I'm not a pro and I don't work in construction, but if you get a direct vent gas appliance, I don't think it affects the IAQ, since the combustion air is bought in directly from the outside. Nothing ever mixes with the indoor air, like in a regular open fireplace or gas stove.

I'm in Fl and we had an electric instant hot water heater in our condo and never had a problem with it. Right now we are renting in another unit in the same building while our house is being built. It has a large hot water tank and I find I have to wait 20-30 minutes after DH showers for me to shower or halfway through, I lose the hot water

You are not going to be happy with an instant electric heater. Mostly, due to cost of running one of sufficient size to do the job well. I agree with Mike, you won't experience any air quality issues with a gas unit. Code requires them to be vented to the exterior even if mounted on the interior.

You might be happier with your decisions if you include your HVAC engineer in the discussion. A dehumidifier and ionization unit for better air quality would be money well spent in the area where you live. I just installed them in a home I just purchased. The improved quality of the air and building envelope was almost immediately apparent.

If we opted for a traditional water heater would the tank be sufficient
to provide 3 to 4 showers/baths running at the same time, for a total of
6 to 8 showers/baths?

We have a standard water heater in the home we're renting now -- the biggest that can fit in the closet -- and if I'm showering, my husband can't start the wash machine without me getting a blast of cold water (and a subsequent cold shower).

My family currently has 7 bodies, soon to be 8, and we all can't shower/bathe back-to-back. We have to wait about half an hour between each person if the next person doesn't want to run out of hot water. The 3 littlest boys can all hop in the tub together, which helps, but somehow I doubt that's how y'all wanna solve the problem.... ;-)

We have 5 people and a 60 gallon gas heated tank. It's plenty big for us. Kids shower 1/2/3 right in a row, and they take long showers (no drought restrictions right now), and we've never run out of water. With guests we've had as many as 5 back to back showers, no problems with running out of hot water either. Modern DW and WD use dramatically less water than in the past, so I'm sure that helps as well.

We generally don't do simultaneous showers, but on the occasion we have the temp is fine, just a little lacking in water pressure - ditto if we run the washing machine while one of us in in the shower.

Have you looked at geothermal heat pumps? You can read up at greenbuildingtalk.com

A couple of thoughts.

In a hot climate, heat pump hot water heaters are usually the way to go.

I suspect that after pool showers are usually quick so capacity issues are lessened.

The tank size and heating source does not affect flow at all - they are independent. Problems with hot water dynamics has nothing to do with tank size.

Tankless electric is not generally recommended.

Solar is worth considering if you have incentives. To give you my example - $7000 for solar. 35% federal tax credit. Utility credit of $3000 (still waiting to hear final number). So net cost is about $2000. A large high quality tank with install - $1200. So the difference is small. The savings per year is probably $200 vs your propane instant and maybe only $100 vs heat pump hot water. While all systems have potential maintenance issues - solar would have the greatest longevity of those options. Standard electric tank has the least maintenance issues and probably will cost you $100 more than your propane per year. Geothermal makes little sense in Florida - you also probably have few installers around.

Now on to distribution. Obviously central tank makes the most sense. Duplicating systems with maintenance issues not to mention up front costs are rarely a good idea. I reread your post. How far are these wings away? Do you really want laundry not near the bedroom? Distance matters of course. On demand hot water pumps might be the answer.

We have a NC oceanfront house with 5 bedrooms, 4 showers. 10+ people at times. No issues with a 80 gallon standard electric. It is a vacation rental so we went with simple. Also harder to get payback with not having year round use - although it is occupied over 50% of the year which I wasn't expecting.

Thank you all for your thoughtful responses. Your personal experiences of different types of water heaters are very helpful.

In response to Springtime, we had hoped that we could organize the plumbing so that it was grouped together but we had site features to work around, such as wonderful waterfront views, an angled, narrow, and elevated (unusual for this part of Florida) homesite, plus floor plan requirements that are specific to the way we live. Don't get me started on 'occupant behavior' :)

In response to Jln333, why are electric tankless "not generally recommended"?

I had hoped to include solar, and may still at some point, but the only suitable roof i.e. not shrouded by trees, will be in front of the house and facing our front porch and arriving guests. Since the house will be single story with a light colored metal roof, the solar panels would be very obvious and very much detract from the home's street appeal.

