as the 2-stage RayPaks. The min-fire output on the EPD110 is ~54K, which means you'd need enough radiation to dump that much heat on each zone.

    With the indirect you have the issues of having sufficient delta-T on the internal heat exchangers and pumping rate to be able to deliver the full heat output of the boiler into the tank. But 2 gpm at the shower head is pretty close to 1000lbs of water per hour, times 70F rise is 70,000BTU/hr. If your boiler output temp is high enough and the pumping rate high enough that the heat exchanger in the indirect can move that much heat, you should be able to shower all day and night with a 40 gallon indirect, no matter what temp (above 105F) you have the indirect set to. The total heat required doesn't change whether you're mixing 140F water with the 35F cold side at the shower mixer or whether you're running 105F out of the tank at 2gpm with nothing being mixed in from the cold side. If properly set up, you'd be there with a 70K of boiler output.

    I'd forgotten about the Baxi Luna series. Min-mod on the smallest of those is ~35K, still way over your zone loads.

    But how much radiation do you have the smallest of those 14K zones? If it's only 25' of fin-tube you're stuck but if it's closer to 50' you'd be OK with the Baxi Luna 3.

    For endless showers on a marginal output boiler or water heater, you can't beat the benefits of a drainwater heat exchanger. A 3" x 60" or 4" x 48" or bigger returns half the heat that is (literally) flowing down the drain to the incoming water, cutting the heat that needs to be supplied by the hot water system (and it's fuel use) in half. In the US it's possible to buy the PowerPipe series at wholesale by opening an account with the distributor EFI (costs nothing, can be done over the phone), but in Canada the best price/performance deals seem to be the buy-direct pricing from EcoInnovation, even though both Sears and HomeDepot distribute the PowerPipe, it's at a very retail-type price.

    It's definitely better to go this route than oversizing the boiler for the zone-loads, especially of the oversized modulating boiler never actually modulates, but instead needs to run high-temp output all the time just to keep from short-cycling.

    How confident are you in your heat load numbers, and how were they derived?

  5. #5


    Thanks but I'm having a hard time keeping up with you.

    DHW: I understand about 105F vs 140F hot using the same BTus. Good point. But please look up the performance figures (recovery) for a 41 gal BoilerMate indirect heater. The BTU rqmt numbers are way larger than 70k. And the wife corrected me- we use a 40 gal tub more than 30 min showers. So your interesting drain recovery idea won't get pursued.

    Flu: lateral run out of boiler will be about 3'.

    Heat Loss: room by room using classic IBR factors. Have done about 15 of them. House is 2x6 frame 1 1/2 story, near coast, 2200SF, 1987, double pane, HDD/gal = K = 9.5. I'm confident.

    Small Zones & Short cycling: All radiators are Petite 7. The 14k zones are about 22'. Wouldn't a modulation burner be a big plus?



  6. #6
    In the trades Dana's Avatar
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    Jan 2009


    A 40 gallon tank can recover with a 30KBTU/hr input (like most standalone gas-fired tanks) or a 500KBTU/hr input (like a sidearm indirect in an apartment building). The only difference is the amount of time it takes. Recovery time performance has no bearing on the continuous flow can be achieved. Continous flow rates are determined solely by the rate at which BTU/hr in=BTU/hr out, which is a delta-T x lbs/hr number.

    What are you using for an outside design temperature? Being near "the coast" means almost nothing. Outside design temps quite differ by more than 20F if you're near south coast of Long Island vs. the northeastern coast of the Gulf of Maine or the Bay of Fundy. But for yuks, lets work backward from K-factor to calculate the implied outside design temp:

    Since K-factors are a base-65F derived number be sure to use the delta between the 99% outside design temp and 65F (the presumptive balance point) rather than say an 70F indoor temp when using fuel use to derive heat loads- it's not a big difference, but a difference nonetheless.

    A K-factor of 9.5 with with an 85% efficiency oil burner implies...:

    (0.85 x 138,000 x (1/9.5) )/24 = 514 BTU/degree-hour.

    To hit a heat load of 70,000BTU/hr means a design temp of:

    65F- (70,000/514)= -71F

    That's pretty damned cold- are you on the northeast coast of Baffin Island or something? ;-)

    Naw, it's warmer than that even there!

    The 99% outside design temp for Fairbanks AK is fully 40F warmer than that! "Near the coast" in Maine you're looking at no colder than about 0F for a design temp, coastal New Brunswick no colder than -5F. If we take -5F as an outside design temp, the delta is (65F- -5F=) 70F, and your heat load is about (514 BTU/degree hour x 70F = ) ~36,000BTU/hr. Even if you keep the place at 80F, and a balance point of 75F you're still looking at under 50KBTU/hr. Most 2200' homes in New England with any sort of air-tightness will come in under 50K @0F, many come in under 40K, even 2x4 houses w/storms over single-panes, not tight newer double panes and R19 2x6 framing like yours, with probably R30+ in the attic.

    To have heat load of 70K at any realistic outside design temp with a K-factor of 9.5 would mean the efficiency on the oil boiler would be something like 150%- ain't happenin'.

    Tell you what- download the NORA FSA calculator, and let the Broohaven Nat'l Labs boiler model guesstimate your actual heat load using your boiler & indirect size/characteristings along with your 9.5 K-factor, provided there is a listed city with a similar local climate to yours (or even a colder location.) My guess would be that even using their 99.5% design temps you're under 45K, since even the smallest oil boilers are going to be 2x oversized for what your actual heat load is.

    Also, since you're heating those (30 minutes x 2gpm) 60 gallon showers and/or 40 gallon daily tub-fills with the oil boiler, that 514 BTU/degree-hour constant is on the high side of the actual space heating load, unless you're using woodstoves or other serious auxilliary heat to offset oil use. You are high-volume hot water users compared to the US average, unless those are soaker-tub fills are regularly "a bath for two". ;-) The indirect should be sized for the tub-fills, the boiler for the true heat load, and if you're looking for the endless shower experience you can get it with a 50K boiler plus a drainwater heat exchanger (as my teenager proves fairly often.)

    Like many other fin tube, Petite 7 puts out ~600BTU/hr @ 180F AWT. At 22' with ~15,000BTU/in you're looking at ~200F boiler-output to actually balance, and not all of the combi-boilers will actually go that high. But if your real heat load is roughly half your 70K number (probably is), and those 14K zones are really 7K, you can still get design-day heat out of the fin-tube with 140F water, and a condensing HW heater like a Vertex or Polaris with a plate-type heat exchanger might be more appropriate if you like very even room temps and long cycles.

    Alternatively you'd probably do OK with a noo-skool 85-86% 50-60K-out cast-iron beastie with built-in outdoor reset that is also tolerant of low return water temps ( like the smallest Burnham ES2, ESC, or Series 3 or similar. ) The new generation cast iron boilers have smart controls to limit short cycling even when under-radiated making use of the boilers mass to deliver a temperature hysteresis around the outdoor-reset setpoint, and internal plumbing & control to tolerate even 110F return water temperatures. They run about ~$2K-USD, a bit less expensive than the modulating combi boilers, yet deliver similar comfort when used with outdoor reset. You can spend the difference in cost on a drainwater heat exchanger for enhanced showering performance. The indirect is (apparently) already big enough for your tub fills provided you set it's temp high enough.

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