Mixing Valve before toilet?

Hey All,

I have a Watts MMV-M1 Mixing valve I would like to install in a bathroom to prevent scalding through flushing or accidental knob bumping/turning. The fixtures in this bathroom are old-school with no such features.

Now, it would be much easier to install this in the basement where I have direct access to the pipes that feed the bathroom, but this would result in the entire bathroom being controlled by the valve (toilet/vanity/tub/shower) as opposed to just the tub/shower.

My question is this: If I install it this way (entire bathroom on mixing valve) am I somehow negating the protection against the dreaded "hot flash flush" since the toilet is on the receiving end instead of the supply end? Or does it matter?

If it doesn't matter, could I put multiple bathroom on this one valve by installing it near the water heater?

Thanks!

A mixing valve will not accomplish the antiscald feature, except to limit the maximum hot temp. available. But what you are looking for is a pressure balancing valve.

Mixing Valve

That valve is listed for single fixture use, you can't tie all the fixtures into it. The discharge of the valve is tied into the hot line of the fixture that you want to control, it has no effect on the toilet. You will have to have a dedicated line to your tub.

If you can access the hot/cold lines that only go to the tub/shower, you can add a pressure balance valve. If not, it might be time to bite the bullet and replace the valve you have with one meeting current standards. THere are some repair plates that are available to cover the larger hole required to install a new valve.

If the mixing valve is ahead of the toilet, then flushing the toilet would still cause the temperature change, and it could be more extreme because of the added resistance of the mixer. If the hot water is at a scalding temperature, then it could be dangerous at ANY faucet, so maybe what you need is a tempering valve at the water heater to reduce the temperature at EVERY faucet, and thus not worry about just the shower.

Jimbo: It is a "automatic thermostatic mixing valve" and from all the certifications (and cost) I believe it is what you describe as a "balancing valve".

Thank you all for your replies! I think I got it now.

From what you have written, you DO NOT have it now. Thermostatic valve, and balancing valve are two different items, and are seldom incorporated into a single device, UNLESS it is a shower/tub valve. In fact, a good fast acting thermostatic valve does NOT have to be pressure balanced because it will modify the temperature without having to equalize the pressures. The thermostatic valve ONLY controls the temperature delivered to the hot water faucets, and does NOT, and in its location COULD NOT, pressure balance the water flow to the shower or anything else.

hj said:

From what you have written, you DO NOT have it now. Thermostatic valve, and balancing valve are two different items, and are seldom incorporated into a single device, UNLESS it is a shower/tub valve. In fact, a good fast acting thermostatic valve does NOT have to be pressure balanced because it will modify the temperature without having to equalize the pressures. The thermostatic valve ONLY controls the temperature delivered to the hot water faucets, and does NOT, and in its location COULD NOT, pressure balance the water flow to the shower or anything else.

Click to expand...

OK, now I am really confused! (Surprise, Surprise! ). Are you saying that it would control the temperature (my goal), but the pressure/flow of the shower could still change? If so that's not a big deal.

It is listed for ASSE 1017, 1069 & 1070 applications which I thought covered all the bases, but obviously I am no expert.. The literature states "The MMV-M1 uses a double throttling design to control both the hot and cold water supply to the mixed outlet. The superior flow characteristics of this valve provide accurate temperature control (±3°F) with low pressure drop across the rated flow range.".

With my limited understanding of the certs, 1017 means I can install this at the water heater and temper the hot lines to all my bathrooms as you suggested. Correct? What exactly WON'T this device do?

Spec Sheet: http://media.wattswater.com/es-mmv.pdf

It would work if you never wanted to adjust the output temperature AND you only used hot, never cold, in the shower. Not exactly what you had in mind. Keeping the hot the right temperature won't help if the cold pressure you are using to get your shower the right temperature stopped flowing. The pressure balance or thermostatic control needs to be after your shower control, not before.

Your best solution is to trash the old valve with one that meets current code. Depending on where you live, making the change you are considering would require a permit, and then they'd make you put in a complient valve. You can repair a non-complient valve under the grandfather clauses in mose locales, but you can't make changes without bringing it up to code.

jadnashua said:

It would work if you never wanted to adjust the output temperature AND you only used hot, never cold, in the shower.

Click to expand...

<Light bulb goes on> Ahhh...I understand now. Like in a locker room shower where you just push the button to turn on the water and it's at a pre-deterined temp. Gotcha.

One simple change you could make is to turn down the temperature at the hot water heater to a safe (non-scalding) temperature. Then, regardless of what happens w/ toilet flushing and non-pressure balanced valves, no one can get hurt. If there is not enough hot water available after making the change, you could consider a tempering valve after the water heater as HJ suggested.