As far as the location of the laundry, I am certain that I do not want it near any bedrooms. I know many people on this site have the opposite opinion but currently we have a 2nd floor laundry between 2 guest bathrooms and reasonably close to the master (I designed it this way) and I detest it! Once the visiting children are in bed the laundry room cannot be used due to potential noise. During the day I have to run up and down the stairs to attend to the laundry. I would much prefer to have it close to the hub of the home where I can easily attend to it and where I can run loads of washing after all our guests are in bed. This is also when I do almost all the daily chores so that I can be free to spend time with our guests during the day. As a retired couple and living the casual waterfront Florida lifestyle, my husband and I do not generate a huge amount of laundry so schlepping it to the laundry from the master wing will not be a problem. It's a straight shot.

As you rightly say, distance matters. The distance from the garage (where a heat pump heater could be located, for example) to the furthest hot water faucet in the master wing is 70 feet. From the garage to the powder room is 47 feet. However all the sinks and dishwasher in the kitchen wing are in a line, the closest 5 feet from the garage and the furthest, a breakfast/bar sink, under 40 feet away. I was thinking that we could install a heat pump heater in the garage (we can do this at cost) to supply the kitchen wing and possibly even the pool bath/powder room? then electric tankless heaters, 1 for the master bath and 1 for the guest baths. I think our biggest demand for hot water year round will be in the kitchen wing, so we could benefit most from the energy savings there. What do you mean by "on demand hot water pumps"? I just want to be sure I clearly understand.

I do understand about potential maintenance issues with multiple systems. However I must say that our existing Rinnai propane tankless heaters were installed 11 years ago and have required only minimal routine maintenance (DH does it). I read that electric tankless require even less maintenance and are longer lived. Is this true?

It seems probable that a perfect solution may not be possible. However is a very good, fairly economical, and convenient compromise a possibility for our dream house?

Just FYI - solar panels don't make me cringe at all when I see them, even on the front of a house. I'm appreciative of any effort to harness renewable (even with a long payback). Also - have you considered the Tesla Solar Shingles?

Its nice to finally see someone else who doesn't have to have the laundry room on the same floor as the bedrooms... :-)

Not generally recommended because the cost of upgrading wiring is not insignificant. Also you have the issue of inadequate temp increase- less of an issue in Florida.

Then there is the potential for peak demand charges. Probably not going to happen but solar installations increase the chance it may happen. The way it works is that you pay a charge for your peak draw in a month. 3 tankless heaters drawing at the same time could be $200 for that month. It is a way of charging for the grid and appropriately assigning costs. The grid has to be able to handle the peak load so charging for that peak makes some sense.

We live with a demand charge. It is $5 per peak kw in a month. I just looked and there is a tankless electric HW heater that is 36 kw. You probably wouldn't need 3 of them that big but check that math. You would probably need 600A service. That is not normal anywhere.

So that is the general reason. But in the right scenario they can make sense just not very often.

Chloecat I like to see solar panels too, in fact we have them on our current home. However the new house will be coastal style with a standing seam metal roof. The available roof on our house starts at 9 or 10 feet from ground level and is at 90 degrees to our front porch and entry door so any regular solar panels would certainly be in our faces. I wish that Tesla would make something that looks like standing seam. I was so excited when I first heard that Tesla had branched into solar panels. I am beginning to think though that we could have almost as positive an impact on energy savings by choosing a heat pump water heater for most of our needs.

jln333 thank you for your response. I was considering using a heat pump for the kitchen wing then 2 smaller tankless heaters for the master bath and guest baths plus the pool/powder. Stiebel Eltron make one tankless that is less than 15kw and one that is less than 20kw. If this makes for a ridiculously large electrical upgrade we may have to reconsider propane.......sigh!

Could you please clarify "on demand hot water pumps" in your earlier post?

On demand hot water pumps:

People with large houses have had single central water heaters for years.

One option - wait for hot water. I know lots of people that do that and they aren't happy about it.

