Swaping out indirect for electric tankless WH

[KeithO]

I think the primary benefit of the tankless heater of any kind is that you don't pay to keep the water hot for 95% of the time when you don't need it. The same way that having a programmable thermostat saves on heating bills, so will having a tankless water heater. If the holding tanks of most water heaters was simply better insulated, it would help in this regards, but anytime a temperature differential exists heat is going to flow.

I personally think that electric water heaters suck, every variety of them. The heating elements have a relatively small surface area and are very succeptible to degradation by disolved minerals in the water. Furthermore, having any electrical device that potentially is going to draw as much current as a welder and that is going to kick on and off every time it is used is not going to be good for the life of other electronic devices in the home. I'll bet the lights dim when one of those beasties kicks in. Lets also not forget that in emergency situations your "dead in the water" again with no heat, or running a "big" generator 24/7.

Another thing worthy of consideration is that when you use a storage type water heater (particularly if it has limited storage), once you start drawing hot water, it causes cold water to flow into the heater immediately. This is one of the factors that limits "available hot water" to far less than the volume of the storage tank itself. If you use 50% of the volume you now have only luke warm water (like filling a bathtub).

 

[cbrodsky]

I think the primary benefit of the tankless heater of any kind is that you don't pay to keep the water hot for 95% of the time when you don't need it. The same way that having a programmable thermostat saves on heating bills, so will having a tankless water heater. If the holding tanks of most water heaters was simply better insulated, it would help in this regards, but anytime a temperature differential exists heat is going to flow.

I personally think that electric water heaters suck, every variety of them. The heating elements have a relatively small surface area and are very succeptible to degradation by disolved minerals in the water. Furthermore, having any electrical device that potentially is going to draw as much current as a welder and that is going to kick on and off every time it is used is not going to be good for the life of other electronic devices in the home. I'll bet the lights dim when one of those beasties kicks in. Lets also not forget that in emergency situations your "dead in the water" again with no heat, or running a "big" generator 24/7.

Another thing worthy of consideration is that when you use a storage type water heater (particularly if it has limited storage), once you start drawing hot water, it causes cold water to flow into the heater immediately. This is one of the factors that limits "available hot water" to far less than the volume of the storage tank itself. If you use 50% of the volume you now have only luke warm water (like filling a bathtub).

I think a lot of these are hand-waving arguments from companies looking to see tankless heaters.

It all comes down to how well you insulate the tank, and it's much much easier to insulate an electric tank as compared to a house, thus the thermostat argument is a bit different. A $200 special at HD will probably be junk, but a tank with $20 of extra insulation will be a great solution. Solar storage tanks are a good example of just how well a hot water heater can hold heat for long periods right out of the box. And of course when that overnight electric cost is 1/2 what the day cost is, you're so far ahead of the game that you can't lose - you may only run 90% overall efficiency vs. 95% in tankless, but that doesn't matter when you're using half-price surplus power readily available on the grid. Granted, not everyone has time of day metering, but this is the future. Peak demand power will only become more and more costly so all those "instant" electric heaters will become expensive boat anchors. The gas powered heaters aren't such a bad idea since they're immune to these cases, but I think the electric examples are a disaster for the grid and a very poor choice for people who are interested in green solutions. There is nothing green about throwing up new peak demand plants (unless they're on your roof) and new power transmission lines to support tankless heater surges.

As for lights dimming, that means you've got a wiring or home supply voltage problem... and having three tankless units all kick on when three people showering sure isn't going to be a pretty sight if you can't supply the hot water tank, much less baking a roast in the oven

Finally, water tanks have phenomenal stratification capability - I can draw far more than 50% of my tank at "hot" temperatures. In fact, having it connected to a solar hot water generation system pushes this to an extreme - it is easy to maintain 40 degree differences between the top and bottom of the tank for hours even with active heating circulation drawing off the bottom and returning to the top.

Had I not gone w/solar HW, I would have transitioned to a highly insulated 120 gal electric tank running off an overnight heating timer - this would have still put me quite a bit ahead of an oil-fired tankless coil.

-Colin

ps - from American Council for an Energy Efficient Economy:

Demand water heaters with enough capacity to meet household needs are gas- or propane-fired; electric tankless water heaters are seldom a good idea.

 

[velvetfoot]

Not that it matters that much, but in winter, heat loss to the house might not be a totally bad thing.

 

[KeithO]

I have about 50ft of plumbing between my hot water heater and the master bathroom. Before I put a circulation pump on it, it would easily take 5 minutes of running the hot water in the bathroom to get to an acceptable temperature, which requies both getting the cold water out the pipes and heating all of the plumbing. Since I have the circulation pump on (thermostatically activated), it has increased my hot water bill significantly, and of course it is useful heat in winter, but the no free lunch rule still applies. In summer I use a timer to turn the circulation pump on and off to have hot water for showering in the mornings.

