HELP NEEDED: HOW MUCH BTU/SECTIONS DO I NEED? ROOMS ARE VERY COLD IN WINTER AND I THINK I NEED TO UP

radiatorcheck

Hi Heat Experts,

We lived through a few cold winters and finally decided to check our heat system in two bedrooms that get very cold in the winter. Our neighbors are not complaining, but out apartment is cold, and my suspicion is that the "upgraded" radiators we have have are too weak for the job.

It would be a huge help if you could help me answer four questions:
1. Are my current radiators too weak for the conditions or if they are good, then I should be looking at a different problem?
2. What are the heating needs in each bedroom in the apartment in BTUs, given the conditions specified below?
3. If I want to install old cast iron radiators, how many sections do I need for LARGE BEDROOM (wall to pipe distance at the bottom is 21.5”, so I have 4 or 6 section or taller radiator that I can fit)?
4. If I wan to install old cast iron radiators, how many sections do I need for SMALL BEDROOM (height to windowsill 26.5”, so I cannot have tall radiator there)?

Floor map and room pictures below.

LARGE BEDROOM:
SQ Feet: 13.6’x11.6’=158’
Current Radiator: Slim Type, 23.5”H x 25.5”W (I believe it is BTU/H OUTPUT=4,654; http://steamradiators.com/orderingpages/charlestonpro.html)
Radiator Type: Steam, 1-pipe
Other Radiator Info: wall to pipe distance at the bottom is 21.5”
Exposure: North
Windows: 2
Top Floor (penthouse is above, but not across the whole apartment)
Current Winter Temperature: Cold…
Good to have for new radiator: thermostatic radiator valve (TRV)

SMALL BEDROOM:
SQ Feet: 12’x11.11’=133.5’
Current Radiator: Slim Type, 15.5”H x 25.5”W (I believe it is BTU/H OUTPUT=2,990; http://steamradiators.com/orderingpages/charlestonpro.html)
Radiator Type: Steam, 1-pipe
Other Radiator Info: height to windowsill 26.5”
Exposure: North
Windows: 2 + wall AC Unit
Top Floor (penthouse is above, but not across the whole apartment)
Current Winter Temperature: Very Cold…
Good to have for new radiator: thermostatic radiator valve (TRV)


Thank you so much in advance for your help!!!

K.

Jamie Hall

Odds are they are too small. However, to properly size them one needs to know the heat loss of the rooms. The way to do that is the square feet of the walls -- not the room -- and the insulation (if any!) and the design temperature outside. From the wall construction and the insulation, one can determine the 'R' factor, and then just take the wall area and divide it by that R, add the window area, and multiply by the difference between the design temperature and the inside temperature -- typically 70. Then do the same thing for the area of the roof which isn't covered by the penthouse.

Add it all up, and there's the BTUh that you need. From that one can find the radiator size...

nicholas bonham-carter

Hatterasguyguy is making an important point here about the control for the system-the thermostat location.
The thermostatic relief vents cannot control the boiler, and make it fire when the indoor temperature is too cold. They must have been added because of a too hot condition.
Ask your neighbors whether they also have cold spells. They may be members of the Inuits, and thus able to tolerate cold temperatures.
Download the heat-loss calculator from the SlantFin website, and use it to calculate the heat-loss of your rooms, to check whether your radiators can supply the needed heat.
I suspect that the system is somehow not running long enough to get steam to your rooms. This is probably a system problem with a lack of main venting, as well as other faulty maintenance issues.
Are you paying for a portion of the fuel cost?, yet never receiving its benefits?--NBC

radiatorcheck

Thank you for the insights.

Hatterasguy,
It's a one pipe steam heat system in my apartment. I do not have a thermostat. The heat just comes on and off, as the building wants it to.
I believe that the neighbors have older type radiators and they said their apartments are warm.

Yes, our radiators get really hot and are impossible to touch (at least if you want to keep the fingers )). It's hard for me to say now if we were cold with the radiators were hot. I do remember that rooms sometimes got warmer, but the apartment was generally cold and we were sleeping with three blankets....

KC_Jones

I am taking a guess here, but I think it is a two fold problem. First I have a feeling the max output of those rads is not enough, but without a heat loss you don't know for sure. You can use the slant fin heat loss calculator to figure it out.
http://www.slantfin.com/index.php/professionals/heatloss
Second is mass. Those radiators are steel and certainly won't have the same flywheel effect as cast iron. Once cast iron gets hot it stays hot for a very long time. Those radiators are steel and will cool off much more quickly so your average output (system on and off) will most likely be lower even if those have the same rated output as a cast iron radiator. So when the system shuts down it cools off quickly. Do you see much greater temperature swings in those rooms than the others in the apartment? Do the heat loss and get back to us, but I have a gut feeling you either need to install much bigger rads of similar design to what you have or switch back to cast iron. I am curious did you have these changed or was it like this when you moved in?

radiatorcheck

Thank you. I will check with the neighbors radiators..

Regarding air vents, how do I know which ones are the "largest possible vents available"? How should those be picked? Also, I wanted to get thermostatic radiator valve (TRV) option, so that I could control temperature in case it gets too hot.

Thank you!

Paul48

TRV's work great, but you need to know what control strategy is used by the building. If it is not a reset control, and the boiler pressure doesn't go to zero, they will not function correctly.

Gordo

A minor point, but those "steam" radiators you show were never properly designed for one-pipe steam.

The reason is the incorrect placement of the vents. Yours are at the top end. They are really hot water radiators that are being fobbed off as suitable for steam.

On "real" one-pipe steam radiators, the vent should be 2/3 down from the top. Check some of the older radiators in the building to see what I mean.

The vents will work where they are, of course, but more than half the radiator will have air trapped in it when the steam gets to and shuts off the vent.

Were there is air, there cannot be steam!

So, if the radiators are too small for the space at their fullest rating, the combination of the poor vent placement makes a bad situation worse.

radiatorcheck

Thank you. It seems that changing my two radiators to old cast iron steam radiators in really the way to go.