Too Hot Upstairs When Cold Outside

PrevailPuzzle · January 31

Hi there, we have a 1 pipe steam system and when it's especially cold weather e.g. -15C/5F, upstairs gets really hot. We are trying to mitigate using our central fan but it's not a good solution.

I currently have 5s on the rads downstairs and 6s upstairs although I think the overriding problem is that we don't have a vent on the main.

Hoping someone could confirm thatand let me know where the vent should go. Is it a DIY job?

bburd · January 31

That is a common problem in older multistory homes with single zone heat in very cold weather. It is caused by the stack effect; cold air enters low in the house, which acts like a chimney; warm air leaves through the upper stories, so the incoming cold air chills the ground floor—where the thermostat is usually located.

You could consider thermostatic radiator valves on the second floor, but they are fairly expensive. Anything else you do to mitigate the problem in extreme cold will have the opposite effect in milder conditions: the second floor will be too cold compared to the first.

When zoning became more common, this problem was solved by zoning the first and upper floors separately.

Jamie Hall · January 31

The main vents should go at or near the ends of the mains — it looks as though you have two of them.

Now. You have run into a quirk of one pipe steam systems which we don't normally run into — in fact which is rather rare. Remember what the radiator vents do — and do NOT do. They regulate how fast a radiator will fill with steam. They do NOT regulate how much steam will eventually fill a radiator when the boiler keeps running.

The reason we don't normally see this as a problem is that in almost all installations the boiler is big enough so that it will eventually cycle off on pressure, at which point the radiator fill process — remember the rate of fill is controlled by the vent — starts over from square one, unless the boiler shutdown is so short that the system never drops to atmospheric.

If you are running very long runs without a boiler shutdown, eventually all the radiators will fill, regardless of the venting rate, and rooms which were normal may become overheated.

Is there a solution to this? Yes, and in most cases with modern digital thermostats its actually built in: it's the cycles per hour setting. For steam we normally say set it to one — but you may find that you get much more even heat with two or even three cycles per hour. Give it a shot.

ethicalpaul · January 31

Here are some things you can try:

Please post a picture of the "end" of your two mains (the part just where it turns vertical to the floor). This is likely where the main vent would be
Put a smaller vent on the upstairs radiators to make them heat up slower. This may not give the desired result during less cold times however so…
You can try putting an adjustable vent on those radiators and adjust them as desired. I have a small valve that closes the connection to my bedroom vent that my wife can close when she is too hot
Or you can try a TRV device on the radiator in question so that it doesn't open the vent if it's already a certain temperature there
Or my favorite solution is you can put a blanket over the radiator when it is too hot, covering part or all of the radiator as desired. By putting a blanket on part of it you make the radiator "smaller" and less able to deliver heat to the room.

jesmed1 · January 31

We're having the same problem in our old 2-story house, for the reason @bburd explained above. The first floor is over an unheated basement, so the floor is cold. Meanwhile the second floor is being heated by warm air rising from the first floor, and its ceiling is insulated (blown cellulose in the attic). So we have a differential of about 3 degrees between first and second floors, despite having a smart thermostat on the first floor with a remote sensor on the second floor. The thermostat averages the temperature on the first and second floor and uses the average to control the temperature. But it can't correct the differential, it can only control the average.

So as other people have said, you have to make your own adjustments to radiate less heat into the second floor.

PrevailPuzzle · January 31

Thanks for the first responses. Switching to variable valves upstairs seems a cheap and easy thing to try which I will do this weekend.

It getting main vents installed likely to help?

Another option - we have Ecobee thermostat and could get an extra sensor to put upstairs and use that as the thermostat overnight.

Interestingly even when it's this cold the boiler is typically running 15-17 mins per hr and 5-6hrs per day. (It's an old house but at some point a previous owner added insulation under the siding and double glazed windows).

I am still struggling to understand where the "end" of the main is and where the main vent would go. It seems we don't have one so maybe I just need to call a pro to get one installed. Should they go in the two circled locations?

pecmsg · January 31

Change the vents

or

Cover the radiators

jesmed1 · January 31

@PrevailPuzzle said "Another option - we have Ecobee thermostat and could get an extra sensor to put upstairs and use that as the thermostat overnight."

Yes. We have an ecobee installed in the first floor dining room downstairs, with a remote sensor on the second floor. You can choose which devices (thermostat, remote sensor, or both) "participate" in regulating the temperature during the different periods of the day (away, home, sleep). In our case, we keep both devices "participating" 24/7. But in your case, you could set it up with only the remote sensor "participating" during the sleep period. Then the ecobee will regulate based only on the remote sensor temp.

dabrakeman · January 31

The Ecobee also has choice of either a +/-1deg or +/-0.5deg swing. As @Jamie was saying you can go to the smaller swing if you are currently using the larger one and this will shorten cycles and make the % radiator fill balance more like it is during more temperate weather. These are assignable to individual programmed comfort settings in your daily program.

I have adjustable vents on virtually all of my radiators and this is one of the many reasons.

PrevailPuzzle · January 31

I have changed the vents and put varis upstairs currently set to 3 (of 8) and put the Gorton 6's downstairs. So I will see how things go and adjust as needed.

I am surprised there wasn't a resounding call to get a main vent installed based on what I'd read.

Jamie Hall · February 1

One problem at a time, @PrevailPuzzle !

Too Hot Upstairs When Cold Outside

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