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I am replacing a 34 year old gas fired forced air furnace with a hi-E sealed combustion horizontal vented unit.I want to eliminate my brick chimney and add a much needed 4 square feet to my tiny kitchen. Only problem now is what type of water heater to use with no chimney/vent. Electric? No. Power vented? I’d rather not. I’ve heard that there are direct-vent models that utilize sealed combustion and vent horizontally.
Anybody have any experiance/input on these units? How does purchase price compare with other types? Any advice is appreciated. DS
P.S.I’m looking for 40 gallon unit.
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Someone's got a prototype of the solution - thermocouple piles to generate electricity from the heat of the flame (and dump the unused heat into the water jacket). So the thermocouples see 1400F on one side and 140F on the other. They extract 5% of the energy as electricity and pass the remaining 95% to the water. But each pile makes only about 10 watts and several would be needed to power a fan for a water heater (the intended application). For an added $400 on top the cost of a standard HWH, you'd have the added efficiency of fan-blown air on the air side of the heat exchanger and the ability to vent horizontally or, possibly, over greater distances.
For now, my local home center, Eagle Hardware in Anchorage has a direct-vent water heater (50 gallons, 42,000 BTU/hour, $497.97). It can be vented horizontally or vertical and doean't need an electric fan in either application. I've spec'd it as the heat source for my domestic hot water and radiant slab heat source. And before everyone starts saying it's not enough heat, the 1000 sq.ft. footprint house is superinslulated in part because of favorable loan rates by the state of Alaska. At -50F outside, I need 18,000 BTU/hour for space heating.
When looking at units with electric fans, be leary of efficiency ratings. Is it of gas only or is the electric usage figured in? BTU for BTU? Or figuring the cost differential for units of electrical energy vs gas for where you live?
*I've used a Polaris water heater for high effieiceny/high output needs. The unit I used has a 50 gal tank, but 96+% efficiency with 100k BTU i n. The vent can be ABS--just warm air coming out. With this output you can run two showers and the washer continuously. It also has outputs for a heating loop. (loop in/loop out plus cold in/hot out) Very pricey ($1300 or so) but replaces two conventional units plus no double wall vent pipe.
*Adam: Does the Polaris use an electric fan? And, if so, what wattage is it (probably on the nameplate)? Thanks, David
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Dan, I had a similar situation. I had heating installer put in "direct vent" heater while putting in new hi eff furnace which vented thru plastic pipe out side wall. Well that was six years ago, and I've relit the darn pilot light so many times since. The bottom line is some form of built in safety, such that without power(ac) for positive exhaust, the pilot is shut down. Sounds good except it happens too often. With every surge or blink of the power grid. I have been told that many water heater manuf. pruduce them. I saw some on the web. Try http://www.plb.com for the plumbing communities advice. Good luck and let me know of positive results as I had to relight again today.
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Bill: Here's a trick I've used on a lot of locations that had intermittent utility power (lots of drop-outs and flickers): Put a uninteruptable power supply (UPS) between the wall and the device. They've gotten quite cheap from any of the mail-order computer vendors. And for something small like the fan and electronics of a HWH, you could get protection from many-minute-long power failures with a very small, cheap unit. -David
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Dan;
My house
b was
equiped with electric forced air & electric hot water. Converting to gas (without an existing chimney or flue) was by a condensing gas furnace (ultra high efficiency) & direct vent gas water heater.
State is the water heater brand. Others make direct vent. The biggest hassle is that relocating a water heater is not just a simple "extending the pipes" as plumbers will tell you. The proper method is to place the tankon an outside wall closet to the high usage zone & run the pipe from there. I was fortunate in the water tank was already on the outside wall.
Generally, 48" is the maximum rise & run for the flue from the tank to the outside wall.
My break even saving on natural gas vs electric is around 10 years in dollars & priceless in comfort.
Cheers; JE
*David;You lost me on the (thermo) pile of ... hot flue air.When you use the domestic water heater for space heating, remember to apply a bit of simple control logic:Shut down the heat circulating pump while you are drawing domestic hot water and make sure the pump will not circulate water if the tank temperature is below a fixed minimum.Cheers; JE
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John: Thermocouples are two bits of disimiliar metal, joined together. They generate a few milliwatts of power at a few millivolts and, singularly, are commonly used as temperature probes because their output is a well-documented function of temperature. By putting a bunch in parallel, you can get higher amperage from them. By putting those assemblies in series, you get higher voltages from the resulting "thrmocouple pile". They are used to generate power in special cases. Most common is the thermocouple pile used in gas hot water heaters to generate the electric power to hold open the gas inlet valve. Rather elegant: if the flame goes out, the thermocouples stop putting out power, the valve closes, and gas flow stops. That's why you need to hold down a button while lighting a water heater - to jump-start the process. Thermocouples also were used on the Voyager spacecraft (the one NASA sent to Jupiter, not the Star Trek one - it uses anti-matter). A nuclear pile (less than critical mass) provided the heat and the thermocouples converted that, at low effieciency, but with no moving parts to electricity).
I agree with you about the desired control logic. For my house, I'm planning an unplugged electric hot water heater (serving as a tank) to be the highest priority zone of the heating system. Rather than create a box full of relays to acheive that, I plan to power the circulator pump for the HWH through the lower thermostat (SPST) on the HWH - when the lower water cools, it gets more heat. But the other circulator pumps will be powered through the upper thermostat (SPDT). If the HWH starts to cool, the space heating pumps are not powered until the water comes back up to temperature. Because I agree with you - hot water while I'm in the shower is more important than if the house drifts down 1/2 a degree. -David
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Thank you John and all others that responded. I should have made it clearer that what I was interested in was a natural draft type sealed combustion unit.If I understand correctly they
use a pipe within a pipe to supply and exhaust combustion air through one sidewall penetration and require no power (additional wiring).I found one on the State website: (www.stateind.com/docs/residential/dvspec.html) .
