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Propane tankless water heater question?


mader656
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Need to upgrade/replace waterheaters. Going tankless plan is a open infloor heat will be heating 5000 square feet of well insulated space with 4 bathrooms. Original plan was a outdoor boiler but you can buy a lot of propane for the cost of one of those and propane is easy. 

How many btu. Needed? Anyone know.

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I'll look at fire hall. We heat a 60 X 60 concrete helicopter landing pad with one. Only  run it during ice or snow storm. We can keep pad around 40 degrees in single digit temps

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A good vendor  of the supplies will have a program/calculator to spec you out on what you need. This should be a no charge service. I put mine in 20 years ago and love it.

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4 hours ago, zleinenbach said:

Figure 20 btu a square foot. Was a rule of thumb that’s been working, and with the turn down ratios of newer equipment over sizing is t AS big of a deal

This. So 100,000 btu output with a good turndown

 

Up here we always try to use outdoor resets and the unit runs more efficient with radiant heat.  The way it works is if it’s warm outside the system runs at a lower temp, say 80* when it’s 35* outside but when it’s 0* outside the system may run at 105*.

The lower the temp you heat the water the more efficient you are on fuel.
 

I would do some research on the tankless domestic water heaters, some require a minimum flow rate, and if I remember you are hauling water or have a limited well. I don’t like the combination units for our climate, you results may vary.

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Also very important is to size the circulators correctly, they are not one size fits all

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1 hour ago, AKwelder said:

Also very important is to size the circulators correctly, they are not one size fits all

Friends was telling  me about a variable speed pump? Grundfos maybe?

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25 minutes ago, mader656 said:

Friends was telling  me about a variable speed pump? Grundfos maybe?

Grundfos does make some, so do others. They also make 3 speed  units and smart units. Sizing a pump comes down to how many zones/loops and the longest length zone/loop. That size pipe/PEX has a head loss per foot.  The circulator has a pump curve that will show you what your GPM output will be at a given head.  There are calculators on line.  
 

or pm me, I can show you some links, or we can see if we can crunch your numbers

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Stay away from variable speed.personally don’t see how the benefits outweigh the costs.

combi units are nice, but if you plan on using a lot of hot water a lot of the times I’d go with an indirect tank. 
 

a lot of options out there for sure!

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I used a tankless water heater years ago and hated it.

The instructions said to clean it every 30 days.

That meant unhooking from the water supply and running a special cleaner through it.

The insides would collect minerals from the water and make it quit working. 

The better half finally put her foot down and we went back to a regular natural gas water heater.

I hope these are better now as my experience was not good?

Using as a boiler will also allow water treatment to be added to the system which will help a lot.

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1 hour ago, Diesel Doctor said:

I used a tankless water heater years ago and hated it.

The instructions said to clean it every 30 days.

That meant unhooking from the water supply and running a special cleaner through it.

The insides would collect minerals from the water and make it quit working. 

The better half finally put her foot down and we went back to a regular natural gas water heater.

I hope these are better now as my experience was not good?

Using as a boiler will also allow water treatment to be added to the system which will help a lot.

They need treated water to function reliably, otherwise you chase problems. We have one at the firehouse, and it is a bloody nuisance. 

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My welding shop is 7800sf heat in the floor, it was new in 2008 up till this past year average heating cost was $78.37 per week with a tankless boiler on propane  I would not change a thing 

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I've had tankless heat and hot water in my house for 5years.  My propane bill vs. the old boiler is less than half.  All we did was change the boiler and the savings paid for the new system in 2.5 years.  I love it.  No more taking hurried showers or having to wait for the water to heat up plus the heat on very cold days is evener.

 

jerry

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I got over 20 years out of a Bosh Aquistair . I never flushed it once. It would likely still be going but I cracked the heat ex-changer when changing a sensor( not enough backup wrench).I replaced with a Takagi tank-less.......I use a small Ecotemp tank-less to run 1800 feet of 5/8"PEX in a 30x60 slab in my basement.  All very good units, the Bosh did not have a power vent like the other two so no 110V required, I prefer that but Bosh has moved out of that business. l will solder the crack in the Bosh and keep it for a spare.

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