Second option - run a loop of pipe that stays hot a good portion of the time. A pump runs and keeps this hot - usually controlled with a timer and thermostat. Wastes a lot of energy and I have seen rules that they aren't allowed anymore - but not sure where that applies. It was part of the 2015 new DOE rule on hot water heaters.

Third option - have a pump that runs "on demand". My father lives in a house in CA that has a push button near the kitchen sink. Built in 1993 but apparently reasonably common there. When he is ready to use the sink, he pushes the button and waits some amount of time ?30 secs. And then the hot water is instant when he turns on the tap. If you have bathrooms far away, they could be tied to the light switch.

Last option - POU water heaters near far away fixtures. This is similar to what you are thinking with multiple tankless electric hot water heaters. It works really well for sinks but with multiple shower setups - it becomes less than ideal. Worth considering but potentially taxing on the grid which may tax you some day.

The 2015 rules do bear mentioning. All hot water heaters above 55 gallons need to be more efficient. Heat pump or condensing gas seems to be required.

With a well designed modern house in Fl, hot water becomes a big part of your energy use if not handled well. Supplying energy will become more challenging in the lifetime of your house.

Sis-- I am hoping for standing seam solar from Tesla as well!! I would likely be first in line if they were to bring that out prior to starting our home!!

In response to Jln333, why are electric tankless "not generally recommended"?

As I said, we had electric tankless in our 1900 sq foot 3 bedroom/2 bath condo with absolutely no issues. We were able to run two showers at one time as well as the kitchen sink, the dw, etc. LOL

I had hoped to include solar, and may still at some point, but the only suitable roof i.e. not shrouded by trees, will be in front of the house and facing our front porch and arriving guests. Since the house will be single story with a light colored metal roof, the solar panels would be very obvious and very much detract from the home's street appeal.

While I love standing seam and I'm using 5V on my house, if I had the chance to use the Tesla panels, I would jump at the chance. However my house is about to be sheathed in the next several weeks so I can't wait for the Tesla panels to be shipped.

I can't tell you how much here in SW FL it irks me not to be using solar.

As a retired couple and living the casual waterfront Florida lifestyle, my husband and I do not generate a huge amount of laundry so schlepping it to the laundry from the master wing will not be a problem. It's a straight shot.

How far of a straight shot? I ask because you mention that you're a retired couple and it sounds like for now you're in good health. However will you still be able to shlep the laundry if you or your better half needs a cane, a walker or a wheelchair. If it's a relatively short distance, it won't be a problem, but if it's across the whole house, it could potentially be a problem.

I tell the story of my Mom who redesigned her whole house to work for her if she ever became handicapped. Except she put the laundry across the whole house to be near her office, so she had to shlep it across the house. And Mom was the type who didn't want anyone else touching her clothing.

Mom also was someone who went to the gym 5x a week, did the treadmill on days she didn't go to the gym and ate healthy. However at age 72, she developed Parkinson's disease. As her disease got worse, she started to need to use a walker and it was impossible to carry loads of laundry across the house. My Dad, who had back issues, had to shlep the baskets for her.

Also remember now you have a one story house so won't be shlepping laundry up and downstairs. Big difference.

I solved the problem with my house by having my bedroom with three outside walls. My laundry is in the hallway leading to the bedroom on an outside wall across from our master bathroom under the stairwell. We do have our guest bedrooms upstairs but the elevator for the second floor guest rooms is right down the hall. So now our laundry is still close to the bedroom for easier shlepping but no noise because it's on an outside wall and not near any bedrooms.

It seems probable that a perfect solution may not be possible. However is a very good, fairly economical, and convenient compromise a possibility for our dream house?

Have you discussed it all with a plumbing specialist? Also I would post on the plumbing forum.

In our current home we installed a propane gas instant hot water heater on the exterior of each of the two sides of the house. This has worked perfectly for us. However for the new house we are hoping that we won't have to install a new propane supply, for cost but mostly for indoor air quality reasons.

Perhaps you already said and I missed it, but, is there a reason you can't install instant gas hot water heaters on the exterior of your new home? If you can, I don't see how that would affect indoor air quality. (FWIW, we replaced our two conventional natural gas hot water heaters a few years ago with two tankless ng hw heaters, mounted on the exterior, on opposite sides of the house, and have been very pleased.)

