Marc Posted December 4, 2010 Report Share Posted December 4, 2010 There are numerous things you need to check when this change is done. Gas is delivered to a normal home through a meter that normally supplies 250 cfh, or 250k btu. The meter must deliver enough gas to supply all appliances operating at the same time. So let's take a look at an all gas house. 250 cubic feet per hour? I'm not a plumber but that sounds like a low figure to me. Marc Quote Link to comment Share on other sites More sharing options...
David Meiland Posted December 4, 2010 Report Share Posted December 4, 2010 There is also the issue of the b-vent, which could be undersized for the additional btu output, especially if it is combined with the furnace. The tankless heaters I've installed do not use B vent? Are there models that can be connected to the existing B vent when a tank heater is removed? Quote Link to comment Share on other sites More sharing options...
dtontarski Posted December 7, 2010 Author Report Share Posted December 7, 2010 Quote: Originally posted by dtontarski Plus - We discussed that PEX should not be used as a PRV extension pipe material. Marc - Sorry for the delayed response. (It's hunting season....not inspecting season up here) You inquired as to whether I was referring to the Pressure Relief Valve when I used the abbreviation PRV - Yes I was. Since posting this, I have been doing some additional online research on this, and as usual, have come up with various opinions on the acceptability of using standard 3/4" PEX on this unit's PRV. First off, the opinions of most is that PEX is an approved Temperature & Pressure Relief Valve discharge piping material. However - one online plumbing forum poster contributed this: "Standard PEX is not allowed according to Watts. I know that there is going to be allot of plumbers out there that are going to say it can be and they do is all the time. As the fittings interior diameter is less than 3/4 inch. And according to the code the pipe cannot be downsized nor restricted. The only PEX that is allowed is the PEX discharge pipe supplied by the manufacture for that purpose. As the fittings are the correct size for the valve. And the pipe has to be secured to the tank. I have yet been able to find anywhere that you can find that correct fitting by itself. Nor a tool to stretch the PEX over the fitting and properly secure it." I spent some time trying to verify this on the Watts site, but I could not. I did however find PEX discharge pipes on both the Reliance and the A.O. Smith sites. (and as previously posted - the Rinnai representative I spoke to implied 3/4" PEX was not approved) One of the key issues that I had not considered prior to researching this, as the above poster pointed out was that "the pipe has to be secured". Further research defined this as secured 32" oc.....because as another poster cited: "Nobody wants TPRV discharge "a-flipping" and "a-flopping" around when exposed to high temp or high pressure relief evacuation." This was likened to a fire hose that got away from the fire fighter....which I thought was a great visual. One of the biggest points of contention was regarding the requirement that discharge piping could not be downsized nor restricted, and what that meant in terms of using 3/4" standard PEX. One poster claimed that this was referring to the nominal size, and therefore even though the inside diameter of 3/4" PEX is smaller than this, that this did not matter. The majority of the posters disagreed with this and stated that the inside diameter was what should be considered....some of what I have previously posted supports this. So, for the moment, I'm going to base my call on what the local code guys are allowing, but I will likely call out that if PEX is being used, that it should be secured in order to prevent "a-flipping and a-flopping"....regardless if this is a local code guy requirement or not. Further dialogue, opinions, codes, manufacturer's listing information, etc. would be appreciated on the discharge piping sizing issue. Thanks. Quote Link to comment Share on other sites More sharing options...
charlieb Posted December 7, 2010 Report Share Posted December 7, 2010 It's clear you seek to report things accurately. I believe most if not all of us here also have the same desire. IMO the order we rank opinions is important. In this example I would first read the manual on the water heater. You may find it interesting to know I recently researched an electric on demand installation, I seldom see electric models, and was surprised to find the manufacturer would did not approve the used of PEX within 3 feet of the appliance. I can under stand your contacting the manufacturer about the reduced capacity of the lines but as Jim stated, the design of the lines in the house are addressed by the codes. I would research the specific brand of PEX to determine if the PEX manufacturer approves connecting their product directly to an on demand WH. I have not found any manufacturers that approve a direct connection to a gas WH. I have also found one that does approve a direct connection to an electric WH. I've not researched the product in a while but the last time I did, none made mention of an on demand WH. Regarding the use of PEX for the PR valve discharge line, I have found it approved for use with a TPR by some manufacturers. None have spoken on it's use with a PR valve. All manufacturer's have requirements for securing the pipe. It is only at this point that I look the installation up in the applicable code. It matters not to me what the AHJ does or does not enforce. If the AHJ does not enforce a particular section of any code I'll inform a client of that but only after educating them about the implications of the defect. I submit this letter as a testimony to this fact. Click to Enlarge 77.45 KB This letter was forwarded by the client to me for my comments. The subject was a sorry Manabloc installation. Having researched the product I had all I needed to outline his options. I find I seldom have the need to call a manufacturer. I use their installation instructions for the basis of my opinion. Quote Link to comment Share on other sites More sharing options...
hausdok Posted December 7, 2010 Report Share Posted December 7, 2010 Structualbility? Guess that was written in hillbillity. ONE TEAM - ONE FIGHT!!! Mike Quote Link to comment Share on other sites More sharing options...
Steve Stanczyk Posted December 8, 2010 Report Share Posted December 8, 2010 There are numerous things you need to check when this change is done. Gas is delivered to a normal home through a meter that normally supplies 250 cfh, or 250k btu. The meter must deliver enough gas to supply all appliances operating at the same time. So let's take a look at an all gas house. 250 cubic feet per hour? I'm not a plumber but that sounds like a low figure to me. Marc That is the standard issued meter up here in Washington. Today's inspection had a 250 for the main house and a separate 175 for the mother-in-law apartment. Quote Link to comment Share on other sites More sharing options...
charlieb Posted December 8, 2010 Report Share Posted December 8, 2010 Structualbility? Guess that was written in hillbillity. ONE TEAM - ONE FIGHT!!! Mike I have an act I perform with clients who are new to the area. I extend my right hand and say "Welcome to Miz zippi". Sometimes I perform this act numerous time throughout the inspection. The letter still makes me chuckle. The issue was not the structure but rather the lack of support for the pipes attached to the manablock.......but y'all understand that. The City of Hillbilly does not. Quote Link to comment Share on other sites More sharing options...
MarlianJoeboy Posted December 11, 2019 Report Share Posted December 11, 2019 Wow! Just when I thought I knew my way around this unit. I come across this. Thanks for the share guys Quote Link to comment Share on other sites More sharing options...
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