To worthy's point--when considering redundant systems you need to weigh the additional upfront costs, operating costs, and maintenance costs against the cost of a failure. Many failures can be predicted and/or prevented with routine maintenance.

Service providers in your area may offer service contracts that will move you up in the repair queue and limit your repair costs in the event of a problem.

I think I agree with worthy's point. Assuming $100-$125/night* for a hotel stay when heat or water fails, it'd take a lot of hotel nights to add up to an additional HVAC system and water heater. (Don't forget that means there are two systems that will need to be maintained and replaced)

I've had major failures at very bad times--but redundant systems wouldn't have mattered.

Imagine if you will, that it's about noon New Year's Day and you had 15 people staying at your house for a holiday house party. Imagine further, a backup in the sewer line under the street. Imagine telling all of those people "no toilets, no showers, no dishes" until RotoRooter does their thing.

That's a failure--and one we couldn't do anything about.

*Prices in your area may vary, obviously. That's easily done where I am in OH, but cheap for other locales

Actually that's true about the HVAC system but what about the hot water? What is the break even in terms of square footage for a hot water system?

We have plumbed for 2 inline WH's. We could not justify it with just the 2 of us - we kept the 2 until the first one failed. We could isolate the 2nd water heater with valves, etc and turn it on with guests and had shut offs placed for easy swapping out. I would think that it's pretty darn easy to get a WH installed fast - esp if you plan ahead with a series of shut offs. Our guests are limited usually to 2 at a time - so YYMV if you host a house full..

I think I agree with worthy's point. Assuming $100-$125/night* for a
hotel stay when heat or water fails, it'd take a lot of hotel nights to
add up to an additional HVAC system and water heater. (Don't forget
that means there are two systems that will need to be maintained and
replaced)

I was thinking the same thing. Maintaining redundant systems "just in case" is a very expensive choice. We've only lost power and water for more than a day (actually more than a few hours) once in my adult life -- yeah, that was a miserable six days, six days for which we Southerners are ill-prepared, but I still don't think the cost-to-value ratio skews positively towards two of everything.

We've only lost power and water for more than a day (actually more than a few hours) once in my adult life

We've lost power for a few days at a time a couple of times--but redundant HVAC systems or two water heaters wouldn't have made a difference--there was no power.

but I still don't think the cost-to-value ratio skews positively towards two of everything.

Yup--and it's usually possible to get same day service on HVAC and plumbing, even if one pays a premium for a holiday or a weekend. It'd be a pretty huge premium, though, before it got to the cost of even a water heater, let alone an HVAC system.

Even with a houseful, (which we often have), I wouldn't spend the money that way on a 'small to regular' size house.

The maintenance and repair is a big issue. Around here HVAC costs about $150 per year for a contract per unit. And then when you measure the life of some things in years and not work done, repairs are double. After replacing my two 6-7 year old compressors in the last year, I would have paid $3000 less if I only had one system.

So for me - $5000 upfront, $3000 extra repair, $1000 extra maintenance for 2 units over 6 years or $140 a month or so. Strangely, I've had a few issues but all have been in mild conditions so our only cold night almost stay at a friends was a power outage.

The older I get the more I appreciate that comfort is king; sometimes economics needs to remain in the text book.

When considering redundant systems, you need not match the full operating capacity of the main systems to be comfortable. For example, a small portable generator that keeps the beer cold and lets you watch the Alabama game on TV may be a reasonable alternative to a super-size, automatic generator capable of powering the entire house while recharging a half a dozen Teslas and selling excess kW's back to the grid. A small hot water heater that will support a single bathroom and a dishwasher might get you through most outages. A couple of ceiling fans and a portable air conditioner might be a good short-term alternative to a full-capacity spare air conditioning system.

You have a good point - redundant is overkill and you would likely be sacrificing efficiency for the everyday. If you oversize HVAC, for example, you may have a problem with dehumidification because the unit won't run long enough to remove moisture. In my climate, that is the major cause of discomfort. Also - you have to "use" the systems (like a "spare" water heater) isn't going to be good if it just sits there unused.

water heaters like refrigerators are 24/7.

(with the exception of tankless options)

next to heating/cooling, water heaters are the next

big energy users.

in my climate, whole house generators are popular

due to inconvenience of occasional hurricanes & weather

related issues.

some opt for for whole house generator options.

others for generator sized for refrig, tv and window unit operation,

and then those who leave, or just ride it out.

I see all points of view in my line of work.

some people will opt for comfort every time at whatever the cost.

others mid range efficiency, and as always the low end just meet

code people.

guess the generator analogy is because that is what I thought

the thread was about when I clicked on it!

best of luck

... a
small portable generator ... small hot water heater ... couple of ceiling
fans ...

I agree with you. When we lost power for six days about a decade ago, we huddled in the living room around a space heater and closed off the rest of the house. We used a small generator to keep a few things running. We cooked on the grill outdoors and went to my husband's office to shower. We made do.

But I think you've changed the subject. These items are a fraction of the cost /work of full-fledged HVAC units and hot water heaters. These things are a reasonable value in terms of cost-to-risk, whereas a 6K HVAC system is not.

