Tankless with varying incoming pressure from well tank/pump?

[rick.a]

I have a small house with a well and pressure tank set to produce between 30-50 lbs. pressure. This works great. We now want (actually need to for space considerations) to install a tankless WH but wonder if the varying pressure from the well tank is going to screw things up with the tankless which probably likes constant flow rates. Tankless will be Rinnai 53i. Small house with 2.5 gph shower as the longest HW draw. Do you think it will be OK?
Rick.

[jadnashua]

What is your supply water temperature year-round? Does it change much in the winter? Compare your incoming water temp with the specs to see what temperature rise you can get out of it, it may be okay in the summer if the water temps are higher, but not in the winter. And, it's not the duration of the draw, but the maximum draw you might want. You can't prevent someone from turning on the washing machine, dishwasher, or a faucet to wash their hands while you are in the shower. If you have a boiler, an indirect may be much more economical, and the tanks are smaller (typically) than a stand-alone tank.

[rick.a]

Thanks for the reply. Winter incoming water is about 45 deg. Summer is about 55. The unit that we have spec'ed should give us the flow rate that we need with the 60 deg rise in the winter. What I do question is whether the fluctuating pressure will cause problems with the Rinnai unit if the pressure goes down during a HW draw.
Rick.

[Dana]

Thanks for the reply. Winter incoming water is about 45 deg. Summer is about 55. The unit that we have spec'ed should give us the flow rate that we need with the 60 deg rise in the winter. What I do question is whether the fluctuating pressure will cause problems with the Rinnai unit if the pressure goes down during a HW draw.
Rick.

As long at the pressure stays within spec you shouldn't have any pressure. At low/very-low pressures (15psi or less) many tankless units have issues, but not 30-50pis.

[rick.a]

Thanks Dana for the confirmation.

By the way, do you know if the plumbing code in MA requires that the T/P relief valve be plumbed to a drain if using a tankless in a cellar (actually a crawlspace with concrete floor)?

Rick

[valveman]

I get a lot of calls from people with this problem. At 30 PSI the system only has about half the pressure than when at 50 PSI. So the flow through the showerhead and tankless heater vary widely. Many times the flow at low pressure is inadequate to keep the heater working. Then at higher pressure it fires off again. A 40 PSI Cycle Stop Valve will maintain 40 PSI constant for as long as you are in the shower. This keeps the pressure and flow steady and the tankless heater never shuts down. When used with a small pressure tank, the pump is running and the CSV holding a steady 40 PSI before you get the water temp adjusted in the shower. When used with a big tank, you just have to wait for the tank to empty, the pump to start, and the pressure to get to 40 before everything steadies out.

[Tom Sawyer]

30/50 won't be a problem. Tankless heaters have a valve in them that adjusts the fire to the flow rater through the unit. We have installed many tankless heaters on well systems with no issues other than water quality.

[LLigetfa]

30/50 won't be a problem...One should not make a blanket statement like that. There is another thread here where a low flow shower head was a problem. The pressure wasn't mentioned but the difference in flow at 30 PSI versus 50 PSI could make the difference. Mind you, something like a low flow shower head could be mitigated. I like valveman's suggestion to go to a constant pressure system.

[Tom Sawyer]

Let's see now, a couple grand for the tankless and then another grand or so for the CSV, yep that makes sense.

[LLigetfa]

...and then another grand or so for the CSV, yep that makes sense.Not sure where you are getting your prices. I'm seeing $200 for the model CSV1W. If I wasn't limited by my micronizer, I'd drop $200 in a heartbeat to get good constant pressure.
http://www.cyclestopvalves.com/st-viewcat.php?cid=11

[Tom Sawyer]

Someone gonna install that for free? He needs to change the expansion tank also. And why go through all of that when the chances are he doesn't need too? If his system is maintaining 30/50 he should be fine.

