satellite water-heater versus recirculation pump

[RustyShackleford]

As part of my endless kitchen re-model, I want to eliminate the long wait for hot water there. I'd been considering a small tankless unit, but thinking a small storage-tank is better (6-12 gallons). But then there's the idea of a circulating pump (from the main 50 gallon conventional electric unit).

Energy usage is my main concern, and that energy goes to one of three places: hot water you use, hot water stranded in pipes after you turn the faucet off, and heat lost into the environment. Seems the first two are the same for both the tank-style and the circulation pump. Heat loss is related to the surface area through which heat is lost (the tank surface area, or the surface area of the piping between the recirc pump and the kitchen, since the pump essentially extends the surface area through which heat is lost), the temperature differential (hot water versus ambient), and the R-value (of the tank jacket, or of the piping), I wrote a little spreadsheet. For (both cases) a 60-degree temperature differential between the hot water and the ambient crawlspace, and R-8 insulation, a typical small tank has losses equal to about 22 watts, and a 20ft round-trip 1/2" pipe has a loss of about 12 watts. That's not much difference: less than $10/year at 10cents per kwh, or 100-200 pounds of carbon for typical electricity. Also, the pump uses some electricity - though of course it can be turned off a lot of the time with a timer, whereas even a turned-off tank heater is losing energy as the water cools off when the timer is off.

Also, the pump seems like more complexity and proneness to failure, and fairly similar in price.

Thoughts ?

 

[jebatty]

I faced a similar situation: electric hwh in the basement right below two bathrooms above and kitchen on the main level at the opposite end of the house. Waited "forever" for hot water to get to the kitchen. Hot water is nearly immediate in the bathrooms.

Solution was a separate 5 gallon hwh installed in the basement right below the kitchen sink and dishwasher. Now both get hot water nearly immediately. Plus, since only 5 gallon of hot water, we use hot water for the kitchen sink with a very conservation mindset, and only run the dishwasher when we know the 5 gal hwh has cycled and has a full tank of water. The 5 gal hwh is 120V and operates on a dedicated circuit.

 

[heat seeker]

I suppose that if you fed that small heater from the hot water line, it may recover faster, depending on how much water you drew. Once the cold water was out of the line, you'd be putting already heated water into the heater. And you'd be able to use more than 5 gallons at a time. Sounds good to me...if I'm right.

 

[RustyShackleford]

I suppose that if you fed that small heater from the hot water line, it may recover faster

That would then give the worst of both worlds in terms of heat waste, since it's increasing the effective surface area through which hot water loses heat to the environment, in both ways. A long skinny cylinder of the hot water line going from the main tank to the satellite one, and the squat cylinder of the satellite unit. I'm sizing the satellite unit big enough I don't think running out will a huge issue - about 10 gallons. And since Bradford-White lets you put most any wattage heating element in, I'll put in a 3000 watt one, which should allow complete recovery in about 30 min.

Solution was a separate 5 gallon hwh installed in the basement right below the kitchen sink and dishwasher. Now both get hot water nearly immediately.

Of course, small local storage-type or recirc pump. Either would give immediate hot water in the kitchen. The question is, which is more efficient, and what ancilliary issues are there ?

 

[Handsonautotech]

Sorry if I missed it but why not just put the hot water on demand unit in? Seems like the simplest and most efficient solution.

I would not want the pump because you would hear it and that would bother me.

The small tank is not going to be as efficient as a tankless on demand unit and you can feed the on demand unit from the cold side so you are not heating the water twice, or you can get an on demand unit that shuts down once the water going into it reaches a pre defined temperature.

 

[RustyShackleford]

Sorry if I missed it but why not just put the hot water on demand unit in?

It would be very inconvenient to get gas to the location (and my gas is expensive propane). It'd also be hard to get enough electrical amperage to support more than 1 gpm or so, which is unacceptable, with the main sink, a prep/bar sink, and a dishwasher, if any two of those were running simultaneously.

I would not want the pump because you would hear it and that would bother me.

Good point.

The small tank is not going to be as efficient as a tankless on demand unit and you can feed the on demand unit from the cold side so you are not heating the water twice, or you can get an on demand unit that shuts down once the water going into it reaches a pre defined temperature.

The small tank would be fed from cold water also. I do not believe tankless is significantly more efficient (see below), and they are moe expensive and trouble prone and more difficult to access parts (my plumber buddy says often you cannot even buy parts, without being a factory-trained tech).

I don't buy into the tankless hype. As I detailed in OP, energy goes into (1) hot water used, (2) hot water stranded in pipes, (3) parasitic losses (i.e. from tank jacket). In my application, with small tank near kitchen, tankless would save me nothing on #1 and #2; it would onbly save me the 20 watts or so on #3. The added complexity and maintenance of tankless is not worth that to me.

 

[jebatty]

I tried an on demand electric heater. Maybe it was the model I used, but totally unacceptable. When faucet first turned on, cold water which quickly warmed to hot. But then turn the faucet off, the heater would still stay "on" briefly to heat water to the shut-off point. Now, turn the hot water faucet on again, and a blast of extremely hot water, then cold water, then water warming to hot again. Repeat this every time you turn the hot water off. Maybe if you just let the hot water run, it might work OK, but we only turn on water for immediate use, do not let the water run like many people do, which to us is a waste of a lot of good water. The 5 gallon satellite hwh also turned out to be a very good teacher on conserving energy and water by reducing waste of both. And we pass that knowledge along to family and guests who tend to let the hot water run while working at the sink -- we remind them to turn the hot water off or there quickly will be no hot water.

Originally I fed the satellite small hot water cold supply from the hot water from the main hot water supply. True, that got more hot water, but also lots of standby losses in the long hot water supply line. Also, it encouraged use of lots of water -- counter-productive to one of the purposes of the satellite hot water heater - conserve energy and water.

My wife and I are quite conscious of conservation in all areas, including conservation of water. Waste not, want not.

 

[Handsonautotech]

Hi, I'm Mike, joined here to do some research on a new wood stove. I currently have an old King Products MI2 and can't find much information on it online. Our house is ~3300 sq ft multi-level and although this thing works, it's far from efficient and is a bit on the small side so it takes quite awhile to get it where I like the temperature to be. I burn mostly oak but mix in some pine, cedar and occasionally other hardwoods when they fall in my lap. I'm not picky and generally take what people would like to be cleaned from their yards.

Let me know if anyone has info on the King MI2, trying to determine if it's worth sprucing up or if I should drop the coin for a new box.

It would be very inconvenient to get gas to the location (and my gas is expensive propane). It'd also be hard to get enough electrical amperage to support more than 1 gpm or so, which is unacceptable, with the main sink, a prep/bar sink, and a dishwasher, if any two of those were running simultaneously.

Good point.


The small tank would be fed from cold water also. I do not believe tankless is significantly more efficient (see below), and they are moe expensive and trouble prone and more difficult to access parts (my plumber buddy says often you cannot even buy parts, without being a factory-trained tech).

I don't buy into the tankless hype. As I detailed in OP, energy goes into (1) hot water used, (2) hot water stranded in pipes, (3) parasitic losses (i.e. from tank jacket). In my application, with small tank near kitchen, tankless would save me nothing on #1 and #2; it would onbly save me the 20 watts or so on #3. The added complexity and maintenance of tankless is not worth that to me.

Sounds like you have your answer.

 

[semipro]

I've found that careful insulation of the pipes between our WH and kitchen made things very tolerable. One section even runs through an unheated garage area.