Frozen pipes with hot water radiators

JRod4578

Hi all, I apologize in advance for any confusion in my post.

My question is if I shut off a hot water radiator, is there a danger of the pipes freezing? I'm not sure of what the configuration is but the radiator in the room looks similar to the ones in this picture.


That is if the radiator is shut off to keep the hot water out of it, is there water still inside the radiator that might freeze if the room gets to a sufficiently cold temperature and/or pressure? From the diagram I posted above I would think all of the water would drain from the radiator by gravity but the pipes leading to the radiator would still contain the water sent from the boiler and the supply pipes to the radiator built into the floor and/or walls would not be in danger of freezing. I would guess these would not be exposed to uninsulated outer walls on principle. But I am unsure and I cannot remove the floorboards to check if there is piping near the (insulated) cold outer wall behind the radiator. Coming from the radiator there are only two pipes exactly as shown in the diagram above with one valve to shut off the radiator. For each room in the building the radiators inside each room can be shut on or off which suggests each radiator or some radiators have individual supply and drain piping. If the supply pipes retain water from the boiler and the radiator and drain pipes completely return their colder water I would imagine there is no danger of frozen pipes in shutting off the radiator. Do you think this is correct and is there a way to determine if water remains in the radiator?

bburd

The radiators in a hot water heating system should always be completely filled with water. They do not drain down between heating cycles.

Radiator shutoff valves for hot water systems are available with a hole drilled in the valve disc to allow a small amount of circulation when the valve is off, which is usually enough to keep the pipes from freezing depending on their exposure. 

JRod4578

Thanks Bburd. I guess I should check the radiator temperature when off with a thermometer to see if it is in danger of freezing. I'm unsure if the shut off valve has a hole in it to allow continuous circulation or if it completely blocks the flow of the hot water. When I shut off the radiator when it is hot there is always a small whining noise and a bit of resistance which is to be expected. But if the valve lets some water through all the times there is no danger of the pipes of the radiator or leading to the radiator freezing when it is off, right?

bburd

The risk of freezing would be far less if there is some water circulation with the valve turned off; but I cannot say it’s zero. That depends on how exposed the radiator and its pipes are to outside temperatures. 

If the pipes are not inside an exterior wall, and the room would be kept well above freezing by the heat from surrounding rooms, then I wouldn’t worry about it.

If the pipes do run inside an exterior wall I would not shut off that radiator; I would wrap it in blankets.

PC7060

JRod4578 said:

From the diagram I posted above I would think all of the water would drain from the radiator by gravity but the pipes leading to the radiator would still contain the water sent from the boiler and the supply pipes to the radiator built into the floor and/or walls would not be in danger of freezing.

 I would guess these would not be exposed to uninsulated outer walls on principle. But I am unsure and I cannot remove the floorboards to check if there is piping near the (insulated) cold outer wall behind the radiator. 

as @bburd said, turning off the valves will have no effect on the water inside of the lines other than reducing the flow.

And it is very likely that the supply lines run in the exterior walls. I have a house built in 1928 and all of the supply lines for the bedroom radiators are in exterior walls. Prior to 1990 when rockwool insulation was blown into wall by previous owner any radiator that was shut down was likely to freeze. 

Why are you wanting to shut down flow? To save money from heating unused room?

JUGHNE

When you shut the valve off does the stem go down and rise up when you open?
If it just rotates maybe 1/2 or 1 turn, those valves usually had a small hole to pass some water.
If you do the blanket cover job then most of the heat would go down the return pipe.
Or if not all the air is bled out of the radiator, then water would only pass along the bottom of the rad, this would shed less heat into that room, provided the pipes are both connected on the bottom of the rads.

MrScott

Wondering what you are trying to accomplish by shutting the boiler off, and for how long you intend to have it off.  If there is other plumbing, it will also be subject to freezing with the heat off.

JRod4578

JUGHNE said:

When you shut the valve off does the stem go down and rise up when you open?
If it just rotates maybe 1/2 or 1 turn, those valves usually had a small hole to pass some water.

