Radiators/BTU's/Watts

Bob Eh?_2

As long as you maintain 190* water the output will be 15960 BTU (you can't heat just half of it perse). The assumtion made for the radiator is that the 190 * is the average temperature (Tsupply + Treturn / 2). All things being otherwise equal you can lower the average temperature from 190* by either less heat input (perferred) or less flow to get your required output.

Most radiator manufacturers can supply you with derating curves showing the BTU output/foot at various temperatures.

I this a standalone system or an add on to an existing system?

If there are other zones that require 190* water to meet the loads then you will need to use a mixing system to lower the water temperature for this room. In any event you need to figure out your loads and radiation for each zone and then try to pick the lowest temperature possible on a system wide basis that meets the design load and mix down from there for over radiated zones.....

Bob

Bill_6

Radiators/BTU's/Watts

I have run the Slant Fin load calc at 0°F outdoor temp (many times). Here's one example.

I have one room with a heat loss of 7038 BTU/Hr. 7038 BTU = 2.06KW.
The rad in there will put out 15960 BTU/Hr with 190 °F water in it. It's a monster. So that's 2.27 times too much. The rad holds 15.7 gallons of water and I multiply that by 1/2.27 and that = 6.92 gallons. I'm thinking if I could heat that 6.92 gals to 190°F it should give off 7038 BTU/Hr.

1 BTU will raise 1 pound of water 1 °F. 6.92 gals = 57.7 pounds.

Now when I figure the power it takes to heat 57.7 Lbs of water 190 °F ( 0 - 190 ) I come up with 3.4KW.

2.06KW versus 3.4KW ? Where am I going wrong ?

Terry

dellta T

the Delta-T looks odd.

high temp may be 190F, But I doubt your starting point is 0F

try 170-190F (20F DeltaT)

Carl PE

.

I have one room with a heat loss of 7038 BTU/Hr. 7038 BTU = 2.06KW. The rad in there will put out 15960 BTU/Hr with 190 °F water in it. It's a monster. So that's 2.27 times too much.

Your math is ok so far.

The rad holds 15.7 gallons of water and I multiply that by 1/2.27 and that = 6.92 gallons.

Here's where you're getting off-track, I think.

I'm thinking if I could heat that 6.92 gals to 190°F it should give off 7038 BTU/Hr.

The amount of heat that the radiator gives off is a function of the temperature, surface area, and the design of the radiator. It has nothing to do with the amount of water inside.

Bill_6

Thanks Bob

I know this sounds crazy but I am going to try an electric element heater and just fill the rad up part way with water. Kind of like those little Wal Mart oil jobs. I already have the heater and have an old rad I can use.

I just couldn't figure out why my numbers weren't balancing. Maybe the 190°F span I used is too much ?

Bill_6

Thanks Carl

I think you're right. I'm going to try heating the rad with a 1000 watt electric heater rod screwed into the bottom where the steam pipe used to go. Should be interesting !

Bill_6

Thanks

If I use 20°F it's 0.34KW. That can't be right. If I use 117°F rise then the equations balance. I just don't know where the 117 comes from. Or if it's correct.

Bob Eh?_2

I don't think you can only partially fill the radiator.... They put bleeders on them to expel air because air is generally a bad thing!

How do you propose to circulate the water?

How about a pressure tank to allow for expansion?

How about a T&P safety valve?

Those oil filled puppies are something quite different from what you seem to be contemplating and obey a completely different set of rules...

I think what you are thinking will at best destroy your radiator, cause flooding, and could turn out to be very dangerous (Large BANG)... I hope we don't read about you in the news....

Bob

S Davis

Bomb

Can you say Bomb because thats what you will have if the control (what ever that might be) happens to fail and this thing keeps heating and produces steam and pressure.



S Davis

Apex Radiant Heating

Carl PE

.

I'm going to try heating the rad with a 1000 watt electric heater rod screwed into the bottom where the steam pipe used to go. Should be interesting !