The decider for me will be whether or not I put radiant heating in the basement. If I do that it would pay me to get a modulating tankless heater that runs full time at the appropriate level and a second for the remote bathrooms. It will take up less space and be quieter than the current water heater and adapt to the demand for heating better (slow steady output fits the heating load better).

 

[cbrodsky]

I have about 50ft of plumbing between my hot water heater and the master bathroom. Before I put a circulation pump on it, it would easily take 5 minutes of running the hot water in the bathroom to get to an acceptable temperature, which requies both getting the cold water out the pipes and heating all of the plumbing. Since I have the circulation pump on (thermostatically activated), it has increased my hot water bill significantly, and of course it is useful heat in winter, but the no free lunch rule still applies. In summer I use a timer to turn the circulation pump on and off to have hot water for showering in the mornings.

The decider for me will be whether or not I put radiant heating in the basement. If I do that it would pay me to get a modulating tankless heater that runs full time at the appropriate level and a second for the remote bathrooms. It will take up less space and be quieter than the current water heater and adapt to the demand for heating better (slow steady output fits the heating load better).

We have a similar issue going to the solar HW tank. Interestingly, there was another thread on that subject recently where people were claiming those thermostatic recirculators save money...

Depending on the system, perhaps you can interface a wireless switch. We installed a TACO on-demand unit that has been going for about $40 on e-bay all summer. I don't see any at the moment, but they have been coming up regularly. They also make a wireless switch kit so you don't have to drop a wire. It looks like a doorbell - just push when you wake up or get ready to run some dishes and it brings the water up in a fraction of the time, only when needed.

-Colin

 

[eba1225]

I had looked at this too but once I saw the electric demand decided that it was not the way to go, although I do have 200A service. It chews up alot of electric. The gas models on the other hand look to be much more economical. I get my hot water from a coil that is run in my furnace, and yes it goes on from time to time just to maintain.

I am considering placing my furnace on a timer during the summer months so that it does not run when not needed.

Erik

 

[Nofossil]

People I know with propane / NG tankless heaters love them. Never running out of hot water combined with lower monthly cost is pretty attractive. Some folks justify it on the basis that they can afford it now, and if things get bad in the future, their monthly fixed costs will be lower.

My brother and I put together what may be the most complex and hair-brained tankless scheme yet. He has a 30 gallon conventional HW tank that can be heated by solar or by the wood boiler. Of course, it may also be ice cold.

There is a pushbutton/light panel next to the kitchen sink, shower, and dishwasher. We have a controller that looks at the top of the 30 gallon tank. If it's hot enough for satisfactory use, the corresponding light is lit, telling the user that there is hot enough hot water. The dishwasher needs hotter water than a shower, and the system knows this. If you want to take a shower or do dishes or whatever and the light is not lit, you press the button.

This causes a circulator pump to come on and circulate water through the tankless heater. This does three things: causes the tankless heater to come on, flushes out all the cold water between the tank and the tankless heater, and starts to heat the hot water tank. If you pressed the sink button because you wanted to wash your hands, the pump is only on for 15 seconds, and you get your hot water just a tad sooner than you would have. If you wanted to take a shower, the pump stays on until the tank is hot enough, then turns on the light.

There's also a bypass valve which when open bypasses the tankless heater so that the house is supplied directly from the hot water tank. This valve is open if the tank is hot enough for the current use.

This gives the best of both worlds - hot water comes from wood or solar if available. If not, the tankless heats just enough water to just the necessary temperature, starting with whatever is in the hot water heater rather than ice cold well water.

I'm afraid I haven't made a page for this project on my web site yet, but I'll post a link when I get a chance to do it.

 

[Vtgent49]

I was told by Houseneeds.com to not use a tankless if your water is preheated by a coil in the boiler or something else. Something about their modulation method. You may be able to plumb around this problem by using a mixer valve.

Also, LP delivered to VT is now 3.87/gallon and could br 5.00 in a year or two. So, all those cost of use comparisons you see need to be adjusted before they make any sense.

