# TANKLESS WATER HEATERS



## Todd (Jul 28, 2006)

Any comments or recommendations on gas tankless water heaters? I hear they use less energy but cost more. Are they worth it?
Do they deliver hot water quicker? I might be needing a new heater soon, old one is acting up and is over 10 years old.


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## RoosterBoy (Jul 29, 2006)

todd I'm glad to see that your thinking about saving energy and yes a thankless is the way to go if you want to save allot of gas or oil on hotwater try to put it in the center of all your hot water needs so you ll get hotwater at the tap fast.

thanks
Jason


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## elkimmeg (Jul 29, 2006)

Rooster care to hazzard a guess why his  only lasted 10 years. What you think builder's special hed did not mention the menufacturer or BTU requirements


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## KP Matt (Jul 29, 2006)

I had tankless water heaters in my apartments in Spain and Taiwan. I never had a problem with them. Except that they used tanks of butane and that you had to call to get more delivered when you run out. I imagine that problem has been overcome. In North America I've never seen motorcycles with three giant tanks of butane strapped onto the rack careening through intersections and the driver with a butt hanging out his mouth. 

One thing I recall is that in both countries those units were always located outside the living space - in the building's interior shaft.


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## EatenByLimestone (Jul 29, 2006)

I've heard of people having to upgrade the incomming NG line to a larger diameter due to the much higher fuel demand.  This would add greatly to the cost, you may want to find out if yours is large enough.


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## PAJerry (Jul 29, 2006)

We've been using a tankless water heater since 1983 - Paloma Model ph-12, natural gas - and I would never go back to a tank.  We raised 3 kids, which meant LOTS of laundry and showers and it never failed us. No one ever ran out of hot water.  A new unit costs about $450 and is worth every penny. I have the unit tucked in under my basement steps and vented out the chimney just like you would a tank, but it hangs on the wall and takes up very little space.  The only maintenance issue I had with ours was that I had to replace a small ignition baffle due to some sediment in the water when we brought a new well on line. 15 minute job and a $5.00 part. 

  In my opinion, a tank type water heater is a real energy waster, especially if there are only 2 people in the house like we are now.  It's like leaving the coffee pot on 24 hours for 1 cup of coffee or letting your car idle in the driveway all day and making one 2 mile trip to the store. Think about it.  Nearly all of the rest of the world uses tankless water heaters so there must be good reason.


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## Todd (Jul 29, 2006)

Thanks for the replys guys. Looks like a tankless can last up to 20 years compared to 10-15 for a tank type. But the difference in unit cost plus installation probably won't make my money back. I'll have to give some local plumbers a call and see what they have to say.


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## cbrodsky (Jul 29, 2006)

The only way I see that these really pay off is if you have them right next to all of your water outlets.

In our house, we have bedrooms with bathrooms that are spread apart so the biggest source of loss for us is the fact that when you need hot water, you have to first fill all the piping running from the central boiler to the point of use.  When you're done, the volume of water in those pipes ends up just cooling down and you lose the heat in 1-2 gallons of water.  And you incur this loss every time you ask for hot water after a delay of an hour or two during which the pipes cool down again.

The other issue of losing heat from your hot water tank while it sits there is easy to overcome.  The price difference in a tankless heater will pay for a LOT of heavy insulation on a water heater.  I don't think that is really a significant difference once you add some insulation to the tank.

So my take would be if the tankless device is small enough that you can locate it much closer to your point of use than your traditional water heater, it's probably a good move.  But if not, there's no sound reason you will save any money - don't get sucked into hype.  Look at solar instead.  We know that we can't locate multiple tankless units near all our points of use so we are going that route as an even greener alternative that makes more financial sense for our situation.

BTW, as for overseas use, in small living quarters it makes sense purely for space reasons.

-Colin


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## begreen (Jul 29, 2006)

The summary is good. Note that the delay getting hot water out of the tap is often a design issue and one common to central tank hot water systems as well. Often abroad it's typical to have multiple local systems. We had 3 in our apt. in India. One for each bath and one for the kitchen. They call them geysers and were electric, so one had to turn it on about 15-30 minutes prior to use, but there was always enough hot water. In Mexico and some parts of France we had gas units, again most frequently at the point of use unless the place was pretty tiny. I think electric was prefered in India due to risk of poor installation in cramped quarters. There have been deaths reported due to CO poisoning.


