Tankless NG HWH vs 50 Gallon HWH
Recently I installed a 6.5’long jacuzzi tub in my bathroom to relax this aching body after work. My existing 40 gallon HWH is fighting to keep up when I need to fill the tub. I am considering upgrading to to a larger tank (50 to 65 gallon) or possibly a tankless unit. Internet searches consistently provide contradicting information. My plumbing wholesaler claims tankless is the only way to fly but he has been full of BS on several previous occasions. Anyone want to give their 2 cents worth? Are tankless units worth the money? Does a high end tankless unit have the ability to provide a family of five with hot water in high demand situations(bathtub and a shower at the same time)? Local folk here in Northern California either love them or hate them!
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For what its worth, I'm going to put in a Takagi T-KD20 tankless WH in our new home that is being built. It will handle 2 showers at once (6 gpm @ 60 degree F rise), so that shouldn't be an issue. The whirlpool tub we'll have will take a lot of water, and the Kohler high-flow faucets can outflow the Takagi, so we'll just have to fill the tub a little slower. Wife says that's fine, she gets other things ready while the tub is filling anyway. I looked at Rinnai on-demand WH's, but as I'm not a plumber, they won't sell to me (other than what is on e-bay) and they won't give me a warranty, so I'll go with Takagi; they don't seem to have an attitude, and the flow/temp curve of the Takagi unit is identical to the large Rinnai unit.
I have a Trinity tankless boiler that heats the radiant floors and provides 6 gal. a minute. 2 showers and a washer at same time no problem.
I have no idea if it is a practical machine w/o radiant.
Nothing worse than a large lukewarm tub ; ^ (
Mike
Trust in God, but row away from the rocks.
I have two Takagi units for two different applications. Both replaced a standard propane-fired HWH and I'm happy so far. The Takagi TK20D replaced a 40 gallon HWH that provided domestic HW in a granny apartment over my garage. It also provides HW for a forced air heater coil. The amount of HW it provides is just fine for the apartment. Output is 140 degrees to the heater coil, but with a tempering valve to drop the temperature to 125° for the domestic HW. The only drawback is there is a slight lag in the time it takes to get HW at a fixture. As the apartment gets little use, the unit is on standby 99.9% of the time. I did the install myself. I am a homeowner and very amateur plumber. All of my solder joints turned out perfect, though I did manage to cut through a 3/4 inch supply line with my sawzall (never told the wife...). This unit works as good as or better than the older 40 gallon tank it replaced.
The other unit is a Takagi TK1S set to supply the rest of my house, whic is two story with a large jacuzzi tub and two teenage boys. My problem is a HW recirculating loop in the house that moves by convection (no pump). HW is available at any faucet virtually instantly, but the heat loss despite heavily insulated HW pipes is enormous. Sucks propane like you wouldn't believe. So the standard propane HWH was almost always on. I replaced it with a 60 gallon Marathon polybutylene electric waterheater with elements disconnected, to act as hot water storage. The theromostats in the Marathon control a recirculating pump that pushes water through the Takagi. What this allows me is low standby loss from the Marathon as it is heavily insulated (something like 3 inches of foam) and no central flue. The storage tank provides HW for the passive recirculating loop and the Takagi periodically turns on to top up the temperature when the HW gets drained down. The tank also provides a significant volume of domestic HW for kids showers, etc, but with the takagi as a backup to keep a high volume of HW coming even when the tank has been exhausted. It's worked great so far. Not the most energy-efficient system because of the HW recirculating loop, but the tank should last indefinitely whereas the old one had to be replaced every 7 years or so, even with changing anode rods, etc. I know the Takagi will have to be replaced eventually, and that probably has to be factored in to the cost,
Hope this helps.
Can you tell me more about your granny apt heating system.
I am in Southern WI and have a loft over a garage that I was going to heat with a Rinnai direct vent and then use an electric or gas tankless for hw. Your solution sounds interesting. . . .
I also want to heat the lower garage level in the winter to keep it at 40 - maybe a bit higher every once in a while.
Where did you get the airhandler and layout info - how do you go about calculating system BTU input/output.