The knob turns I think less than one full turn between on and off. It does not move up or down at all. From what you described it could be a type that allows water through even when the hot water supply is supposed to be off. I'll see if I can post a pic of the control.

JUGHNE said:

Or if not all the air is bled out of the radiator, then water would only pass along the bottom of the rad, this would shed less heat into that room, provided the pipes are both connected on the bottom of the rads.

I don't fully understand the bleeding of a radiator so I'll have to learn more about that. The top is very hot as is the bottom.

JRod4578

PC7060 said:

Why are you wanting to shut down flow? To save money from heating unused room?

MrScott said:

Wondering what you are trying to accomplish by shutting the boiler off, and for how long you intend to have it off.  If there is other plumbing, it will also be subject to freezing with the heat off.

The room gets stifling with the radiator turned on. It's very small and has little air exchange. I usually turn the radiator on only for fear of the pipes freezing when it gets too cold. It's primarily a comfort thing. If water is always in the radiator this seems a precautinary principle to follow. There is no other plumbing in the room but I can't be sure where the pipes are without doing some investigating.

This might be off topic but I have also wondered how the other rooms affect the whole house heating. Is it better to shut off some of the radiators or to leave them all on so that heat is distributed more evenly throughtout the house? For example on the first floor the rooms are all open to each other so only one large radiator is usually on and the ones in the other rooms are shut off so I don't worry about them freezing with the good air flow between rooms. In the room upstairs with the radiator in the question the door is usually kept shut so the room becomes very hot. Even with the door open there is little air flow to the other rooms. It's one of those open the windows in winter temptations to lower the temperature.

bburd

The thermostat is on the first floor, correct?

So your heating system is trying to satisfy the thermostat while only one of several nearby radiators is turned on. That will make the heating cycle longer. It will also cause (or worsen) short cycling of the burner, which will increase fuel consumption and shorten the equipment’s life.

That is why the bedroom with the closed door is overheating.

Try turning on the other radiators on the first floor. Keeping them off is preventing your heating system from distributing the heat efficiently. If that is effectively one large space,  it will be more comfortable; your upstairs overheating problem will probably go away; and your fuel bill will probably drop.

JUGHNE

What temp comes out of your boiler?
Is it a cast iron boiler?

JRod4578

bburd said:

The thermostat is on the first floor, correct?

So your heating system is trying to satisfy the thermostat while only one of several nearby radiators is turned on. That will make the heating cycle longer. It will also cause (or worsen) short cycling of the burner, which will increase fuel consumption and shorten the equipment’s life.

Yes, the thermostat is in the first floor in the main room with the large radiator that is never shut off. I'm not sure I understand the heating cycle part.

bburd said:

That is why the bedroom with the closed door is overheating.

Try turning on the other radiators on the first floor. Keeping them off is preventing your heating system from distributing the heat efficiently. If that is effectively one large space,  it will be more comfortable; your upstairs overheating problem will probably go away; and your fuel bill will probably drop.

I can suggest turning on the radiators but unfortunately as far as the context goes this is for my parents house. They're satisfied as long as they have heat and not too worried about the efficiency or equipment life. They're concerned about the bill of course but I don't think they're eager to replace the furnace as that would also cost them.

JUGHNE said:

What temp comes out of your boiler?
Is it a cast iron boiler?

I'm not sure what temperature it is or what material it is. I'll have to check it. It's an oil burning furnace that might be original to the house which was built in the 1950's.

bburd

@JRod4578, you wrote: “ Yes, the thermostat is in the first floor in the main room with the large radiator that is never shut off. I'm not sure I understand the heating cycle part.”

If that first floor is effectively one large space and some of the radiators are turned off, the circulator pump must run longer to deliver enough heat to that space to satisfy the thermostat. The burner will turn on and off to maintain system water temperature while this is happening. 

Turning off some radiators reduces the ability of the heating system to deliver the heat from the fuel into the house. In an isolated room with the door closed, this will save fuel. In an area with a thermostat, more fuel will be burned.

With all of the radiators turned on, the space will come up to temperature more quickly and the heating system will shut down. The space will also be more comfortable and less drafty. In addition, the upstairs rooms will be less likely to overheat.