Thank you again for all your responses. Perhaps we should all contact Tesla to request standing seam solar panels? Wouldn't you think that they would be even easier to produce than the shingle and tile styles they have now?

In response to Sammy, we originally designed the house with a propane gas log fireplace, a gas range as well as gas tankless water heaters. We then decided to eliminate the fireplace and range mostly for indoor air quality reasons which meant installing a new propane supply and piping to both wings of the house just for hot water. At that point it made sense to consider other heat sources and I thought that electric tankless would be the answer especially as they can be installed close to the points of use. We could always return to having propane tankless, as like you, we have been more than satisfied with this arrangement on our current house but it would mean dedicated gas tank(s) for the tankless heaters.

CP I will take your suggestion to post on the plumbing forum. Your endorsement of electric tankless keeps us considering them as an option.

I have been following your building story with interest as we began ours around the same time (and I believe from your posts that we are about the same age). I foolishly anticipated that we would be going through all the stages of building at the same time as you and since you are only a few miles down the road from us, thought we would be comparing useful notes! Yet here we are, you are starting to put in lovely finishing touches to your new house but for various reasons we have not yet moved from first base!

As far as the location of the laundry is concerned, thank you for the warning. I am sorry that your mother's health declined the way it did despite taking such good care of herself, it is certainly a cautionary story for us all. My father was still easily climbing on to his roof to maintain it, digging drainage ditches and riding his bicycle many miles until cancer abruptly felled him at 82. My mother, a cancer survivor at 87 years lives alone, maintains her own garden including still planting trees, mowing the grass, doing all her own cleaning, decorating, shopping etc and walks 2 or 3 miles a day, and sometimes up to 6 miles to visit her friend. She would be shocked that anyone would think this is in any way exceptional. I know my parents' active lives do not guarantee that I will be so fortunate, just as your mother's decline happily does not bode ill for you. You are right though that we should plan for any eventuality. In our case we decided not to limit our current active lives in order to be braced for possible disability in the future. Our new property is not suitable for a disabled couple. If the time comes when we cannot haul our small amount of laundry the approximately 50 feet from the master wing to the laundry we will be out of there. The property is 3/4 of an acre with a dock, boat and seawall to maintain so we will only stay there while we are still fit and healthy. If a disability is temporary we can get help until we are back on our feet. Our plan is to leave as soon as we can no longer maintain the property.

Thank you once again jln333. So much to think about.

I have been following your building story with interest as we began ours around the same time (and I believe from your posts that we are about the same age).

Oh my! You started 2 1/2 years ago too? It's not easy.

I foolishly anticipated that we would be going through all the stages of building at the same time as you and since you are only a few miles down the road from us, thought we would be comparing useful notes!

Message me. Let's compare notes and builders.

Yet here we are, you are starting to put in lovely finishing touches to your new house but for various reasons we have not yet moved from first base!

???

As far as the location of the laundry is concerned, thank you for the warning. I am sorry that your mother's health declined the way it did despite taking such good care of herself, it is certainly a cautionary story for us all.

Thank you.

In our case we decided not to limit our current active lives in order to be braced for possible disability in the future. Our new property is not suitable for a disabled couple. If the time comes when we cannot haul our small amount of laundry the approximately 50 feet from the master wing to the laundry we will be out of there. The property is 3/4 of an acre with a dock, boat and seawall to maintain so we will only stay there while we are still fit and healthy. If a disability is temporary we can get help until we are back on our feet. Our plan is to leave as soon as we can no longer maintain the property.

And that's a valid decision too. Luckily down here there are plenty of excellent choices including some fabulous condos.

My Rinnai is in the garage. Even so, I've never smelled any gas or noted any combustion products. As pointed out, it brings in outside air and vents everything with a blower back out again.

Thank you Ron. The indoor air quality issues were with the range and gas log fireplace. We would be OK with putting Rinnais on the exterior walls, as we have on our current home, but I was trying to avoid bringing in propane gas just for water heating.

