Anyone else plumb their hot water for a return loop?

[Kingcreek]

When we built a master suite on the the house 8 years ago we went to a 50 gal hot water heater to handle the addition of a 3rd full bath with 2 shower heads and 2 vanity sinks. A friend of mine was helping me with the plumbing and suggested a return hot loop at the time. I hadn't heard of it before but it made sense and it has worked great. Hot water is almost instant since it only has to come from the "T" 3' below the valve instead of all the way from the heater tank.
I ran 3/4" copper to the farthest point with 1/2" T to all valves and then a 1/2" line back to the drain out on the water heater all insulated. There is a constant slow gravity flow out the top through the loop to the return that keeps the temp of the water in the line hot.
I had to replace the HWH today and the extra plumbing is a bit more work but not terrible. I removed the new plastic drain out and screwed in a 3/4 nipple out to a 3/4-3/4-1/2 T for the return and another nipple to a drain faucet.
I had 3 friendly sales associates at Menards and none of them had ever heard of plumbing this trick. Just wondered if I'm the only one. The friend that suggested it is no longer with us.

[never_retreat]

Only did it once to a friend's really long ranch. We added it after the fact because hot water was a 5 minute wait.
Insulate the lines or you end up with extra heat.

[K Frame]

No. It works, But it can increase your fuel costs dramatically.

They have pumps that do the same thing.

Sent from my SCH-I545 using Tapatalk

[Hawkmoon]

I haven't seen it in a single family house, but the apartment complex I lived in when my first wife and I were first married had one. We were at the far end of the complex from where the boiler room was located. A few months after we moved in, we started having VERY long waits for hot water -- especially early in the morning. The live-in super insisted it was a problem with the boiler, and he claimed he could fix it by boosting the pressure. (!!!) Took me three months of dropping hints to get through. One day we got home from work and the super's wife stopped by to proudly announce that her husband had found the problem and fixed it -- he replaced the circulator pump on the hot water loop.

The systems I've seen all use a circulator. The idea of using the drain outlet and making it gravity flow is a neat idea.

If the loop isn't insulated you lose some efficiency that way (although you get some [almost] free heat in the basement). Or, just insulate the pipe in the loop.

[Kingcreek]

The line is entirely insulated. I doubt if fuel costs are any higher because without it we would be running lots of not yet hot water. No circulation pump but just the gravity flow seems to work. There is probably almost 50' of run to the shower and it's hot within a count of about 4.

[AmbulanceDriver]

Huh.  Never heard of that.   But if/when I replumb this place with PEX, I think I'm going to do something like that.....   

[KD5NRH]

https://www.ecosmartus.com/product/ecosmart-ECO-11-13-kW-Electric-Tankless-Water-Heater

$204 on Amazon, and under $200 on eBay most of the time.  They have a whole range of wattages for whatever you're trying to do, with sizing charts for each, so I'd think one in each bathroom would be cheaper than a full-house re-plumb and constant reheating of water that cools off in the lines.  I know we had a couple of customers that were quite happy with the 11 as a whole-house heater for a <1000sf 2/1-1/2.  Dial it up to wash clothes or dishes, or set the exact temp you want for a shower.

Can't find a price for this little critter https://www.ecosmartus.com/product/ecosmart-ECO-11-13-kW-Electric-Tankless-Water-Heater or I might be tempted to get one and shut off the gas water heater at my place; no W/D, and I rarely wait for hot water when I'm just washing a dish or two, so the shower is the only place I really want a steaming tap, and no running the tank empty is a very nice feature.

[K Frame]

" I doubt if fuel costs are any higher because without it we would be running lots of not yet hot water."

Think again.

A 24x7 gravity flow takes hot water out of the water heater and returns it to the water heater as cooler water needing to be reheated. Running water at the tap to bring hot water up only happens in most homes for a few moments.

If you insulate the pipes to cut down on heat loss, that can defeat the entire concept of gravity flow and you're back to running out water to bring hot water up. You can insulate the pipes to the top of the loop, but the return loop needs to remain uninsulated for it to work.

Basically it's the old adage... You can't get something for nothing.

This was discussed on a forum I was on some years ago. One of the people posted some studies that indicated that such a set up has the potential to increase fuel usage by upwards 20 to 30% or more depending on the length of the loop, the temperature differentials, etc.

There's a device on the market called the Hot Water Lobster. Basically it's a $200 gravity loop.

You can buy powered pumps with either timers (http://www.homedepot.com/p/Hot-Water-Recirculating-System-with-Built-In-Timer-0955800/100426993) or manual start (push buttons) that do the same thing and cost about the same amount.

[Kingcreek]

the entire loop is insulated but there is bound to be some heat loss along the way- enough to keep a low flow (that and a top-out/bottom-return) I can accept that for the convenience. I timed it this morning to the farthest valve, wide open was warm in 2 seconds and hot in 6.
I have ball valves at each end of the return and could easily shut off the loop to test. Estimating energy usage would be difficult because we have a 1000gal LP tank that only gets filled when under 20% and also fires the boiler heat and gas range.

[Brad Johnson]

Add a circulation pump and you have a standard residential hot water circulation system. Keeps everything in the system at whatever temp your water heater is set to.

