Tankless water heater

[turbodog]

I see a lot of people, here and in person, talking about 70F setpoints.

I suspect some of this is bad thermostat placement and/or air infiltrating BEHIND the thermostat... attic air being pulled inside due to negative pressure.

I'm running 75F in summer with the unit on recirc and dehumidify. Blower speed will drop to very little with very cold air coming from registers. This was able to drop indoor humidity 5-10%, down to 45-50%.

If you've got bad circulation, poor returns, air infiltration, etc I can see where some want 70F. Honestly, 75F is as low as I can go w/o people putting on long sleeves when they come over.

But I did, during building, plug all holes for wiring/plumbing w/ foam through the top plate, caulk around the green plate, and use cellulose insulation everywhere. The house is tight.

 

[turbodog]

... Or maybe he explained that the newer more efficient systems (at the time 1986) used larger condensers (heat exchanges) and smaller compressors.

The condensing coils have gotten a LOT larger over time. My recent 4 ton unit, purchased ~2 years ago, is ~5 feet tall.

2 speed compressor. Variable speed air handler. Paid the HVAC guy to check/balance airflow @ registers. Best money spent in a LONG time.

 

[TPA]

Currently 2am ET as I type this.
Outdoor temp: 81F.
Outdoor dewpoint: 80F. (~96%RH).
Indoor temp: 78F
Indoor dewpoint: 51F (~40%RH)

and it feels absolutely lovely.

@Poppy : For reference, 72F @ 45%RH = ~49F dewpoint, so close to the same physical amount of moisture as what I have with the higher setpoint, with absolutely miserable conditions outside. I actually think we're on the same page when it comes to dehumidification. With such a high (80F) dewpoint outside, you really don't want to get the home much cooler, as the insides of the exterior walls will sweat, rotting the house.

My goal is getting the evap coil as cold as possible without icing it up. The colder the coil, the more moisture (latent load) removed from the air. A compressor puts out a fixed amount of BTUs. You can use those BTUs to condense water or cool air. I choose to put most of my eggs in the condense water basket.

How you get there varies.

In my temporary condo, there's an old, ratty single-stage 2-ton AC with a PSC (non-variable) blower with matched coils. It's temporary, so I just tossed a DPDT switch on the blower motor which goes between high and low speed taps, based on my Ecobee thermostat's humidity output. The Ecobee is set up to call for cooling if humidity is above my setpoint.

At my real condo, there's a beast of a system. PLC-controlled. Multi-stage, multi-coil, zoning. It has a "cooling" coil and a "dehumidify" coil, and supports re-heat. It also powers air curtains by the sliding glass doors. It also compares supply air vs. dewpoint so that the vents don't sweat. Darn close to perfection IMHO, but also a hoot to watch a residential HVAC tech take a look at it. Commercial refrigeration guys take to it almost immediately.

 

[Poppy]

With such a high (80F) dewpoint outside, you really don't want to get the home much cooler, as the insides of the exterior walls will sweat, rotting the house.

@TPA Gee, I never knew that nor considered it.

It sounds like your condo environment control system is awesome!

 

[PhotonMaster3]

My tankless is a real turd. It was quite expensive (built a new house a few years ago). Sometimes it takes 10 to 15 minutes for the house for the shower water to get hot. I've tried every setting on the useless iOS apps that come with it.

Meanwhile my dad's ancient water heater instantly blasts out piping hot water anywhere in his house.

Just by experience though. I've heard other people who like them.

 

[BVH]

Do you have a hot water circulation loop and pump in your water system? Our showers are about 120 pipe-feet from our tankless. Our recirc pump plugs into a remote controlled outlet. Activate any of the remotes throughout the house and the pump will start and trigger the tankless to start. It takes about 8 minutes to bring hot water back to the pump/heat the loop. It's our habit to light off the pump 5 or so minutes before we're going to do dishes, run the dish or clothes washer or shower. If we don't preheat the loop, it will take about 5 minutes for hot water to reach the shower.

 

[letschat7]

These always seemed to good to be true.

 

[Galane]

I've often wondered if a small electric tankless heater in the supply line to a water heater would work to stretch out how long it can go before running out of hot water. The tankless would only use electricity when water is flowing.