Thanks,
Jim
Well, this isn't going to sound very scientific. The original install when the house was built was a 40 gallon MorFlow American power vented HWH that was apparently designed for simultaneous space and HW heating. As far as I could tell the only difference between it and a regular HWH was a shorter warranty, higher cost, and an extra HW outlet near the top of the tank. My contractor got a small air handler from the First Co. and I assume figured out the BTU/hr and the space that needed to be heated from the First Co's charts. The air handler had an integral recirculating pump that was pretty small. So the situation was that the old HWH failed and I installed the tankless unit and just hooked it up to what was already there.Some words of advice: The integral recirculating pump was a Taco 1/30HP or something like that and was hidden inside the air handler. The contractor did not recognize this and installed another Taco pump (same size) outside the unit. The HWH (and tankless now) are on the wall at chest level in the gaage below. The air handler is above the ceiling in the second floor apartment. There is about a 16 foot elevation rise from the tankless to the air handler. That little Taco's pump profile is OK for a horizontal run of that length but underpowered for that vertical rise. SInce this is a closed system, you'd thing it wouldn't make all that difference, but the flow I get (according to the flow meter on the tankless) is maybe 1.4 gpm. The two pumps in series didn't make any difference. In fact, when I first installed the tankless and metered the flow for the first time I was surprised at the wimpiness if it and thought it was due to the two pumps in series. So I took the external one out and still got the same flow.I think if I replaced the little recirculating pump with a bigger one having a pump profile designed to handle the vertical rise (and more GPM) I would get better quality heating. The heater heats the apartment OK, but it takes a long time to get it up to temperature. Getting the circulating HW temperature up and pushing more of it through the air handler should give a significant improvement. As it is, we are in coastal California and it rarely freezes here so we haven't stressed the system very much. Where you are it would most definitely require a bigger coil and a higher GPM.My tankless is a Takagi TK20D power vented heater so it draws combustion air from the outside. There is some lost into the garage and the garage is definitely warmer than outside in winter, but the temperature obviously isn'r regulated. The heat comes from radiation from the 4 inch stainless steel vent, which in my case has about a 3 ft vertical rise off the top of the tankless, then a 90° elbow into the wall and out. If you had a longer run of vent you would likely get more heat into the garage, but I don't know how to calculate this. I suppose you could install an air handler/coil in the garage with a separate recirculatyion pump and thermostat if you need a more regulated temperature.Hope this helps.
FWIW, height on a closed system has no bearing on head loss for the pump. Head loss through the two different coils is probably the problem.
Well, that would make sense. I wonder what the flow would be through only the one coil in the air handler. I never check the flow when I had the air handler/standard water heater combination.
There should be flow/head loss charts for both. Add the head loss together and check against the pump curve chart.
Talk to your electrician - yuo may be able to add another line into the extg tank. As you may know, there are 2 elements that flip-flop heat depending upon the temp...putting both elements into action may provide the amount of water you want.
All the best...
To those who know - this may be obvious. To those who don't - I hope I've helped.
Our setup is similar to the one described by jgealy - combo tankless WH/boiler with a 30-gallon electric converted to a storage tank on the DHW side. We differ in that ours doesn't have a recirculating loop.
In terms of fuel savings, the tankless uses about 15% less gas than the average quality tank heater it replaced. And based on those savings alone, it's hard to justify the additional expense of a tankless system because you could buy two or three tank heaters with installation for the same outlay.
In our case we had other considerations (available space, building codes, etc.) that made the switch worthwhile.
We have a Trinity tankless boiler, and it makes more hot water than we can use. It's perfect in the winter when the radiant floor keeps it going all the time. This was our first summer, and we have found that it has trouble making small quantities of hot water for a long period of time. I actually have to run the bathroom sink hot water on low to take a long hot shower. I think it will be fine after a couple changes in plumbing it, just havn't gotten around to it. Anyway the moral of the story is that it is possible to have a tankless unit that makes all or more hot water than you can ever use. Just choose a unit big enough for your demands. As for the savings. Our hot water bill is about half what it was with our 40 gallon tank. Our summer gas bill dropped from about $38 a month to $17 - $23 now. And this is with higher gas prices. Our only other gas appliance is our stove and it still gets the same useage.<br><br>
My only concern about the system is that it is complex. I have already replaced the flame sensor in mine. It lasted only a little more than a year. Repairs are reasonable if you can do them yourself. On the other hand traditional waterheaters have a long history and generally go a long time without repairs due to their simplicity. There is a tradeoff for everything I guess.
I've been there and done that.
5.5 foot tub (though) and 36" wide ( I think Jacuzzi stated that the tub held, in theory, 55 gallons, but obviously when you put a person in it, the water is displaced).
Anyway, a tankless unit WOULD provide you with "endless" hot water. The question for you is:
Is it worth the cost? (to have a "small" unit, capable of service one "thing" at a time, like the Bosch-125, INSTALLED by a "pro") In my area, the cost for that unit with installatio was about $1700. The cost for Rinai (larger unit) was closer to $2800 for STARTERS.
In my case, the units would not work due to venting/combustion intake requirements.
However, I then got a 50-gallon NG hot water heater (Bradford White, deluxe energy model), with a VERY quick recovery time with 10-year warranty for about $1000.00 (that was NOT including installation.)
I can tell you, with THIS unit, I can fill the tub and not run out of hot water (and I have the water temp about 125). Of course, that assumes the other jacuzzi tub on the 1st floor is not being attempted to be filled (but the heater will recover the 50 gallons in about 30 minutes or so).
My only "beefs" with the tankless units:
a) Cost. Cost. Cost. (if you can do it yourself and maintain the warranty--depends on the vendor-- you can save a lot of money, but it's more complicated than hooking up a hot water heater)
b) Flow rate. The larger units needs a larger flow to "kick in".