Posted on 12/11/2013 6:43:34 AM PST by knarf
I'm electric tank now and am considering electric trankless, but gas is a possibility
I’ve had a gas unit for 7+ years (Takagi brand). I did cost more initially, but I recouped the investment after about 5 years of use, as my monthly bills went down significantly - both because there is no pilot light, and because I only heat water when I need it, rather than keeping a hot-water supply constantly hot.
We absolutely LOVE it. You never run out of hot water, which is great when you have a house full of guests, or have a small window of time in which to have multiple people shower, do some laundry, and run the dishwasher.
I would not consider electric - as others noted, too long to heat up, plus more costly than gas for the same heat/volume output.
When installing gas, the plumber had to run a 3/4” pipe to supply the fuel (regular gas line, as with a stove-top or standard water heater won’t cut it). Plus there was a double-wall stainless vent pipe required. I also installed a pipe for outside air to feed into the combustion chamber, rather than drawing from the garage utility closet.
My natural gas bill went from $30/mo., give or take, to under $20/mo. during the summer months (when I’m not using gas heat). No real way to tell what the savings were the other months, but I assume they would be at least equal if not better.
If there is a down-side, it’s that these can only heat and deliver so many gallons per-minute, so using 2 showers plus another appliance (washer, dishwasher, etc.) will mean colder water than desired. Make sure you spec a unit with the highest GPM (gallons-per-minute) rating you think you’ll reasonably need.
That is good to know. Idaho isn’t so harsg and the only succesful installations I know of have two in line. I tried one to no avail and went back to the trusty old tank.
>> See my #92 <<
Sorry, knarf, I didn’t see you drop this in.
I don’t know how much LP the tankless heater uses.
I can’t even hazard a guess as I could be way off.
Right now my stove uses a 5/16 flex copper line to feed it ... about 55 ft from the source.
We live in a mobile home so the piping is that PEX 1/2" plastic crap .. very easy and fast stab coupling to work with.
I don't THINK I need to change the water lines.
Our friends have one and they love it. After a local flood, we used their shower for a week or so, loved it. Only difference was that the water took a bit longer to come through hot. They had a gas one, not electric.
3/4" gas feed sounds like I'd empty my 100 gallon tank pretty quick.
I really need to research volume usage.
Researching it is your best bet.
I know that since the tankless units do not try to keep water warm (like the tank units), and only fire up when hot water is demanded, they use less gas overall.
I also so no difference in time to get hot water to the showers over the tank unit, as it had to push the cold water out of the lines as well.
We may use more gas due to the fact I have the temperature set all the way up (about 160°). When water comes out of the kitchen sink it is scalding hot. That’s the way I like it. :)
Got one last year.
Good: You never run out of hot water, and by only heating the water you need when you need it, gas bills are lower. Small wall mounted unit leaves more usable floor space in the utility room. In a large home you could have several units each serving a section. No problem that we’ve noticed with bath and kitchen fixtures on at the same time.
Bad (but not very): 10-15 seconds longer than from a storage tank after you turn on the shower or spigot to start getting the hot water. It requires a minimum water pressure to kick on, so it won’t heat just a trickle of water, needs a slow stream. Can’t get really hot water into our front loading washer because the cool/cold in the pipes goes in first, and the small amount of water this washer uses does not give it time to heat up. Warm is getting stuff clean, so no harm.
I’d do it again.
Different flows - pick the one you need.
You had a defective unit with a bad sensor or something.
Very unusual.
Sorry, as an electrical contractor I can tell you of dozens of cases where the heat was slow, inadequate or other problems.
Glad you are one of the cases with none......but your experience is anecdotal. Mine is empirical.
Navien units are condensing and high efficiency. Little
loss to flue.
My folks researched different companies and different types of heaters when we were building the house. A propane unit was not feasible due to size. The electrical one is 15x15x4, really compact and serves the house well. It’s only my mom and dad living in the house but when company comes over (like me, my bro’s and uncle) there still is no problem. Two can shower at the same time. (different bathrooms before some snarky person comments LOL)
Hi Arlis,
I have no doubt that you have seen many cases where the units under-performed or had problems, but there has to be some common factors as to why they don’t work in cases, and why they work flawlessly for folks like SkyDancer and myself.
