Water heater capacity for occational use ski cabin

[dnr]

Hi,

I have a ski cabin with a 60 gal water heater. There are two showers. This house was built originally for a couple, but when I use it I have as many as 14 guests stay at a time during ski season. Even if people take quick military showers, when you get to the last few people they end up with cold showers. Not sure if this is due to the heater capacity, or if due to the mountain cold water (probably just above freezing) that is flowing in to the tank. To make maters worse, this heater runs off slow burning propane and is at high altitude - seems to take anywhere from 2-4 hours for the tank to get hot even at max temperature setting.

There is not a lot of room anywhere to put a second tank, so

What are my options to enhance capacity ?

I've heard that the on demand systems have flow problems. Has anyone tried putting a on demand system between the water main and the input to a conventional heater such that the incoming water is much warmer ?

Tend to use this cabin on the order of 30-40 days during the Winter when this is a problem. When the house is empty we turn the heat down to bare minimum. So energy cost is not a super big concern -- main issue is I want people to be able to take a nice hot shower after a long day skiing.

Any other ideas or comments appreciated, or if you can point me to some existing threads which cover this topic, I'd really appreciate it.

Thanks!

[tom]

Get a bigger tank? 80 gallons? Tom

[BobK207]

I have the exact same situation but have a 75 gallon tank (also propane fired)

I just make sure I get to the shower first. :)

The killer is that the cold water is ~40.......so you use 2 gallons of hot to 1 gallon of cold. If I want to use the tub I've got to start fiilling it with all hot water & finish off with tempid.

I checked into a demand water heaters (Bosc & Taguchi) but both the mfr reps said that at high altitude the perfromance really drops off.

They said that a tankless wouldn't handle the whole house but if it was hooked up to a single shower it "might" work. Plus you've got to consider the instantaneous btu delivery capacity of your propane tank & piping

So really your only choice is a bigger tank unless you're ok with the tankless for the single shower thing.

A 100 gallon tank is only 28" diameter by ~70" high maybe you might room for it.

an alternative is to consider waste water heat recovery, if your house is amenable to it, (geometry & plumbing wise) you might consider

their website is a mess but the concept & product are sound.

I've spent a fair amount on their website trying to figure the tihngs out.

In a ski situation most of the hot water use is for showers. These things are perfect for heat recovery in a continuous flow situation and properly sized that can "extend" gas fired water heater capacity by a factor of about 3.

BUT the installation can be a problem ........... ideally you need 40 to 60 inches of drop from the shower drain to the sewer outlet for the installation to be simple.......... otherwise you'll need a waste water pump.

cheers Bob

[nicksanspam]

There's probably not a lot of room for a greywater heat exchanger either. The one Gary Reysa and I are working on would be about 3' diameter x 6' tall, with the greywater I/O near the top. If the 4" x 100' black corrugated drainpipe spiral were flat (eg hung under a basement ceiling), it would be about 7' in diameter.

That could increase the capacity with good final temperature regulation, compared to putting the tankless after the tank :-)

Nick

[hallerb]

yeah your best bet is probably putting a tankless, the highest btu your propane tank will support immediately before the standard tank. you will likely need to upgrade your propane setup..

with the tankless first this will temper the incoming water, warming it enough that will allow your regular tank to finish it off for a stable temperature.

[mm]

A small point. I don't think the "even" makes sense. The higher the setting, for sure, the longer it will take to get there. If by "hot" you mean the same temp regardless of the setting, it's going to take the same length of time, because most heaters heat at full blast until they reach the temp they are set for. Setting it to 140 instead 120 won't lengthen or shorten the time it takes to get to 120.

Set the temp higher so people will use less hot water and more cold water? This won't shorte the time before the first shower is possible, but if they don't shower then, the water will get hotter.

If it's really hot there may be a danger (especially children?)

What about limiting the flow of hot water (somehow) to make it last longer and putting in an on demand heater to warm the cold water to mix with the hot water. Or some strange combination of your current WH and an on-demand heater, since neither alone is enough. I just thought of this. For all I know it is a terrible idea.

That's similar. or the opposite, of what i just said.

[Grumman-581]

When I was in the Navy, at one time, the shower for our berthing compartment had rather *hot* water... You had to turn the cold water on first and then just barely crack the hot water valve... If you did it the other way, you had very wet steam coming out the shower nozzle... It was dripping one day and I cranked down on the valve to stop it... Cranked down on the hot valve, no difference... Cranked down on the cold valve, still no difference... Cranked down *really* hard on the hot valve and it went from full off to full on... I leaped out of the shower and half of me was lobster red... I traced down the hot water line and once I came to the heat exchanger, I found a temperature gauge... It was showing 250F hot water... The only reason it was liquid was because it was under pressure...

The Navy is really big on impressing upon you to take "Navy Showers" instead of "Hollywood Showers"... Since you have to make your water by distilling it aboard ship and distilling means fuel, they want you to use as little water as possible... To ensure this, they eventually changed all the shower heads to a type of shower head that about the size of a hockey puck and was on a hose... The shower head had a push button on it and you could only get water as long as you were pressing against the spring loaded button... Spray yourself, put the shower head down, soap up, spray the soap off... You definitely used less water that way... After a long day of skiing, I suspect that most people want a long shower... On the other hand, perhaps the OP should just suggest group showers...

