Proper venting of domestic water heater

Stokehold

I am installing an American 50,000 BTU propane power vented heater model PVG6250T60PV. This will be used not only for domestic water but also a radiant heat zone in the basement.
For a horizontal through the wall installation, the venting usually sloped upwards with approx. 1/8" of rise per five foot of pipe away from the power vent assembly. If condensation was a problem, a condensate trap was used.
This particular install requires the vent pipe to be pitched 1/8" downward from the power vent and makes no reference at all to an alternate upward pitch with condensate trap. American simply states they want the condensate to flow away from the heater. Incidentally, Bradford White also wants the downward pitch but allows for an alternate install using upward pitch and trap. American also does not want a termination elbow but requires the termination to extend 12" straight past the wall with a rodent screen if needed.
None of this makes any sense because flue gases are going to vent much more efficiently traveling upwards irregardless of a power vent.
Having to maintain that downward pitch on longer more complicated runs (like mine) can stack up and is causing some problems.
My questions here are:

Why did they change the venting?
Can I still pitch the pipe upwards and use a condensate trap?
Why would condensation be a problem in a horizontal install but not a vertical?

American has not helped me at all on these issues. I cannot get past the help desk and you probably understand the frustration there.

Harvey Ramer

You can put a condensate trap where it's needed if you install it properly. Have you calculated the total equivalent length of your vent run and compared it to the specs in the manual? It wouldn't hurt to have a professional do the venting for you. Or at the very least, get it inspected after you are done. Best to play it safe with combustion products.

Also, of equal importance. Are you isolating your radiant loop from your domestic hot water with a heat exchanger? The 2 waters are not allowed to mix. If they do the implications could be a serious health risk or even death.

Jamie Hall

The thing to note here is that the condensate has to drain somewhere. If it is draining back to the heater, you must have the condensate trap.

The exhaust gas, however, with a power vent will work equally well with either slope -- and sloping away from the heater eliminates all of the problems associated with the condensate trap and drain (although it may be a little hard on the flowers or what have you outside... it should certainly not drip on concrete!)

hot_rod

if it is used for heating and has the potential to run a lot you will be surprised how much condensate you need to deal with, plan on that if you slope out. Also the iceberg that may develop where it terminates.

I'd also caution against mixing potable and heating water.

Stokehold

Thanks for the feed back! I really appreciate all comments and
I understand about the condensation and the need to either drain outside on a down slope OR catch the condensate in a trap if the vent is sloped upwards.
What I don't understand is why American Water Heater gives no provision concerning this model for using an up slope and trap. They want the vent pipe sloped at 1/8" down per five ft.
I need to run upwards for this install and want to know if I can safely circumvent their install directions and use a condensate trap. Their technical department seems unable to answer this simple question. As stated before, other manufacturers such as Bradford White allow either as long as the condensate is drained and does not enter the blower. Also, why does it seem condensation is more of an issue with a horizontal install? Are you not going to have this problem on a vertical install if the vent passes through an unheated area?
As far as using potable water for heating, these newer high output water heaters have side taps specifically for connecting a coil and air handler. Some radiant floor companies use the open system DWH for both potable as well as heat. Interesting to note here is that those particular systems draw makeup water into the tank through the radiant tubing in the floor. This way the water is always clean and never stagnates in the heating system. At first glance, you might think this would cool the floor down, but unless you are taking a two hour shower, the thermal mass of a heated concrete floor will not cool down that quickly. Once the potable water valve closes, in this case a shower, their is no longer a need for makeup water and the circulators continue to move heated water through the floor. Unless you need to run a glycol mix or are attaching an outside boiler to this setup, there doesn't appear to be a need for a heat exchanger. This is, of course, assuming that the components in the heating side contain no lead and are compatible with potable water. The PEX tubing certainly shouldn't pose any threat. There are also less components because this is an open system and generally will not require expansion tank, air separator, etc.
Again, all comments are appreciated!

hot_rod

It may be the way the manufacturer had that particular product listed and tested?

