sizing a water heater

Tom_53

I have a customer that just installed a 70 gallon tub. They are running out of hot water. They have a 30 gallon oil fired heater. Iam considering a 50 gallon bock and a f5 riello. There boiler is a Utica Starfire 111, 4 section, & f5 riello. When the boiler was installed it included a switching relay with priority, for the possible future indirect. I am not sure what to recomend, what do you think?
Thanks in advance,Tom

Alan R. Mercurio_3

Ok first you need to measure the doorway the water heater is going through.. ~ I'm just kidding here's a helpful link for you.

sizing a water heater

Your friend in the industry,
Alan R. Mercurio

www.oiltechtalk.com

Tom_53

To Alan

Hi Alan, Thanks for the response. I can not get on your web site. I tried a new password, I GAVE UP! I miss your old format on OTT.
Thanks again,
From Tom

Alan R. Mercurio_3

Tom, You're very welcome and I apologize for the difficulty you're having getting on the web site. If you would like e-mail your phone number to me and I will contact you tomorrow so I can help you get back on the site with our fellow technicians.


Your friend in the industry,
Alan R. Mercurio

www.oiltechtalk.com

Dave Yates (PAH)

calcs

Take your bathing temp (let's say that's 106 F) minus the incoming temp (say 40 F in winter) divided by the storage temp (120 F?) minus the inlet temp (40 again). That's the percentage of flow that represents the hot water injected into the mix.

Turn on the shower; adjust to suitable temp; time the fill for a 2-gallon bucket; and you'll be able to pin-point the amount of hot water needed for any given time the shower will be utilized. From there, all you need to do is find a good match - be it a storage type or direct-fired water heater.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Mark Evans

First Hour Rating- sizing a dhwt

Tom,

The First Hour Rating is the peak hour demand for a given installation. In a residence, that will normally be in the morning, but check their schedule. There is a HUD-FHA Table that provides minimum recommendations for average households based on the number of bathrooms and bedrooms.

For 1 to 1-1/2 Bathrooms

1 Bedroom

20 Gallons Storage
27 K Btuh min. input
Expected First Hour Draw 43 Gallons
Recovery 23 Gallons

2 Bedrooms

30 Gallons Storage
36 K Btuh min. input
Expected First Hour Draw 60 Gallons
Recovery 30 Gallons

3 Bedrooms (same as 2)

30 Gallons Storage
36 K Btuh min. input
Expected First Hour Draw 60 Gallons
Recovery 30 Gallons

2 to 2-1/2 Bathrooms

2 Bedrooms

30 Gallons Storage
36 K Btuh min. input
Expected First Hour Draw 60 Gallons
Recovery 30 Gallons

3 Bedrooms

40 Gallons Storage
36 K Btuh min. input
Expected First Hour Draw 70 Gallons
Recovery 30 Gallons

4 Bedrooms

40 Gallons Storage
38 K Btuh min. input
Expected First Hour Draw 72 Gallons
Recovery 32 Gallons

5 Bedrooms

50 Gallons Storage
47 K Btuh min. input
Expected First Hour Draw 90 Gallons
Recovery 40 Gallons

3 to 3-1/2 Bathrooms

3 Bedrooms

40 Gallons Storage
38 K Btuh min. input
Expected First Hour Draw 72 Gallons
Recovery 32 Gallons

4 Bedrooms

50 Gallons Storage
38 K Btuh min. input
Expected First Hour Draw 82 Gallons
Recovery 32 Gallons

5 Bedrooms

50 Gallons Storage
47 K Btuh min. input
Expected First Hour Draw 90 Gallons
Recovery 40 Gallons

6 Bedrooms

50 Gallons Storage
50 K Btuh min. input
Expected First Hour Draw 92 Gallons
Recovery 42 Gallons

Hope this helps.

Mark.

chris_24

that seems

a bit low to me.

I guess there is an average for everything, but in reality, ask your customers what their needs are, how long of a shower do they take, then based on the heaters recovery rating, you can size your heater.

