Tankless Task: Can I hook up a 160 amp water heater?
January 27, 2019 11:13 AM Subscribe
YANME: Whoever installed my breaker box 18+ years ago failed to fill in the little box that says AMPS. How do I tell if my loft (which used to be an office) can handle the amperage to install a 160 amp tankless water heater? FWIW all the breakers add up to 555 amps (pic).
I've never heard of a residential box being more than 200 amps, but I just an interested homeowner, not an electrician. There should be a master breaker *somewhere* that keeps the circuits fed by this box from drawing more than its leads are rated for. There isn't another breaker that's outside the frame of the photo? Usually it's centered in the box above or to one side of all the others, and it should have a rating that is whatever the rating of the box is.
posted by Gilgamesh's Chauffeur at 11:56 AM on January 27, 2019
posted by Gilgamesh's Chauffeur at 11:56 AM on January 27, 2019
Best answer: Service ampacity cannot be accurately determined by the sum of the branch circuit breakers since service sizing calcs (therefore the service size) are based on anticipated load of a whole dwelling and each branch breakers is sized to protect the max capability of the branch circuit wires. These calcs assume (correctly) that not all circuits are 100% utilized at any given time. You will need a qualified person to perform a service sizing calculation taking into consideration your existing loads and the added load of a electric tankless water heater.
Your best bet in determining your existing service size is trying to find your service disconnect or the breaker that feeds that panel (unless one of those blurry breakers on the bottom is actually a feed in). The Amps might not have been labeled because it is entirely possible that that is a 200A panel being fed by wires and a breaker that max out below 200A, especially if this is a multi unit structure. For example my house has a 200A service, with 5 breakers at the meter, four of those feed high-power circuit and the fifth is a 90A breaker that feeds a lighting and receptacle panel (which is a 200A sized panel) in my garage.
It is unlikely you will be able to add the tankless to that panel, I doubt it is rated for anything close to a 160A branch circuit and it does not look like you have the spare slots to add four 40A two pole breakers. Even if all of the 15A single pole breakers are replaced with tandems.
If this is a multi unit structure, it may have a much larger than 200A service that is being split to each dwelling, in that case you might stand a chance of having an entirely separate feed installed for just the tankless hot water.
posted by token-ring at 12:16 PM on January 27, 2019
Your best bet in determining your existing service size is trying to find your service disconnect or the breaker that feeds that panel (unless one of those blurry breakers on the bottom is actually a feed in). The Amps might not have been labeled because it is entirely possible that that is a 200A panel being fed by wires and a breaker that max out below 200A, especially if this is a multi unit structure. For example my house has a 200A service, with 5 breakers at the meter, four of those feed high-power circuit and the fifth is a 90A breaker that feeds a lighting and receptacle panel (which is a 200A sized panel) in my garage.
It is unlikely you will be able to add the tankless to that panel, I doubt it is rated for anything close to a 160A branch circuit and it does not look like you have the spare slots to add four 40A two pole breakers. Even if all of the 15A single pole breakers are replaced with tandems.
If this is a multi unit structure, it may have a much larger than 200A service that is being split to each dwelling, in that case you might stand a chance of having an entirely separate feed installed for just the tankless hot water.
posted by token-ring at 12:16 PM on January 27, 2019
You can find your service ampacity by looking at the label on your main breaker. It's probably 200. The right way to find out if you have enough overhead for a major electrical appliance like this is to pay an electrical engineer to go through your annual consumption figures and basically run the numbers. Unless you have a 400A service though (Which, do you live in a mansion? Not a McMansion, a mansion. No? Then you don't.) you pretty much don't have enough overhead. An electric stove is 50A. An electric dryer is 40A. Either one of those alone puts you over budget, before we even think about any other electric items in your house.