Yeah we have heard that concept of "free cooling" by running cold water through the tube before it hits the water heater

The issue becomes the temperature being below what is required to prevent bacteria growth, and the potential to have a lot of loops that don't get circulated daily with 140° plus temperatures. So studies now say 158° throughout the system to kill bacteria.




I understand combined systems are still promoted, but it makes the licensed plumbers very nervous as they bear the responsibility & liability should some get sick, or dead.

The plumbers code is "To Protect the Health of the Nation"

SWEI

Stokehold said:

these newer high output water heaters have side taps specifically for connecting a coil and air handler.

Right, and that's what they got their listing for -- usually with a rather short limit on the pipe run. They are typically programmed to cycle 140+°F water through the coil every so often even when there is no heating call.

Some radiant floor companies use the open system DWH for both potable as well as heat.

Some internet parts pushers that is.

Jamie Hall

Bottom line here: if you want to stay safe and healthy, any hot water which is stored for any length of time must be at 140 or higher (this, incidentally, can be hard to do with some water heaters -- some of the newer ones can't be set that high...). Then you mix it down to get safe water at the tap.

Can you do that running your water through your radiant loop? You don't need to run "some" water through it; you need to run enough water through it so that the whole loop gets above 140. That doesn't sound like a radiant heating system to me, but maybe I'm missing something.

And don't count on just drinking bottled water. Some of the worst nasties (e.g. Legionaire's) are acquired through inhaling the mist... from your shower...

Shortened bottom line: bad idea.

Stokehold

I want to thank you guys for your input and expertise! It changes my perspective on using a potable water heater for radiant flooring. Everything you stated makes perfect sense and I am seriously thinking about scrapping the whole plan.
BUT, not to be redundant, I want to absolutely understand:
IF the makeup water to the DHW is always being pulled through the radiant zone, then the water in the zone would always be fresh, even during the summer months. This is assuming all loops are perfectly balanced and flow equally. The way this system was explained to me is that makeup water to the heater always flows through the floor first, even during the heating season and that the cold water cannot really cool down the thermal mass of a concrete floor unless your potable hot water needs are excessive. So, if clean water flows through the system every time a shower, sink, dish washer, etc. is used, how can the water stagnate and cause bacteria growth? The loops are being used as a cold supply line to the DWH. If bacteria can still develop here, then why is this not a problem in the cold water lines themselves. On that point, we have a partial bathroom in this home that sees little use. I advise my wife to run water a minimum of five minutes every week or so to prevent stagnation. Yes, if the heating loops are dormant for any length of time, bacteria is a major concern. Again, I apologize for being redundant and I do not want to appear thick headed, but I have to absolutely understand. You guys have pretty much convinced me though: BAD IDEA!
One final question on the original post regarding venting. Is ice a problem in a vertical vent traveling approx. 18 ft. through almost entirely unheated area? Is a heating tape required here?

SWEI

Stokehold said:

IF the makeup water to the DHW is always being pulled through the radiant zone, then the water in the zone would always be fresh, even during the summer months. This is assuming all loops are perfectly balanced and flow equally. The way this system was explained to me is that makeup water to the heater always flows through the floor first, even during the heating season and that the cold water cannot really cool down the thermal mass of a concrete floor unless your potable hot water needs are excessive. So, if clean water flows through the system every time a shower, sink, dish washer, etc. is used, how can the water stagnate and cause bacteria growth? The loops are being used as a cold supply line to the DWH. If bacteria can still develop here, then why is this not a problem in the cold water lines themselves.