Listen very carefully.

YOU ARE BUILDING A BOMB!!!!

Do NOT install an element in the radiator.

Mike T., Swampeast MO

Greatly Agree

Even though that 1kw electric element can only put out about 3,400 btu/hr into a radiator capable of delivering 16,000 btu/hr or so it's still a danger.

If the water level got rather low you would produce steam as not enough of the radiator would be in contact with water to liberate the heat. Without a vent (and numerous other safeties) BOOM!!! When a radiator freezes solid a chunk is frequently thrown across the room--let it be filled with steam to the point of bursting and chunks will be through the walls and ceiling and any body in between!

Please don't attempt such a thing!!!

Jeff Lawrence_24

Do you

mean something like this?

I found this at a jobsite. It was the second try after the fireplace heater didn't work for the radiant.



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Carl PE_2

mean something like this?

Well, something like that, but not exactly. The photo you posted shows some top-notch hillbilly engineering, but at least it's hooked up to a hydronic system with an expansion tank and a safety valve somewhere. I hope.

Bill, a steam radiator is different than a hot water radiator. They are not interchangable.

A steam radiator is not a pressure vessel.

Please go back and google "water heater explosion" to see what happens when steam has nowhere to go. Several of Dan's books discuss boiler explosions in detail. There was a thread here a few months ago about a guy who put a roll of copper in his fireplace and blew out the front of his living room. This is not something to be taken lightly.

Bill, I don't want you to think I'm a jerk, but I don't want to read about you in the paper either.

jerry scharf_3

try this on

Bill,

The water in a hydronic system is a vehicle with BTUs riding on it. Water supplied at 190 and returned at 170 is our favorite 20F delta T. If you work out all the numbers, a 1GPM flow with a 20F delta T transports (delivers) 10MBH. The amount of water the radiator holds is of no consequense. To get 15.9MBH out of the radiator, you need a 1.59 GPM flow through the radiator at 20F delta T. For the same output, if you speed the water up delta T goes down and if you slow the water down the delta T goes up.

jerry

Bill_6

Wow

Thanks for all responce. A lot of bomb warnings. With that 1/8 NPT vent hole I didn't think I'd have worry TOO much about that. Do you think it wouldn't vent any pressure ? Along with the vent hole my intention WAS to find the amount of wattage to give off 7000 BTU's at max power on the coldest day of the year. For that rad I've calculated 790 watts. My test was with a 750 watt heater.

Steve Paul

Cast iron steam bomb

Bill: Do you have a death wish? You are about to create a steam bomb. Water heater elements are meant to be installed in water heaters! There, they are Supervised, controlled and protected by, DISCONNECTS, THERMOSTATS, HIGH TEMPERATURE LIMIT SAFETY CUT OUT SWITCHES AND TEMPERATURE AND PRESSURE RELIEF VALVES. In addition they also have a constant supply of water to prevent dry firing. What you are suggesting is extremely dangerous and shows a lack of education, experience and knowledge. DON'T DO IT!!!

ScottMP

NO IT WOULD NOT !

Bill thats a MANUEL vent it will nt automatically vent and air or PREASURE.

Bill, these are NOT arrogant proffesionals who don't want to help a homeowner. These are PROFFESIONALS trying to save your home and possible your life.

What you are attempting to do is dangerous and the fact that you still feel it could be accomplished worries me.

Here is a photo of a cast iron radiator when its freezes and breaks. The missing piece usually imbeds itself in a wall. Would you want your child next to this ?

Scott

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gerry gill

Bill- have you ever

seen the shrapnel created when a frozen radiator explodes? same thing..the only difference is that yours will be hot shrapnel..i'm not saying dont experiment, heck i'm known for my experiments, but once you have a design on paper, please run it past all these gentleman just in case you overlooked a safety issue..okay...were only on this side of the lawn once.

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