Estimating the volume of water in radiators

Shahrdad

I have been looking for a way to estimate volume of water in my 1890s cast iron radiators. Most of them are 38 inches tall, 9 inches wide, and have three columns. I also have three rads with four columns that are 44 inches tall and 11 inches wide. Total EDR all for the radiators is 1,414 Sq Feet.

Looking through the archives, I saw a couple of old post where someone suggested that for this type of rads, there is approximately 0.07 gallons per Sq foot of EDR, which makes the water content of my radiators around 99 gallons. Another thread gave a formula of 1.5 pints per sq foot of EDR for column rads, which gives me 2,121 pints. 2,121 pingx / 8 pints per gallon = 265 gallons. The two results aren't even close.

What rule of thumb do you use to estimate the volume in old radiators?

Thanks!

S.

Jamie Hall

I presume this is for estimating the total water volume for a hot water system? Since for steam the internal volume is irrelevant...

The problem is that the internal volume will be remarkably different for different designs.

Can you disconnect the radiators from the system? And do they have a bleeder? If so -- no problem. Disconnect the radiator and cap one end. Connect a hose to the other end in some ingenious manner. Open the bleeder. Fill the radiator with water. Get a bucket or other measuring device and empty the radiator into the bucket with the hose...

Shahrdad

It's for the radiators, which I wasn't planning on disconnecting.

Alan (California Radiant) Forbes

Starting with a cold system, you could turn off the radiator that you're working on and get the system nice and hot. Turn the system off and do the reverse: turn off all the other radiators and open the one you want, to measure the time it takes for hot water to leave the radiator after you turn the system on again. Chart the duty point of your pump and you will arrive at a GPM that you can multiply by the time it takes for hot water to circuit the radiator.

DanHolohan

I don’t have access to it now, but B&G has a technical booklet called Air Control in Hydronic Systems. Gil Carlson wrote it. He included a chart for estimating radiator volume, based on system Btuh load. 

Shahrdad

DanHolohan said:

I don’t have access to it now, but B&G has a technical booklet called Air Control in Hydronic Systems. Gil Carlson wrote it. He included a chart for estimating radiator volume based on system Btuh load. 

Thanks Dan. Maybe I can find a version of it on line.

S.

bburd

There must be radiator volume charts because that’s how we size expansion tanks: system water volume.

DanHolohan

@bburd that’s exactly what’s in the booklet I mentioned. I just don’t have it with me. 

bburd

@DanHolohan The part that confused me about your message was that the water volume is “based on system Btuh load”. And radiation type, I assume.

DanHolohan

@bburd As I recall, it gave two types of older radiators (thin-tube, column), baseboard, convectors, and then related this to Btuh so you could get a cumulative average volume for the whole system. I think piping was included in that chart. Wish I had it here. It was very easy to use when sizing compression tanks.

DanHolohan

Found it! Look on pages 41 and 42.

https://documentlibrary.xylemappliedwater.com/wp-content/blogs.dir/22/files/2013/02/TEH-1196B.pdf?_ga=2.213283924.1732199087.1615158279-1043986236.1615158279

Shahrdad

DanHolohan said:

Found it! Look on pages 41 and 42.

Thank you Dan. I've been learning about compression tanks, and sizing them simply by BTUs without considering the volume of water in the pipes and radiators didn't make a lot of sense to me. This is great.

S.

DanHolohan

Happy to help!