What I find either crazy or drastically over-inflated claims are the "3000 watt" 110 volt mini tankless water heaters sold through sites like Ali Express and Temu. I dunno where in the world electric code allows pushing 3000 watts through a 110V circuit but it's not the USA or Canada. We're limited to a max of 2000 with a practical max of around 1600. Most portable heaters here are only 1500 with a very few going to 1600 or a bit higher.

I suppose one could run an 8 gauge, 40 amp, 220V dedicated line and split it into a pair of 110V connections and run two of the heaters in parallel. Last I looked, splitting a 220V line into a pair of 110V circuits wasn't forbidden, but I suspect electric inspectors would frown on trying to pull 3000 watts through each side.

What has become a thing in the USA is cranking up the temperature of the water heater to melt your skin off levels, then putting on a mixing valve that blends cold water into the output to bring the temperature down to a safe level. That uses more energy heating the water hotter, but effectively increases the capacity of the water heater. Definitely want the safety pop off valve in working order and the mixing valve to be some type of fixed setting or one that can't fail in a way which shuts off the cold mixing.

My house water heater is set to 116~118F and it's fine for the dishwasher and shower, with a touch of cold too for the shower.

 

[Poppy]

I thought 12 gauge copper is good for 20 amps, and 10 gauge is good for 30 amps, for less than 100 foot runs.

 

[Galane]

I thought 12 gauge copper is good for 20 amps, and 10 gauge is good for 30 amps, for less than 100 foot runs.

I ran new 8 gauge wire for an oven with stovetop through conduit. That replaced the 10 gauge that was in use in the conduit, and the original 12 gauge that had been 'abandoned in place'. 1945 quick build house for men returning from WW2.

I discovered a US Navy spoon and fork under part of the floor that was built atop a former back porch, so I'd guess circa 1945 a former sailor and his wife, possibly with baby in arms, walked into their new, shoddily constructed but astonishingly affordable bungalow.

 

[turbodog]

Do you have a hot water circulation loop and pump in your water system? Our showers are about 120 pipe-feet from our tankless. Our recirc pump plugs into a remote controlled outlet. Activate any of the remotes throughout the house and the pump will start and trigger the tankless to start. It takes about 8 minutes to bring hot water back to the pump/heat the loop. It's our habit to light off the pump 5 or so minutes before we're going to do dishes, run the dish or clothes washer or shower. If we don't preheat the loop, it will take about 5 minutes for hot water to reach the shower.

My comment is more about the process itself. If anyone has to spend 5 mins multiple times a day waiting on hot water... then you've sold your precious time for a few dollars of savings.

10 min x 365 days x 10 years = 25 DAYS of your life, waiting on hot water.

And since these are waking hours, or which a day only has 2/3 of, this really equates to 38 days of waking time.

In short, I use a circ pump with a series (2x40) natural gas system that runs from 5am till 9pm every day... no waiting unless I get up in the middle of the night for some reason.

Does it cost a few dollars a month in electricity and nat gas? Yes

Is it worth every penny? YES.

Could I tell a difference in the bills the month the pump failed and I had to find a replacement? No.

Does it save water? Yes.

 

[turbodog]

I thought 12 gauge copper is good for 20 amps, and 10 gauge is good for 30 amps, for less than 100 foot runs.

I learned, when I helped my mother with a 160ax240v electric on-demand heater that wires/breakers have different ratings for intermittent loads and sustained ones. IIRC it mainly has to do with wire heating and insulation breakdown. This would apply to something like a water heater.

 

[BVH]

We don't wait around for hot water. We are busy doing other things. In addition, the tankless is not running for 12-14 hours a day if on a schedule you show above.

 

[ampdude]

I'm sorry, but this will not add a lot to the conversation. All I have to say is that most modern appliances are GARBAGE. My mother had a Frost Queen freezer from the late 60's that still worked great. I have a new $800 dishwasher I bought a year ago that has two dozen or less cycles on it and already doesn't work. It gives two error codes since August. A tech came out for the warranty after a week and a half and said so, and said they gave him the wrong part. So he put it back together and left. I was told I would be on a "priority list" for service. That was three weeks ago. It's now day 42 and I'm still waiting to get this fixed. Not sure it will happen in the next month even. What is going on? How about just... turn the dishwasher on, turn it off. Not have a million different stupid cycles that nobody uses or wifi access or other weird psycho stuff that no one cares about.. just a thought. Just make working stuff again. Whoever thought a DISHWASHER would need a PC BOARD... I couldn't have imagined it in my wildest dreams years ago. Just another modern piece of junk.