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## RoosterBoy (Jul 29, 2006)

elkimmeg said:
			
		

> Rooster care to hazard a guess why his  only lasted 10 years. What you think builder's special hed did not mention the manufacturer or BTU requirements



Lot's of reasons a hot-water could fail early #1 if he keep-ed the temperature in the tank real hot that will promote scale build up
also hard water is bad for tanks anodised rods. also not sure what he has if it's a indirect hot-water then it should have lasted a little long but then again it depends.

if it's electric the changing the Col's and rods and a good cleaning and checking his water for hard. may bring it back to life
i am no hot-water heater expert i just know how to install them. and im just telling you what i have seen

but most of the time cheep hot-water tanks last about that long ;-)  if i was him id get a tank-less put it in the center of where all his hot-water use will be and he will enjoy the savings and the unlimited amount of hot water.

thanks
Jason


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## KP Matt (Jul 29, 2006)

Another small reason why they're more popular in warmer countries - if your climate is cold enough to need a woodstove, then for at least half the year the heat that a hotwater tank loses is not wasted. In warmer countries a hotwater tank is radiating unwanted heat most of the year.


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## Todd (Jul 30, 2006)

RoosterBoy said:
			
		

> elkimmeg said:
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Family of 4, Richmond 40 gal, 40,000 btu gas heater, tank is set at medium. I have well water with high iron, water softener and carbon filter, I removed the anode rod 3 years ago, was told it would help with the egg smell. Also drain it every year and have never seen any sludge or deposits come out. Last couple days the hot water seems fine.


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## Rhone (Aug 2, 2006)

I think I can give a pretty good comparison if you're referring to tankless vs. tanked instead of on-demand vs. tanked.  

Tankless models hold around 3 gallons or so of water and maintaining it at 120 or whatever you set the temp at.  So, a tankless model still idles when you're not using water, but maintaining 3 gallons instead of 40+ is better.  I have a Peerless boiler with a Beckett pump that's tankless for a family of 2, my parents also have a Peerless boiler with a Beckett pump and family of 2 except theres is configured with an 80 gallon tank.  We both burn wood for heat.  I had a problem that wasted 75 gallons of oil and ended up using 331 gallons for the year.  My father went through 330 without problems so the tankless is better, I should have used only 256.  I also used my tankless to heat my house for half of fall and spring my father didn't.  I think we both use the same amount of hot water.   That's around $187 in savings for the year.  

You can do some things with tankless you can't with a tank if you want to risk some wear & tear on it.  My tankless will be fully hot in 7 minutes after turning on.  I turn mine on/off freely as if on-demand, usually turning it on when I get up and my wife & I take our showers then we shut it off.  If at night, we turn it on, let it warm up the water and shut it off.  That creates enough hot water for up to 4 hours of washing hands, etc.  The problem with on/off is the gaskets are expanding/contracting and getting wear but I can't see how that process puts any more wear & tear than a tanked system.  This next is hard to explain.  I basically heat my house for free while we take our showers.  In winter, I have to turn it up to 170-190.  Waking up and turning the boiler on in winter, it's ready after 7 minutes but stays on heating the water the entire time I, or my wife are taking a shower trying to get the water to 190.  Instead, we turn on the boiler, turn on the heating system, in about 8 minutes it's hot enough for our showers and while we take a shower it's now heating the water we're using and heating our house at the same time.  After we're done, we go up there and shut it off along with the heating system.  That's a hard one to explain, basically instead of wasting the oil used to heat the water beyond 120F when taking our showers in winter, we're using it to heat our house instead.  One wastes the energy, the other uses it.  

So, I think there's an improvement but very hard to say exactly how much because there are differences.  I have insulation on all the pipes within 6' of my boiler my father does not.  I can shut my boiler off when not in use with little consequence, my father can not.  My fathers shower is approx 30 feet away from his boiler, mine is 10 ft.  My wife uses more hot water than probably all the others discussed combined, to offset her I do things much colder than all to probably be pretty close in the end.  I use mine for heating in parts of spring & fall, my father does not.  Anyway, with all the pluses & minuses I think a tankless system is 10-20% improvement over a tanked and I happen to probably get 20-25% because I take full advantage of the tricks a tankless system offers that a tanked system can't... but to the detriment it adds more wear & tear.


