shower valves and tankless

[morpho]

Okay, first I'll say I am aware of the shortcomings of Tankless units. But I have lived with one for 7 years and not had a problem with it at all.
I love the stupid thing!

BUT! I have been using it in a cabin/makeshift setting where I simply had Cold water pumping into it and out to a shower head. (no valve and no cold to mix into it)

Well I am about to do the plumbing to the bathroom in my new house and it's going to be a right proper shower with hot AND cold runnin' water!
My concern is what effect a pressure regulating or thermostatic valve will have on the Tankless.

(my preference would be to have old school manual valves hot and cold and the two simply meet and mix but these are no longer allowed by code....the tankless already serves as the scald protector as it is set to a specific temp and never fluctuates)

Anybody have some advice?
Some experience?

Thanks a bunch.

[cacher_chick]

Not sure what you suspect, but a tankless works with a current model shower valve the same way that a tank heater does. We set either style water heater to 140F and leave it there.

[morpho]

Thanks for the response,

I have read various concerns/problems with different valve types creating situations where the tankless unit is affected by the valve mechanism. I have read reports that they can make the unit shut off etc.
chances are there will be no problem, but it would suck to get it all set up and closed in the wall, only to find out that when mars is lined up with the moon and the valve is a pressure regulator type....I get (or more importantly my wife) a cold shower.

[jadnashua]

Some tankless heaters have built-in flow restriction. That can mean that the hot and cold are not balanced, and that can affect some valves. How often, I don't know. It's probably less of a problem with a thermostatically controlled valve, and may not happen with your setup.

[morpho]

I guess the only thing to do is pick one, instal, hope for the best and be prepped to replace it with a different kind of valve.....after my wife has finished chasing me around the house after yet another cold shower!

[Dana]

Not sure what you suspect, but a tankless works with a current model shower valve the same way that a tank heater does. We set either style water heater to 140F and leave it there.

There's no point to running a tankless at 140F, and that only exaggerates other issues, including more rapid scale-up and liming. Interactions with some types of anti-scald valves are also more likely due to the pressure difference issues as Jim noted.

While I agree a thermostatic valve is less likely to be an issue than pressure balancing anti-scald valves, set it up with the tankless set to 110-115F (as low as is tolerable for a tub-fill), with the thermostatic valve wide tweaked to the same or slightly higher temp as the tankless so that all the flow is through the heater. With the somewhat higher flow the tankless will then regulate temp better and have fewer flame out or delayed-ignition issues. If it's shower-only (no tub), you can probably set it as low as 105-106F and get satisfactory results. The flow through the tankless is somewhat higher, but the firing rate will be the same as if it were set up with higher-temp/lower-flow output.

[morpho]

Dana,

Thanks for that insight.

I wouldn't have cause to have it anywhere near that kind of temp as we don't have a tub and I like the shower at about 105-110.
So I guess I'll try a thermostatic valve and see what's what.

I came across these:
http://www.deltafaucet.ca/bath/details/r10000-unbx.html
which gives the option for different cartridge's

Okay.

Thanks again everyone.

[morpho]

Hey Dana,
In a perfect world.... would old school pre-scald proof shower valves work best?
I know this is considered bad form when it comes to the code, but is this the ideal for tankless?

Thanks

[jadnashua]

The output of a tankless when it's reaching its max capacity can change radically based on the volume of water it is requested to flow...this would be radically transmitted to a conventional valve without one of the antiscald technologies in it...so, IMHO, a straight valve with a tankless would be worse than a required antiscald one. Even if your shower was the only hot water user, anything that affected the cold volume/pressure could affect the flow through the tankless and thus change the temperature outlet. The internal controls just can't respond that quickly in a tankless, a pressure balance antiscald valve can. Most thermostatically controlled valves need less than a second to compensate for variations, so you may or may not notice, but you won't get scalded.