Hot water tank for liveaboard

[GRIT]

We'll be launching our boat in the fall, and are finalizing some our equipment choices.

My wife works in an office, and she's going to want nice hot showers before work. We'll have a 5kw hydronic heater, which will run before and during her shower. So she'll be starting with a fully heated tank.

So my question is this: For those of you with experience using heat exchanger equipped hot water tanks (calorifiers), how large a tank would a person need to have a 10 minute "hot" shower, while the "engine" is running? A 10 minute shower equates to about 30 litres of water.

I can speculate, and calculate, all on my own; so I'd appreciate hearing from those with actual experience, rather than those who would like to guesstimate.

Thanks.
Paul.

[Boatguy30]

Instant propane is way to go. He careful with install as most/ none rated for marine use.

[Stu Jackson]

Originally Posted by svquintana

>>>>>>>>>>>>>>>>how large a tank would a person need to have a 10 minute "hot" shower, while the "engine" is running? A 10 minute shower equates to about 30 litres of water. >>>>>>>>>>>>>>>>>>>>>>>

Paul,

30 litres is about 8 gallons. Tanks come in 6 and 11 gallon sizes. If she takes an 8 gallon shower that uses up all of a six gallon tank and more than half of a 11 gallon tank.

You says "engine" is running. Do you mean the heater? Rather than your propulsion engine. Do you have an electric element in the water heater?

The reality is that showering on board rarely has the user running the water all the time. One wets up, turns off the water, shampoos and soaps up, and then rinses, without the water running all the time like in a shower at home.

If, however, she chooses to do so, you'll find yourselves struggling to refill your water tanks, perhaps unnecessarily. Unless you tap into the dock water with a pressure reducing inlet fitting.

How long is her hair? Really. I recall Lynn Pardey's story about her long, luxurious hair and how she bathed on board in a small tub they placed at the base of their companionway. I don't think that's what you had in mind, though.

[GRIT]

Thanks for your replies. I should have included a little more information.

The hydronic heater is an espar, 5kw. (Thanks for the propane advice, but we've done that before, and it just isn't what we want.) and the tank choices are 40l, 75l and 115l by Torrid or Isotemp. We would run the heater before showering, and during showering. Anyone with any experience there? Water isn't an issue at 30l per shower.

As an estimate, a 30l shower would use about 20l of hot water out of the tank, which is about 5 US gallons. (Those in the UK may refer to those as gallonettes.) But I'd like to hear from someone with experience with a similar system.

Cheers.
Paul.

[ranger58sb]

FWIW, we have an 11-gal electric water heater, the heat exchanger function is not connected, and between us we never run out of hot water during two sequential "Navy" showers. Plenty of hot water remaining for dishes, too...

I suspect that means the water heater just creates "new" hot water faster than we use it in the hot/cold mix.

Not sure how (if) all that might translate to the heat exchanger/engine running version...

-Chris

[CaptTom]

I don't think you'll go wrong with any of them. 11G (41L) is enough to give us two showers and still was dishes in hot water, plus have some left later for hand washing.

Recovery time from stone-cold is about 1/2 hour for a usable amount, 45 minutes before the unit is fully hot.

But you're not going from stone-cold. Also, hot water is drawn from the top of the tank, so even if it takes a while to heat the rest, you're always drawing the hottest water. You also mix it with cold (as stated above.) Another option is to set the tank hotter, and use a thermostatic mixing valve to stretch it even more.

That said, I don't see any down side to a larger tank, except possibly a small standby loss. Too small to worry about, IMHO.

[GordMay]

Originally Posted by CaptTom

... Another option is to set the tank hotter, and use a thermostatic mixing valve to stretch it even more...

A good idea, in any case.
Remember, to minimize (Legionella) bacterial contamination, water must be stored at 60°C (140°F) or higher, and should be equipped with anti-scald devices (at the tap) to deliver water at 49°C.
Such a strategy should both minimize the risk of scalding and the risk of legionellosis.
However, studies (in Quebec) have shown, even when the thermostat is set at 60°C, a high percentage (approximately 40%) of residential electric water heaters remain contaminated because of the lower temperature, about 30°C to 40°C, at the bottom of the tank. This is of less concern with our (relatively) smaller tanks, which have higher rates of turnover.

[gghanger]

I totally agree with Boatguy30....
If you have access to propane..you would have access to unlimited hot water! Some years ago I was an installer for Bosch thankless water heaters. I never installed any heaters in a boat. I am not sure how to install a exhaust flue...also you have have out side make up air...don't want any one to die from carbon monoxide...
Bosch makes a number of different models...stay with the simple one with a pilot light...it is the most reliable.
If anyone has a set up like this...I would like to hear about it.
This is just a personal opinion.....

[wrwakefield]

Paul,

We installed a 40L Isotherm SPA model water heater with mixing valve built into the heater. It provides plenty of hot water for two of us to take long showers. If the engine is running [our hydronic heat source...] it virtually provides an endless supply of hot water.

The best torture test was when we had a family of 6 onboard for 10 days [away from the dock...] We typically have guests shower while we are motoring toward that day's anchorage while the watermaker is running... This family had 4 teenage girls with long hair.... I took the last back-to-back shower [the 8th...] and the water was still too hot to use without mixing in some cold...

If you are interested, there are additional details about the water heater install- and more metrics- in this series of blog posts.

Best wishes finding what is best for you.

Cheers! Bill

[roberthowell]

certainly get the biggest tank that will fit a happy wife makes a happy life and it should b duel heated ( electric, engine) so u do not have to run the engine when u have shore power.

[Cheechako]

I would get the larger 11 gal heater. We always had 6 gallon and were fine, but she may want more. The reality is boat pumps will not flow water like at home so the water pressure out of the shower head will not be like home. It will be a bit wimpy. For this reason I never really wanted to take a long shower like I might at home. The other issue is the longer she takes a hot shower the more condensation will accumulate in the boat.

[Qayaq]

Hi.
I've got a 25 litre tank, I fitted a water saving Anion shower head (Ebay) ran hot water from my calorifia 240v or engine. Fitted a thermostat to the hot cold (ebay) So there is only 1 on off tap for the shower, so as the hot tank empties the temp stays constant.
I shower in it every day and anyone that uses it just goes wow. When I,m trying to save water with the anion head not on full I can get away with about 5 ltrs and it still feels like a decent shower. This also helps if you are short on hot water, my hot tank is turned up to about 75 degrees c and the hot cold thermostat mixer is adjustable and normally on 38 deg c. So on shore power have way plenty hot water and use about 30 litre when having a fantastic shower. The key to a great shower is The Anion head and a thermostat.
Hope that helps

[Cadence]

Would seem tank size is a moot question if the engine if brought up to temp. prior to the shower.

[sailingunity]

We had an 11 gallon on board. Never used the electric element, as we motored most everywhere (ICW). We found that more than adequate, and in fact the heat would stay in the tank for a while, so we didn't have to time our showers with engine running time.

[GRIT]

There are some very good replies here, thank you all. It looks like most would agree that a 40l tank would do the job.

I see Isotemp has a 50l tank, so I think I've found a winner there.

You've all been very helpful with your replies; Thank you.

For the Propane aficionados... We had a propane instant water heater on our last boat, which worked great, but we had issues getting propane in some countries. In Europe (camping gaz) we found that adapting the tanks to fit our system was a bit messy. The other option of "gravity" feeding propane from one tank to another is a non-starter for me.

We would, therefore, prefer to use diesel for this particular task.

Cheers all.

Paul.