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## the_guad (Aug 2, 2006)

Don't forget that with an ondemand tankless system you may need more than 1 depending on your peak hot water usage.  I was going to get 2 but didn't have the electrical capacity and ended up going back to a standard tank.  You need a couple hundred free amps for the electric models and I think 2 free circuit slots.

In short, I would have gone tankless if I could have.


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## jabush (Aug 2, 2006)

Todd said:
			
		

> Thanks for the replys guys. Looks like a tankless can last up to 20 years compared to 10-15 for a tank type. But the difference in unit cost plus installation probably won't make my money back. I'll have to give some local plumbers a call and see what they have to say.



A buddy of mine is going with an (electric) on demand system, but he is installing it in-line above his existing 50 gal tank.  That way he has a supply of water that's at room temp instead of heating 50 degree well water.  That might be worth a look if you have room and your current tank isn't leaking.


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## saichele (Aug 3, 2006)

The tanked water heaters aren't necessarily energy hogs.  i got a mid-grade 50 gal shorty at lowes 2 yrs ago (about $300) and wrapped it in a foil backed fiberglass blanket.  And we keep it pretty low (about 115F).  But it'd big enough to fill the tub or take a shower and so on with mostly hot water (as opposed to mixing) and the relatively low gradient to the basement air temp, combined with the thick blanket, keeps gas use down to about 20 ccf/month.  

We go through about 12000 gallons of water a month, maybe 1/4 is hot, so 3000 gallons.  About 25000 lbs.  Heating that from 55 to 115 requires 60 * 25000 = 1,500,000 btus, and we use about 20 ccf/month (some of the gas is cooking, but lets ignore that).  1.5 MBTU required / 2.0M BTU used  - So it's not super efficiency, but >75%.  I bet if it were sitting thee at 150F all the time it would be a lot more, even though we use less water.  

Steve


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## BrotherBart (Aug 4, 2006)

I know. I watch these water heater discussions with great interest. My three hundred buck electric water heater set at 120 and wrapped in fiberglass blanket puts out everything we need, when we need it, and if the A/C ain't running the electric bill is $80 a month. I can't see any payback to the exotic stuff, much less heating water with oil or gas.


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## Rhone (Aug 4, 2006)

Hey, you peaked my curiosity to see if a higher costing oil boiler gives you a payback over choosing the low cost electric tank but higher cost of electricity.  In my area, a 92% efficient condensing oil boiler will run $5000 including installation.  Although they say 92% I'm using 82% because you know how those efficiency things go.  Will I ever recoup my $ choosing it over a $300 water tank & extra insulation but higher cost of electricity?  

I found out where I live it would be wiser to pay for the boiler, oil, and maintenance/year I'd start pulling ahead with the boiler system after the 4th year and at the 15 year mark I'll be around $10k the richer.   Not to say it will apply to anyone else, where I live electricity is off the charts and every dollar I spend in oil I have to pay $2.66 to do the same using electricity.  This makes me think of my future, as next year I plan on switching over to a solar domestic hot water system with electric backup.  Electricity costs so much I may be better off keeping my oil boiler and using it as the backup instead of paying for electric backup to my water tanks (I'm planning on 3 tanks).


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## saichele (Aug 4, 2006)

Sure, and if you're using the boiler for heat anyway, it all makes sense.  We have GFA heat, so no help there.

Inthe shoulder seasons, our combined gas and electric runs about $80.  Last couple months more like 150.  Winter a little over $100, but burning 100/mo in wood.

Steve


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## Sandor (Aug 4, 2006)

I think doing calculations based on today's energy rates is a bit misleading when doing cost analysis.

I would add about 5-10 percent year after year to oil/gas/electric costs as a ballpark when doing forward calculations for payback.

I really don't do the analysis any longer, I just buy the most effiecient anything I can.

Glad I left Maryland, most electric rates in that state increased 30-60 percent due to deregulation restrictions ending. Talked to my mom in MD yesterday, and they got wacked with a 30% increase.


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## jabush (Aug 4, 2006)

Sandor said:
			
		

> I think doing calculations based on today's energy rates is a bit misleading when doing cost analysis.
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> I would add about 5-10 percent year after year to oil/gas/electric costs as a ballpark when doing forward calculations for payback.
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Actually it was more like a 17 percent increase (July 1st) this year for BGE customers in MD.  Next year they will get us with the rest of the hike, which will be another 55 percent.  Either way it sucks!!