If you dont mind me asking, how does price of one of these compare with a standard gas water heater?
thanks again, DS
*David;I'm very familiar with thermocouple & thermo(couple)piles. Thermopiles besides providing more power are nice due to the thermal inertia. They do not overreact to fluctuations in temperature. I learned to weld the tips to prevent the couples from untwisting. I got so good at welding them, I got the job for making them for the entire department at College.I re-read the post & see you are being tongue-in-cheek on using a large enough pile to power the flue boost fan.You need to examine the (cold) water heater control logic a bit more. I spell it out for others reading the posts.Most new units have a S/DPDT (single or douple pole double throw) upper thermostat control. If the top element is OFF the bottom element is free to cycle to maintain heat or for light usage. If the top element is ON it locks out the bottom element. A way out of this is to re-wire the WH for dual feed. You have to label the hell out of it if you use dual feed. This will also double the recovery wattage. Areas that have dual rate on electricity will commonly use dual feed. The cheap (& interuptable) power feeds the lower element. The high priced stuff feeds the upper element.You still need relays to control the circulating pumps. The thermostats on WHs can barely handle switching the resistance loading of the elements. A 1/3 hp induction motor is not in the rating & you might end up fusing the contact. A couple of ice cubes (relays) in a service box, track mounted & socketed will serve as a nice power center. The WH thermostat controls will run the relay coils nicely.cheers; JE
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John,
What does "This will also double the recovery wattage." mean? I followed both threads fairly well until...Are you talking about the no longer used electric heating elements...btus of heat? help...
Jack : )
*John: I wasn't being tongue-in-cheek about the pile powering a fan. But it was only a report of a prototype and I have reason to wonder if anyone can get an improved water heater to market if it costs any more. Saw a research paper on thermocouples run off the exhaust heat of a diesel truck. Wasn't viable for real world use, you'd still need an alternator for stop-and-go traffic and when using lots of accessories.I understand how people limited to electric hot water can benefit from a dual feed HWH. But I've got the option of paying $0.38/100,000 BTU with natural gas or $2.45/100,000 BTU with electricity. So I'm planning on a direct-vent natural-gas water heater (only one in order to minimize cost and penetrations through the building envelope) and using the electric HWH only as a code-approved, pressure-rated, mass-produced, cheap tank. I know that electrical contacts should be downrated for induction loads, typically 1/3- to 1/5 of their resistive ratings. Using the HWH thermostat (rated for 4500 or 7000 watts) to switch a 1/25 hp circulator pump (30 watts average, 1 amp@115volts full-load) is quite a down-rating.I worked through my logic on the controls again and I'm pretty sure it does what I want: Send heat (from the other, natural-gas fired unit) to the unplugged electric HWH when the lower water is cool and send heat exclusively to the electric HWH when the upper water is cool.
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AJ;
With a dual electrical feed, the upper & lower elements can operate simultaneous in periods of high demand.
Many residential water heaters use a staged control logic. The lower element will operate first and heat the fresh water usually introduced to the bottom of the tank via the dip tube. This is a low usage (demand) situation. If the demand continues, the cool water level in the tank rises to the upper element thermostat. When the upper control calls for heat, the normal closed contact in the thermostat opens. That NC contact supplies juice to the lower element opens. The lower element does not operate again until the upper element recovers.
My dual feed is at my sister's beauty shop. Natural gas is not available and LPG costs rival (normal) electricity rates. The local electric utility offers dual rate electric if you have a back-up source. The cheap electricity is approximately 1/2 cost of the normal rate and provided on the condition of interuptable in high demand sitations of the grid. Don't know if a (affordable) dual energy source water heater exists (boiler, yes) so we went with dual feed electric.
The lower element is on the reduced (dual) rate and the upper is on the regular rate. The lower element is set a bit lower than the upper element, too. This usually assures it run on the cheap electricity.
The FA furnace is dual source, but LPG is the back-up. I think she uses 50-100 gal. of LPG per year. This is through NW Minnesota winters.
I thought David was planning to use the heating elements in conjunction with the circulating pump for the floor grid.
Better explanation?
JE
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John,
Thanks for explaining your post. I think i've got it! Very techy to mess with electric water heater and I assume it voids warranties and moves liability to the modifier but I may have to use your trick some day, I like it.
By by the way the reason I needed help with all besides the fact that I prefer graphics over written hand waving, is that David's ideas of changes had nothing to do with your two element suggestion. He's not using electric, just getting a "cheap tank" pre-fitted with two controls for running his heating home and potable water system.
David,
Good system, too.
Jack : )
*David;Sorry for the delay...I've been traveling outside the US and can't justify hooking up...Yep, fan comes on when the heater kicks in. Not sure what is draws, but plate sez less than 7 amps at 110V. (Does the fan offset the benefit of the efficiency? Never thought to calculate.)BTW, it is rated at 110Gal per Hour at 100deg F temp rise and 124.5GPH at 90degree rise.
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I am replacing a 34 year old gas fired forced air furnace with a hi-E sealed combustion horizontal vented unit.I want to eliminate my brick chimney and add a much needed 4 square feet to my tiny kitchen. Only problem now is what type of water heater to use with no chimney/vent. Electric? No. Power vented? I'd rather not. I've heard that there are direct-vent models that utilize sealed combustion and vent horizontally.
Anybody have any experiance/input on these units? How does purchase price compare with other types? Any advice is appreciated. DS
P.S.I'm looking for 40 gallon unit.