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Water Heater Help
Ridgefire:
--- Quote from: menace on December 29, 2011, 03:55:55 pm ---I have a "bare bones" tankless unit and love it! it is rated as a single appliance model or about 4.5gpm and raising the water by 80-90 degrees max Mine was $450 from amazon.com and I installed it myself:) so its paid for itself many times by now.
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I have an unfinished basement so space isnt a concern. I must be over looking this heater on Amazon. Could you please help me out a bit on finding it on Amazon. I'm in northern Michigan, so I would assume we have the same type of season change in water temp.
Howard_Casto:
--- Quote from: Vigo on December 29, 2011, 03:04:51 pm ---I love working on electrical too. :cheers:
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Electrical I don't mind... mostly because I don't have to worry about water leaking and people can use the toilet while I work. ;)
I hate running stuff to the breaker box though. Crawling under the house and trying to fish a big heavy line through a pipe iwht about 1 inch of room in it isn't fun.
I'm all about the Pex myself.... that and compression joints. I keep and few of them and a 10 foot length of pex at all times. Now if we get a leak I can swap it out in about 15 min.
Now woodworking and remodeling I don't mind. I actually enjoy doing that sort of thing. If you fix a pipe or outlet you are merely maintaining the house... nobody will know what you did. If you re-do a whole room you actually get some results and you don't feel like Sisyphus pushing his rock up the hill. ;)
MonMotha:
--- Quote from: menace on December 29, 2011, 03:55:55 pm ---Efficiency: a "modern" gas fired water tank is about 50-60% efficient--some people think because there is a blower on it, it must be more efficient. The opposite is true. the blower uses energy to speed and cool the exhaust gases so they can be vented via a sidewall in system636 piping. (formerly ABS). My unit is about 80% efficient but there are much better units out there. In the real world we pay the minimum gas charge ($16) from may till october (southwest ontario here) with regular useage
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Where does that extra heat go if it's so inefficient? I'm not doubting the overall efficiency number, but if the flue gases are cooler than another comparison model with comparable thermal capacity, where's that extra heat going if not up the flue? It has to either be to the water (which would mean it is indeed more efficient) or into the surrounding inside ambient.
The reason for the power vent is generally that they are sufficiently efficient that the flue gases would not be warm enough for natural convection to ensure reasonably complete exhaust, so forced convection is required. This is one reason why all natural gas furnaces greater than ~80% efficient have to have a flue gas inducer fan that runs at all times during the combustion cycle.
menace:
I bought my water heater years ago (5 years now) so I doubt amazon carries them anymore.
As far as the venting goes--its the velocity that makes the difference. In a natural draft vent, you have a larger vent cross section and therefore a much slower exhaust. So in any one section at a given time you would have more waste heat energy. In a power vent unit, its mixing house air and exhaust air and expelling them at a high rate so again if you were to take a slice of vent the amount of just exhaust gas in that slice would be lower and therefore less waste heat. But if you add up the slow big slices and compare them to fast little slices, it works out about the same.
Because a furnace puts out so much more heat (say 75,000 BTU/hr for average home) compared to a water heater (30-35,000 BTU/hr) it needs to be more efficient to use the same venting trick. Mid efficiency furnaces (say 85% efficient) still need metal vent pipes and vent motors to vent the waste heat. Its only in the 92%+ range that plastic can be used.
The gas code (here anyways) changed on power venting piping since it was found that ABS was expanding too much under the heat load and splits would develop. Now they use a system636 piping which has more tolerance for heat. Its also a good cash cow for unscrupulous HVAC guys to say your ABS is "not code" and threaten to shut down your furnace unless you switch over ($500-1,000 usually). Truth is, if the pipe isn't leaking, you are under no obligation to switch.
MonMotha:
--- Quote from: menace on December 30, 2011, 07:25:13 am ---I bought my water heater years ago (5 years now) so I doubt amazon carries them anymore.
As far as the venting goes--its the velocity that makes the difference. In a natural draft vent, you have a larger vent cross section and therefore a much slower exhaust. So in any one section at a given time you would have more waste heat energy. In a power vent unit, its mixing house air and exhaust air and expelling them at a high rate so again if you were to take a slice of vent the amount of just exhaust gas in that slice would be lower and therefore less waste heat. But if you add up the slow big slices and compare them to fast little slices, it works out about the same.
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Going to all the trouble of forced convection just to increase flue gas volume sufficiently to cool it off enough to use plastic piping at the expense of efficiency seems like an awfully complex and expensive (in up front unit cost, let alone operating expenses) proposition just to get around the need of metal ductwork. It's not like it's particularly hard or expensive to install, and most existing construction will already have it anyway.
If people are actually making designs like that, well, they might be a bit "slow". Doubly so for anybody who buys one without understanding what they're doing. I guess I can't say I'm totally surprised, though. The units I've looked at with forced convection venting are indeed a fair bit more efficient than typical models and certainly no worse, but then I'm not normally looking at bottom of the barrel stuff in this market.
In the US, at least, the Energy Star guidelines for "high efficiency" gas fired storage water heaters call for 67% or better transfer to the tank. The specs for gas condensing units call for 80% or better, and many units apparently hit 95% or even a little better. Units that meet these standards (especially of the former type) are readily available but somewhat uncommonly used and by no means cheap.
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