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## Sandor (Aug 4, 2006)

jabush said:
			
		

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Yep. My mom has SMECO - Southern MD Electric Cooperative. Maybe there is more on the way for her.


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## jabush (Aug 4, 2006)

Sandor said:
			
		

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Sorry...I assumed (wrongly) that she was a BGE customer.  I think the other utilities in MD have been increasing their rates all along, but BGE people will take huge hit over the next couple years.

I think I'll insulate my water heater soon.


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## Sandor (Aug 4, 2006)

jabush said:
			
		

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I used to work in Baltimore City and you should have seen the line of trash trucks heading in to the BGE generating plant of of 95!

So, your paying money to have Baltimore City and County burn their trash!


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## richg (Aug 8, 2006)

I replaced my electric tank with a Bosch tankless. It has dropped our electric bill by $50.00 per month.


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## Mo Heat (Aug 9, 2006)

richg said:
			
		

> I replaced my electric tank with a Bosch tankless. It has dropped our electric bill by $50.00 per month.



Is that because the tankless is Natural Gas and your old tank DHW heater was electric? If so, did your NG bill increase at all?


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## jabush (Aug 26, 2006)

Coaster said:
			
		

> *Tankless Heaters are Merciless to the Electrical
> Grid*
> 
> Oct. 18, 2005
> ...



Now that is very interesting.  I never would have thought of the big picture implications.  
Good find.


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## BrotherBart (Aug 26, 2006)

Kinda the same thing as the local sewer utilities at halftime during the Superbowl.


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## cbrodsky (Aug 27, 2006)

Coaster said:
			
		

> *Tankless Heaters are Merciless to the Electrical
> Grid*
> 
> Oct. 18, 2005
> ...



Interesting article.  

I think the real solution to the hot water question is well insulated storage linked to a network controlled pricing system.  As utility companies gear up to supply data over the same utility lines, and wireless communication technology becomes pervasive, it's not ridiculous to think your hot water tank could get a signal to load up at 3AM when your local grid has no demand for the power on it - the power company can give you a great discount while making more money selling power that is otherwise worthless.

Same reason timer-controlled plug-in hybrids could be so useful to take advantage of off-peak production.

-Colin


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## brian_in_idaho (Aug 29, 2006)

Another item to consider with tankless designs, since they heat on demand, they need to put ALOT of watts into water in a short period of time, hence you have high peak demands and therefore lots of current draw.  I haven't looked that much, but I suspect that the power draw is far in excess of the 30 amps typical for a fixed system, that can tolerate a more gradual buildup in heat.  The reason I bring this up is that your wiring will probably need to be considerably larger wire (priced copper lately?), and if you have 2 of these, you may put quite a drain on a 200 amp service, especially with other loads.

check out the ones here:
http://www.gotankless.com/downloads/twh_brochure.pdf

The 3 gpm unit requires a 120! amp breaker.

Bri


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## got wood? (Sep 20, 2006)

My cousin is a plumber (30 years) in Oregon and he said one of the more efficient ways to reduce your hot water demand started with the pipes and not the heat source.  His opinion is that if you have a circulating loop of hot water throughout the house (assuming reasonably well insulated pipes), you get hot water instantly and don't run several gallons first for trivial things like washing your hands, etc.  He claimed that water leaving the hot water source at 120 or so degrees returns a few degrees cooler from its loop-trip to be re-heated up by just a bit of fresh hot water.  He likened it to spinning a basketball on  your finger and using your other hand to hit the ball in order to keep it spinning.  He said a circulator pump runs at 20-40 watts...Interesting idea for new construction, but converting an otherwise star-pipe topology to a loop might be a bit much for us non-plumber-types.


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## brian_in_idaho (Sep 20, 2006)

got wood? said:
			
		

> My cousin is a plumber (30 years) in Oregon and he said one of the more efficient ways to reduce your hot water demand started with the pipes and not the heat source.  His opinion is that if you have a circulating loop of hot water throughout the house (assuming reasonably well insulated pipes), you get hot water instantly and don't run several gallons first for trivial things like washing your hands, etc.  He claimed that water leaving the hot water source at 120 or so degrees returns a few degrees cooler from its loop-trip to be re-heated up by just a bit of fresh hot water.  He likened it to spinning a basketball on  your finger and using your other hand to hit the ball in order to keep it spinning.  He said a circulator pump runs at 20-40 watts...Interesting idea for new construction, but converting an otherwise star-pipe topology to a loop might be a bit much for us non-plumber-types.



