Tankless Water Heaters

[mwlogs]

Hi Group,

I did some Googling, and read a bunch on the issue of tankless water heaters but didn't get a good feeling for whether one would be the right choice for my brother and sister-in-law. Here's their situation:

Live in Ohio (USA) All electric home, probably 10-15 yrs old. Three sons ages 2yrs to 8 yrs

2.5 bath home, normal laundry, DW, etc.

I'm feeling that the initial cost of a 'whole house' unit large enough to support them, coupled with the fact their actual hot water use is probably going to be high enough that the heat loss of water just sitting in the tank will offset the savings offered by 'on demand'. It seems the real savings of on-demand is in the low usage level. Am I wrong here?

Additionally, with the fact that in mid winter the incoming water temp here in Ohio would be around 50 degrees and they may not get the desired hot water when they want it most.

Finally, the overall electric requirement seems it could be an issue as well. The larger whole-house models seem to require 150 amps. I couldn't find a rating for a standard electric tank (all gas in my house, so nothing to look at to compare), but I didn't think a tank was more than 50-60 amp.

Any advice appreciated!

Mark

[buffalobill]

in general: for family with kids, electric tanks are slow recovery so you get the biggest one you can afford that fits into the space and the electrical service available. think about how much energy it takes to bring 32 degree lake erie tap water in buffalo ny to 150 degrees for plenty of hot water in our gas fired 75 gallon tank for 4 adults, a dog, and dishwasher and laundry. we overcame the running out of hot water with a high recovery 40 gallon when we changed to a 75 gallon. your ohio relatives have buffalo ny latitude's cold water. also: "On demand hot water system? from Noah Lamy The relative energy efficiency of these systems depends a lot on other factors such as the amount of heat loss from a more traditional storage tank system or the length of time hot water is stored before it is used. In practice they require a good deal more energy per volume of heated water than conventional systems and they cannot usually provide enough hot water for more than one fixture at a time. The traditional storage tank type of water heater can be quite efficient if the tank and the hot water pipes are properly insulated. The on-demand type heaters have their uses in the appropriate situation. I have found them practical and efficient in situations where hot water is used only occasionally such as in some shop situations or where a fixture is at a considerable distance from a traditional storage tank water heater, such as in a guest house or pool house. They can also be handy if you are adding hot water to a structure that has been cold-water-only and the cost or inconvenience of adding a complete hot water piping system will be prohibitive." it says at:

[buffalobill]

comments from:

tankless models:

[Donna]

I can't tell you whether a tankless heater is right for your brother and sister in law. I can tell you that in our situation (central new england, two kids, older home) it was NOT feasible for us. When we bought our house, we were initially excited about the fact that there was a tankless system, but after a year of lukewarm showers and not being able to wash in hot enough water, we just had a tank put in. That works *much* better for us.

HTH

Donna

[Joseph Meehan]

Well, IF you get sufficient capacity to handle the load, you will have lower electric bills. However you are likely going to need more than one unit or you are going to need to manage the usage so you are not letting anyone shower during laundry or you will not be able to wash dishes while someone is showering etc.

Considering your household and the likely use of hot water in the coming years, I would go for conventional tank type heater. You will save on the installation and on the likely need for a new higher capacity electrical supply.

[m Ransley]

Do you know that even with Ng being much higher today your electric cost is still apx 50% more than NG. They should convert to Ng heating and apliances.

A whole house or more than 2 use Electric tankless will need 200 A. Do they even have a 200A service or 200 Amps free, I dought it. Install and upgrade would be thousands. A 160 Amp Bosch is rated 1-2 use, it is rated near their 117000 Btu Ng unit. For a family you need a Bosch- Rinnai-Takagi, Ng 190000 Btu unit, or maybe a 200 amp electric unit. That means new service, and very heavy wiring, very very expensive.

A Tankless saves less the more people use it, especialy with Electric tanks having less standby loss, a higher Energy Factor.

Add to that the kids Knowing unlimited HW is avalaible with Tankless their bills may actualy go up.

I have A Ng tankless, it saves me 25$ a month, single use. But with a family and Electric, I would pass, but I would go Ng on everything else. Even a Ng tank would be an improvement. Research at "Energy Star" to learn.

