Tankless for occasional use in new addition guest bath

[Optiker]

I've browsed some of the posts on tankless water heaters and get the impression that in general, folks aren't too happy with them. My sister had a whole house system in a very large house, and I wasn't thrilled with it the first visit when I was showering, but in later visits, it seemed much better.

I'm adding an attached garage and a 450 sq-ft bonus room to my home, with a small bathroom - shower, toilet and sink. It's at the far end of the house from the existing water heater, which is adequate for current needs, but I'm concerned that it would not be enough for use by guests in the new bathroom for showering.

My current solution is a tankless water heater for the new bathroom. Our well water (not hard enough to use a water softener) is probably in the low 50-deg range, and we don't anticipate much use other than for occasional guests since we primarily use the master bath at the other end of the house for showering. I don't particularly want to add a second hot water storage tank system, and am not particularly concerned with how long it will take for energy cost savings to pay back the cost. I am concerned about having adequate hot water for showering, that stays reasonably constant - constant enough to not alternately freeze and scald a person taking a shower.

Before reading the posts here, I had pretty much settled on the Eemax EX280T2T, series 3 system, based on wanting about a greater than 60-deg temperature rise at 3 GPM, so that my outlet temp would be around 110-deg with 50-deg inlet temp. I haven't looked long and hard at prices, but one web source advertises this system at about $725.

Comments? Am I making a mistake to go that route? Pros/Cons?

Thanks!
Optiker

[Dana]

Have you factored in the costs of the power-service upgrades you'll likely need to be able to pull this off?

Or maybe you have enough spare capacity (and wiring) to just add a 240V three 40A dedicated breakers for just the hot water heater?

If the bonus room is over the garage you'll have enough vertical space to install a 5-6 foot drainwater heat recovery unit below the shower to heat the cold water feed to the shower, which would cut the load on the the hot water heater in half during showers. It'll run you about a grand for the hardware, but doesn't add much to the installation costs of a shower & drain. (If the heater were closer you could get even more capacity-extension out of it by letting the heat recovery unit feed the cold-feed to the hot water heater as well the cold feed to the shower.) With a 6' x 3" drain you'll get ~40% improvement out of it feeding just the cold water to the shower. With a 4" diameter unit it'll break 50%, maybe hit 60%. It would take heat the ~100-105F water going down the drain and raises the 50F incoming water to ~90-95F, at 1-1.5gpm cold-side flows, dramatically reducing the mixture drawn from the hot water tank. If feeding both the shower and the tank the potable-side would be higher and temps somewhat lower, but the total heat recovered would be more. Only if your guests are the "endless shower" type would you be running out of showering water if you have one of these installed.



Longer and bigger diameter typcially means better performance within a manufacturer's line, and going as big as what reasonably fits is probably worth it if you're tapping off the main HW heater. Natural Resources Canada pays for standarized testing of different models, and maintains a comparative performance list here. Take ~10-12% off the NRCan numbers, if configured to feed shower-only, not the hot water heater. The US distributor for PowerPipe is EFI, and they will sell them onesie-twosie at wholesale if you open an account. (You can open an account over the phone with a credit-card number. They're a very reasonable outfit- they don't mark up shipping with handling fees, etc.)

If you have enough vertical room for even a stubby one downstream of the main shower near the hot water heater it can pay back reasonably if you heat hot water with electricity at national-average rates, provided yours is a showering family, not tub-bathers. If you heat hot water with propane or oil the payback is even better. But the payback in extended showering time is immediate. (If you lived 300 miles further north you could get a subsidy for installing one.) It pretty much doubles your showering capacity, even though it does nothing at all for tub-fillling.

[Optiker]

Dana..

Thanks for the reply. Gas is not an alternative as we don't have natural gas available and propane would require a whole new installation. Electric service is already in place with more than enough capacity, and our rates in the Mid-Columbia are relatively low. The new shower, as well as the existing shower, is on the ground floor and about 16" above horizontal drain run. While using the heated drain water to preheat inlet water sounds great, there just isn't much vertical space.

This forum does have me considering alternatives, though I had hoped to get more replies. At this point, I'm not seeing a lot of alternatives to tankless other than a second standard hot water storage tank. Any suggestions on sizing for this kind of application? Peak demand would be 1-3 gpm for showers, since the only other hot water needed there is a bathroom sink - no laundry or dishwasher on that system. Also, the fact that it is used so seldom, while making any installation pretty costly relative to am0ount of use, also would make it costly to keep hot water available in a tank full-time.

My wife visited Scotland a few years ago and stayed in a B&B there. She tells me that they have their hot water to the guest rooms and cottages on a switch so that it can be turned on in prep for arrival of guests, but left off most of the time. Any comments on that for a standard tank system?

Thanks!
Optiker

[jadnashua]

A tank can take awhile to heat up, so you need to anticipate your needs, or if it is small, restrict the volume you use. If it is well insulated, it doesn't cost that much more to keep it on. Used infrequently, there is the potential for the water stored in a tank to start to grow things.