I'm doing that at my place, the plumbing loop is in place, I still have to install the water heater and pump (new construction).  I installed a parallel loop to the main "trunk line" I have feeding the house, there is maybe a 10 ft run max from the trunk to each fixture.  My only concern with the circ pump is that you are constantly pumping hot water through some 100 or so feet of pipe, loosing heat all the while.  I need to research effective pipe insulations and get it in place.

For DIY plumbing PEX pipe is your friend, I have soldered some amount of copper, PEX is much faster to install.


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## cbrodsky (Sep 20, 2006)

got wood? said:
			
		

> My cousin is a plumber (30 years) in Oregon and he said one of the more efficient ways to reduce your hot water demand started with the pipes and not the heat source.  His opinion is that if you have a circulating loop of hot water throughout the house (assuming reasonably well insulated pipes), you get hot water instantly and don't run several gallons first for trivial things like washing your hands, etc.  He claimed that water leaving the hot water source at 120 or so degrees returns a few degrees cooler from its loop-trip to be re-heated up by just a bit of fresh hot water.  He likened it to spinning a basketball on  your finger and using your other hand to hit the ball in order to keep it spinning.  He said a circulator pump runs at 20-40 watts...Interesting idea for new construction, but converting an otherwise star-pipe topology to a loop might be a bit much for us non-plumber-types.



Interesting idea, but fundamentally flawed - all that constant circulation of hot water = more heat loss, plus you're paying for electricity to drive that process.  If you didn't lose heat by circulating that hot water, then you would always have on-demand hot water - it would stay hot in the pipes.

In fact, by constantly refreshing hot water in those pipes, you actually accelerate any heat loss you normally have after shutting off the hot water because you maintain a larger thermal differential all the time.

It will certainly accomplish your goal of instant hot water, but it'll be pricey.  That being said, there are systems like this that bridge your hot/cold water lines to do something similar, and when I have excess free solar HW in the summer, I could see using one...

-Colin


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## begreen (Sep 20, 2006)

Flawed assumption. The system should only circulate hot water when the loop drops below a set temp point. And a good one will have a timer on it so that it doesn't run when not needed. I installed a tiny Grundfos Comfort Pump and love it. The hot water lines are all insulated and I would guess that it runs for about a minute every 30 minutes on average. The loop temp is set low, comes on at about 105 degrees and off at about 110. 

I thought they might go up, but our electric bills went down as soon as we stopped running water in the upstairs bathroom just to get it hot. Difference - before about 90 sec. to get hot water. Now, about 5 sec. With 4 people taking showers that can add up quickly. We pay for our water and it's expensive, so it was a double savings.

http://www.plumbingsupply.com/grundfoscomfort.html


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## cbrodsky (Sep 21, 2006)

BeGreen said:
			
		

> Flawed assumption. The system should only circulate hot water when the loop drops below a set temp point. And a good one will have a timer on it so that it doesn't run when not needed. I installed a tiny Grundfos Comfort Pump and love it. The hot water lines are all insulated and I would guess that it runs for about a minute every 30 minutes on average. The loop temp is set low, comes on at about 105 degrees and off at about 110.
> 
> I thought they might go up, but our electric bills went down as soon as we stopped running water in the upstairs bathroom just to get it hot. Difference - before about 90 sec. to get hot water. Now, about 5 sec. With 4 people taking showers that can add up quickly. We pay for our water and it's expensive, so it was a double savings.
> 
> http://www.plumbingsupply.com/grundfoscomfort.html



Yes, you don't wait for hot water, but that's because it runs to fill the line up all the time before you get a chance.  Without such a device, you would be charging your lines up with hot water only when you use hot water.  But by keeping the pipe hot, you are regularly using up hot water every 30 minutes keeping that line charged up to temperature.  You can reduce this behavior with a timer, but not eliminate it.

Comfort device, yes I can buy, and will probably put one in our house.  Possibly even cost saving if you're paying big $$$ for water/sewer expense on that first bit of water you throw down the drain waiting for the hot water to come or doing rainwater collection with your backup being trucked in water.  But not energy saving - doesn't come for free.

Perhaps Grundfos' website says it best in their FAQ:

"Does a hot water recirculating system use up a lot of energy?  Both options use energy. But not as much as most people think."

