Oddly, I don't think we are too different in our opinions. We both appreciate either side can easily manipulate the numbers to justifiy their case.
I like the idea of a better "overall" solution. The combi approach is interesting. I would like to see more solar thermal applications and I can see how you could intergrate with this approach. I think a major stumbling block with solar WH is the cost to garuantee constant hot water. A solar water heater could provide 90% of your HW needs but that last 10% will cost you. Either in capital (Tankless) or standy loses with a tank heater. If you could have a combi system that could easily incorporate thermal solar plus with some heat storage options, it becomes attractive in overall energy use.
My winter cold water supply can and has approached 33 degrees. The most temp rise most of the tankless can provide is maybe 90-degrees. Considering it has to run through nearly 40' of pipe to get to my shower, even at all hot, there may not be enough hot for a comfortable shower - it does cool off along the way regardless of the insulation. It all depends on where you live, and your expectations. Some of the tankless restrict the flow to maintain the temp rise, some don't, and the output just gets colder making getting just the right temp nearly impossible to attain.
I'm glad I switched to an indirect...obviously, that's not an ecconomical option unless you have a boiler, but I do, and did...much better!
Important note - I'm not a pro
Retired Defense Industry Engineer
That is meaningless. There are shower heads, and there are shower heads. The type of shower head makes a huge difference on what the water flow feels like when it is compared with the maximum flow rate.
Around here, the state water authority went around and changed everyones shower heads to a low flow air mix type of shower head. Mix some air in with the water, and the spray feels nice and strong. I have never measured the maximum flow rate.
There are full flow shower valves and adjustable flow shower valves. If you can't adjust the flow for comfort, then the shower head determines the flow rate. I can adjust my flow rate for comfort, then I measured the result.
The point was you can run out of temperature rise with a tankless to make those calculations useless!
We had a 30g oil fired that went & we switched to a 50g high efficiency electric - no gas to the house. We need a new boiler so I want a hot water coil i n the boiler. In the winter the boiler will run & take the load off the electric. In the warmer weather a solar heater will assist. We have about 80 psi here, pretty good flow.
Between these 2 methods I'm hoping to cut the electric use
It's 12 degrees out & my input Temp is around 46-48. The basement has dipped to 54 from normal temp of 58-63. The next fgew days will be even colder
I'm not sure what the gpm is, but I've been in lower psi areas & the flow for taking a shower is poor. Some of this may have to do with the design of the shower head
DIY Handyman (not 4 hire)
I have enough to do to my own house
Maximum temperature rise depends on the flow rate required.
My longest run is about 60 feet and is insulated. I set the heaters thermostat for about 125 degrees measured at the kitchen sink. I have never had a cold shower. I always have to mix in cold water for a comfortable shower.
To maintain the water temperature my particular heater uses a modulating gas burner (25K to 125K BTU) which is controlled by a thermostat that measures the outgoing water temperature. It has a fixed flow restrictor that limits flow to a maximum of 3 1/4 gallons per minute. Not sure of the maximum rise that I can out of the unit, but it is around 85 degrees right now (40 degrees input - 125 degrees output).
I just noticed that the MWRA web site has a link to the toilet section of the Terry Love web site.
Last edited by Ladiesman271; 01-15-2009 at 10:43 AM.
From what you said I thought it was a mandatory replacement program. It would be nice of there was a "loaner" shower head program. Take a low flow shower head home (with deposit) & try it out, if you like it keep it - if not return it
There are still a lot of high gallon toilets out there
DIY Handyman (not 4 hire)
I have enough to do to my own house
It was "mandatory" to a large extent. Over ten years ago they had crews go around town and provided and installed everything at no charge. I still have all of my 50 year old toilets. The MWRA installed water dams in each one of them. The shower heads are rated at 2.2 gpm or lower. They are the air mix type, so the force of the water feels higher than a standard flow unit
Seems like the water consevation programs have helped out with water use.
"Operation WaterSense, a joint program of MWRA and its communities, offers conservation services directly to MWRA communities. The program has helped reduce demand from 330 million gallons of water per day to 220 million gallons of water per day, and has helped residents control their water, sewer and energy costs."
Many if not most newer solar heated homes are using tankless HW heaters as backup and "finish" heat for lukewarm storage, and in that application it's the right way to go. Also, more and more people are moving toward low-temperature hydronic heating in their freshly insulaton-upgraded & air infiltration upgraded homes too. When a tankless modulating HW heater's burner exceeds the house's design-day heating load by a factor of 3 or 4, using an oversized cast-iron boiler just to be able to run an indirect-fired tank isn't very efficient (still probably better than a tank HW heater + a right-sized cast iron boiler though). Utilizing a modulating mid-efficiency burner like a tankless as the combined system's heat source then becomes more cost effective up front, and significantly more efficient. With a tankless the modulation factor "right sizes" it semi-automatically to match the actual instantaneous heat load, whether the instant demand is for hot water or to run a hydronic heating zone.
