Need help making the right decision on tankless

Discussion in 'Tankless Water Heater Forum' started by HDClown, Jan 14, 2010.

  1. HDClown

    HDClown New Member

    Messages:
    14
    Location:
    Central Florida
    I live in Orlando Florida area, so it's warm-to-HOT 9-10 months out of the year. Our cold months are usually in the 40's, but we've seen high 20s and low 30s the past few weeks (which is unusual to see for that length of time). We might see 1 week total of those temps on average.

    My house is re-piped with PEX. ALL of the hot and cold water supplies runs through my attic. In the summer, I get boiling hot water instantly, very shortly after it gets lukewarm, and then back to hot water. In the winter, I get extremely cold (Freezing cold sometimes) water, and then 20 seconds later (depending on proximity to the HWH), I'll get my hot water.

    I have a 40 gallon HWH that's about 18 years old. It's on my list to replace this month or next, as a pre-emptive replacement, and it's obviously not energy efficient by today's standards (although that's the least of my concerns). House is 1850sq ft with 2 bathrooms (1 with regular tub, one with walk-in shower). We MAY (it's a good 2 years out, if it even happens)expand the house adding a new master bath with a new walk-in shower and large soaking/whirlpool type tub.

    I've talked to 4 different gas/plumbing companies now about tankless/tank. They are all pushing tankless. 3 of the 4 said they wouldn't bother with indoor because I need venting upgrades, so they all said outdoor. 1 of the 4, who happened to be one of the least expensive, said he would do indoor, and he wouldn't need to modify the roofing. He said he would slightly enlarge the flange on the roof, and then feed the new SS vent through it, and seal it with some kind of sealant that was not effected by the hot temps.

    All 4 companiese have recommended the Noritz 751 (now branded NR98). Due to incentive programs with my gas company, I'm end up looking at roughly $500 out-of-pocket cost for the outdoor mount noritz, or about $200 for the guy who wants to do the indoor. I'd have zero out of pocket cost to just get a new 40gallon tank. Tax rebate on the tankless would help offset part of that out-of-pocket cost. These costs are really not a concern however, but I just want to cover all my bases.

    One of my main concerns with a tankless is noise. The indoor and outdoor mount locations are against my 3 year old daughters bedroom. I did some tests with a cordless drill (around 70dB SPL), and if the drill touches the wall, you hear it loudly. If it doesn't touch the wall, you can't hear it at all. So the vibrations caused by the fan in a tankless, transferfing through the walls, would not be very good. There is 1 position outside that I can mount it where it's against an exterior garage wall, but it's right by the front of the house and exposed (next to my electrical meter). I don't like the idea of the exposed shut-offs and the unit from an aesthetic unit, and other people possibly trying to mess with it.

    My other concerns is my repiping and water sandwiching that may come into effect, or issues with the units operating properly in summer due to burning hot water being in the pipes initially. My wife and I are already used to turning on the hot water and having to wait 5-30 seconds for the temp to normalize, and I'm not really expecting this to change by getting a tankless. I don't want it to get to be hugely worse however.

    Have I had demand issues with my 40 gallon tank? Nope, not really. Only time I have complaints is when it's in the mid-to-low 30s or worse and I'm using my master bath which is across the house from the HWH. I constantly have to turn to the hot water side to keep warm water. Will a tankless fix this? Don't know the answer. Is it my reason for looking at tankless? Not really. So, why look at tankless? No particularly wowing reason. I wouldn't mind having the space in my garage occupied by the tank unit to be free'd up. That's about the only reason I've come up with. Don't care so much about energy savings, being green, etc.

    So, after all this, I'm still undecided on what to do. Hoping for some people with first hand experience and more technical knowledge to weigh in on my concerns and applications relative to my environment/situation.

    Thanks!
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,948
    Location:
    New England
    You didn't indicate whether you had gas or electric. On either one, you might be looking at a utility upgrade to enable a tankless plus, they have more maintenance requirements, especially if you don't have soft water.

    A 40-gallon tank won't cut it trying to fill a large soaking tub. But, depending on you inlet water temperatures, doing it fast with a tankless might require a much bigger unit.

    You need to look at your maximum simultaneous useage requirements to size the unit along with your average and peak inlet temperatures.

