Calculating Propane Usage and BTUs for Tankless Hot Water System

Discussion in 'Tankless Water Heater Forum' started by Diavolicchio, Dec 11, 2009.

  1. Runs with bison

    Runs with bison Member

    Aug 23, 2009
    This seems to be pretty common with small vendors. I'm of the opinion that it is best not to oversell something. It is better to over deliver than under deliver. It doesn't do anyone any good to sell somebody something that doesn't fit their application. My personal numbers might come out wrong at times because I missed something, but it isn't intentional or an attempt to misrepresent.

    I used the GFX data to work up heat transfer coefficients and create estimates of the maximum I might expect to recover from the two showers it could be connected to. With my low flows and short showers it works out to only about 30 ccf/year with a 60" G3 GFX in the 3" drain size. It wouldn't surprise me if it was 5 ccf/year less due to dead volume/lag effects--this is a large relative effect for our short duration shower habits. The 60" S3 would yield about 28 ccf/year but would allow for three simultaneous shower operation.

    The 60" would be a bit tight, but should fit my application. Failing that I would drop down to 40".

    That's a good point about taking less pressure drop than a tankless.

    The typical target market for these is pairing with electric water heaters since the energy cost for heating water that way is about twice as great. I can't support much capital at $25-30 year savings...but at $50-60/year I could make a case for it. If we took 10-15 minute showers and/or 2.5 gpm showers then it would also greatly improve the economics. DWHR makes a fair bit of sense for the colder climates with several months more per year of very cold supply water.
  2. Dana

    Dana In the trades

    Jan 14, 2009
    Be sure not to confuse GFX Technology with Eco-GFX. There has been some (intentional, IMHO) obfuscation using similar model names, which helps to confuse the sitution. In NRCan documentation GFX usually refers to Eco-GFX. GFX-Technology is apparently currently reselling WaterCycles equipment to the US market, and it's at the lower-performance end of the spectrum on the NRCan standardized 2.5gpm tests. ALL will do significantly better percentage-wise at the lower flows you're talking.

    There can be paybacks beyond the annual CCF when designing a system. The dynamic BTU/hr or kilowatt return is real power, and can be used to reduce the size of both the storage and the burner/heater behind it. If you can knock 30K off the boiler size or 20 gallons or 50F off the storage and still meet the peak load, it can mostly pay for itself up front in reduced hardware cost.

    For me it allows me to run the Rube-Goldberg contraption of a combi-system at a much more favorable burn rate for heating efficiency while still guaranteeing I never run out of hot water for showering. And by avoiding a situation where mi esposa might be screamin' at me or the kid from a tepid shower, it's paid for itself already! :)

    NRCan's models aren't terrible, and will probably model your lower-flow situation reasonably, but with shorter, fewer, lower flow showers you're still only looking at a few tens of CCF, provided your hot water heating system is better than 50% efficient.


    There's a lot in there- look at figure 9- while a PowerPipe may be lower head than a tankless, most of the competition isn't. (The Retherm 60 does OK though, but it's heat transfer efficiency is somewhat lower.)

    (My kid probably uses more hot water in showers than your whole family does.)
  3. Diavolicchio

    Diavolicchio New Member

    Dec 11, 2009
    Union, Maine (Midcoast) USA
    I've discovered a decent amount of information online regarding the Canadian version of the GFX known as the Power-Pipe ( If you're considering a drain heat recovery system, please at least consider the following information before making any decisions about the type you end up buying:

    * * * * *

    [FONT=&quot]"The Powerpipe is an illegal copy of the original GFX. The Powerpipe also uses recycled copper that is not recommended for potable water by the US and Canadian copper association due to contamination." … “The posted results on the renewability (POWERPIPE) websites are false. The testing at Natural Resources Canada show that these numbers are far from the truth. Heat recovery from a Powerpipe is 30-35% while the GFX is 40 to 50% as posted on the WWW.GFXSTAR.CA website. BUYER BEWARE OF FALSE CLAIMS MADE BY RENEWABILITY†(from[/FONT]