[valveman]

A shower head that puts out 2.5 GPM at 40 PSI, will do less than 2 GPM at 30 PSI, and more than 3 GPM at 50 PSI. Varying pressure in a shower is annoying and makes it hard to keep the temp adjusted in the shower. Many times the tankless heater won’t stay on because of the varying flow caused by the varying pressure. Constant pressure keeps the flow constant and the temperature from a tankless heater constant.

Depending on which model you choose, the CSV will cost anywhere from $90 to $245. This size CSV can be used with a 4.4 gallon ($75 tank) instead of an 80 gallon ($500 tank). CSV’s always more than offset their cost by greatly reducing the size of pressure tank needed. A CSV that cost $925 will control a 150 GPM pump with as little as a 44 gallon size tank. A system that size without a CSV would need a minimum of (six) 80 gallon size tanks. So a $925 CSV would save you $3,000 worth of tanks and do a much better job.

The CSV will also work with a micronizer. You just need to set the CSV close to the off pressure of the switch. Ie; 40/60 switch, set the CSV at 58 PSI.

[LLigetfa]

Someone gonna install that for free?Sounds strange, coming from a DIYer... As for the expansion tank, we don't even know what the OP has or if it even needs changing.

Anyway... sounds like you've already formed an opinion on CSVs and I'm not trying to change it. Just don't care for misinformation and FUD. I never suggested the OP had to go with a CSV, only said that I like valveman's suggestion to go to a constant pressure system. If a low flow shower head presents a problem, there is always the option to switch it out. God knows, I pay a lot of money to condition my water and I want a good constant high pressure with good flow in the shower. Not everyone does.

[LLigetfa]

The CSV will also work with a micronizer. You just need to set the CSV close to the off pressure of the switch. Ie; 40/60 switch, set the CSV at 58 PSI.I don't want to derail this thread, but I will respond to this statement. My micronizer stops sucking at 40 PSI because the flow rate at that pressure is reduced. A CSV will flow limit at or above the setpoint so for the duration of the shower, there will be no aeration at the micronizer and the only aeration would be in the aerator tank which is considerably less. Any iron that does not oxidize and precipitate will pass through the filter and foul the softener beads. What gets past the softener smell like a bloody nose in the shower.

[valveman]

If your micronizer stops sucking at 40 PSI, it is already not working during the upper half of your 30/50 cycle. So I guess your hydro tank is large enough that you get the aeration that you need? That is kind of the same thing that happens when the pressure goes above the setting of a CSV. I have been told this still allows plenty of aeration, by many who have this type system.

[Tom Sawyer]

What I am saying is that we have installed over a hundred tankless units on well systems running 30/50 and have had zero pressure problems with them. They are designed to handle pressure differences. That's the whole deal with them. Open one faucet get hot water, open another and the fire gets bigger and you get hot water. I suppose that if he DOES have a problem, installing a csv might be a solution but I would just up the pressure switch to 40/60

[valveman]

30/50, 40/60, or 50/70 it doesn’t matter. The same showerhead will still flow less water when you are at the low end of the pressure than when you are at the high end. When the pressure to the showerhead varies, so does the flow rate and temperature. What I hear is when the pressure and flow rate is low, many times the tankless heater won’t fire off. When the pressure and flow is high, you need to add more cold water to the mix. Tankless heater or not, varying pressure and flow in the shower can make maintaining the water temperature a problem. This is unlike city water pressure, which stays fairly constant.

Of course all the people I hear from have this problem. So I don’t know how many people do not have this problem or just learn to put up with it. If you have this problem, I know constant pressure from your pump will solve it. If you don’t have this problem, then constant pressure from your well pump just solves a lot of other problems.

[Tom Sawyer]

http://www.rinnai.us/documentation/downloads/U287-182100_V53i_and_V53e_Manual_EN_FR.pdf

Rinnai and every other tankless that I have installed have a minimum pressure requirement of 20lbs which is a good 10 lbs below pump cut in. Does anybody really think that tankless manufacturers would manufacture a product that could only be used on city water? Above is the manual link for a rinnai V53. Note that the unit ( and others ) are designed to modulate the fire in order to compensate for varying flow and pressure rates. Again, out of a few hundred installed, low or varying pressure has never been a problem.