    You might want to consider one of the heat pump water heaters...a side benefit is it cools the space around it by extracting the heat and putting it into the water. This might be a nice side benefit to essentially cool the garage while heating the water rather than the opposite.

    Read some of the other threads to gather up some ideas.
  3. Dana

    Dana In the trades

    Messages:
    2,812
    Location:
    01609
    Tankless units are EXREMELY quiet compared to an electric drill- most are much quieter than a bathroom exhaust fan.

    Your coldwater/boiling-water sandwiches from the attic plumbing won't be noticeably affected by going tankless- it's already WAY beyond what the most sensitive people complain about with tankless units. You can mitigate that effect greatly by insulating those attic pipes with 5/8" wall closed cell (R4) pipe insulation though. The initial draws of the day (or after hours-long stagnations) will still exhibit the issue, but subsequent draws within 30 minutes will be all but gone, and still noticably abated with a 1-hour stagnation:

    [​IMG]

    You can get the thicker stuff at some plumbing supply places or Grainger, but not the big orange or blue box stores (which only carry the R2, 3/8" wall stuff as a rule.) If it's a well-ventilated attic, you might go for the 3/4" or 1" wall stuff. Insulating both hot & cold feeds will moderate both winter & summer issues by quite a bit.

    If there's space for it, burying the pipes in 6-8" of cellulose insulation would have a similar effect, and lower both the heating & cooling loads on the house. (Cellulose is preferable to fiberglass here, since FG is somewhat translucent to infra-red radiation at thicknesses of less than 8" and some heat radiating through the FG would be absorbed directly by the PEX.) If there's already a substantial loading of insulation in there, you'd have to verify that the joist/trusses could handle the extra static load if you went the burial route. (Figure ~1lb/square foot for 8" of open-blow cellulose.)
  4. HDClown

    HDClown New Member

    Messages:
    14
    Location:
    Central Florida
    I currently have gas with a 2lb meter. No upgrade is needed. If I replaced my tank, I'd likely upgrade to a 50 gallon unit.

    I read people saying all the time that tankless units are worthless for filling soaking tubs, and they quote the GPM rate of the fill valve relative to the heated flow rate of the tankless. But someone pointed out to me that this is not accurate way to do it, as you are not filling with purely hot water, but a mix of hot/cold. In any event, I'm not concerned with sizing the tankless to accomodate a soaking tub, because there is no given for such a tub. If I did this renovation, I would deal with adding a 2nd unit, upgrading the existing, or tank back in to accomodate filling the tub.

    The flow rate of the Nortiz N-0751/NR98 is 7.5gpm @ 45 degree rise and 9.8 @ 35. From others I have spoken with, they've indicated this is much more capacity that I need for my 2 bath house when factoring in our climate. Inlet water temps get up there in the summer, and are certainly nothing I would even consider remotely "cold" in the fall/spring, so my warm environment living area has a substancial impact, which is why I pointed out my locale.

    Dana, my pipes are already insulated, but it's probably R-2. Some of it is also burried in insulation (blown in) but I'm not 100% sure if it's cellulose or fiberglass The blown in insulation was added after the re-pipe, I just don't remember the kind. In regards to noise, the technician I spoke iwth today said he would equate the noise to be similar to a modern home air conditioner cooling fan. Is that not correct?

    The technician I spoke with today had told me I need to be careful when dealing with my re-pipe through the attic, and some brands of tankless won't fire the burner properly when they see very hot water coming in from the attic, at least until the regular temp water started to flow through after the water sitting was flushed. Was he making this up or is it something I need to be concerned with?

    I'm glad water hardness was mentioned. Our city water is towards the hard side. How do I have to factor this in on a tankless, and what kind of maintenance will this cause for me? My wife has been bugging me to get a softener for years, and it's on my to-do list for 2010 as well.

    Considering the some of the more common benefits of tankless (being green, saving on gas use) are very low on my list. What other benefits do I have to gain from going tankless? Compared to living with a tank for the past 6 years, will I find myself having to "live with" any type of change in how I am used to my hot water functioning as it does today, by going tankless?
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,948
    Location:
    New England
    If you have hard water, you may have to delime the tankless system at least once a year. You need special valves installed and a pump to pump the special cleaner through the thing. Otherwise, the guts will grow a mineral coating which will decrease the ability for the thing to transfer heat. You don't see that as much with a tank since the peak temperatures aren't as high. To get a tankless output hot, you need a very intense heat source - more so than in a tank, and it precipitates out the minerals much more efficiently...you need to keep the guts clean.
  6. Dana

    Dana In the trades

    Messages:
    2,812
    Location:
    01609
    Definitely get the water softener, and plumb the tankless with isolating ball valves to make deliming easier.