That, I can agree with 

-Colin


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## Homefire (Sep 21, 2006)

These circ systems for the home should be on a timer that you set to run when you 
normaly use water, say for the morning shower or after 5 
when everyone is hom. Then set to turn off at bed time and while your at work..
Not perfect but it will save a bucket load of electricty to heat that little bit of water to wash  your hands.


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## cbrodsky (Sep 21, 2006)

homefire said:
			
		

> These circ systems for the home should be on a timer that you set to run when you
> normaly use water, say for the morning shower or after 5
> when everyone is hom. Then set to turn off at bed time and while your at work..
> Not perfect but it will save a bucket load of electricty to heat that little bit of water to wash  your hands.



Folks, believe it or not, these do not save you heat.

Without such a device, you flush out the cold water in the pipe, and when hot water gets there, you wash.  When you're done, only the hot water left in the pipe cools down, and it cools down once.   That heat is lost.

With such a device, for a period of time you are keeping that pipe hot even when not using water, losing heat before you even decide to use hot water.  And when you're done washing, the pipe will still have hot water.  But instead of letting it cool down, you continue to put heat into it to keep it up to temperature until the timer turns off.  And you lose more heat by holding it hot that long.

Heck, even the manufacturer makes that point clear on their website... it does cost energy.  Maybe not a lot, but it's most certainly not saving energy.

-Colin


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## Homefire (Sep 21, 2006)

NY Soapstone said:
			
		

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But you don't stand there forever waiting on the water to get hot as it is already hot and instead of the luke warn water going down the drain it returns to the tank as opposed to cold water from the well or street. There is most certainly an electrical savings. IMO


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## begreen (Sep 21, 2006)

Colin. These units have a thermostat.  -*- They don't run all the time. -*-  Ours runs about  24 minutes per day total.

 It's also an error to assume that the hot water heater is going to kick on just because the pump as running. It doesn't always and won't unless the tank temp drops below the set point. What I think the pump manufacturer is trying to cover is for installations where the pipes are not insulated. But I can say from direct experience, insulating them makes a big difference in the frequency of cycling of the pump and the length of time it runs.


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## cbrodsky (Sep 21, 2006)

BeGreen said:
			
		

> Colin. These units have a thermostat.  -*- They don't run all the time. -*-  Ours runs about  24 minutes per day total.
> 
> It's also an error to assume that the hot water heater is going to kick on just because the pump as running. It doesn't always and won't unless the tank temp drops below the set point. What I think the pump manufacturer is trying to cover is for installations where the pipes are not insulated. But I can say from direct experience, insulating them makes a big difference in the frequency of cycling of the pump and the length of time it runs.



I don't think you're understanding the point - you only lose heat out of the hot water pipe if you keep it hot.  So, your thermostat is designed to do just that - keep the entire hot water pipe run hot - all the time.  Whether you're using it or not.  And by keeping something hotter than the surroundings, you will lose heat.  No different than your house - keep it hot all day, lose more heat.  How it does that is somewhat immaterial - energy is energy.  Keep it hot for a longer period of time, you lose more heat to the outside.  Nobody is saying it always runs your water heater, but it is regularly taking hot water out of your heater and refilling it with lukewarm water even when you don't use your hot water.  That is wasted energy plain and simple, and it will cause more total usage in the long haul.

All of this can be reduced with pipe insulation, timers, etc... but none are as energy efficient as just letting the cold plug of water in the pipe go down the drain, and using the hot water when it arrives.  (obviously if you flush it way beyond that point, then yes, you are wasting a lot more)

Don't get me wrong - I see why people like them, I'm sure it's not a huge loss of energy, and I'll probably put on in our house - with solar HW I won't even worry about the loss.  However, you guys want to believe you've somehow beaten basic thermodynamics and heat transfer.  More power to you, but even the manufacturer admits that there is lost energy when you install such a system.  Right on their website.  Why in the world would they admit that if it wasn't true?

-Colin


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## velvetfoot (Sep 21, 2006)

The heat is not really wasted during the heating season since it warms the house, no?


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## cbrodsky (Sep 21, 2006)

velvetfoot said:
			
		

> The heat is not really wasted during the heating season since it warms the house, no?