The big things in sizing a tankless are peak use and inlet water temperature (which relates to the maximum temperature rise (delta-T) required to get it to a comfortable use for the requested volume). The math to figure out the size is fairly easy given those variables. Whether you have hard water or not can be an issue. Some come with easy means to delime the thing, if not, you should consider adding those valves and fittings to do it. A tankless requires periodic maintenance, a tank generally doesn't. A tankless will cost more to fix, if it breaks, than a tank, but the whole thing MIGHT last longer. Standby losses are lower on a tankless since essentially, nothing is being heated until you call for water. If you exceed the capacity, the temperature generally drops, or the volume does, and this can be a pain. As long as you don't exceed the capacity of the unit, other than the fact the thing generally costs more initially, it has some advantages.

[skyemom]

NO..NO

I had the Navien 180A installed Oct 2010 into a 1951 classic Ranch house I am renovating and what a disaster this has been ! I am a retiree and live alone so don't use a lot of HOT water but want it when I need it. This thing is horrible...just Horrible. The plumbers also installed new furnace and gas lines so coverted old electric water heater to this gas model. Never told me anything about WAIT time for hot water..Tank is on the wall near the kitchen and bathroom but every time I want HOT water I end up waiting min. of 1-2 miniutes for it to get HOT...it goes through a lukewarm; then COLD then to HOT...Kitchen never actually has worked right in 6 weeks since it's been installed and numerous calls to manufacurer by plumbers. Plumber has exact system in his house and loves it but there are 4 people living there. I think this product is NOT designed for ONE person or low demand person. I have problem in bath when I want added HOT water...it goes through same cycle and takes sometimes 3 minutes going to COLD before you get HOT water. Nefver had this is 61 years of living with old type heaters.
Can't even rinse utensils in when cooking if you shut off faucet: same cycle happens. USELESS if you ask me. I hope they will take it out and just give me a conventional higher efficiency heater that works. I have arthritis and this cold water things is hurting me mevery time. DO NOT buy it. If I had known any of this I would never have agreed to this

[Dana]

Skyemom: The lukewarm & cold water symptoms you are experiencing are almost could be a (user) programmming problem. The 180A (as distinct from the 180- non-A variant) has a mini-tank inside it, but it has to be set up to maintain the minitank at temp for the time of day that you're using it or you'll get exactly those sort of problems. The installer SHOULD have set up the programming to make it most conveninent for your daily schedule. When the mini-tank is cold at the start of a draw the time-to-hot will be long, and the temp won't be stable until the tank reaches the setpoint.

If you can't figure it out by reading the manual, call Navien customer support and let them talk you through the setup. It's conceivable that your plumber just doesn't get it, and has been asking the wrong questions (?).

There could also be interactions with other gas-burners on the system if the regulator at the meter is under-rated for the total load, or the plumbing is teed to the different appliances, or the gas distribution plumbing is undersized, etc. A big-burner tankless like the -180A could easily need twice the fuel flow as smaller-home furnace.

Whatever the cause, as-installed this unit is NOT behaving correctly, and if the installer hasn't been able to fix it's personality defects, odds are you'll need to get a certified tech to figure out why. The installation & setup is more complicated than furnaces or tank hot water heaters- they're more akin to a modulating-condensing boiler than any other gas appliances.

[Optiker]

Based on everything I've now read here and elsewhere, and my specific needs, I guess I've decided to take the plunge and buy an electric tankless water heater. I'm about ready to place an online order, but want to take one more shot at any helpful information.

As in my original post, I had planned on buying an Eemax EX280T2T, series 3 system, to get the 65-deg temp rise at 3 gpm figuring that for my needs, it might be a little more than needed, but I'd rather be conservative.

In browsing around a bit more, especially brands that I recognize, I see the Bosch AE125/PS28T for a similar price, and with similar specs. I have a higher level of expectation with Bosch than Eemax, just because of brand familiarity.

In case you haven't followed the thread, this is NOT whole house, but for shower/sink needs in a bathroom that is adjacent to a newly added "bonus room". The hot water needs will be occasional, when the room is used for guests, not needed for daily use at all. I am not concerned that the energy savings will not pay back in my lifetime!

Any helpful comments?

Thanks!
Optiker

[nukeman]

The big question is do you have the electrical needed to power the thing?

- The unit that you mentioned (Eemax) requires 120A at 240V capacity. This will take (3) 40A breakers in your panel (6 spots). You will also need to run 3 sets of 8/2 ROMEX from your panel to the WH (or one large SE cable at can handle the 120A). The unit may not have lugs large enough for the SE cable, so you might be stuck running the 8/2.

Just the wire itself won't be cheap (and could be $$$ if you need a lot of it). Also consider how much it will cost of run the wire (labor) if you don't want to do the work yourself. Do you have unfinished space between the panel and the WH location to run the wire or will you have to open walls? Do you have room in the panel to use up 6 spots? Will the 120A demand leave capacity for anything else to run at the same time? Do you have a 400A service or is it 200A?

Really, you should just look into a tank WH. The tank will cost less and only requires (1) 30A circuit (one run of 10/2 wire instead of three runs of 8/2). Takes up 2 spots in the main panel instead of 6. Much cheaper/easier solution. Standby losses are low and you could just kill power if it is not being used for an extended duration.

The tank could be small to save on space, but often the larger tanks actually cost less because they are much more common (40-50 gallon would probably be best for your budget).

[Optiker]

Time to fish or cut bait!

Between what I've read here and failing to get any encouragement from local friends who are more knowledgeable than I, I've backed away from tankless and decided to just go with a tank water heater, and leave it turned off when not needed. Guests who drop in unannounced at the last minute will just have to wait for their shower!

Thanks for your input!
Optiker