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Tank or tankless water heaters - what's better?

 
pollinator
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....on the other hand, y'all are robbing yourselves of a great way to boost your immune systems to Legionella pneumophila.... :-)    But interesting discussion from an energy-saved standpoint.  Our old electric hot water heater soon will be crystallizing it's innards to its death from calcium deposits.  Are the specs regarding 'on-demand' hot water heaters (gas or electric) for low use households convincing enough to go that route in the future?
 
gardener
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On demand natural gas or propane seems viable to me. I can run a sizable system with a 20lb propane tank. The only issue was finding a bigger supply line from tank to unit. Ones used for a propane barbq grill dont feed the gas fast enough.

It could also be a back up to a solar system. Like when gas kicks in on a hybrid car that starts out with electric. The same could be done with water.

I have heard nothing positive about electric on demand units. Particularly as retrofit. It might be the high demand of electricity needed while its running. Like it equals the total capacity of an older house.
 
pollinator
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My solution is to put the hot water tank on a separate breaker, then turn it on 1 - 2 hours before I need it, then I shut it off.

It gives all the advantages of the tankless water heater without the cost, yes you have to wait for a hot shower, but you get a hot shower without keeping the tank running all the time you don't need it.

 
pollinator
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Mart, I used a programmable light switch, a decora style with a little screen on the switch.  That way the water heater came on before I got home and was ready when I did.  If you have an electric unit you'd have to use it with a relay.
 
steward
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John Weiland wrote: Are the specs regarding 'on-demand' hot water heaters (gas or electric) for low use households convincing enough to go that route in the future?



I just installed an on-demand or tankless water heater. It's propane fired. It made perfect sense to my wife and I for our needs. I really like it for several reasons. My favorite reason is it only makes hot water when we need it. No keeping water hot 24/7. It also makes hot water almost instantly from when it turns on, only having to wait for it to travel through the plumbing and will compensate for demand regardless of how many faucets are open. It has a digital thermostat. I keep ours set at 115 degrees. Lastly, and some design thought that I really like, is it has bypass valves at the inlet and outlet. I can turn off the water in and water out, and open two other smaller valves, one each on the inlet and outlet, and flush the mineral scale deposits out of it with vinegar, keeping the heat exchange efficient as the years go by.
 
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James Freyr wrote:

John Weiland wrote: Are the specs regarding 'on-demand' hot water heaters (gas or electric) for low use households convincing enough to go that route in the future?



I just installed an on-demand or tankless water heater. It's propane fired. It made perfect sense to my wife and I for our needs. I really like it for several reasons. My favorite reason is it only makes hot water when we need it. No keeping water hot 24/7. It also makes hot water almost instantly from when it turns on, only having to wait for it to travel through the plumbing and will compensate for demand regardless of how many faucets are open. It has a digital thermostat. I keep ours set at 115 degrees. Lastly, and some design thought that I really like, is it has bypass valves at the inlet and outlet. I can turn off the water in and water out, and open two other smaller valves, one each on the inlet and outlet, and flush the mineral scale deposits out of it with vinegar, keeping the heat exchange efficient as the years go by.



We have had a tankless propane water heater for a number of years now and love it....there has to be enough water pressure for it to work so not useful with gravity flow....certainly is one solution to water sitting in a tank for prolonged periods of time.
 
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We bought a Bosch Aquastar 125k btu natural gas model back in 2007 and only sold it because it wasnt convertable to propane. It lowered our gas bill but it also replaced an old and ailing tank heater, so its hard to compare.

We loved the endless hot water but didnt abuse it. Ours did not modulate and did not have a temp setpoint, just a low to high dial. It is ideal to have a heater which can boost temp of preheated water or let it by at a very low input in response to storage temp and also be able to serve hot water at full capacity from ground temp if called to do so.

The one i installed for a client as a backup and booster for solar thermal storage was a 200k btu Takagi/A.O. smith and was a great machine for the purpose.

If you do not have alot of periodic hot water use and primarily are home beginning and end of day, the information i have is you avoid major standby losses vs commonly used tank storage unless it is in heavy use throughout the day which narrows the gap and lenghtens the time to makke the difference in cost of purchase and install.

High performance tanks change this up a bit in some scenarios, but if you only heat the water as it is demanded logic points to higher efficiency. As far as efficiency vs cost of either to buy and operate, i couldnt tell you from observation, ours was expensive at the time an was more about not wasting fuel rather than cost.
 
Judith Browning
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it has bypass valves at the inlet and outlet. I can turn off the water in and water out, and open two other smaller valves, one each on the inlet and outlet, and flush the mineral scale deposits out of it with vinegar, keeping the heat exchange efficient as the years go by.



Ours has this set up also and we just ran the vinegar through it and took off the cover, etc. to dust and check the burners and thermocouple (?) ....all set to go again but having an issue with it shutting off sometimes after just turning it on.  This is why we cleaned everything and replaced the ignition batteries but it is still happening.  

We've only just turned the setting over to 'winter' and  have always used the lower gas and water settings and it is plenty hot...too hot at the kitchen sink and hot enough in the shower.
 
gardener
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I have used Paloma, propane on demand water heaters since the 1980's.
My first was a small ph-5 model!  I loved it as a single guy. I traded that one in for a ph-12 model in the 1990's.  We still have it and it still works flawlessly.
I would use nothing else.  I believe that when the kids were here it may have used more propane (teenage showers).
Now that it is just the two of us nothing could be finer! All the hot water you want but no extra!   The endless hot shower!  As Judith mentioned, they require pressure however our gravity water hits the house at 125 psi... so we got the pressure thing covered!
Only maintenance I've done, is to clean the inlet screen of debris (gravity water) and remove the outer cover  and blow off the dust.  If you don't do the dust blowing they will give a dust explosion from time to time...  not really that dangerous , but  loud and scary!
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Paloma PH-12
 
pollinator
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In some parts of the world, houses don't have central heating or humidity control systems. New Zealand is a good example because it gets cold and damp in the winter.

I've lived with both systems, and the one big thing I missed with hot water on demand in a cold damp climate is the absence of the hot water closet.

Before the insulation in hot water tanks got really good, they used to place the tank in a cupboard and that is where you kept linens, towels etc. All that linen helped to increase the insulation around the cylinder, and the linens were always warm and dry. In the same environment with hot water on demand, linens often feel slightly damp, and can get mildewy if stored for long periods.
 
pollinator
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I am not sure there is a better, or a worse...it really depends on your application.

I cannot have a tankless hot water heater because of two reasons:

1. We are a family of six, (5) of which are female, and of those, (3) are teenagers. That just means we exceed the recommendations for what the tankless hot water heaters have for hot water used per day. (Anything over 40 gallons of hot water per day they suggest going with a tak hot water heater).

2. The distance from where we would install our tankless hot water heater is too far away from our use points (sinks, etc)

Because of those two extremes, it is just best for us to have a conventional hot water tank. When that goes, (I bought it when I was wed to my first wife, and that was (3) wives ago), so it is due to go soon. (The water heater that s, Katie is sticking around). I will put in a BoilerMate and heat my domestic hot water with my homes propane boiler.
 
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