Radiator vents as riser vents?

Alow · February 2

Hi - amateur/homeowner here. Our building has five risers. Three of those risers have obvious venting at the top of the riser on the top floor. Two do not have obvious riser vents. Instead it seems the riser goes straight into the radiator.

Is that typical?

If so, what is the recommended venting strategy for these lines? Vent add if they were risers so they fill up at the same rate as the other lines?

Thanks!

Photos are of the top floor radiators and the riser directly below them

Alow · February 2

What kind of looks like an insulated riser on the first photo is just a facet of the wall lit more brightly

dabrakeman · February 2

What issues are you having?

Jamie Hall · February 2

Riser vents and radiator vents really do two different things. Riser vents are like main vents — only for the riser, of course. What they do is help steam get to the radiator quickly so it starts heating. Radiator vents, on the other hand, control how fast the steam can get into the radiator, and thus can (within limits) control how much heat the radiator will put out.

Now risers are often short and relatively small diameter, so venting them fast is often not required — so vents on the risers are often left off. But in tall buildings or buildings with long risers for some reason, they can be helpful.

Alow · February 4

Thanks y'all

I've got two issues:

1) heading imbalance or stratification. The top floor doesn't get warm enough.

The lower floors will heat up enough to turn off the thermostat before the top floor gets to desired temp. I am now using a smart thermostat with additional sensors, so I could let the to floor govern the calls for heat. But there can be a 5+ degree temp difference and the lower floors overheat.

My thinking is to get the top floor to fill first out at least at the same time, the system could run less. I am going to test trvs in two rooms prone to overheating.

2) I have water sputtering out of some air vents. These radiators are notably pitched the wrong direction. I'm hopeful re-pitching will solve it.

ethicalpaul · February 4

Pitching radiators won't help. The vents are possibly faulty, or your pressure is too high, or both.

Getting steam to fill all mains and risers before very much steam gets into radiators is a good goal.

Alow · February 5

Spitting isn't the right way to describe the street coming out of the vents. It's more like a stream from a little water gun.

Given I have radiators at the top of risers without any other venting is it best to put vents on them to try and match the other risers' vents? As in have them expel their volume of air in the same amount of time? Any risk to the radiators/vents of having larger vents? Whistling maybe?

Pressuretrol is set to about 1.5 less 1 on the differential. Could try a little lower

Thanks for your consideration!

Jamie Hall · February 5

Keep in mind in your mental image that riser vents (or main vents) and radiator vents have two different functions, and they don't usually match up well.

The purpose of riser or main vents is to get air out of the piping going to the radiator as fast as possible. They want to be large.

The purpose of the radiator vent is to let air out of the radiator at a controlled pace, and thus control the amount of heat relative to the maximum heat the radiator can produce. They should be sized for that — and are, therefore, usually if not always much smaller than a riser or main vent would be.

In the case of a short riser or runout, this may not make much difference — the volume of air in the pipe is relatively mall. Taller risers or longer runouts it can make quite a difference, and trying to get the air out of the pipe by using a fast vent on the radiator can mean losing control of the heat output of the radiator.

ethicalpaul · February 5

If you have steady water actually squirting out of a radiator vent, the radiator sounds likely to be partially full of water. There's no way I can think of that a vent would be shooting that much water otherwise.

The supply valve seat might have rusted and fallen, blocking the exit of water (or the valve might not be fully open).

Or you might have very bad carryover that is flooding boiler water all the way up to the top floor.

If you make the top floor radiators do all the venting for the risers then those radiators will get hot very early and the top floor will probably be overheated. It would be better to find someplace on the riser or where the supply valve is on those radiators to add a vent for the riser alone.

Pressuretrol is set to about 1.5 less 1 on the differential. Could try a little lower

Do you have a 0-3psi vent on your boiler to ensure it's not going higher? High pressure alone won't make your radiators fill with water but it is undesirable.

Radiator vents as riser vents?

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