[valveman]

Again, I get a few hundred calls every year where varying flow and pressure from well systems are a problem for tankless water heaters. People figure out pretty quickly that the problem happens when the pressure from the well pump system is varying. Since there is actually nothing wrong with the tankless heater, they probably don’t call the person who installed it. They search for ways to stop the pump pressure from varying, which is why I get a lot of these calls.

What they tell me is that when running one low flow shower head or one small sink faucet, the tankless heater only works during the higher pressure part of the pumps cycle. Which means there is not enough flow at low pressure to fire off the heater. Keeping the pressure constant also keeps the flow and temperature constant. This has made a lot of well owners happy with their tankless heaters, and kept the plumber from getting calls to replace them.

[Tom Sawyer]

If that's so then there is an issue with the tankless heater

[LLigetfa]

If your micronizer stops sucking at 40 PSI, it is already not working during the upper half of your 30/50 cycle. So I guess your hydro tank is large enough that you get the aeration that you need?Yes, but probably only because the micronizer aerated water already in the tank from the first half of the cycle mixes with the non-aerated water from the second half of the cycle. Only about 21% of the air is oxygen and I don't know how much of it gets consumed or how fast, but the consumed oxygen in the tank quickly gets replenished on the next pump cycle. A fish tank without an aerator still has some oxygen from surface exposure but the fish sure notice the difference.

[valveman]

Hot Water Capacity
0.6 to 5.3 GPM at 45°F Rise

“When I was using the hot water, the water got cold.
If you adjusted the flow from the tap to lessen it, you
may have gone below the minimum flow required. The
Rinnai water heater requires a minimum flow rate to
operate. (See the specification page for the flow rate
of your model.)”

“Ensure you have at least the minimum flow rate required to fire unit.”
“18. What is the minimum water flow required to operate a Rinnai tankless water heater?
Please keep in mind that the Rinnai tankless water heater needs to see over 0.6 gallons per minute of water flow through the hot side to ignite and to stay in operation. If the flow rate falls below this level, the unit will turn off because it senses that hot water is no longer needed. There are several possible solutions to minimum flow rate issues: lowering the temperature on the unit to a more comfortable temperature to avoid cutting in too much cold water, cleaning the inlet water filter on the cold water inlet of the unit (sediment build up in filter can decrease flow into the unit), cleaning or removing the aerators from showerheads or fixtures, or replacing low flow showerheads or fixtures.”


Anyway you slice it, low flow through tankless water heaters is a problem. The more your pressure varies, the harder it is to maintain the minimum flow required to keep the burner on. The best I can tell it has a turbine type flow sensor. Flow sensors are notoriously unreliable and troublesome. If you gradually bring the flow up to .6 gpm, the turbine probably won’t start spinning. If you abruptly turn on more than .6 gpm, the turbine flow sensor will probably start spinning. That is until there is a little build up or wear on the flow sensor. And I have never seen a flow sensor that is accurate enough to work at exactly .6 gpm.

Even if everything is working perfectly, and you mix in some cold water to a low flow shower head, you may have .6 gpm flowing at high pressure, but not at the lower pressure. So the burner turns on and off during a shower, which is the complaint I always hear. The manufacturer even says…. “There are several possible solutions to minimum flow rate issues”. So there are ISSUES with low flow.


Their solutions include cleaning the water filter, removing aerators, or replacing low flow showerheads. All of these solutions are ways to increase the flow. Maintaining constant pressure from the well pump will also increase flow, compared to letting the pressure decrease as it does on the low end of any pressure switch setting.