The growth rate of Legionella is highly dependent on temperature. Below 68°F it goes dormant. Above 140°F it dies. As you pull cold groundwater through a radiant floor in the summer, it will warm up. When you turn off the hot tap, those floor loops will stagnate, probably somewhere in the 75-80+°F range during summer. Parts of the floor where the sun shines will probably hit 90°F. PEX is a wonderful material, but like all plastics biofilms tend to form there.

https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_7.html

Stokehold

This topic is really beginning to broaden. Actually, it's getting kind of scary! It would probably be better to put in a tankless heater for the radiant heat and be done with it. I am certainly not going to fire a 50,000 BTU tank just to heat a few basement loops. How long does this stagnation take? There is another issue here:
My potable water source is a 1/2 acre pond approx. eight feet in depth that is treated with alum for coagulation of fine particulate and chlorine for bacteria. The water is then filtered through sand and charcoal. These systems are very common in rural northeast Ohio because well quality varies so much.
It has been a very hot dry summer and I am sure the water that is being pumped from that source is above 68°. My home is approx. 84 ft. long. The longest cold water run is approx. 60 ft.
If I understand you correctly, if that "cold" water sits for any length of time in that longer run, it can stagnate within that potable piping and there could be a chance for Legionella? There doesn't appear to be any difference in this scenario than the water moving through the floor loops. If stagnation can occur that quickly in the loops, then it would seem that that is likely within the entire potable system.
Final question:
IF an open system is used for DHW and radiant heat, IF the makeup water to the tank is always moving through the floor first, and IF the makeup water returning from said radiant heat loops enters a tank with a min. 140° temperature, is the system safe? Still risky?

Jamie Hall

On the stagnant water in the cold water piping -- two thoughts. First, 60 feet of half inch copper is about half a gallon of water. Therefore, if you run about half a gallon before showering or drinking, you've purged that 60 feet. Probably good practice. Second, is there any chlorine residual after the charcoal filter? I'd expect not, but if there is then you have very little to worry about indeed. On the other hand, you could still have a potential problem (if there is no residual) with water in the radiant loops, although you could potentially resort to running the water long enough to purge all of them too.

I at least would rather see you go to a closed radiant heat loop system, running at whatever temperature is needed for it (probably around 90 at the most), fired either with a high efficiency tankless or, better (they last longer) with a high efficiency boiler and isolated from the domestic water entirely. I'd even go so far as to put an rpz backflow preventer on the fill connection, even if the fill valve was "always" closed. Yes, it is a little more complex and yes, it is a little more expensive -- but I've always been a belt and suspenders kind of guy when it comes to safety...

hot_rod

I was thinking along the same lines as Jamie, suppose you brush your teeth and only flow a small amount of water, you may not flush the loops

100 feet of 1/2 pex holds a gallon of water. How many feet of tube will be in the loops? You may need to run 5, 10 gallons every time. That is also wasting chlorinated and filtered water into the septic. Seems a waste and un needed expense?

A simple Hx, pump and fittings would give you piece of mind and protect your families health

Stokehold

First, I want to thank you guys again for your comments. I am getting a bit of education here!
This is making more sense now. Actually, I would have to run 11.750 gallons through this zone to completely purge. I had this very discussion with my better half last evening. We do try to conserve water, especially during the dry conditions experienced this summer.
A boiler does make more sense if I put a coil in my furnace. I currently have a four ton geo thermal unit with LP backup that keeps the house like a freezer in the summer, but I am not too fond of it when the temps dip below 20°. However, this would be somewhat pricey.
I guess the best thing to do is install the DWH and isolate the radiant. I actually have a brand new flat plate Hx around here somewhere.
This all leads back to my original post on proper venting. I will not be able to vent horizontally because of clearances to windows, doors, corners etc.
I have found a way to put a vertical vent through the roof without too much difficulty. The problem is that 10ft. of the 3" PVC pipe will be exposed in an isolated corner of the garage. Two questions here:
1) Is it OK to have that pipe exposed, or do I have to construct a chase?
2) Since the vent is going to be almost entirely run through an unheated section of the home, is ice going to be a problem? Heating tape required here?