New home build- considering electric tankless or multiple point of use

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Mtnmama

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Hi,
I've been reading these forums for ages but never joined. We are building and have run into a major dilemma so sorry for a long post. Hot water options for us are electric tank, heat pump tank, tankless or point of use units. We have 320 Amp electrical service but have no gas available on the property. At the base of the mountains in CO with a 17 ft gallery well near a stream so we'll get a lot of snow melt water...according to the map our lowest water temp is 40 degrees but it might be even colder in winter.

I have been looking at the Stiebel Tempra 36+ unit which it seems could get us 3.5-4 gpm at a 60-70 degree temp rise- enough for two people to shower at the same time (we have low flow showerheads and other trim). The plus features reduces water flow when more demand is requested (someone running a faucet for example) but doesn't mix in cold so no temperature shock. I love the idea of how small this would be and the unlimited hot water idea, although I do understand we would have to be mindful not to be doing too many things at once especially in winter. I have read about recirc pumps and though I wouldn't want to have one going all the time because that seems to defeat any efficiency the tankless brings- but I do see the value in the push-button activation D'mand setups. Maybe there is an even better way than recirc.

My questions are this - is this a viable approach? The plumber our GC brought on admitted he had never installed such a system and knows nothing about how they'd work in our setting. Our GC is pushing toward heat pump tank but I read those need a 10x10+ room to work and we don't have more than 2' width in a long closet. While we are ok not running all 3 showers at once, I am wondering how it will work if someone is showering and other people are trying to wash hands or someone starts up the washing machine or dishwasher. Now those appliances are both water efficient and have integrated heaters but I know they do still pull hot water before heating it up further so I don't know in reality how this is all going to function. Obviously we don't want to end up with tepid water in the dead of winter. We have a 3 story house and could locate the Tempra on the second floor so most fixtures and showerheads are within 25 feat of the unit. However our kids' bath would be more like 50 feet away, so that one concerns me (2 young kiddos). We also have a first floor guest room that while close to where the tankless would be - would have it's own kitchen sink, bathroom sink and shower, and compact laundry for occasional family visiting. Maybe this area needs its own setup?

My husband is thinking multiple point of use units throughout the house would be better than one central tankless. I cannot for the life of me figure out how to coordinate all these together, especially considering high electrical draws. Do we need one or more in every bathroom, kitchen, and laundry? Could one unit be piped to serve more than one fixture? The point of use units also seem not to heat as efficiently as far as temp rise although I understand for one shower you don't need so much. Again our plumber said he had only installed the under-sink varities in commercial settings and had no idea about a whole house setup. I'm a bit lost on this part.

I've read so much about it my head is spinning and yet I don't have a clear solution. I really want to make this work - especially because we are doing new construction so can plan it ahead the right way. But I need some professional advice. If you've read this far, I thank you!! :)
 

Jadnashua

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IMHO, it's not particularly practical to use an electric tankless system for whole house use.

A typical gas-fired one of sufficient size for most people (in the USA, anyways - we like lots of hot water!) is 199,000BTU. That converts to 243A, if you could find one that large. Well, it would be somewhat less, since it would tend to be more efficient than the gas-fired one, so maybe in the range of 200-220A verses 243A. And, some would find that that size tankless is too small if they have especially cold incoming water to heat up. Your water may or may not be hard, and if it is hard, you'd need to perform regular deliming of the heat exchanger to keep the performance up. FWIW, one that size in electric would be drawing over 58Kw/hour, but nearly nothing when no hot water is being used. A tank-type would spread that load out over a longer period as you drained it, then it recovers, keeping the peak load much more reasonable.
 

Dana

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Electric tankless units may become a liability if the utility ever assesses demand charges (they're coming- sooner than we'd like). Demand charges are regularly used as part of the rate structures for commercial and industrial power users, but still a bit rare for residential rates in the lower 48 (less rare in Alaska). For commercial users with demand charges the demand charges are of the the largest line item in the bill.

The charge is usually based on the average power use in some pre-defined interval for the heaviest interval during the billing period. Eg: If you're assessed $10/kw in demand charges for the heaviest use 15 minute interval, taking a couple of showers with that 36 kw Stiebel Eletron could theoretically add as much as $360 to the bill (!).

With the push-back on net metering of roof top solar many utilities are currently investigating residential demand charges as part of the rate structure as a means of recouping the sunk cost for the grid infrastructure needed to support peak loads a the average draw from the grid dwindles with more & more behind-the-meter generation. Even at $2/kw an electric tankless is a liability. This is coming to a utility near you sooner than you might think.

Mid-winter incoming water temps in Boulder are under 40F, and the temp at the showerhead is about 105F, so you have to assume a 70F rise. A couple of low-flow 2gpm shower heads is 4gpm, or ~2000lbs/hr. At 70F rise that takes 2000lb x 70F= 140,000 BTU/hr, which translates to 41,000 watts. That's more power than the Tempra 36 can deliver, which means you have to go with ultra-low flow showerheads. If the washing machine or dishwasher draws hot water when somebody is in the shower it won't be pleasant.