[Tom Sawyer]

well then, that's it. From now on, every tankless heater that gets installed in residence with a well is going to need a CSV installed, so customers can expect to add another 5 bills or so to an installation that is already costing them 25 hundred or so. I'll be sure and order a case so's I have them on hand LOL

[valveman]

If the well pump had been set up correctly to begin with, it would already have a CSV and small pressure tank. There would be no problem with varying pressure for the water heater. There would be no excessive cycling, so the pump/motor, pressure tank, pressure switch, check valve, and control box would all last much longer. And the homeowners would already be enjoying city like, constant pressure.

If the well pump was not set up correctly, this would be your chance to make it so. Then the homeowners would be praising you for giving them the best shower pressure they have ever experienced, plus be able to take as long a shower as they want, because of unlimited amounts of hot water from the tankless heater.

Adding a CSV to an existing system will cost from $90 to $245. If the CSV had been installed with a small tank originally, it would have saved about $300 over using a large pressure tank. If the system was originally installed with too small a tank, the money that wasn’t spent on a large tank, can be put to better use by installing a CSV now.

There are really only two reasons a CSV is not used on every pump system. Either the pump installer isn’t experienced enough to understand all the problems a CSV can solve, and all the benefits for the customer. Or the installer does understand all the problems a CSV can solve, and doesn’t want his customers enjoying those benefits and cost savings.

[Tom Sawyer]

Nice post, thanks

[LLigetfa]

Now if only we could solve the recirc problem so easily. How to get instant hot water at the end of a long line? Used to be, you installed a recirc pump but now with tankless, that won't work unless the pump exceeds the minimum flow rate.

[rick.a]

Hi, I'm back. Well, this thread certainly grew some legs.

Ok, this is what I have and what I intend to do. Unless you talk me out of it. :-)

I have a small cottage with just my wife and myself. I modified the crappy orignial well setup that this place came with 4 years ago with info. that I learned from this forum, which I consider quite invaluable. I have a 1/2 HP Goulds J5S pump (came with house) sitting in a pump house over a shallow well, next to a lake. Water is 15 ft down, and only 2 feet deep, but has never run out. The house is back 150 ft from the well and about 60 ft HIGHER. I have a 4 year old 20 gal. Wellmate low profile pressure tank in my non freezing crawlspace with a 30-50 switch. 3/4 inch PE running from pump up to the house. Everything currently works GREAT. Except for the massive 40 gal powervent Rheem WH in the bathroom. We will be renovating the bathroom in the spring and the WH must go (it's getting old anyway). Thus the need for a tankless in the crawlspace. To repeat, the prime motivation for the tankless is SPACE.

We don't use a lot of hot water (or cold for that matter). I did not install a CSV originally because we really don't draw water for very long. Only the one shower uses water for more than 1 minute. During a shower the pressure drops and the pump kicks in, but the flow of the shower exceeds the capacity of the pump to push up the hill, and so the remainder of the shower is at a slightly lower pressure. My 2.5 GPM shower head probably goes down to 2 GHP for the last few minutes of the shower. So there is no pump cycling during the remainder of the shower. The low capacity pump acts like an "auto CSV". The lower flow is not a concern for us when showering. But there is no way that this flow is less than .6 GPM, so the Rinnai should still fire for the duration of the shower.

So, what I intend is to just install the Rinnai as soon as the snow in MA is gone (we have to move the propane tank for this install) and we will see how it goes with no CSV. If pressure fluctuations cause problems with the WH, I have no problem installing a CSV to eliminate the fluctuation. But I don't want to have to install a smaller tank, until my tank needs replacing.

When my pump craps out, I will probably install a bigger one and then go with the smaller tank and CSV and have more pressure all the time.

I will update this thread after the tankless is installed. Wish me luck.

Rick.