[hallerb]

people tend to shower till they are warm. After a long day in the cold this only makes things worse. a low flow shower head can help but the tankless first feeding a regular tank would help a lot. if thats not enough he could upgrade to a higher btu 100 gallon tank after the tankless then set that tank HOT like at max then add a tempering valve that would mix hot and cold water keeping output at 125 degrees to prevent burns.

the biggest gain would be the tankless and a good propane upgrade

[m Ransley]

A Takagi or Rinnai 190000+ btu unit will do the job itself without a tank if the Gpm of the shower head matches flow capacity and temp rise of your propane tankless. You need to know exact gpm output of showers, incomming water temp lows, and measure temp drop from present tank to shower head. Proper gas flow is the critical part 190000 btu is im sure more than your present furnace, you need to have gas flow measured with competing apliances on with a manometer. You might need all new propane pipe and regulator to get the flow needed. I use a small 117000 bosch with 35f incomming water I get a hot 105f shower without unit set on high, without a real restrictive shower head. You can get 1.2? gpm heads that a small 117000 Bosch will handle 2 showers, with 190000 btu you wont have an issue or need a tank , unless altitude issues cannot be rejetted for.

I would hook up the tank but have a bypass valve set up since you may not need it. Gas flow measured, incomming water temp low measured [ but figure 35f] shower gpm output, and temp drop in pipe are what you need to know.

I have my tank I replaced infront of the tankless , it is there only to temper water to house temp. The most efficient, best unit made is a Takagi TK1 a 94% propane fuel unit. I dought you will need the tank but keep it inline with a bypass anyway.

Contact Takagi and Rinnai to go over the specs you need and for real guidance, there might be a high altitude larger model avalaible that is jetted and sized to get full Btu. It is all in temp rise, gpm, gas supply+competing users, line temp drop, and knowing incomming temp low.

People unhappy with tankless are the ones that did not calculate everything first, or installers cutting corners and guessing on gas supply and pipe sizing.

[Ecnerwal]

Step one - have a qualified propane service technician check the thing out and make sure that the burner is adjusted and working properly.

Seems to me that there might (depending on location of shower) be plenty of room for the copper system where the outgoing shower drain water preheats the shower cold water supply (or even two of those stacked, one feeding the shower cold and the other the water-heater inlet cold). This is a commercial product (I forget the name), essentially consisting of a copper drainpipe with a soft-copper water line wrapped around it and soldered to it. By warming the cold into the shower it reduces hot-water-use per shower.

Simple to install if there's a basement (or first floor) under the shower, more complicated (wants a pump to elevate the drain water) if the shower is on the lowest level of the building.

[nicksanspam]

GFX, but that needs lots of vertical space, and it's only 60% efficient.

Maybe it's time to build a low deck with another fully-enclosed shower or a hot tub, which would lose less heat with a pump but no bubbles...

Nick

[Edwin Pawlowski]

In spite of all the ideas, no one has mentioned the simplest yet. Group showers. Divide the guests into three or four teams. They won't care what the temperature is.

[Philip Lewis]

but the individual shower times might get longer. ;)

[No]

M Ramsleys post has a lot of detail that may seem like mumbo jumbo at first but the bottom line is that a properly sized, properly installed demand system will be exactly what you want.

[Chris Lewis]

According to dnr :

The tankless solutions discussed elsewhere are probably the best, assuming your propane system can keep up to the gas demand.

Another possibility is to raise the tank setting, so you have more heat energy available from it.

Alone, this isn't a good idea, because of the scalding hazard. Some states mandate settings no higher than 120F... unless you have a tempering valve.

If you set the temperature up high (eg: as high as 180-190F) and used a whole-building tempering valve set to, say, 120F, you'd have more heat capacity without the scalding risk, and you're still "legal".

Switching to decent low-flow shower heads (if you haven't already) will also help.

[BobK207]

OP-

At what altitude is the house?

How big is your propane tank & do you shar it with other homes?

cheers Bob

[meow2222]

If space is lacking, suggest making a pancake shaped drain heat exchanger and fitting it underneath the shower tray. The tray then goes back 4" higher than originally.

Or a square tray with baffles fitted to control drain water flow direction, and paralleled microbores running along those channels to prewarm the cold feed to the shower.

The most primitive possible version, something one could set up in minutes, could be nothing more than a copper coil placed in the existing shower tray, with wood strips on it to keep feet off the cold copper. Could be used as a temp measure while a permanent design was done.

Also ensure shower enclosure is fully closed to minimise conduction and evaporation losses.

NT

[nicksanspam]

suggests:

Hmmm. Something that sits inside the tub, eg 2 18"x36" copper plates

1/4" apart, bolted or brazed together with internal copper bar spacers and a rubber mat or feet beneath, with a male hose thread at each end?

Or an all-copper bathtub, with tubing soldered beneath?

How would we keep it from cracking and leaking?

Nick

[Grumman-581]

Nope, I mentioned it 4 hours before your post...

[Grumman-581]

Another solution that I haven't heard might be for you to use a demand heater on the cold water supply to the shower, not just one to the existing gas water heater... That way, the cold water that is being mixed at the shower head is not quite so cold and it wouldn't need as much hot water to get it to a comfortable temperature... At the very least, a demand heater on both the supply to the hot water heater and one on the cold water supply to the shower combined with increasing the temperature setting on the existing hot water heater should work...