    Most peops I've discussed the large soaking-tub & spa issues with go tankless in ORDER to be able to fill the whole thing and not run out of hot water without having to go with multiple 100 gallon tanks. Your flow from a tank might be better, but the do run out in very large draws...

    I've never heard a tankless from any vendor that was as loud as an air conditioning compressor. It has to be very quiet and I have to listen intently to hear the tankless in my basement (a Takagi, vented 12' away from my bedroom window), but I have no problem at all hearing the AC compressor 20' away from the window even over the air flow from the supply register. The tankless is at it's loudest when doing a flue-purge at the end of a burn, and even then it's significantly quieter than the bathroom fan, as heard from rooms other than the bathroom. Noise shouldn't be much of concern.

    Being green/fuel-use are pretty low on the list of actual reasons people go tankless. # 1 is never running out of hot water (serial showerers) #2 is space savings, #3 is large-tub filling capacity. After that it get's a bit broader, but fuel/carbon-output etc is down around #4 or #5, not a primary driver. (I initially did it for reasons #1 & #2, but have since replaced the initial tankless with an indirect-fired tank, but using a tankless as the heating system boiler for it's modulating aspects.)
  7. Scott D. Plumber

    Scott D. Plumber In the Trades

    Messages:
    67
    no problem

    you won't have eny issue with noise. No vibration is transfered to the wall and that is what you hear with the drill test.

    THe Noritz is a good unit, you'll like it.

    As for cold water sandwich, get a Hot Shot expansion tank and have it installed on the hot main just downstream of the heater. It is BOTH and Expansion tank and Storage tank and holds about a gallon or so of water. This will eliminate the cold water sandwich. It may raise your lag time just a little on a draw for a cool system but that's about the only down side.
  8. ChuckS

    ChuckS New Member

    Messages:
    96
    Location:
    Aurora, CO
    I have a recirculating loop that eliminates my sandwich problem. The way mine is setup the loop comes on automaticaly when any hot water is demanded and turns itself off once the aquastat reaches 120'

    Mines was modeled after this one. I got the flo switch off **** for about $30. Make sure to get one that trips at low flow like .5 gpm.

    http://s480.photobucket.com/albums/rr167/PRYGAARD/

    There is also a tankless unit that has a small (like 2 gal) tank inside that is supposed to eliminate the sandwich effect.

    Here are some thoughts mentioned above about adding a tank to the tankless system

    http://www.finehomebuilding.com/PDF/Free/021192082.pdf

    Also remember most tankless units qualify for the tax credits...
  9. Youngdogs2

    Youngdogs2 New Member

    Messages:
    2
    Location:
    NH
    Check out the Eternal Water heater manufactured by Grand Hall in Texas. The Eternal is a hybrid water heater that is a cross between a Tankless and a Tank. The best of both worlds with no sandwich affect and a 20 year warranty on the product. I have installed a few and even though they are a bit more expensive as fllor mount units, I have just seen the new wall mounted units that are in Orlando this week at the ASHRAE show.

    Checkout Eternalwaterheater.com
  10. Dana

    Dana In the trades

    Messages:
    2,812
    Location:
    01609
    His cold-water/hot-water sandwich problem is orders of magnitude bigger than a typical tankless, and are completely unrelated to it. Using an Eternal or the mini-tank buffers & the like won't touch the attic- heated hot AND cold plumbing, which are very much the problem.

    In warmwater areas the coldwater sandwich issue is such a NON issue anyway, it's hardly worth discussing. In places where the incoming water is well under 50F, yeah, that's noticable (but still usually tolerable except to the princess who couldn't stand the pressure of the pea under the stack of matresses. :) )

    Spending money on those "solutions" that won't even touch the problem seems silly.
  11. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas
    You may have seen the new Eternal in Orlando but, I have news for you, they are not in production or distribution yet. Will this new model solve the chlorides attacking the welds causing leaks so soon?
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