Only if they are within a sealed heated envelope of the house.  (which they should be... but often aren't...)  And of course if you're using electric to heat that water, pretty expensive way to throw heat into your home.  Not to mention much of the year, it will work the other way, and dump heat into your house which now you have to get out of the house with A/C so you still come out behind there 

I'm sure the actual loss is relatively minor, but point is that it's not zero.  Simple common sense tells us that, and even the manufacturer makes that point clear.  And the further your pipes run, the greater the volume of water your constantly refreshing with new hot water, and thus the greater the losses.

-Colin


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## got wood? (Sep 21, 2006)

I think what you're saying NY Soapstone is that it uses energy, but how much is the question.  Let's take a simple example: compare a `star' or `home-run' to the hot water source example (what most of us have) to a loop setup.  Let's say it's a kitchen sink that is 25' away from the hot water supply with 1" properly insulated copper piping.

pi*r^2*h will give you the cylinder volume in cubic inches of the pipe, divide that by 231 to get gallons. 

3.1415*1^2*(25*12)=942.45 cu/in or 4.08 gallons of cold water in the pipe for a non-loop system.  You want 1 gallon of hot water in the kitchen, that would require 5.08 gallons of hot water to purge the line and deliver the hot water (not counting heat loss of that 1st gallon of water in cold pipe).

In a loops system: 3.1415*1^2*(50*12)=1884.9 cu/in of hot water in the pipe loop or 8.16 gallons.  You want 1 gallon of hot water in the same kitchen, that would require 1 gallon of water from the hot pipe.

What I've ignored here is that it took 8.16 gallons to heat that pipe in the loop system, so for that 1 gallon, it's actually 9.16 gallons.  What about 30 minutes later you want another gallon of hot water.  Standard non-loop system would require 10.16 gallons to deliver that 2nd gallon of hot water, the loop system would require 10.16 gallons.  For the 3rd gallon an hour later, we're looking at 15.24 gallons in the non-loop configuration and 11.16 gallons in the loop configuration.

This example ignores the fact that additional hot water would been needed to keep that loop hot...how much is something I do not know off the top of my head.  Would it require 2 gallons of hot water added over 2 hours to maintain a desired temp?  I don't know.  How much energy does a circulator pump draw if it comes on every 20 miunutes for a minute or so?  Maybe 50 watts, maybe more but not much.

This was a simple example of course.  If you have multiple bathrooms, kitchen sink, dishwasher, clothes washer on this loop vs. a star topology to each hot water fixture, I think the savings might become more apparent.

my $0.02


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## cbrodsky (Sep 21, 2006)

got wood? said:
			
		

> I think what you're saying NY Soapstone is that it uses energy, but how much is the question.
> 
> This example ignores the fact that additional hot water would been needed to keep that loop hot...how much is something I do not know off the top of my head.  Would it require 2 gallons of hot water added over 2 hours to maintain a desired temp?  I don't know.



I agree, and I think the basic key here is just what you state - you can't ignore that loss, but it's also very hard to estimate not knowing specifics.  All we can say is that the wasted heat here is > 0.  The circulator manufacturer admits this issue and encourages you to minimize this component as much as possible using extra pipe insulation and timers, but it will never go to zero.  They pitch it on raw water volume savings and convenience - not energy savings.

If not using a circulator, the pipe would have cooled to a certain point requiring you to draw in new hot water to fill the pipe and meet demand.  In the simplest case, suppose that entire 8 gallons is at room temperature - now you refill it.  But if you had a circulator, you still have to draw in enough BTUs with fresh hot water to maintain the same 8 gallons at the hot water demand temperature.  Additionally, you have to do this both when using it and when not using it.  Even more, the rate of heat loss will be greater because you constantly maintain a larger temperature differential to ambient conditions at all times.  Finally, the icing on the cake is you pay some small amount of electricity to drive this entire process with a circulator.

So, when you sum all these issues up, there is some real loss.  The amount will vary tremendously from one situation to another.

-Colin


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## brian_in_idaho (Sep 25, 2006)

I think homefire is hitting on one of the key points.  With a non-circulating system, it's true that you loose more heat out of the pipe, delta T is higher all the time, driving more heat loss.  However, the difference is that with this system you are still returning 100 or so degree water to the tank.  With a "standard" system, when you flush out the cool water in the line to your fixture, you are replacing that water in the tank with 50 degree or so "cold" water, in effect loosing the additional 50 degrees of temperature difference, and however many watts/btus that were in the line.  If I get the chance to play with some scenarios and typical heat loss calculations I will.

