View Full Version : Hot water heater

Harry Goodwin
08-13-2005, 9:40 PM
Well, you will agree this is off the topic.
I have a hot water heater in the attic.
It's old and we are planning replacing it elsewhere.
Are the hot water heaters that do not have a tank any good.
Will it provide enough water for shower and dish washer.
Will it destroy my water bill any worse than the tank type.
I will need to build an outside bldg if I go the old tank type.
Thank you all for your help Harry

John Hart
08-13-2005, 9:47 PM
Harry, here's a site... http://www.rinnai.us/index.asp This system mounts out of the way, uses no tank and will supply hot water for the whole house. Supposedly, it is cheaper than running a tank....although, I have no personal experience with it.

Michael Perata
08-13-2005, 11:31 PM
I have a hot water heater in the attic.

Harry - if you already have hot water in your attic, why do you need to heat it.

(Sorry, couldn't resist :rolleyes: )

Randy Meijer
08-14-2005, 4:41 AM
I have no first hand experience; but have done a bit of reading and everything I see about tankless water heaters is fairly positive. You will be looking at a bigger investment up front; but lower monthly utility bills because you won't be maintaining a tankful of hot water for 24 hours a day. Payback time depends upon a lot of variables including local gas or electricity rates. I bet you could get some good figures from your local gas or electricity company!!

Note: I did read about one guy who couldn't install a gas unit because the location he needed to use could not be properly vented. These things provide essentially an unlimited amount of hot water....you can't run them out of hot water.

Frank Hagan
08-14-2005, 11:33 AM
The tankless style hot water heaters are rated in a certain "gallons per minute" of hot water. That's an important measurement; with modern flow restrictors in your shower and at your sinks, you should do fine with a 5 gpm model. 3 gpm won't be enough without flow restrictors, but will work if you are using the flow restrictors and don't have other large usage. 3 gpm will not fill a large tub well enough. Even 5 gpm might not be enough if you have a large tub you want to fill with hot water. Sometimes this GPM rating is expressed in "first hour" or "recovery" terms; there's a pretty good explanation of it at http://www.consumerenergycenter.org/homeandwork/homes/inside/appliances/waterheaters.html

Also, remember that the energy effeciency numbers are a lot like those MPG ratings on the cars ... they are taken in controlled lab environments. You can easily goose them up by playing with the combustion (amount of air and fuel), or varying the inlet temperature of the water. (I work for a manufacturer of commercial and residential water heaters, and the temptation to cheat is great when competitors do it. We manufacture or distribute both tank-type and tankless water heaters).

The other factor we have run into are the smaller diameters of the tubing. You should ensure you have less than 10 grains per gallon hardness in your water, or you may find a very expensive repair to remove lime deposits in the exchanger. My company sells a combo boiler / water heater, and the flat plate water heater does great, except in hard water (the other components on the thing have been troublesome; computerized controls have a very high failure rate on appliances, and while my company has been covering the costs for consumers well past the one year warranty, most companies do not).

Finally, you have to consider the cost of these things. I don't think we're at a point where they make sense (yet). They advertise "up to 96%" effeciency on some of them. Older tank-type water heaters have effeciencies as low as 78%, but newer ones are in the 82 - 84% range. The energy savings between 82% and 96% is 14%. If you only heat water with your gas, its easy to calculate, but most people use home heating, cooking, etc. The labels on the tank-type water heaters will show a yearly cost of $150 to $200.

14% of $200 is $28. How many years will it take to pay back the higher cost of the more effecient unit? With a tank-type water heater costing $300, and a tankless hot water heater costing $2,000, you have a 60 year pay back period. If you get lucky, and energy prices double, then you only have 30 years to recover your initial higher cost.

The tankless may last longer, but they do have higher frequency of repair. I see "25 years!" touted, and I think its an exaggeration. There are more components to fail in the unit. If it uses a "hot surface ignitor", plan on replacing it every two or three years at about $150 (if you do the service yourself, it will be around $80 for the part). In six years, you could have bought another tank-type water heater. (The hot surface ignitor will fail faster if it shares your shop space, and the unit takes combustion air from the shop ... so duct in combustion air if that's the case). Even the direct spark models are experiencing some "burn through" where the spark contacts the burner.

The higher effeciency units often use direct venting with a combustion fan; for the most part, these components last a long time, but 2 - 3% will fail within 5 years. Cost to replace a combustion fan will be a few hundred dollars.

The tankless water heaters solve some problems ... space, venting, etc. But they do it at a cost.

[edited to fix a typo regarding hard water]

Lee DeRaud
08-14-2005, 11:45 AM
Note: I did read about one guy who couldn't install a gas unit because the location he needed to use could not be properly vented.I inquired into this when I needed to replace my gas tank-style heater recently. To meet current code here for the tankless unit, I would have had to tear out the existing vent all the way up to the roof (two stories) and replace with larger-diameter double-wall stainless vent pipe. Just the cosmetic repair for the walls affected would have cost more than replacing the failed unit.

As I said to the guy at the time, "not gonna happen".:eek:

Harry Goodwin
08-14-2005, 2:49 PM
Thanks for all your wisdom. It provides a way out at least. I can either put it upstairs again with a regular electric or the tankless but at least no outside bldg. Thanks again. Harry

Frank Hagan
08-14-2005, 9:23 PM
Well, your electric heater is probably the most effecient you can buy anyway ... resistance elements transfer nearly 100% of the heat to the water without all the fuss about venting, etc. But the electricity is more expensive than gas, so you can still save money by "wasting" 15% of the gas to carry the flue products up the vent with a conventional tank-type water heater.

Any gas fired unit over 85% effeciency will probably need the stainless venting, but you can often side-wall vent them. The stainless vent kits run about $400 for an "up and out" installation, and about $700 for a kit that goes through a two story roof. So the venting alone is more than a tank-type water heater.

Jeff Sudmeier
08-14-2005, 9:26 PM
I have a regular tank style unit, but it is power vented using PVC. I think only the non-powered vents need stainless Venting.

John Hart
08-14-2005, 9:36 PM
I have a regular tank style unit, but it is power vented using PVC. I think only the non-powered vents need stainless Venting.

I don't understand what you're talking about here Jeff. What is "power vented using PVC"? Please pardon my ignorance sir.:o

Frank Hagan
08-15-2005, 12:56 AM
I have a regular tank style unit, but it is power vented using PVC. I think only the non-powered vents need stainless Venting.

Well, I forgot about the plastic venting ... and you're right, it is allowed on some appliances. It has to do with the vent temperature, and the more effecient units do lower the vent temp because they are taking more of the heat out of the combustion process and putting it into the water. Then you need a fan to help get the vent gasses out.

There are four categories of venting, having to do with the configuration of the vent and whether it is a positive pressure vent, negative pressure vent, and whether flue gasses can cause condensation in the vent. If it can condense in the vent, you have to have non-corrosive vent. The appliance will have instructions that state what kind of venting you can use (none of my company's products allow plastic venting, except in one case, and in the size for that boiler the CPVC is more expensive than the stainless kits).

PVC and polypropylene are used as venting materials for some condensing appliances that have low temperature vents. The older, HTPV pipe was recalled (if you have an appliance with gray or black plastic vent pipe from the early to mid-90s, email or PM me as it might be the recalled vent pipe; the CPSC and manufacturers have set aside funds for replacement).