The square footage means nothing in terms of how much water you can use. How many bathrooms? Any soaking tubs? Dishwasher? Big washing machine? Any other hot water uses?

Your gut feeling about tankless is correct. The lifetime costs of purchase and fuel are very high. Promise me that you will go to the DOE or unbiased sites and do some calculations if someone tries to steer you in that direction. Alternative heating options (heat pump or solar) might make sense, though, depending on rebates in your area and the climate, Where are you?

How long will you be in the house? It seems like indefinitely since you wrote, "should I ever sell it". If it is at least 10 years, and you are going gas, install the HWH size you need now and let the chips fall where they may. The pros here may say it is not practical or possible, but if it is, just be sure the, space set aside, the flue and the pipes will support a larger water heater.

75 gallons is the biggest "standard" size for residential. They make 100 gallon heaters, but they cost a bundle for some reason. You can compare prices, but if you are going bigger than 75, you probably will be better off with the tankless once you factor in operation costs.

I don't think it is debatable that conventional water heaters are more reliable than tankless at this point. That doesn't mean that tankless aren't reliable, just that conventional water heaters are incredibly reliable products. They are self contained and pretty much idiot-proof.

For me, it would depend on how the house is laid out. If the bathrooms are all close together and the kitchen/laundry much further away, I might use two smaller heaters rather than one big one. Rather, I might put a 50ish near the bathrooms and a 10-20gl electric near the kitchen/laundry.

The other question is, will you have company over using those other 3 bathrooms at the same time? If not, then smaller is better.

I have two full baths. The house came with a 55-57 gal unit. I replaced it with a 65gl unit. I NEVER had any issues with HW availability. I replaced it with a 50gl unit when it started leaking. What I notice now is the newer unit tends to cycle more than the old one.

My parents house is spread out, with there being 40ft runs from the heater to each end of the house. My father replaced a failed gas unit with a 40 gal size unit. That thing used to run nearly continuously when I visited. They also said their gas bill increased.

I've seen 80gl units at HD and Lowes.

Thanks Weedmeister and billl. That is a huge help. It looks like I should go with a tankless or two water heaters? The house is a little spread out and I might add a washer/dryer to the master bath when I redo that in a couple years. Do you know if a tankless would be equivalent to two water heaters? I dont know where I would put a second water heater and I really need to move into this house soon. I am worried about the extra work it might take, but maybe it wouldnt be too big a deal. I will talk to the plumber monday. He has been out of town all week and unreachable by phone.

I will only have family visit in a couple times a yr. and I dont think more than two showers will be used at once.

I have a 3,000 square foot home, with a 60+ foot run between the tankless heater (Navien, NR 240-A) and the master bathroom, which is the water outlet that is the furthest away. The water has to run the entire length of the house...from the south wall to the north wall.

I just had the Navien installed Wednesday. I'm single so I only use multiple sources when I wash, run the dish drawers while I shower. And I've not done that yet. I'm having a family-of-4 house guests later this month, so I'll know more then.

What I can tell you after living with the tankless for just a few days is that the hot water is arriving at my outlets more quickly than it arrived from the 14 year old gas hot water tank -- I'm sure it's because of the recirculating feature I had installed (that's why it's an "A" model). It's not instant hot water, but it's certainly faster than the old tank. I like that feature because I was tired of washing my hands in cold water or letting the water run for a long time before it reached the outlet in use.

My house was built in 1978, so it is older, with 3/4 inch lines. And I have pressure issues (I'm at 62, measured at the house's main incoming water line), but that's related to the city plumbing and my location at the top of a huge hill....Not a problem caused by either the tankelss or gas heaters. The lower-than-normal pressure affects both hot and cold water. I've learned to live with it, because it just can't be fixed...Unless I add a pump, like I did with the yard's sprinkler system...and I'm not willing to do that.

Still, even with the less than ideal pressure, I've got plenty of hot water and I'm very happy with the new Navien.

If you go the tankless route, I recommend you really research the competing brands to ensure you're getting something that will last, doesn't require annual cleaning or servicing, etc. And offers a good warranty.

I chose Navien because of its condensing design, its use of stainless steel heat exchangers (instead of the more commonly used copper, which require the annual de-scaling, servicing, etc.), and its 15 year warranty on heat exchanger, 5 year warranty on parts & 1 year on labor. The plumbing firm I purchased this from here in Utah has been installing Navien for several years, with a 1-year guarantee that if the home owner is unhappy with their Navien tankless heater for any reason during the course of 1 year, the local company will remove it, and fully refund the cost of the tankless heater. I think that's a pretty remarkable guarantee. This firm also sells Eternal....these are the only 2 tankless systems the firm sells.

Hope you're successful in finding what you want. If you see yourself living in the house for a long time, I certainly wouldn't hesitate to purchase a tankless system, doing the thorough research to ensure you get a product you'll be happy with.