[trader4]

Anybody figure out how an on demand unit could require a good deal more energy per volume of heated water? I could see how that might be possible if one were comparing only gas units. It's possible the gas tank type heater would be more efficient, recovering more of the combustion heat. But I tend to doubt it could be a good deal more. As for electric units, they are going to use exactly the same amount of energy to raise water termp.

and they cannot usually provide enough hot water

[m Ransley]

People fail to Size the units, if Sized right they can heat any amount of water needed. Sizing is flow, incomming temp lows, heat loss to the shower head, Voltage drop or variations, of Ng pressure drop, competing units and proper pipe sizing. They work, but few figure out what the manuals specify and blame it on the units. Tankless anything takes alot of research and testing to be sure you will be happy.

[Paul M. Eldridge]

There is one other thing to consider: time of use rates (TOU). In Ontario, *all* residential customers are being converted to TOU.

Under the new rate structure, it will be considerably cheaper to heat water during off-peak times and store it for use during the shoulder and peak periods. In this case, a large, well-insulated tank controlled by a timer or similar control device would be a far better choice.

In future, I wouldn't be surprised if more jurisdictions move to mandatory TOU pricing, because it makes good sense for utilities to flatten their load curves.

Cheers, Paul

[Douglas.Andrew.Baker]

Given that they are all electric, it would probably be cost prohibitive as they would need multiple units to achieve a reasonable flow at the temperature (city water temp vs. outlet temp) rise thye are likely to experience. If they get a Nat Gas or Propane line then a single unit might make sense (if they went with one of the largest available).

Nevertheless, to appropriately assess the situation you need some more facts: Specifically you need to know what they believe their maximum simultaneous hot water usage might be. For example, if they are expecting to be able to take 2 showers, run the DW, and wash clothes simulataneously then you get a very different answer than if they are willing to live with never using more than 1 source of hot water at a time. Figure on 2.5 GPM per outlet while in use and you'll quickly come to a total GPM that the tankless unit needs to produce.

approx. 70-80 degree temp rise (depending on water inlet temp and how hot they like their water) and see whether the unit can provide the necessary volume of hot water.

Doug

[Robert Gammon]

So with high 60s to mid 70s inlet water temp and a rise of 45F, the large units (185K to 190K BTU input) will easily supply 3 simultaneous use, and hot water recovery via GFX and/or geothermal heat pump could make this even higher!!! Course, geothermal heat pump only assists in this process UNLESS you get their option to produce all hot water (i.e run heat pump JUST to generate DHW thru a heat exchanger inside a dedicated DHW tank)

[hallerb]

standby tank heat lost isnt wasted enegy in tthe winter since it helps heat your home.

only in the summer is it wasted and since the entire building is warmer the loss is less.

a 120 degree heater sitting in a 40 degree home looses lots more standby heat than the same 120 degree heater sitting in a 80 degree basement

there are super high gas condensing hot water tanks that elminate the standing pilot and are fan vented like 90+ furnaces these 98% efficent hot water tanks are a good solution. Pelonis is one brand

at very low flows a tankless may not trip on leaving you with cold water for say a sink.

[mwlogs]

80 degree basement??????? Holy S^&% Batman - where the heck do you live that your basement gets to 80? Even around here in central Ohio I don't think even a partially exposed basement would get that hot on the hottest day of summer!

All that said about heat loss from the storage tank I have to wonder. My tank is in the basement where it is a pretty constant 60-70 degrees most the time (I keep the heat off in winter and A/C on part way in summer to help with moisture). I do spend a good bit of time down there and recently have been listening for the tank to cycle thru when no water has been used. It seems that it normally goes several hours before having to recover.

Based on this, I think the bigger loss I'd like to avoid is that which occurs between the tank and the faucet. Not that I think there is any way to prevent the loss between water uses - even insulated pipes will only hold the heat for a short time - but if I'm losing 5-10 degrees while the water runs from the tank and the faucet during each use and I can eliminate that, I can set the tank that much cooler and save on both - the overall cost of the hot I use, and the cost of keeping the tank hot bwtween uses.

Comments?

Mark