 

[mikeyny]

You all can do whatever floats your boat, but the best way to do it is the free way. That big old yellow sun up there is kind of like a big piggy bank to me. All summer long The sun heats my water for me. I don't have to do a darn thing. Build a couple home made solar panels and plumb them into any tank you have and start banking the money. My gas usage went from 80 to 100 therms down to 15 to 25 therms a month. The system paid for itself in a matter of months. Every time the gas co raises the rates I save more money. So stop dilly dallying around trying to shop for the best deal or most efficient thing to buy and build yourself a solar collector. And oh I forget to mention there are 9 of us living here taking showers and doing laundry every single day of the year. So there ya have it My rude and crude advice to all of you is just "shut up and do it". It really works. (thats my favorite quote, not really meant to piss anyone off)
Mike

 

[hvcompton]

Be sure to check out the titan. Made in use. I have a titan n120 I just got a few days ago. I will be installing it soon. 170 bucks. Its for the entire house not just smal apartment model. Bigger ones are for cold climates.

220 60 amps.

 

[pdboilermaker]

I have a Noritz tankless lpg, love it. It fills my wifes whirlpool tub just fine. According to the doe website, if you use 60 gallons of hot water per day at $1.25 per gallon, you will save $34.00 per month. Dont forget about the $300.00 tax rebate when figuring your savings.

Your tax rebate check could cover the costs. Check out irawood.com for many brands, electric, gas, and lpg.

 

[pdboilermaker]

https://www.hearth.com/econtent/index.php/forums/viewthread/13183/P15/ oh yes, check out this thread and there are a couple more in the DIY forum section

 

[galindog]

Hi. I am new here and was wondering if you guys can help me with this issue. I have a 2000 sq ft house in CT w/ baseboard hot water heat. I bought a wood stove which heats about 80% of the house nicely. It has brought down oil usage from about 1200 to 600 gallons of oil. The boiler is 3 years old with an 83% efficiency rating . It has a tankless coil for domestic hot water use and it seems to me that firing off the furnace from April to September just to heat the water is a waste. In my conversation w plumbers, 1 of them suggested installing a 50 gallon electric water heater or propane water heater and connect the pipe leaving the boiler into the cold water intake of this heater. He explained that the water would come into the house ,get heated by the tankless coils in the boiler , go into the electric water heater at a warmer temp and out to the faucets. By doing it this way, the water would have a much faster recovery rate since the electric water heater would heat up the water faster since the it is coming into the tank already "pre=warmed" . The oil savings would come in the warmer months when I could turn the furnace temp from 160 to about 100. I realize that my elec bill would go up but with elec at 18 cents per kwh and heating oil around $4.5, we've reached the tipping point a while back . Thanks .

I find the idea from castiron of turning off/on the electric water heater using a timer very intruiging since most of the water is needed for 1 hour in the AM and 4 hours in the PM.

 

[Vtgent49]

Galindog,

I agree that a 50 gal elec addition is good. The preheated water should just about eliminate the electric usage in the winter.

However, I'd consider getting a solar/electric tank (like a Vaughn) and adding a single solar panel and pump. That will greatly reduce your summer fuel/elec costs, and might help in the winter. A tempering valve will help also. Your goal should be to turn that boiler off for 7+ months, not just to turn it down.

You can get various state and Fed tax credits (if you add the solar) and those credits will apply to the whole job. Thus the additional costs for the solar will net out very low.

Al

 

[galindog]

Thanks for your reply Al. My only concern about the solar setup is that I've read in various places that turning off the boiler totally would not be a good idea during the summer months because the boiler seals shrink, parts gets rusty, etc. In addition, would the solar be for merely pre heating the water for the elec hot water heater. I live in Ct with a lot of trees. The sun hits my roof only from 9:30 to 3:30. would that be sufficient? Thanks again

 

[Vtgent49]

I mean that the boiler should be off, not drained, but letting the water cool to room temp, vs. keeping it standing at 160 F. So, the seals etc will still be wet. Frankly, that type of system should be outlawed. It's design criterea was "least dollars possible" for the builder, not the homeowner.

9:30-3:30 will get you 80+% of the useful sunlight. Worst case is that you have to add another 800 dollar panel to double the solar input (I have 3). If you are maximising for Summer, a lower angle is fine. Mine is on a 4:12 ratio roof, thus way flatter than the 43 degrees reccommended for year round optimization. My electric backup is set to go on at 105 F, and the breaker is off. Hopefully, the solar will suffice til it's time to fire the wood boiler, which might be late Sept. in VT. A 4-5 hour wood fire heats the 80 gal DHW to 140+, enough for 2-3 days. 4-5 hours of sun is almost as good.

For cost analyzing, I'd assume oil will be 10 bucks, sometime during the useful life of the solar add-on. That makes it easier to figure a reasonable payback, which could be 1 year with tax credits, and if you do some work yourself. (Diesel is 11/gal in London right now.)

Again, my suggestion was to do both a tank and solar at the same time, so the credits pay part of the tank as well.