It would not be accurate to think of a tankless as 'two tanks'. The tankless operates (heats the water) only when there is a need for it (demand). Tanks heat the water and store it for later. With tanks you talk about 'recovery time', the time to raise the new cold water up to hot. Fast recovery is good when you have a lot of usage (several users taking showers in a row). Recovery is not an issue with tankless.

I am no expert on this, but anecdotally it seems to me that singles and couples do ok with tankless. The problems seem to develop (too much usage and gas cost) when larger families are involved.

Thanks guys. Well, I spoke with the plumber today. I asked about adding a second hot water heater, closer to the master bath, but that sounds very expensive.

My options seem to be tankless or a 75 gallon hwh. I told him I would let him know tomorrow AM. He thinks the 75 gallon will be enough. The people at work with homes this size all have two water heaters and say that one 75 gallon is not enough. I am so confused.

Have the people at work with homes this size or you crunched the numbers to see how much it will cost you over the equipment life to heat your water? The answer is almost certainly that "tankless" means expensive.

Thanks ionized. I think the tankless is actually cheaper over the life of the unit. I have been doing some reading on tankless and I am beginning to think this isnt for me. For one, I read that the flow rate will be less than a regular water heater. Does this mean the water pressure will be less? The plumber stated that the recirc. will decrease the pressure by 20%.

Also, I am reading that you cannot run two items at once with the tankless. I work a lot and when I get home at night, I usually throw a load of wash in and head to the shower at the same time. I am leaning towards the 75 gallon water heater, as the plumber suggests. I hope I am understanding this all correctly!

Rocky,

I'm not trying to talk you into or out of a tankless. Factually, I can tell you that this afternoon I took a long shower while my dish drawers were washing away, and I didn't suffer a drop in pressure or a change in temperature of water. My long shower went off, just as if there were not other water outlets in use. In just the few days I've had the tankless, I often wash the dishes while I'm working at the sink, using hot water, and haven't noticed any change in water pressure or hot water availability while doing those chores simulataneously. I've not yet washed clothes while showering, or had guests who showered the same time I did. That's coming later this month.

While I didn't experience any degredation in hot water flow or availability with the dish drawers on, I don't know what my shower would have been like if there had been 4, 5 or more hot water uses going on in my house simultaneously.....But as a single, that's rarely going to happen.

Regarding flow rate, the Navien literature says that for cold water entering the tankless that measures 55 degrees, the hot water flow rate will be 7.7 gallonds/minute. Utah's cold water is considered 55 degrees, and that temperature is fairly constant year round. If the cold water entering the tankless is warmer, 60 degrees, the hot water flow rate increases to 8.6 gal/minute. If one lives in the south with really warm cold water, say 70 degrees, the hot water flow rate is 11 gal/minute. Similarly, if your cold water temp is really cold -- 40 degrees-- the hot water flow rate will drop to 5.9 gal/minute because the tankless must slow down the flow rate to heat the water.

The 7.7 gal/minute has so far worked for me. BUT, I don't have one of the modern showers with lots of nozzles shooting out lots of hot water. I cannot imagine that a tankless heater could support that kind of shower arrangement.

It's all so confusing! Will your plumber give you a tankless customer so you can talk to these people and find out how this works for them, why they like it or don't like it? That info might be very useful for you.

Thanks Beth. I really appreciate your input. I will talk to the plumber about it some more today. A lot of people at work have tankless (and they love it), but they all have two sources of hot water. If I had the cash, I would put tankless in the master, and the hot water heater for everywhere else.

If you have decided against tankless for other reasons, so be it. If you are tempted again, or for the information of others, here is a worksheet to determine what kind of water heating works best for you. Just to throw you another curveball, if your climate is hot and humid, a heat pump water heater might be your best bet in the long run.

http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=13010

It is really hard to beat the low cost of the very conventional tank water heaters. The expense of any other kind makes catching up a long process. That is especially true if you don't use a lot of hot water as a single person. That would be even more especially true if you are a single person at home most of the time and use hot water periodically through the day. If you are working outside the home, the stand-by losses push you somewhat closer to a demand water heater of some sort.

In addition, there are some other strategies for improving water heating at the DOE's web site. Reviewing what might be most appropriate for you. Since you are in a remodel situation, have you considered installing a drain heat recovery system in your most-used shower?

Your shower (unless it is a fancy one) should be around 2.5gph. Same for the kitchen faucet. The DW and W may be a bit more each, but not that much. What Beth stated about the flow rate is correct, the higher the cold water temp, the more hot water is produced. Remember, the on-demand heater heats as water is flowing. There is also a minimum flow rate before the unit will activate.

You should NOT use a recirculator with a tankless, IMHO. It would seem to me to defeat the purpose since it would be activating the unit all the time (unless on a timer and even then it would cycle on and off continuously).

You would consider using a recirculator in the MB with a tank unit (again, on a timer or a switch) so that you have 'instant' hot water at your shower/sink. The cold water in the HW pipe gets pushed back to the tank for reheating and storage where it belongs.