Brad

[Perd Hapley]

https://www.ecosmartus.com/product/ecosmart-ECO-11-13-kW-Electric-Tankless-Water-Heater

$204 on Amazon, and under $200 on eBay most of the time.  They have a whole range of wattages for whatever you're trying to do, with sizing charts for each, so I'd think one in each bathroom would be cheaper than a full-house re-plumb and constant reheating of water that cools off in the lines.  I know we had a couple of customers that were quite happy with the 11 as a whole-house heater for a <1000sf 2/1-1/2.  Dial it up to wash clothes or dishes, or set the exact temp you want for a shower.

Can't find a price for this little critter https://www.ecosmartus.com/product/ecosmart-ECO-11-13-kW-Electric-Tankless-Water-Heater or I might be tempted to get one and shut off the gas water heater at my place; no W/D, and I rarely wait for hot water when I'm just washing a dish or two, so the shower is the only place I really want a steaming tap, and no running the tank empty is a very nice feature.

My Dad has a set-up you would love. Water going into the electric heater is pre-warmed in an old water heater tank, placed above the wood stove. He took another old tank, and made it into a solar water heater, but hail storms kept busting up the plexiglass on top of the insulated box that he built for it.

[KD5NRH]

My Dad has a set-up you would love. Water going into the electric heater is pre-warmed in an old water heater tank, placed above the wood stove. He took another old tank, and made it into a solar water heater, but hail storms kept busting up the plexiglass on top of the insulated box that he built for it.

One thing I've thought about for a preheat is catching the heat off the refrigerator coils.  Bonus in a hot climate of not having them just warming up the kitchen.

As for the rooftop rigs, Lexan helps a lot, or a flat black metal collector.

[Brad Johnson]

Hybrid circulation/on-demand systems use a small water heater, say five gallons, to fill and maintain the circulation system, then have an on-demand unit plumbed in for when the taps are opened.

Brad

[Perd Hapley]

As for the rooftop rigs, Lexan helps a lot, or a flat black metal collector.

It was at ground level, actually. I don't think they have it anymore.

[JonnyB]

A plumber talked me out of a second water heater ten years ago, and installed a circ pump. We had a 105-gallon electric heater with a mixing valve; water was at 150 degrees, mixed with cold water to get 120 to the tap.

The pipes (Wirsbo) weren't insulated.

We had nearly instant hot water - too hot, as it would circulate the 150 degree water. We turned off the pump for awhile, and found that our electric bill went down by $40 per month. To check, we turned it back on for a couple of months. Bill went back up, so we turned it off and left it off.

jb

[zxcvbob]

A plumber talked me out of a second water heater ten years ago, and installed a circ pump. We had a 105-gallon electric heater with a mixing valve; water was at 150 degrees, mixed with cold water to get 120 to the tap.

The pipes (Wirsbo) weren't insulated.

We had nearly instant hot water - too hot, as it would circulate the 150 degree water. We turned off the pump for awhile, and found that our electric bill went down by $40 per month. To check, we turned it back on for a couple of months. Bill went back up, so we turned it off and left it off.

jb

Maybe you could rig it to start the pump when you turned on the bathroom light?  Or you need some kind of thermostat to only run the pump when the water in the lines cools.  (the pump is on the return line, right?)

I wonder how efficient it would be to have a 2.5 or 3 gallon electric WH at the farthest bathroom where you want quick hot water, and plumb its inlet with hot water from the main WH?

[KD5NRH]

I wonder how efficient it would be to have a 2.5 or 3 gallon electric WH at the farthest bathroom where you want quick hot water, and plumb its inlet with hot water from the main WH?

Or a relatively low-wattage tankless; once the inlet water temperature exceeds the set temp, it's not going to be doing anything anyway.  Plus, what I've found frustrating in a few places is just wanting some hot water to wash my hands, and having to wait 2-3 times as long as the shower or tub for the sink faucet to be able to clear the line.

Of course, sizing is tricky, since Fed regs limit the shower head to 2.5GPM at 80PSI.  (At time of sale, of course.  If you've drilled out or "accidentally lost" the constricting bit then you're just going to have to measure.)  I'm not sure about city supplies, but I know our balance tanks were usually set somewhat under 50PSI.  (According to popular Mechanics, 40-50PSI is normal for residential customer on a municipal system.)  How that affects the flow rate depends on several factors, but the easiest way to figure it out is a good old fashioned bucket of known volume and stopwatch.  

It also comes down to what you're willing to accept for the delay time; if you're satisfied with just knocking the chill off until the main supply gets there, one of the 110V <=15A heaters may be enough, and won't require any rewiring, (Some of these are actually mini-tank, but may be more space-efficient than the typical cylindrical tank mini heaters.) or some 15-30A ones use two circuits, so you're still only dealing with normal 110V wiring.  
YMMV, though; the only sizing info I can find on them is "x GPM @ 105 from y inlet temp," whereas they will, of course, allow a higher flow rate and heat from a lower inlet temp, but just won't get the water all the way to 105F.  IME, 98F is not uncomfortable regardless of ambient air temp, so you can easily stand a 7F drop there without standing around shivering until the main hot water shows up...with a bonus of not dropping below that if the main heater runs out while you're showering.