Need Help choosing tankless. Clueless

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First, thanks for the great fourm.

I'm currently looking to upgrade my standard water heater in the very near future. I've done tons of reading, as far as brands and ratings. I'm still very confused. So I figure I'd ask the experts. Not just the manufacutres website claming there the best.

I dont have any questions on the physcial install, I'am a airline mechanic by trade, so I understand how things work and how to put them together.

This will be for a 2000 sq ft home with 2 1/2 baths. No deep tub (but might plan for one down the road) There is currently only 2 of us, but for future plans and resale, I want to have a system for the home at 5 people.
Questions:
Brand?
Rating?
Any with a stainless steal heat exchanger?
I'm in Michigan. It gets cold. Very cold.

Thanks in advance.
 

Lifespeed

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First, thanks for the great fourm.

I'm currently looking to upgrade my standard water heater in the very near future. I've done tons of reading, as far as brands and ratings. I'm still very confused. So I figure I'd ask the experts. Not just the manufacutres website claming there the best.

I dont have any questions on the physcial install, I'am a airline mechanic by trade, so I understand how things work and how to put them together.

This will be for a 2000 sq ft home with 2 1/2 baths. No deep tub (but might plan for one down the road) There is currently only 2 of us, but for future plans and resale, I want to have a system for the home at 5 people.
Questions:
Brand?
Rating?
Any with a stainless steal heat exchanger?
I'm in Michigan. It gets cold. Very cold.

Thanks in advance.

With cold water near freezing you would actually need two large tankless WH in parallel for simultaneous showers, etc.
 

Dana

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If your house is heated with a hydronic boiler it's probably better overall to go with an "indirect" water heater tank heated by the boiler, operated as a "priority zone".

If not, it's probably cheaper and more efficient to go with an HTP Phoenix Light Duty, (it's "Light Duty" only in comparison to commercial hot water heaters for very heavy hot water loads), sized for the biggest tub you have to fill, rather than ganged modulating tankless heaters. IIRC the 50 gallon version runs about 2 grand, not sure how big the upcharge is for the bigger ones. The recovery rate on the 50 gallon version is still 2x faster than a typical 40-50 gallon gas HW heater, and may be enough unless you're filling a monster spa tub. If you're planning on buying a deep soaker tub you may want to up-size it to the 60 gallon version, but probably won't need the 80.

The instantaneous flow rate would be significantly higher than a pair of tankless units and the efficiency could be comparable or better since it can't/won't short-cycle. It has enough burner to run a single shower 24/365, but it's small enough at 76,000 BTU/hr that you won't have to upgrade your gas service and gas plumbing to handle a pair of 199,000 BTU tankless burners. (With a drainwater heat exchangers you'd be able to run two showers 24/365 with the 76K burner on the Phoenix Light Duty.) A pair of tankless units will almost always require a meter-swap, and a separate 1-1/4" gas run from the regulator to each tankless. In most cases a 76K burner like the Phoenix Light Duty can use the same 3/4" or 1" gas lines that your old hot water heater used, but that needs to be sanity checked as part of the installation. The all-stainless tanks with better-than average heat exchangers should run for better than 20 years, as long as you have reasonable water quality.

Another choice would be a Polaris, which is more expensive than the Phoenix Light Duty. The Polaris unit have impler burner that don't modulate and will sometimes short-cycle, but they have a pretty good track record overall. Even the smallest Polaris has a 130,000 BTU/hr burner, which may require upgrading the gas plumbing in the house, the biggest ones are 199,000 BTU/hr which will always require a dedicated 1-1/4" home-run gas line to the regulator, and may push the whole house burner load total over what the existing meter & regulator can handle.

The lower cost glass lined versions such as the Vertex and Vertex 100 may seem attractive on price, but won't last nearly long, and have a somewhat spotty service record.
 

solalo

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The only tankless water heater I know that has a stainless steel heat exchanger is Navien. It’s got a bunch of other extras that make it great such as a small built-in tank and a recirculation device. Other highly rated products are Takagi, Rinnai and Noritz.
As for the size, 199,000 BTU is as big as a home water heater can get and it should be enough for any number of people even in Michigan. Here is a review of best tankless water heaters that covers how you decide the needed size with a map of tap water temperatures in addition to discussing the pros and cons of prominent brand names. I should add the review looks a bit biased against Navien. People who ran into problems with it are probably people who did not get it installed well. The truth is Navien is very expensive but I really see it as a reliable brand with unique features.
 

Jadnashua

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You can run the numbers yourself...it's all about flow rates and temperature rise. It takes one BTU to raise one pound of water one degree. The tankless unit is not 100% efficient. A typical shower is restricted to 2.5gpm max per head. Where I live, I've measured the winter-time cold water at 33-degrees F. You'll have some losses in temperature between the heater and the shower head, and you would probably want to not be using all hot, so the temp out of the tankless would need to be somewhere near 110 or higher. A dishwasher, unless it has a built-in heater, doesn't work well without hotter water. Most of your laundry can be done with cold or warm, but some things clean better with hot. So, you might need as much as 80-90 degree temp rise. The advertisements are for incoming water at typically about 50-degrees. Throw in colder water, and it throws off the output an equal amount or drops the max flow rates.

Especially if you could use an indirect off the boiler, the efficiency loss with that type of tank is minimal, and you have unlimited initial flow rates at the temp you want.
 
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In my previous home w/ 50 gallon tank we had cold enough winters that entering water was around 35-40 during deepest winter. I never had a problem with 2 or even 3 showers running simultaneously, although I should add that we did use 1.6 gpm shower heads. The tank could also fill a whirlpool tub if the tank was set to around 130 F (at lower temps I had to stop the flow and let the heater recover for a few minutes before finishing the fill.)

I don't have a feel for how a tankless unit would work in a cold winter environment as the tankless' I've used have been in a warm climate. The Rinnai 75 I've used in a rental home your size in desert climate has done fine with multiple higher flow shower heads running even with the clothes washer drawing during wither, but the incoming water here is not really cold even in mid-winter. I've increased the temp from 120 to 130 F since uninsulated lines under slab are delivering water that is often too cool. If you have your home built, insist on insulating all the hot water lines. I did this after the fact on most of the hot water lines in my previous home (because I could access most runs from utility space) and it made quite a difference, especially for short draws a few minutes later.

If you have an HE frontloading washer and need to wash in hot water at times you will want to use a higher temp as mentioned above. And with tankless you might find it necessary to run a nearby tap at a low flow during the fill to keep the heater from cutting out. The HE frontloaders I've used do short intermittent draws for awhile before doing a long draw to finish the fill. Once the fill is finished or constant, you can close the other tap.
 
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