What does a thermostatic valve do while "waiting" for hot water?

Still debating the merits of balanced pressure vs. thermostatic for my new shower, never having owned either before.

Since I'm on the 32nd floor of a building, I have to turn on the shower and wait for several minutes to get hot water (the boiler is in the basement). Currently I've got an old Speakman mixer from maybe 40 years ago (although I replaced the valve cartridge about 7 years ago). Not sure if it's balanced pressure or just a mixer, but I just turn the handle to about where it usually sets the right temp and wait a few minutes for the hot water to arrive.

If I now go with a thermostatic, what will it do as it tries to hold a constant temperature? Does it run full hot and cold until the temp comes up to the desired pre-set?

I'm curious how this valve works, and if it is going to have any issues given the fact I have to wait so long for hot water.

Taco makes a manually-triggered circulator pump that sits between the hot and cold lines at a given fixture to pull the cold water out of the hot line and send it back down the cold line until the hot line is hot. I have one of those pumps under my kitchen sink, and the pump stops instantly just as soon as the hot water reaches it (so no significant amount of even warm water gets forced into the cold line). Or, a pump like that could also be set up with a timer so the hot water could be waiting for you, and I believe there are also some pumps that keep the hot line hot at all times ... and if there is a check valve in your cold line that would prohibit you from circulating water into it, the pump could be plumbed to dump its cold discharge into a drain just like you are already doing. With something like that in your system, your concerns about types of valves might disappear.

It runs full flow hot, until the hot arrives, then blends in cold to maintain the set temperature.

leejosepho said:

Taco makes a manually-triggered circulator pump that sits between the hot and cold lines at a given fixture to pull the cold water out of the hot line and send it back down the cold line until the hot line is hot. I have one of those pumps under my kitchen sink, and the pump stops instantly just as soon as the hot water reaches it (so no significant amount of even warm water gets forced into the cold line). Or, a pump like that could also be set up with a timer so the hot water could be waiting for you, and I believe there are also some pumps that keep the hot line hot at all times ... and if there is a check valve in your cold line that would prohibit you from circulating water into it, the pump could be plumbed to dump its cold discharge into a drain just like you are already doing. With something like that in your system, your concerns about types of valves might disappear.

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Thanks for the creative input. This would be great, but probably won't work in my application. Because it's a 1930 apartment building with solid masonry walls and floors (and everything is crammed into pretty tight spaces), there would be no place to put the pump without doing major demo. Also, my building would likely require special approval/paperwork, etc. for anything other than plain vanilla plumbing. Even approval for a whirlpool tub would take a miracle. Cool idea though.

Redwood said:

It runs full flow hot, until the hot arrives, then blends in cold to maintain the set temperature.

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Got it.

Does a balanced pressure valve also run full flow hot until the hot arrives?

Also, does a thermostatic valve protect against temperature changes with pressure drops (i.e. a toilet flushed nearby) as well as a balanced pressure unit of similar quality?

As long as the pressure is proper, a pressure-balanced valve doesn't care what the water temperature actually is...it will flow the blend you have set. A thermostatically controlled valve in theory would get warmer quicker because it would only be calling for hot water until it came, thus full flow verses partial flow for the pressure-balanced valve.

I've got a Redy-Temp recirculation system. It installed underneath the vanity. The hassle is you need an outlet to run it. If you can reach an outlet, and can live with the loss of space, installation was all of about 5-minutes. It is self-contained with pump, check valves, an a thermostat you can adjust, to indicate how warm you want the water before it turns itself off. Remove the faucet to shutoff valve hose from the shutoff, reinstall on the outlet of the device, then add new lines from the device back to the shutoff and plug it in. You're done. If you want, you can insert a timer so it doesn't run when you're away or asleep.

Note, with any recirculation system, if the water gets turned off, running this type of pump with no water in the lines will ruin it quickly (another good reason to use a time for when you are away).

Palladio said:

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Since I'm on the 32nd floor of a building, I have to turn on the shower and wait for several minutes to get hot water (the boiler is in the basement)....

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Large buildings should have a hot water loop with a large supply line and a small return line with a small Taco type circulator pump that circulates water back to the supply tank. That way all taps wait for hot water only for the length of a branch line, typically only a few seconds. Otherwise you'd have to wait a lot longer than a few minutes to get hot water- if you got any at all!