I have been doing a lot of reading and thinking on this subject and I may have a solution. Please all let me down gently if you think I am wrong :)

We could put a heat pump water heater in the garage to supply the 4 sinks, dishwasher and washer in the nearby kitchen wing. There is an unshaded south facing roof over the master bath that may be ideal for solar panels to heat the water for our master bath. I would have to check whether the storage tank could be installed in the attic above the master bath. There is easy access to the attic. Then we could install an electric tankless heater for the 2nd floor guest bathrooms and the pool/powder directly below them. This less economical system would really only be used when we have guests. 3 systems to purchase and maintain, yes, but this solution would provide plenty of hot water where and when we need it with very little energy use at least 80% of the time. Presumably we would not then need to do a hefty upgrade to our electrical service and would not need to have a propane tank and piping.

I would say - needlessly complex. Of course it would work and be super cheap to run. But you spend a lot to save a little. Unless your habits just include a lot of hot water use.

I am getting ready to make some of the same choices but my plumbing is more compact. For me solar or heat pump. I had planned for tankless electric for distant sinks and I still may do that. But they just aren't that distant. The kitchen sink might get one.

I would back up and ask - how important is instant hot water at the taps? Because you probably don't have it now.

I have to comment at the concern of laundry location and bedrooms. Ours is right next to our son's room. We have other bedrooms he could use but doesn't. Because of our demand based electricity, we often run the dryer at night after he goes to bed. My wife uses these tennis ball looking things instead of dryer sheets and they make a racket. And yet we are building the laundry right next to our bedroom next time... We thought about it and you never run the washer at night - since you would have to put stuff in the dryer while you are asleep. And dryers are really quiet without the balls. Even with the balls, you usually run a dryer when you are awake. Lastly, just soundproof that wall. So many options. Of course the other big advantage (other than carrying laundry a distance) of having them next to each other - hot water points are close to each other.

Hmmm! I really thought I had the solution! More thought needed obviously. Thank you for your thoughts, jln.

One of the disadvantages of a one room deep design to maximize views and light is that it is more difficult to group plumbing. Also due to the way we live, with many extended stay visitors every year, one of our priorities is for privacy for our master suite. This means it is tucked away in a relatively remote wing. As for the laundry location, I would in fact run laundry at night after the children, and even the adults, are in bed. I am a night owl and this is the time I do the chores, including laundry. Right now it is frustrating to be unable to do this. We also have a central vacuum but unfortunately the motor had to be located in the laundry room so I am unable to use it at night. The new one will be in the garage, far away from all bedrooms.

Our new house could be redesigned to make a more compact plumbing plan. (Redesign would no doubt cost more than the water heaters.) I fear though that some of our priorities would be sacrificed. Your point about my solution costing a lot to save a little is valid. To mitigate that cost, we are able to purchase, install and maintain the heat pump at cost and there are federal rebates (and possibly utility) rebates for the solar. Our concern other than energy use is wasting water, an increasingly precious resource in Florida, if not the entire world. This is why I hoped to have the water heaters as close to points of use as possible, rather than for the convenience of not having to wait for hot water to arrive. However your comments have given me pause - perhaps we should simply keep the solar heater for our master suite but use the heat pump to supply both the kitchen wing and the guest baths. The guest baths are 30 feet from the closest hot water supply pipe (unless we use Pex with home runs from the garage). There would be a little waste water until the first shower received hot water but this would be during only a few weeks of the year when our guests are here. If we correctly size the tank our guests should not run out of heat pump heated water as it would be unlikely we would be running the washer and dishwasher at the same time as their showers. Perhaps if they did ever run out of hot water it would lead to some modification of "occupant behavior" that Springtime mentioned! ;)

Even if we don't yet have a perfect plan, we are much closer now to a good, economical solution for our water heating needs. I am excited to think that we could after all use solar, in addition to a heat pump, to heat all our water. I know CPartist refined her house design with the help of everyone here and now I am benefiting from similar generous inputs. Thank you!

My excitement about using solar was short lived. Our solar company says that solar hot water heating is a dinosaur. They say that even if we did install it payback would be 30 plus years and that's without the extra costs to beef up the attic to support the tank or extra pay for the plumbers to haul the storage tank up there.

I did send a comment to Tesla asking for standing seam

We found solar was a non starter here in this part of FL. Not enough incentives and too long a payback period unfortunately as I wanted to put it in.

Thank you doc, me too!