electrical needs for tankless water heater
16 years ago
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- 16 years ago
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Electric Tankless Water Heater advise needed.
Comments (4)The problem is that tankless heaters can heat water for an indefinite period of time (you never run out) but they can only heat so much water at one time (gallons per minute). Think about how long it takes to heat a gallon of water in a pot on the stove. It takes a huge amount of energy to heat, say five gallons, in a minute. A standard shower is about 2.5 - 3 gpm. An electric heater would draw about 120 amps to heat water 70 degrees (from 35 to 105) at that flow rate. You are looking at twice that amount for two of the children's showers at the same time -- and that's about it. The rest of the 400 amp capacity of your electric service would have to go to everything else in your house. In fact, depending on your electrical demands, it might not leave enough. Gas tankless (or condensing tank unit) can do a better job of delivering the required amount of heat at one time -- but I'm assuming that gas isn't available. Your multi-head showers are probably that rate for each shower head. It's really easy to get to 10 gpm or more. At that rate, you can empty a 70 gal water heater very quickly. I can't really help you out much more, you have pretty serious hot water demand and you need someone who can go design your system for you-- including the implications for electrical service and hot water storage. As an aside, I think people get enamored with the multi-head showers without a full understanding of what that requires in terms of plumbing and utilities to run. You might also consider a waste water heat recovery system. They reduce the system demands by pre-heating the incoming cold water using the warm water that is going down the drain. These don't normally have a payback except in situations such as yours....See MoreTankless Electric Water Heater Below an Electrical Panel
Comments (1)It's prohibited for one. And for two, to actually run an electric tankless will require most of the power that you currently have in your panel. 125-200 amps are needed. If you live in a cold climate, electrical is not really doable at all because of the incoming winter water temperature. Gas tankless is much easier to retrofit, and even it may require new gas service for the home....See MoreTankless Electric Water Heater Below an Electrical Panel
Comments (9)Have to disagree with GreenDesigns who states, "they offer almost zero improvement in efficiency of a new high quality tanked electric heater. ...electrical tankless is only truly practical if designed for a new build from the beginning. Retrofitting is extremely expensive and won't give you a payback for the cost differences inside of your lifetime." I put a whole-house electric tankless in my 1906 house and will never store water in a tank again. Absolutely love it! It's mounted on the wall, directly to the side and just above the dryer. I did not bother to hide the water lines inside the wall, but since they're [mostly] hidden by the dryer, who cares? Sometimes, putting plumbing pipes in the wall is highly overrated. Mine is in the bath/laundry room and I've never found it to be unsightly. Yes, the tankless requires quite a bit of power: Mine requires two, double-pole 60amp breakers with 6g wire. So, here's where distance from the electric panel is a cost consideration....See MoreElectric tank or tankless water heater v. Propane tank or tankless
Comments (8)If you're really sure you want tankless (and you kinda seem to be), I'm not going to argue with you. I'll just say a couple of things and then I'll bow out. Disclaimer: I'm not an expert on these matters. They just interest me and I hope to be more energy independent in the future, so I read up on them. I always welcome corrections from knowledgeable folk. First point: IMO electric resistive heating of ANY kind basically just doesn't play nice with PV, off grid or on. The only time it really makes sense is when you're off grid and your system produces more energy during the day than you can store in your battery. This can also apply to some extent if you're intertied and your utility pays you wholesale or less when you sell your power, essentially penalizing you for conserving. Either way, dumping your excess PV energy into water heaters is one way to store it for later use. However, it should be obvious that to store that energy, you have to use traditional storage water heaters, not tankless. Second point: Peak demand matters. It matters to your electric utility, and it matters to your bill. You probably know more about CA rates than I do, but it appears to me that right now California is more into time of use (TOU) metering than peak demand metering. However, more and more utilities are adopting peak demand metering for residential customers (they've had it for business for ages). So even if you're not dealing with it now, it may well be in your future. Demand based metering watches your power (not just energy) usage. The higher it is, the more you pay for all your electricity. In one demand scheme, you pay a surcharge based on your peak power usage (in kilowatts), In another, the price they charge you for every kilowatt hour you use depends on your peak usage -- the higher your peak, even if it's only once in the month, the more you pay per kWh that month. Let me give you an example of the second scheme. Let's say your house's big energy hog right now is an electric range.. Most of the time, you just use one or two surface units at a time. So your peak demand is relatively low, and you pay (say) 14 cents per kWh most months. But when you cook Thanksgiving dinner, you have all the surface units going, plus the oven, and a microwave. On that one day, you have a much higher peak demand. Your utility takes note. And that month, you pay 20 cents per kWh for EVERY kWh you use all month. So even though that month's usage is only a little higher than usual, the final bill for the month is MUCH higher. Now imagine what could happen to your bill if you add an appliance that increases your peak demand every day of every month. Guess what: when it comes to peak demand, tankless electric water heaters are MONSTERS. Think about it. With its mild climate, California is a great place for heat pump storage water heaters. That's what I'd get if I were you. Not tankless, and definitely not electric tankless. And that's all I have to say about that....See MoreRelated Professionals
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