 

[LuxLuthor]

As usual, I'll be the outcast here.

I put a tankless water heater in my (then fiancées) house, when we were doing construction to add on a new Master suite, in 2018.

Her then current water heater was on its last leg, so I decided to go the tankless route, as we would have 3 full bathrooms after completion.

Multiple showers/baths a day (we have 5 living here), and my stepdaughters' "hours long" showers (or so it seems, LOL) and ALWAYS hot water available.

Every year I have it "flushed/cleaned" and can tell you that in the 5 years we have had it, not a single problem or regret.

Who knows what the future will bring, but so far, I am a fan and highly recommend them.

That was my experience using a Navien brand for 8 years in CT without any problems. Forgot to backflush it, so obviously we didn't have hard water.

Installed a new one in home here in Mississippi where we have soft water, works perfectly for up to 6 people. Will get this one back flushed yearly though.

 

[LuxLuthor]

@TPA
I guess we'll have to agree to disagree on the definition of dehumidify. My definition would be that a dehumidifier actually removes water from the air.
Your's apparently defines it as reducing the relative humidity, by increasing the temperature, so that the warmer air has a greater capacity to hold more water.

My position is that a properly sized AC unit can reduce the humidity to 43% at 72F. Personally I'd be more comfortable at 72F than 78F. My daughter would prefer 70F or even 69F.

Of course with varying outside temps and varying humidity, one AC unit can not be perfect for all scenarios. For example when it is 74F with 99% humidity, my central AC will not run long enough to remove enough water, before it shuts off at the thermostat setting of 72F. It will leave the house cool and damp/ clammy. So on those odd days, I may run the heat and the AC at the same time. Energy Efficient? NO. But I pay the bills around here, and I want to be comfortable. Just label me spoiled.

Same here, except I have two 6 ton outside compressors for two Rheem air handlers

 

[TPA]

My dad custom-built my childhood home. As it was a one-off, there were some design...eh.. deficiencies. One was that the master bathroom was on one end of the house, and the water heater was on the completely opposite side, and water was plumbed in sequence, all the way around the house. IIRC it was 5+ minutes to get water to the master bathroom sinks. At some point they added a small 110v tankless heater in-line with the hot water line. So, you now had reasonably warm water within 5 seconds. When the real hot water finally arrived, the in-line would shut off. That one actually lasted for 20+ years (when the house was demolished), and I suspect it was because it was too weak to get the water hot enough to dispose of its pollutants/deposits.

I'm sorry, but this will not add a lot to the conversation. All I have to say is that most modern appliances are GARBAGE. My mother had a Frost Queen freezer from the late 60's that still worked great.

I'm with you on this... All of the appliances at my condo are 22 years old...and even after multiple hurricanes and terrible power, they still work. I tried firing up the fridge this week and even after it's been shut off for a whole year, it came right on.

 

[Galane]

I want to see someone try one of those "3,000 watt" 110 volt tankless water heaters sold on Temu and Ali Express. That would require 8 gauge wire on a 30 amp circuit, and that isn't happening with the plug in cords shown in the sales listing images.

 

[Poppy]

I want to see someone try one of those "3,000 watt" 110 volt tankless water heaters sold on Temu and Ali Express. That would require 8 gauge wire on a 30 amp circuit, and that isn't happening with the plug in cords shown in the sales listing images.

I guess it is like chinese lumens.

 

[TPA]

My house water heater is set to 116~118F and it's fine for the dishwasher and shower, with a touch of cold too for the shower.

Careful on that. That's the prime territory for some nasty bacteria to grow. https://www.corroprotec.com/blog/does-hot-water-kill-bacteria/

My degree is in microbiology...and my water heaters are set to 140F, for a reason.