Using a low-head reverse-indirect HW heater as both the space heating buffer and the hot water heater makes for a very nice space-efficient package too. With a single buffer that all heating zones draw from/return to in place, once properly adjusted, the delta-T that the burner needs to support varies with the volume & temperature of the return water from the zones. The flame modulates up & down as the zone demands kick on & off, and only when all zones turn off and the high-limit aquastat on the buffer tank trips does the tankless flame turn completely off. This is a tried & true system architecture adapted from large building heating plants, but applied in micro-scale to micro-zoned residential structures. Actual fuel savings are usually well into double-digit percentages with this approach compared to bang-bang on/off controls.
BTW: Many manufacturers void the warranty for tankless HW heaters used as boilers in heating systems, but I'm not sure why this should be so. If the system has even 10-15 gallons of buffering capacity the number & depth of thermal cycling will go down relative to HW use only. Takagi seems to be the only manufacturer actively encouraging combi or space heating use across their entire product line, but there are many many Rinnais and others running (off warranty) heating systems. A relative newcomer to the US market, Navien has pre-engineered some heat-exchangers & controls to make (un-bufrered) combi-system design easier: http://www.heatingbox.com/
Navien condensing units seem to have a following among the solar-heating combi-crowd, but take "condensing" with a grain of salt here, eh? (I haven't seen any test data, but the "98% efficiency" number they tout is likely only going to hold true when the water entering the heater is well under 50F, whereas in most heating applications return water much under 100F isn't the norm. It might hit 88-89% combustion efficiency in a heating application though- better than the ~85% combustion-efficiency of a standard tankless running ~100F return water (the eKoComfort measurements). I'm not sure the condensing unit it's worth the extra money though- the difference price could buy you another 40 square feet of installed flat panel, with a bigger reduction in annual fuel use in much of the lower 48. (I'd leave that up to the local solar designer to do the math on, but it's worth asking the question at design-review time.)
As houses become tighter & better insulated to the point where instanteous heat load far outstrips HW heater output capacity, a wave of combi systems (includting tankless HW heater types) is coming. Time will tell where the costs & benefits break down, but it's getting harder & harder to rationalize clunky oversized cast-iron boilers as fuel prices rise when low-mass modulating systems are available, and more efficient. My design-day heat load is about 30kbtu/hour, in an area with about a ~6800 degree-day climate. I could clearly run both heat & HW combi off a 199kbtu/hour in (~165kbtu out) tankless with margin to spare, getting far more use & value out of it than if used merely as a HW heater. For that matter, I could heat both my house & HW with most 50gallon gas tank heaters too (I've considered it, calculated it, modeled it, since the up front cost is SO cheap, but...), with a 10-15% comparative performance hit. YMMD.
Given some of the threads here outlining problems with Takagi units and getting the problem fixed I'll pass on the Korean Takagi...
I'm in the Northeast with some pretty cool water temps about now. I will state IMHO that the only payoff I see in tankless is with gas fired units for a situation where the home owner want an unlimited amount of hot water within the flow rate allowed by the heater(s) installed. I.E Large family with back to back to back showers and baths, larger tubs, & carwash showers. Show me otherwise and somebody is cooking the books!
:-) :-) :-) :-) :-) :-)
Yabbut, you don't get it, they're not Takagis they're Naviens- Naviens go to eleven, Takagis only go to 10... ;-) (Some Noritz models are Takagis- barely more than a nameplate change. Ever wonder why some Noritz models use Takagi remote controls? )
But in fact Naviens are their own design, probably come with their own unique sets of misery! ;-)
The scuttlebutt that some of the design team came from Takagi doesn't say much either way about 'em. They coulda been the guys who specified or designed the less-than-fully-reliable flame detector for the TK2, but they just as easily have been the guys who wanted to do it right, but were overridden by the group consensus or management, and thus were happy to bolt to a more receptive Navien when the opportunity presented itself. (I've seen many variations on this movie.) Chryslers didn't become Fords when Iacocca bolted either.
Whether the Navien proves more reliable than the competition remains to be seen, but local technical support and parts availability are useful for any device this complex. Tanks are definitely simpler beasts, with more limited sets of problems (but I've seen issues with electronic ignition on tanks less than 2 years old too, eh?) The complexity buys you some efficiency, but only at some cost. It's not a "set and forget" world, and is becoming less so every day. Where the cost/benefit is for anybody has a lot of factors (damned few of which were addressed in the CU article.)
When will this topic just DIE.
I will sum up tankless water heaters;
Expensive to buy
Expensive to have installed
Somewhat less expensive to operate
May not produce enough hot water
Work better in warmer climates
Work better with good water conditions
May not meet code in all localaties (remember the code does say that you have to provide hot water to all fixtures in the home)
Require regular service
Cause heated arguments that never ever seem to end.
Here I'll put the damn link up! Maybe he'll go away then!
I'll let someone else be the guinea pig!
When I hear nothing but good news I'll jump on the band wagon....
I'll breath until then thanks.
Last edited by Redwood; 01-15-2009 at 04:50 PM.