I hate running out of hot water, and I am NEVER the first one in the shower EVER!! size the thing according to the needs of the clients, after all we are all about comfort here.

Unknown

Great tables!

If that 70 gallon tub only has 1 bedroom near it, a 20 gallon tank is big enough?????

Give me a break.

Noel

Tom_53

no showers

Informative tables, but showers are not the the problem. The guy has a 70 gallon tub and wants to fill it with hot water. 30 gallon oil fired unit is not working. The boiler does not have the btu s to suport a large indirect, 60 0r 80 gallons. Other opinions are appriciated.
Thanks, Tom

Firedragon_4

Although we spend an entire book

explaining the math to do this with in "The Hot Water Handbook', sometimes simple is best.

With tank type heaters the best rule of thumb is simply to 'calculate all of the capacities of the tubs and figure on a one-on-one gallonage basis. 70 gallon tub, 70 gallon heater.

That really covers the 80% Rule on cold-water feed, the Btus, etc. it's simple and it works, FACT!

www.firedragonent.com

Firedragon_4

BTW,

you could tack a booster system onto that 30 gallon and probably get away with it. Call the guys at TFI-Everhot to be sure, it's their tank.

http://tfi-everhot.com/

Scott Gregg

Right...but

Using that rule with a Bock 70 gallon also gets you able to fill the tub and support a shower right after filling it!

One can also set up a Bock water heater temperature to 160* (Even on the 50 gallon unit) and use a mixing valve to knock down the temp to 125* or so. This will keep you from running out by using less hot water during a peak draw. A Bock is built to handle such things.

There is more than one way to skin a cat.

Firedragon_4

Yup, but

when comparing heaters make sure that the ratings are based on the same recovery rates. Make sure the rise is the same too, inlet water temperature vs. supply temperature.

Dave Yates (PAH)

Why not nail it down accurately

Might as well hit the numbers spot-on.

http://www.contractormag.com/articles/column.cfm?columnid=204

http://www.contractormag.com/articles/column.cfm?columnid=212




To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Tom_53

final decision

I glad i have a computer, all this input helped me decide what to do. 1st choice was a 70 gallon oil fired hwh, would not fit. 2nd choice is a 50 gallon aquabooster from the existing 30 gallon water heater. Piped in series for a total storage of 80 gals. I have never tried this but i think it should work.
PS If it does not work i will let you know.
Thanks again to all who responded.
Tom,Long Island

Bruce M.

On Demand Hot Water Heater

How about an on demand hot water heater.

Unknown

Tom, look at this thread

http://forums.invision.net/Thread.cfm?CFApp=2&&Message_ID=166139&_#Message166139

Jack_21

Rinnai on demand

Should you choose to go gas on this. If the tub is supplied with 1/2" you aren't going to get much more than 5gpm to the tub. If it is 3/4 then that is another matter. A Rinnai 2520FFU will give 4.5gpm at 70F rise. If you are in a tub over 105 you are no longer bathing you are par-boiling. If they want faster fill and have larger supply then you can use two. The advantage to these on tubs is that I have hardly ever taken a bath that within several minutes you didn't need to peak the tub with more HW. With the on-demand you can stay in a hot bath as long as you wish. The customer can enjoy the appliance.

Jed_2

So, where ya been, Jack?

We've missed you.

Jed

Dave Yates (PAH)

great application

if you do your homework and know the incoming coldest water temp, flow rates to calculate demand and the real GPM rates the units are capable of producing - not the pie-in-the-sky projections some manufacturers are touting in order to gain sales.

Short rule of thumb: gross input Btu's, multiplied by .82 or whatever the steady-state efficiency rating might be, and divide that by 833 for GPH & then divite by 60 for GPM.

For instance: 189,000 x .82 = 154,980 Divided by 833 = 186.05 divided by 60 = 3.1 GPM

Takagi's charts show various incoming water temps & are pretty much dead-on for GPM rates at the temps shown.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"