Multiple point of use electric units might fix the screaming shower situation, but further aggravates the potential future demand charges problem.

The standby losses of an electric tank are low, and the upfront costs are low. In some locations (currently the PJM mid-atlantic region) "smart" hot water heaters or standard hot water heaters can pay back the homeowner for letting a third party aggregate the control of one or more of the heating elements to be uses as a "virtual generator" into the ancillary grid services market (stabilizing the grid frequency & voltage), paying on the order of $100/year. One such aggregator using hot water heaters for this purpose is Mosaic, who explains how it works on their website. That's a net benefit to the grid, in stark contrast to the net abuse of the grid infrastructure done by high current intermittent loads such as tankless hot water heaters.

A Supreme Court ruling last year upholding FERC Order 745 required that demand-response approaches grid stabilization & capacity issues had to be allowed to compete directly against power generators for those services, and though the local market rules have not been fully developed in all parts of the US, this too is likely to be coming soon to a utility or grid operator near you.

The grid and electric utility situation in Boulder is currently in a state of flux, with the city negotiating transfer of control of the local grid from Xcel. To be sure, the need for ancillary services will not be going away, but it's not clear who will be managing distributed demand-response or demand-charges, either of which could have a dramatic affect on whether an electric tankless solution is financially viable for you. Call the utility-see if they offer any compensation grid-smart water heaters, or if that's something currently under discussion. (Adding smarts to an existing standard electric is neither expensive nor difficult, but if they're incentivizing grid-aware water heaters it's worth taking them up on that!)

Heat pump tanks are a bit noisy, but they reduce the cooling load during the summer season, at the expense of increasing the heating bill somewhat in winter, and might be a "right" solution, especially if residential demand charges are on the horizon. One or two heat pump water heaters or standard water heaters with grid-smarts are probably a better way to deal with avoiding calling water from 50 feet away than a fleet of point of use tankless or tank-lets.
 

Dana

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BTW: WiFi water heaters are becoming pretty common, even for uses other than aggregated demand-response programs, with quite a selection available even at box stores.
 

Inkiii5

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To Dana "$10/kw" ??? You mean 0.10cents a kw

I dont know how you came up with that calculation of $360 a month




The way I see it

Point of use at each bathroom sink, laundry and kitchen would be better and cheaper than any propane/natural/ etc....


A gas fired tankless water heater- lets take the lowest BTU available which is 160btus

For 160000 BTU
On propane: 1Gal of propane will produce 95000BTU so lets take 160 divide by 95 = 1.68Gal So running your tankless for 1 hour will Burn 1.68Gal of propane. Currant propane cost in my area Im in NY upstate 1.99$ a gal multiply by 1.68 = $3.35 for 1 hour of usage for your 160btu tankless water heater.

On Natural Gas: sold in increments of 1000Cubic Feet - roughly 1 to 1 ratio so 1CF = 1000BTUs so for 1000CF u get 1million BTU
averaged $9.80 per thousand cubic feet in January 2017 in my area upstate NY. So for $9.80 I get 1million BTU divide by 160btu = 6.25
Take $9.80 divide by 6.25 = 1.56$ so to run your Natural Gas Tankless for 1 hour will cost you $1.56

Natural Gas Twice as cheaper than propane

Now for Electric.
in my area cost 0.11 cents a kw
going with a whole house electric tankless NOT WORTH IT

A 24kw times 0.11 cents = $2.64 running it for 1 hour-cheaper than propane but much expensive than natural gas.

Atmor ThermoPro 24kW/240V Digital cost


There are smaller units like 13kw times 0.11 = $1.43 using it for 1hour which beats natural gas
Rheem - RTE 13 Electric Tankless Water Heater, 4 GPM


Like your bathrooms are 0.5 gpm faucets you can get away with 6kw unit which will cost you 0.66 cent of running it for 1 hour
no need to wait for water to get to the faucet instant hot super cheeep

Considering its a NEW construction I would buy multiple electric units for each sink
Bathrooms sinks 6kw
Bathroom shower 13kw
Kitchen & dishwasher 13kw
laundry sink and washer 13kw

each 13kw unit cost $300 and 6kw 150$

Slightly over $1k


A GAS tankless water heater $1.3-2k

Ohh yeah and your 36kw
Stiebel Eltron
36kw times 0.11 = 3.96 $ almost $4 for every hour of usage


People say electric is expensive thats because they live in an old house and are NOT able to run electric wire to each point of use unit. Like some of these require 6awg wire and double circuit barkers etc... And placing just one whole house electric unit is not effective nor efficient.

Smaller kw unit for each sink/point of use/etc.. much effective and cheaper just run all your electric wire properly to each location.
 
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Jadnashua

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You realize that 24Kw/hr = about 82K BTU, so you're not comparing apple to apples. If you limited your water use on the propane or NG counterparts to the volume of the same hot water a 24Kw unit could produce, you'd have to nearly halve their costs.

You need to compare BTU (or equivalents) to BTU costs for a fair comparison.
 

