Heating bathtub water

Nevada · #61 10/18/14, 11:01 PM

Quote:

Originally Posted by AmericanStand

To put my $500 tankless heater in cost me about $500.
To support its 200,000 BTU I had to replumb everything from the propane tank to it. Then re did the hot and cold water lines....GRRR

200,000 btu/hour is a nice system, about 8 GPM. I'd love to see some photos.

Looking at the chart, you probably had to go to 3/4" pipe for propane to get 200,000 btu/hour at any distance to speak of. I'm going to go to 3/4" pipe also just for my 80,000 btu/hour heater, but natural gas has a lot less heating power than propane has. I've got about a 40 foot run to make, with a few 90s.

I'm not sure where you are. Las Vegas is a good place for tankless because inlet water temperature doesn't get very cold. We can get away with smaller tankless systems around here because our city water is about 20 degrees warmer in the winter than in colder northern climates.

AmericanStand · #62 10/19/14, 09:28 AM

Ground Temps here run around 55 degree F.
I was looking at one of the cheeper units but a little on the iffy side as to capacity.
Menards had a GREAT sale on these ( I think) at under $500.
Im quite happy with it so far I can run hot water for dishes and fill the tub with hot water at the same time.

AmericanStand · #63 10/19/14, 09:35 AM

http://www.menards.com/main/plumbing...304-c-8690.htm

Not the greatest but very acceptable so far.

Nevada · #64 10/19/14, 10:39 AM

Quote:

Originally Posted by AmericanStand

Ground Temps here run around 55 degree F.
I was looking at one of the cheeper units but a little on the iffy side as to capacity.
Menards had a GREAT sale on these ( I think) at under $500.
Im quite happy with it so far I can run hot water for dishes and fill the tub with hot water at the same time.

You should be able to take two showers and run dish water at the same time with a 200,000 btu/hr heater. That's a nice unit.

Our incoming water temps run about 70 in the summer and 60 in the winter. I know that temps can fall below 40 in colder locations, which really impacts tankless heaters.

Quote:

Originally Posted by AmericanStand

http://www.menards.com/main/plumbing...304-c-8690.htm

Not the greatest but very acceptable so far.

Did you have to buy the vent kit separately?

arabian knight · #65 10/19/14, 12:22 PM

Yes that was another reason I thought against a on demand water heater the temperature of the water. Especially in the winter. I am on well water, and last year my water was COLD and I mean cold. The extended cold temps put the frost down 3 feet at least.
And just for giggles I tested how cold that water was, as I do some in home testing of commercial coffee brewers for a friend of one, and it was taking a pretty long time to heat 2 gallons of water up in some of those brewers. Most of those brewers have around a 1750 to 1850 watt heating element.
So I also have a very nice digital thermometer to get a accurate reading on the temp, because the hotter the water is during brewing the better the coffee is, I set it between 190º to 200º.
Anyway, I tested my waters temp and it was between 39 and 40 Degrees~! Now THAT is COLD WATER. An dyeing that cold is why my electric water heater uses a nice amount of electricity over the winter months, just filling the sink to do dishes you have to run the hot water for some time just to get the pipes warm enough before it even reaches the sink. LOL

Nevada · #66 10/19/14, 12:38 PM

Quote:

Originally Posted by arabian knight

Anyway, I tested my waters temp and it was between 39 and 40 Degrees~! Now THAT is COLD WATER.

To work really well your application would probably require two tankless heaters in series, the first to get the water to about 85 F and the second heater to get it up to 120 F. Tankess heaters are typically designed to increase water temperature by 50 degrees F at the nominal design throughput. Having your water heated from 40 F to 90 F wouldn't provide you with a very satisfying shower.

Here's a clip that shows how two tankless heaters piped in series work. Notice that the model of heater they used was a small capacity 87,000 btu/hr model (about 3.5 GPM), but that throughput is satisfactory for a large home because of the combined heating capacity.

arabian knight · #67 10/19/14, 12:49 PM

That was nice, I will think on it.

Nevada · #68 10/19/14, 01:01 PM

Quote:

Originally Posted by arabian knight

That was nice, I will think on it.

But I see your point. You have to buy two heaters instead of one, and you have to provide pipe capacity for 160,000 btu/hr instead of 80,000 btu/hr. That's going to get into a lot more money than just replacing your tank heater.

I had the advantage of the system actually costing less than a tank. But we'll see how that cost goes after I upgrade my gas pipe.

arabian knight · #69 10/19/14, 01:14 PM

Quote:

Originally Posted by Nevada

But I see your point. You have to buy two heaters instead of one, and you have to provide pipe capacity for 160,000 btu/hr instead of 80,000 btu/hr. That's going to get into a lot more money than just replacing your tank heater.

I had the advantage of the system actually costing less than a tank. But we'll see how that cost goes after I upgrade my gas pipe.

And having two tanks like that or have a good quality regular water heater that is already in. Costs start to get on the high side of things to make a switch.

AmericanStand · #70 10/19/14, 02:26 PM

Mine came without a vent kit but that was a minor expence.

The way I understand it I can get a 70 degree heat rise on 10 GPM or 140 on 5 gpm

Nevada · #71 10/19/14, 02:33 PM

Quote:

Originally Posted by AmericanStand

Mine came without a vent kit but that was a minor expence.

The way I understand it I can get a 70 degree heat rise on 10 GPM or 140 on 5 gpm

The specifications for your unit are a 30 degree rise at 10 GPM, or a 70 degree heat rise at 4.7 GPM. Interpolating, that's roughly a 50 degree rise at 8 GPM.

Normally the gallon per minute rating is the throughput that gives a 50 F temperature rise, so you have about an 8 GPM heater.

unregistered5595 · #72 10/19/14, 03:36 PM

You guys are all so smart, practical smart. I enjoy reading threads like this. In some way, you've all helped me in times of needing knowledge. Thank you. ~Feather