    [FONT=&quot]“Purchased this and found out the building inspector refused to authorize it. Something to do with the fact the UL certification is not applicable to potable water and since the device does not have ASTMB88 stamped on its copper, it was not considered safe for potable water.†[FONT=&quot] (from[/FONT][/FONT]

    [FONT=&quot]“Powerpipe is made with recycled copper from China. The company makes false claims. I purchased 4 units from power-pipe and they were recalled due to lead in the braze. Two of the replaced units were leaking at the joint and 2 others were clogged with metal shavings in the fresh water feed. Highly not recommended.[FONT=&quot]…How does ********* EXPLAIN THIS? I looked at one of these at RONA and noticed only a UL label on the pipe. No NSF 61 (toxicity tests for potable water) was written on the pipe. I called Renewability and they said they were UL certified for use with potable water. I did some more research and it looks like they make this same claim on several Powerpipe documentation. When asked if Powerpipe was safe for use with potable water, UL answered..."Searching for file number MH29466, I see that the file is held by the company Renewable Energy Inc. It appears that their Power-Pipe Series heat exchangers are listed as Specialty Heating-Cooling Appliance Accessories under UL Category Code MJAT (USA) and MJAT7 (Canada), but they do not appear to be certified to any drinking water safety standards."… "Powerpipe is made with recycled copper from China. The company makes false claims. I purchased 4 units from power-pipe and they were recalled due to lead in the braze. Two of the replaced units were leaking at the joint and 2 others were clogged with metal shavings in the fresh water feed. Highly not recommended… To set the record straight - Powerpipe is an IMITATION of GFX. “ (from[/FONT][/FONT]

    [FONT=&quot]“To set the record straight - Powerpipe is†a toxic-GFX not approved for potable water; advertised by Conservation Mart as “Power-Pipe™ (formerly known as GFX)…†@[/FONT]

    * * * * *

    I'm not endorsing any particular model or manufacturer; I simply thought that people considering a GFX should consider this information before making any rash decisions about what to buy and from whom.

  4. Dana

    Dana In the trades

    Jan 14, 2009
    Diavolicchio, MOST manufacturers of drainwater heat recovery heat exchangers are in Canada, not just Renewability/PowerPipe. (Watercycles, Retherm, Ecoinnovation, etc.)

    Take all that crap you read about licensing & labeling issues with a pound (not a mere grain) of salt. This is an industry that's been in a pissin' match for over a decade. Until/unless there's been a ruling of LAW that a patent has been violated or labeling mis-used or any of the other allegations floating around out there, I prefer to just stay out of the splash and rely on 3rd party testing on performance data. YMMV. The US & Canada are both first-world countries with first-world legal systems- let the players duke it out in court if they think they have a case. Repeating the allegations in a forum posting adds no light, only heat to the subject (and not to the incoming water.)

    Ever since Renewability's number started edging out the competition the grousing has gotten louder. But if they have a case they should present the evidence to a judge. Neither you nor I are in a position to verify the validity of the above claims, no basis on which to accept the veracity of the folks making them.

    Indeed, Beauchemin of Ecoinnovation seems to spend more time bitchin' online about Renewabilty than properly marketing his own stuff. But what's the source of his cred over the other players? As a disinterested party all I see is assertions being made by a company whose goods under-perform those of the company they're bad-mouthing in the NRCan 3rd party testing. I bear him/them no ill will, but I'd prefer it if they'd just put-up or shut-up, take it to court if there's a case to be made. (Get him on the phone and I'm sure you'll get an earful! :eek: )

    And since when did "Anonymous user" on some web forum have any cred?

    I'll take NRCan's 3rd party test results over what anybody else has to say, and let the rest of the BS twist in the wind. There's more smokescreen than substance behind it, near as I can tell.
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