Inkiii5

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You realize that 24Kw/hr = about 82K BTU, so you're not comparing apple to apples. If you limited your water use on the propane or NG counterparts to the volume of the same hot water a 24Kw unit could produce, you'd have to nearly halve their costs.

You need to compare BTU (or equivalents) to BTU costs for a fair comparison.


I think you gotta look at it from a different perspective

How often and for HOW LONG do you wash your hands at the bathroom sink ? for hours ? NOOOO, more like less than 20 sec each time you use a bathroom. So why have a higher BTU boiler of any type for those 30 sec of water that you want to use to wash your hands.

If you got a tankless GAS boiler its rated at 160BTU or some+ regardelss for how long you use it it burns the same. So im simplifying in HOUR of usage compare

maybe be the 24kw = to 82k btu but thats more then enough to use a sink for few seconds in bathrooms/ laundry/ kitchen and you might even get away with a shower.

Im not comparing that a 24kw as a WHOLE HOUSE single stand alone unit. But as a single point of USE which is much cheaper and much more effective.

what Im saying is install EACH unit dedicated to each sink
so if you install a 24kw on each shower you have I would assume 2 maybe 3 showers that you have in your house 24kw times 0.11 cents thats $2.64 an hour of usage. Maybe a female would take an hour long shower and it would cost $2.5$ anything else 15 minuets and your out and it that price it beats Natural Gas





Soooo every time you use your sink for those 10-30 sec to wash your hands your 160k btu boiler activates and over time it will add up to 1 hour of usage which will cost you MORE than an electric 6kw unit.

And then consider a time it take to reach the faucet of the warm water from the boiler thats located in the basement, easily 50-100feet of piping. I end up rinsing my hands with cold water before warm water even gets to my sink - PURE WASTE
 
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Master Plumber Mark

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Just A common tank type water heater will do you fine for decades You could install a Rheem Marathon 75 gallon
tank type heater with a lifetime warranty and never have to worry about this issue again for decades........



Why in the world would anyone want to go to all this hassle just to have something that probably will not function
properly and will probably need to be de-limed bi-annually to keep it working properly???

Is there some sort of "male ego" issue involved here ??
Him needing the biggest and most baddest toys in the mechaniical room??
 

Jadnashua

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A gas fired device only uses those BTU's while it is firing...and, a tank-type heater and a tankless device will need EXACTLY the same amount of BTU's to heat the same amount of water. With a tank, you get maximum flow at your desired temp until you've exhausted the tank. With a tankless,, if you exceed it capacity, you get colder water out of it, and it is directly linked to how cold the inlet water is...a tank doesn't really care - it's output will be the same until you've exhausted its capacity. It might take longer to heat up that colder water, but on a tankless, you'll just get colder water out of it, and may never get the temperature you want.

So, if you need 24Kw of electricity, you'll need to burn about 82KBTU, which means it would need to run about 30-minutes, if it were a 160K BTU device while the tankless would need to run for an hour to heat the exact same amount of water.

You need to look at the amount of energy used, then the pricing for that energy...not how long it needs to run to produce it...IOW, price the quantity of energy needed, regardless of how long it is actually running. In almost any area of the USA, NG is cheaper (assuming you have it available), then often, propane, then electricity. Now, a heat pump may beat NG, but it will be slower to reheat the tank.

You need to size a tank or tankless for your maximum intended use. Then, keep in mind that many places either have or are moving towards a charge called a demand charge. IOW, you pay a fixed price to have a certain capacity, even if you don't use it all of the time. THen, you pay a separate charge for the actual energy you use. A NG tank, because it typically has longer to recover and isn't doing it 'instantly', means a demand charge will often be much less than an electrical one.
 

Master Plumber Mark

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Lord, everyone here makes this so much harder than it has to be...

I guess its a way of having fun figuring out the demand and making fancy
calculations that dont mean squat .This is a complete and total circle jerk

upload_2017-4-18_7-4-23.jpeg
42311986-albert-einstein-law-theory-and-physics-mathematical-formula-equation-doodle-handwriting-icon-in-whit.jpg


1. he lives in colorado , near the base of the mountains,
and the water is bitter cold in the wintertime ......duh..
2 all you really have to factor into this big equation is how pissed off
his wife is gonna be when she can only get a luke warm shower.....

Therefore, You are not factoring in the complaints of wife and company to this equation...


Example...
To keep my wife happy we have a 75 gallon gas heater in the basement...
I dont give a shit what the cost is as long as I dont have to hear endless nagging and complaints....
like "honey we dont have enough hot water" or honey the water is just lukewarm
and if this dont get fixed soon I am going to a hotel to get a hot shower..


Complaints like this can drive a person crazy after a while and also make you look like a .......total complete dumb ass...... in your wifes eyes for installing something like this in your beautiful new home in the first place..

Just ask your plumber what he thinks you should install in your total electric home . If the plumber is having mis-givings about your fancy contraptions , this ought to be the first warning sign that you are probably screwing up....big time......

crazy-shit.jpg


 
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