Chisue, this is one of my favourite subjects. Dual and redundancy for sure, HVAC, hot water, humidifiers, dehumidifiers and a host of other appliances and systems. Here for two wings of the new build. Guest bedrooms in one wing while family areas, laundry, master, kitchen, office etc. in the other wing, which will see more use. Both heater and hvac systems will have options of feeding either wing or whole home, in addition to using wireless air flow duct zone dampers plus motorized duct dampers. I'll be working with an HVAC designer soon to discuss capacity and layout. I need to design a few integration features but dampers will integrate with fire and sprinkler control systems for smoke and fire containment.

Ground based solar and a whole house generator will provide an adequate level of redundancy; our servers run 24/7 for years without suffering a power failure and need an air conditioned environment (wish I could replace all with water cooled systems, few are). Will need advance planning when we move though servers are clustered; no one will ever feel a break when we move over a few days just four miles from here. Sorry for going on here (as usual) but I develop fault tolerant systems; my dad who is still alive, developed redundant communication systems for fighter jets, so you know where I get it from.

Redundancy is like insurance: The cost has to be appropriate for the risk being mitigated.

That was one of the reasons we went with two mini-split HVAC units. We rarely run the one in the master BR, but it would give us a place to live in comfort if the main one went down, and the draw is so small that a fairly small generator (which we have) will run it. I can get by for a few days without hot water, should it ever happen.

We pay for one visit (twice a year) to service both HVAC systems. We do pay for two Aprilaire filters and two flow-through humidifier filters per year. (I buy them online.) The annual contract to inspect two systems isn't *double* the cost for one. The amount of ducting is the same as for one.

Each furnace is sized to heat/cool/humidify it's own area of this long-ish, single-story home in the Chicago area. Two thermostats keep each area comfortable. (If one fails, the other can keep us going until a weekday, even at times like this, where we're to go from 9F at night up to 27F.)

We had many electrical failures in our old home of thirty years. Twice we feared frozen pipes during long outages. We paid $250/night to stay in the only nearby hotel that accepted pets -- and that we could reach in those storms. We haven't had electrical troubles here, but we did price a small-capacity, natural-gas-fired generator. It would cost more than a new furnace -- and would have its own maintenance issues.

This house is 15 years old. It's 2900 sq ft. with three full baths. Each water heater *can* be isolated. However... I am evidently capable of using half our total, two-tank capacity when I shower -- since that's how I knew one tank was failing! (I have other redeeming qualities. LOL)

I don't think this is quite the extravagance some of you thought it was. I posted this as a possible consideration for new builds.

I have a zoned HVAC system - one for 1st flr; 1 for 2nd. It's great!

Few years ago after multiple power outages that lasted for 7-10 days each, I bit the bullet and bout a whole house, natural gas powered generator. It powers everything but the lights in my daughter's old bedroom (no biggie), and the electric clothes dryer - when I replace it, I'll get gas as the piping is already there. I have clotheslines in my basement and do very little laundry being a household of one, so it not working would not be an inconvenience. Of course since it was installed, we've had 2 power outages - one for 2 hrs and one for 8 hrs! But it's a nice feeling to not have to worry. I have chronic pulmonary problems and need electricity to do 2 breathing treatments daily, so no worry there or when I go out of town for an extended period.

At my age, I would not be without it.

Chisue - I do feel like we jumped all over you.

Having built with 2 systems 7 years ago, I have regretted it. Our service people do charge double for 2 units. Strange but true.

Living in the North is a different animal of course. But much much wiser today to build really tight and then you could use a electric resistant heater to survive until a repair was done. Or a gas fireplace.

Having 2 water heaters is a bit much since the horror of not having hot water is a minor issue. The energy hit of that is pretty significant. And failure rates are pretty low.

I get it. People have money and like to prepare for the 0.1% of the time. But looking at dollars and cents, it doesn't usually justify it. I could have paid $500 a night, had a massage, and ate at a fancy restaurant the few times I have had a failure and still come out ahead.

We have four HVAC systems servicing a 5600 sq. ft. house. Two humidifier systems and a whole house generator. Worth every penny, but we live in the Northeast and have had numerous power outages over the years.

The sort of back up I'm planning doesn't duplicate systems. Propane gas heat and town electric power, wood burning stove, back up generator to the critical items (hot water, heat, fridge, stand alone freezer, some lights...), next year adding on whole-house solar. (And of course, there'll be the grill.) Humidifiers/dehumidifiers will be individual units where needed. Oh, and the heating system is being set up for conversion to geothermal. (Air duct system.)

I was without power for a LOT of 2011. I don't want a repeat of that! (My only backup then was dry ice which I seriously lucked into, and the grill. And the fact I could shower at work.)

We lived on the end of a power run in a traffic heavy area that was full of old trees. Our power used to go out all the time, if the wind blew too hard we were without power. Oddly enough the other side of the street was on a different run so we would occasionally stare longingly at their lit up house. Usually it would only be off a couple of hours, just long enough to screw up all your clocks but nothing too bad. Finally, I broke down and bought a whole house generator, after one particularly bad outage.

Our power never went out again, and I don't mean the generator worked to keep the lights on, I mean they changed the lines or something and we never lost power again.

I know this isn't helpful but I get a kick out of it.