JRod4578

bburd said:

If that first floor is effectively one large space and some of the radiators are turned off, the circulator pump must run longer to deliver enough heat to that space to satisfy the thermostat. The burner will turn on and off to maintain system water temperature while this is happening.
Turning off some radiators reduces the ability of the heating system to deliver the heat from the fuel into the house.

Ah thanks, that makes sense.

bburd said:

In an isolated room with the door closed, this will save fuel. In an area with a thermostat, more fuel will be burned.

With all of the radiators turned on, the space will come up to temperature more quickly and the heating system will shut down. The space will also be more comfortable and less drafty. In addition, the upstairs rooms will be less likely to overheat.

If the radiator is on in such a small room with door closed and all or most of the other radiators are on, the temperature in all radiators will be evened out, right? But if the radiator in that small, isolated room is off, it will contribute to the uneven heating.

I guess they are turning the radiators off to affect temperature in certain rooms only as was my main question to shut off the radiator to prevent overheating. That said if we wanted to leave the radiator in the isolated room on only enough to keep the pipes from freezing the only way to do this would be to change the set temperature on the thermostat for the whole house?

If I understand this right, if we put a radiator with a smaller surface area in a room it would have the same effect as turning the radiator off since the other radiators in the house would have to supply more heat to the whole house. This would result in the furnace running in more heating cycles and more pumping of hot water, and higher fuel consumption and fuel costs, right?

Jamie Hall

The fuel consumption -- barring the inefficiency of cycling and so on -- is determined almost entirely by how warm you keep the structure, how the structure is insulated, and how cold it is outside. In short, the building heat loss.

With hot water heat (or two pipe steam) you can always turn the valve down to reduce the heat from a radiator. I myself wouldn't turn it down all the way -- particularly if the radiator or its pipes are on an outside wall -- but you certainly can turn it down to reduce the heat output. You don't have to change the set temperature of the rest of the house.

If the doors to the various cooler rooms are closed, that may save some fuel and also won't affect the rest of the house.

I would have all the radiators in the main space on, and set the thermostat for that space to what you want in terms of comfort. Then you can reduce the heat in other rooms as you like, by turning those radiators down.

JRod4578

Jamie Hall said:

With hot water heat (or two pipe steam) you can always turn the valve down to reduce the heat from a radiator. I myself wouldn't turn it down all the way -- particularly if the radiator or its pipes are on an outside wall -- but you certainly can turn it down to reduce the heat output. You don't have to change the set temperature of the rest of the house.

Does turning the valve only partially on wear it out more? I am hesitant to leave it partially open and don't want to switch it too often to keep it from wearing out. Would it help if I take a pic of it?

As far as the other rooms of the house go they are usually comfortable even with the other radiators off. I would like to see them turned on most of the time. Actually I think they're off because we've got some furniture blocking the radiators. Otherwise I don't know why they keep them off on the main level.

Jamie Hall

The valves will be OK turned part way open. In fact, they are designed to be used that way, and for just the things you want.

Now if you are constantly turning them on and off and fiddling with them, like a sink faucet, the packing will wear -- but I dare say that's not what you are going to do.

JRod4578

Jamie Hall said:

The valves will be OK turned part way open. In fact, they are designed to be used that way, and for just the things you want.

Ok, thanks. I will try turning the valve down but leaving it on in the room.

Jamie Hall said:

Now if you are constantly turning them on and off and fiddling with them, like a sink faucet, the packing will wear -- but I dare say that's not what you are going to do.

Not too much fiddling - I usually turn it on and off only a few days when it gets especially cold. If it stays warm enough to prevent freezing with the valve partially open I will be set. I should really get a thermometer to check the radiator temperature. I have one in the room but that's only for the air temperature.

PC7060

@JRod4578 - Just curious why you don't set rads to comfortable level for that rooms and let it alone. Trying to control the heating bills??

JRod4578

PC7060 said:

@JRod4578 - Just curious why you don't set rads to comfortable level for that rooms and let it alone. Trying to control the heating bills??

It's usually comfortable enough without having the radiator on at all in that room even in the winter. But I was concerned the radiator pipes might freeze when it gets too cold outside.