Even an 80A Tesla charger is a problem for most residential services, and needs to be de-rated for safe installation.
posted by Anticipation Of A New Lover's Arrival, The at 1:11 PM on January 27, 2019
Even an 80A Tesla charger is a problem for most residential services, and needs to be de-rated for safe installation.
posted by Anticipation Of A New Lover's Arrival, The at 1:11 PM on January 27, 2019
Oh, and you could totally get a service upgrade to 400A but if you had it done through my company you'd be looking at north of $5k for that, maybe a lot more if you're on an underground service and need to trench for a bigger conduit.
posted by Anticipation Of A New Lover's Arrival, The at 1:16 PM on January 27, 2019
posted by Anticipation Of A New Lover's Arrival, The at 1:16 PM on January 27, 2019
Dangit, I missed that little (pic) link at the end. You have a 200A service. I mean, the main breaker isn't showing (it's either out of frame at the top of the panel, down in your building's basement or electrical room or wherever the main load centers are [in which case what you've shown us is technically a 200A subpanel], or outside by the meter [in which case you have a meter/main combo]). In fact if your unit is in a multi-family building then any panel inside your unit is pretty much guaranteed to be a sub even if it has a main breaker on it, because the electric code says you can't have your main breaker more than 10' away from the electric meter, and your meter is not inside your apartment. Anyway though, I look at a lot of residential electric services and that is for sure a 200A panel on a 200A service. 400A panels are way beefier than that, 100A panels are usually much smaller, and a 100A main breaker serving a 200A panel (not impossible, but uncommon) would be popping all day long if it had that much load on it. So, you have 200A service.
If you want to do electric hot water but you want something more efficient than an old-school electric hot water tank, you could look into electric heat pump water heaters, which are quite spiffy. If you don't have an unfinished space like a basement you could install it in though (I'm never clear on what people mean by a "loft," but I assume it's some form of condo unit and you only have finished space with maybe a small utility room immediately adjacent to a finished area) I probably wouldn't go that route, as the compressor on those things makes noise. You're probably best off with a tankless natural gas/propane water heater.
posted by Anticipation Of A New Lover's Arrival, The at 1:45 PM on January 27, 2019 [1 favorite]
If you want to do electric hot water but you want something more efficient than an old-school electric hot water tank, you could look into electric heat pump water heaters, which are quite spiffy. If you don't have an unfinished space like a basement you could install it in though (I'm never clear on what people mean by a "loft," but I assume it's some form of condo unit and you only have finished space with maybe a small utility room immediately adjacent to a finished area) I probably wouldn't go that route, as the compressor on those things makes noise. You're probably best off with a tankless natural gas/propane water heater.
posted by Anticipation Of A New Lover's Arrival, The at 1:45 PM on January 27, 2019 [1 favorite]
Don't even think about installing a tankless heater if you are on well water.
posted by Raybun at 3:33 PM on January 27, 2019
posted by Raybun at 3:33 PM on January 27, 2019
That's only a 24 circuit (well 24/36) panel. In an apartment/office/subdivide space around here it wouldn't be unusual for that panel to be fed with a 100 or 125A feeder (and only at 208V to boot). It's also extremely common here to feed a 200A rated panel with a smaller main breaker because the panel+breakers is cheaper than the 100A version (I know, right). TL; DR: you have to see your main breaker to know what your service is rated for.
At any rate the stabs on that panel aren't rated for more than 60A meaning even if it was empty you wouldn't be able to feed a 160A load with a breaker in that panel.
posted by Mitheral at 8:32 PM on January 27, 2019
At any rate the stabs on that panel aren't rated for more than 60A meaning even if it was empty you wouldn't be able to feed a 160A load with a breaker in that panel.
posted by Mitheral at 8:32 PM on January 27, 2019
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As someone who's been down the whole-house tankless road, electric's just not worth it. These units verge into the industrial category, if you will. They're a burden on a 200A residential service, as we see here. We tried one at about 80A and that wasn't close to being able to handle the whole house. Then we tried a larger unit 120A and that also didn't keep up. In the end, we abandoned the electric units and installed a propane fired unit, which works fantastically. It easily handles kitchen sink, washer, and shower all at the same time. There's no issues with overtaxing the main panel.
Have you priced a 160A breaker? I suppose it might be wired for (4) 40A breakers.
posted by humboldt32 at 11:43 AM on January 27, 2019 [2 favorites]