Perhaps the layout of the house (multi-story), or the type of plumbing (Pex vs. Copper), consistent water pressure issues or some combination of factors.
I’ll probably never know but that’s the darn electronic engineer in me ... always wanting the details. :)
You are probably correct, but while I hear in the industry all the negatives of the electrical units, I have never heard the specifics so I cannot analyze let alone comment on what the problems are.
I do know I almost never hear of problems with the gas units.
Tankless electric is fine if it’s 3-phase power. If not, there will likely be other elec distribution wiring costs involved.
Nat Gas tankless, also is fine, but you are probably looking at 1MBTU/Hr to support 20gpm continuously. For a household, you can probably get by on the 200KBTU/Hr units with a std 1” gas line (if my memory serves me correctly) say with Delta P of several lbs pressure NatGas.
Here are the things you need to factor:
Which energy sources are most viable in your location? Electric AC, Nat Gas, Propane, Elec DC (Photoelectric), Solar Heat.
Factor out your loads. Shower, tub, dishwasher, washing machine, How many bathrooms? How many fixtures per bathroom? How much kitchen use. Any other water heating demand?
Figure out your diversity factors. i.e. how much of that load occurs at one time and how much may be spread out sequentially.
The advantage of tankless over a standard HWHtr, is that you are not reheating the water over time to make up for heat losses in your storage tank. That heat loss actually consumes several times the cost to heat the water actually used when averaged over the day when only used over say 3 - 30 minute periods throughout the day.
The disadvantage of tankless is that your heating rate to keep up with your hot water demand, may require industrial sized heating systems, oversized by a factor of 3-10 of your regular system. Maintenance will tend to correspond with the high stress systems, than the household models.
Safety in numbers,....the larger market might provide less expensive capital costs, by 20% to a factor of 3 depending upon the equipment availability.
I’m running about 20 outdoor restrooms with 8 showers each, 9 lavatories, and a janitor’s sink. They have 240SF of Solar water heating panels and four 250kBTU/Hr Takagi Propane Instant Hots, with 2 80gal HotWtr Storage tanks.
The solars can support 1 shower and one lavie periodically used throughout the day, depending upon outside air temp, mixing rate with cold water, cold water temp, and time of day of use. anything greater than that requires the instant hots. Instant hots are used to reinforce the hot water storage tanks from the solars to maintain a given hot water service temp to all the domestic hot water piping.
These systems require 2”-2.5” nat gas feeds, depending upon gas pressure and capacity of the Nat Gas distribution systems. That means your Nat Gas meters tend to be very pricey. For residential use, your .75” gas line or 1” line and meter are probably more than adequate. If you also run a swimming pool heater, you might need a larger feed and need to look at available gas pressure and allowable delta P (change in pressure drop allowable from the gas company’s perspective).
If electric, 3 ph systems are much more versatile.
Arguments between heating efficiencies aren’t always consistent. Both Elec and Gas tend to have some inefficiencies. Gas tends to release lots of BTU out the flue. Elec might not always efficiently heat the resistance coil heating elements. Can also look at inductive heating which also may decrease efficiencies in time over several years.
If you can find one, take a look at a MEAN’s cost estimating guide for plumbing or HVAC systems. Their UNIFORMAT II breakdown of Solar and Tankless systems are typical industry system designs, just as robust as many professionally designed systems. They also breakout all the pertinent costs for construction. Then run the numbers for your particular design.
Even if somebody’s past example had good results, they always will depend upon the situation and local economics.
Shop the unit prices on ebay anf different search engines to find typical systems used in your area.
Asian countries have been using these as typical residential systems, same with ductless HVAC systems, and they can produce some very efficient units.
So in our shower, we have a 6000W Panasonic unit. Works OK until it gets about 70 degrees. Our next house will have 8-9000W units at about $200 each.
To me it seems smart to just add the heaters where you need them. I would probably design a house to maximize these as instead of replacing a house unit, you just get a facet unit.
Yes, highly inconvenient to not have hot water at every faucet.
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