[mcconnellplumbing]

Specs say the Rinnia and Navien will fire and operate on .75 gpm water flow. Assuming a shower head with 2 gallon flow rate, and 75% hot water to cold water ratio, it still should stay on if the flow rate is 1.5 gpm (.75 of 2 gpm)

[valveman]

My 2.5 GPM shower head probably goes down to 2 GHP for the last few minutes of the shower. So there is no pump cycling during the remainder of the shower. The low capacity pump acts like an "auto CSV".

That is exactly what is happening, and it works good. Althought that won't happen if you get a bigger pump. Which is when a CSV will be helpful.

[ballvalve]

Sell the junk tankless on g-bay and put in a electric, superinsulated, with switch. You will be thousands ahead in the life cycle of btu use and frustration.

[rick.a]

OK, it's done. I have installed the tankless (several weeks ago) and have used it long enough to report back to everyone.

I have a Rinnai 53i and this unit just fit into the tight vertical clearance in my crawlspace. I got this specific model because of it's low vertical requirement. Space consideration was the #1 reason for switching to the tankless.

Propane company did the gas part of the install. I did the plumbing. Very straight forward, especially since I redid all the plumbing in the house as part of a bath remodel.

The 30-50 water pressure fluctuation from my well pump/tank system does not seem to make any difference. It works fine. We experience about a 10-15 second additional wait for hot water, and this is acceptable. Flow rate is fine (but the incoming water temp is warmer this time of year). We don't like the cold water sandwich and don't like it when the hot cuts off when the flow is too low. We hand wash dishes. I may install a small electric "buffer" tank downstream of the Rinnai which should solve those issues.

By the way, does anyone know what the hit may be in flow rate/pressure if I install a sediment filter (just after the well tank)? I fear sediment buildup in the heater since it may be prone to plugging up. I installed a 10" cartridge housing but have not yet put the filter into it yet. If I use a 30 micron filter will it block much flow? By the way our water is crystal clear and no sediment is showing in the clear empty housing. Might this mean that I don't even need a filter, or is this false logic and small particles are flowing through?

thanks,
Rick

[ballvalve]

My well water could be bottled, but the electric elements build up huge deposits of calcium that hinder their operation unless they break off and drop to the bottom of the standard tank unit. Which they do if using a HIGH watt density element.

If I had a tankless, I would spend hours a year filling it with lime away and trying to get a brush throught it to remove the lining that makes the efficiency about 1/2 of advertised.

tankless are foolish when the best is a $200 tank that has only 2 or three parts and sit on every shelf in America. Many life cycle cost tests prove it.

Sediment filters dont help with dissolved solids which tankless units like to extract.

[LLigetfa]

My well water could be bottled...Ja, mine too, as mineral water! Despite having both an iron filter and water softener, I still see a lot of mineral buildup on my fixtures.

[rick.a]

Well in that case, I should be fine. The tested hardness level in our water is very low. We also have never seen any buildup at any fixture.

But I still would like to know how much pressure we would loose if I install a 30µ cartridge filter. Or for that matter is it just a waste of time to use such a filter.

[DonL]

Like BallValve said; "Sediment filters dont help with dissolved solids."

You would just have put a filter in it and see what you get.

The flow rate changes as it gets plugged up.


DonL

[jadnashua]

Any filter acts as a restrictor, and it gets worse, as mentioned, when it starts to actually collect debris in the filter media. Now, how restrictive depends on the size and design of the filter and the filter housing, which should be stated in the specifications. It will have some nominal pressure drop across it that will increase as it fills up. It isn't a bad idea to plumb pressure gauges on the inlet and outlet, as they will give a good indication (while there is a flow) of how plugged the filter is without having to take it apart to look (which may not tell you much). Note, with no flow, the gauges (should) read the same on the inlet and outlets...it only changes while there is flow.

[ballvalve]

I DO use filters in order to save getting junk in fixtures. Usually 5 or 10 Micron.

[master plumber mark]

i think I would be more worried about the incomming pressure
and when the well kicks on ....

how hard is the water anyway... they claim you need a water softener if you have more than 11 parts hard water...

good luck with this one