In a high rise like yours there are likely several of these systems, otherwise the top floor would get little pressure and the bottom would get a lot! (32 floors = 320' = 140 psi). Or possibly pressure reducing valves serving one or several adjacent floors. You should talk to the building Super and see what type of system you've got, and if he can check the circulation pump that serves your unit to make sure that its operating properly.

valve

A circulation loop does nothing to ensure pressure at the upper levels. The type of motor in the thermostatic valve determines how quickly it responds to major temperature changes. A pressure balanced thermostatic valve would handle that particular problem.

hj said:

A circulation loop does nothing to ensure pressure at the upper levels. The type of motor in the thermostatic valve determines how quickly it responds to major temperature changes. A pressure balanced thermostatic valve would handle that particular problem.

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Are most high quality thermostatic valves (i.e. Grohe) also pressured balanced? I don't see much mention of this looking through the online catalogs.

Southern Man said:

Large buildings should have a hot water loop with a large supply line and a small return line with a small Taco type circulator pump that circulates water back to the supply tank. That way all taps wait for hot water only for the length of a branch line, typically only a few seconds. Otherwise you'd have to wait a lot longer than a few minutes to get hot water- if you got any at all!

In a high rise like yours there are likely several of these systems, otherwise the top floor would get little pressure and the bottom would get a lot! (32 floors = 320' = 140 psi). Or possibly pressure reducing valves serving one or several adjacent floors. You should talk to the building Super and see what type of system you've got, and if he can check the circulation pump that serves your unit to make sure that its operating properly.

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Thanks for all the information. Very interesting and informative. Now I am really curious how the whole building system works and will have to ask the super and plumbers.

One thing to consider is that this building was built in 1929-30, and I'd bet that most of the plumbing is still close to the original set up. So it would be using technology from that era. I don't know anything about the system, other than that like most older NYC buildings, there is a large water tank on the top floor, and that all the heat in the building is steam powered.

Also, my apartment was added about ten years after initial construction in space that was formerly storage space above the regular floors. So whatever plumbing/branch lines I have are not original to the building plan. Maybe that accounts for why I have to wait several minutes for hot water?

According to the Grohe literature, they are both designed to compensate for water pressure fluctuations.

Grohe calls both the thermostatic and pressure balanced valves "Safety Valves", and they are also both supposed to have anti scald and shock capability and will shut off completely if either the hot or cold water supply is cut off.

jadnashua said:

A thermostatically controlled valve in theory would get warmer quicker because it would only be calling for hot water until it came, thus full flow verses partial flow for the pressure-balanced valve.

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So what I should see in a thermostatic valve in this situation is a lower pressure flow of water (all from the hot line that is not "hot" yet) until the hot water arrives at the preset temperature, then the shower pressure come up to full as the cold water is mixed in to compensate? And as you said, the shower should come up to operating temperature more quickly than with a pressure balanced valve, due to the increased flow from the hot water line on start-up.

So maybe I'm digging too deep here, but what happens if the valve is a thermostatic and pressure-balanced valve? Inquiring minds want to know.

Palladio said:

Thanks for all the information. Very interesting and informative. Now I am really curious how the whole building system works and will have to ask the super and plumbers.

One thing to consider is that this building was built in 1929-30, and I'd bet that most of the plumbing is still close to the original set up. So it would be using technology from that era. I don't know anything about the system, other than that like most older NYC buildings, there is a large water tank on the top floor, and that all the heat in the building is steam powered.

Also, my apartment was added about ten years after initial construction in space that was formerly storage space above the regular floors. So whatever plumbing/branch lines I have are not original to the building plan. Maybe that accounts for why I have to wait several minutes for hot water?

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The roof tank is used to pressurize the plumbing system. There's probably a pump in the basement that boosts the street pressure (probably about 80psi) to fill up the tank. Then water is distributed from there.

I'd agree that's the likey reason for your hot water wait. You're probably a bit of a distance off the loop. If it really bothers you, I'd suggest putting a small electic tank type heater in your apartment. I'm not sure how small they make them, but a 5 gallon tank could supply a shower for 3 minutes until the hot water arrives.

The pressure shouldn't change, nor should the volume. You'd just notice that it eventually got to the set temperature.

Pressure Balancing and Thermostatic are 2 different methods of anti acald protection, they would not be used together.

A thermostatic valve blends hot and cold to maintain a set temperature. Usually they will maintain that temperature within +-1 degree.

A pressure balancing valve maintains an even pressure between the hot and cold supplies. If someone flushes a toilet and the cold pressure drops the pressure balancing unit will lower the hot pressure to match and vice versa for a hot pressure drop. The user selects the mixture % of the hot and cold thus selecting the temperature. The valve does not sense the temperature of the mixed water. Ptressure balanced units will maintain a temperature of +-3 degrees.