Bri


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## cbrodsky (Sep 25, 2006)

brian_in_idaho said:
			
		

> I think homefire is hitting on one of the key points.  With a non-circulating system, it's true that you loose more heat out of the pipe, delta T is higher all the time, driving more heat loss.  However, the difference is that with this system you are still returning 100 or so degree water to the tank.  With a "standard" system, when you flush out the cool water in the line to your fixture, you are replacing that water in the tank with 50 degree or so "cold" water, in effect loosing the additional 50 degrees of temperature difference, and however many watts/btus that were in the line.  If I get the chance to play with some scenarios and typical heat loss calculations I will.
> 
> Bri



That is true that there is potential to recover some of the heat, just like using timers to only run part of the day, and other tricks to minimize the impact.  But at the end of the day, heat is being lost... there is no escaping that fact with these systems.  The hot water cools down a bit in the hot water pipe, is then sent back into the cold water line, where it cools some more, and then it eventually goes back into the water heater to heat back up again.  This cycle continues as long as you are running a circulator.  That takes heat that you don't have when not using a circulator.  Think of your water pipes as relatively ineffective baseboard raditors - you are just constantly churning hot water through them and they radiate it out, albeit slowly.

-Colin


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## begreen (Sep 26, 2006)

Yes there will be a minor heat loss, just as there is from the hot water heater itself. But there will be much more heat lost with incoming 45 degree water replacing depleted hot water in the tank. If this incoming water is run just to get the tap or shower hot, it is much more wasteful and takes much more energy to recover from. Have 4 people doing this with every shower and face washing in the sink every day and it really adds up. If you are paying for your water it adds up more than doubley quick.

Also, the loop in our system does not feed back into the cold water. We have a 3/4 HW feed going upstairs. Just before the 2nd floor shower I have a tee where a 1/2" recirc line returns to the pump which circulates back to the bottom of the HW tank. It doesn't touch the cold water line.


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## cbrodsky (Sep 27, 2006)

BeGreen said:
			
		

> Yes there will be a minor heat loss, just as there is from the hot water heater itself. But there will be much more heat lost with incoming 45 degree water replacing depleted hot water in the tank. If this incoming water is run just to get the tap or shower hot, it is much more wasteful and takes much more energy to recover from. Have 4 people doing this with every shower and face washing in the sink every day and it really adds up. If you are paying for your water it adds up more than doubley quick.
> 
> Also, the loop in our system does not feed back into the cold water. We have a 3/4 HW feed going upstairs. Just before the 2nd floor shower I have a tee where a 1/2" recirc line returns to the pump which circulates back to the bottom of the HW tank. It doesn't touch the cold water line.



I think the basic point is still lost on most in this thread - the circulator is still costing more than the alternative of no circulator.  Remember, the only reason the circulator runs is because you are losing heat.  

I'll try to explain another way...

Case 1 - you use hot water, and then you go away.  You do not come back for hot water until the pipes have completely cooled to ambient, thus your heat requirement to prepare for next use is to bring groundwater up to hot water temperature for whatever volume of piping you have.

Case 2 - you have a circulator.  In the time it took the pipe to cool in case 1, you have had many repeated cycles of injecting hot water to sustain a higher setpoint temperature in the pipe and discharged some lukewarm water back to the hot water tank.  This is assured because in case 1, you cool from say 120 to 70.  On the other hand, every single time you drop below say 110 in case 2, you refill that hot water line with 120 degree water.  So you do this again and again compared to case 1.  Over the same time period as case 1, you have worked to maintain a higher differential temperature between your hot water line and ambient.  This drives increased heat loss from your hot water line.  Heat loss is proportional to the difference in temperature of your heat source and surroundings.  This loss assuredly exceeds any recovered heat you gain out of sending the partially cooled water back to the hot water tank.  That step of course helps, but you are still behind.  Why?  This just boils down to fundamental thermodynamics and heat transfer principles.  You cannot run this cycle without losing heat in the process compared to doing nothing, letting it cool, and warming the pipe up again only at the time of use.

Surely there are some other chemical/mechanical engineers on the thread that could take a stab at explaining this point?

It has also been pointed out that the manufacturer makes it clear that there is some moderate energy penalty.  Additionally, it has been pointed out that these devices come with timers.  Why?  If you gain energy savings by running it, why not run it all the time?  The answer is because it in fact increases heat use and the timer is key to help reduce those losses.  Entropy always wins.

-Colin


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