# Boosting the output of a central heating radiator

The indoor temperature is hovering around 20C on a regular day, I'd like to kick it up to 24C and not have to use electric radiators to supplement the heating.

In this apartment there are old soviet style radiators that look like this:

They are cast iron, burn your hand kind of hot, entirely non-adjustable and from the looks of it terribly inefficient at spreading the heat from the central heating system into the room.

This only has the potential to work because the central heating fluid going out of the radiator is basically just as hot as it is coming in. So I thought, why not extract more heat from it? I could increase the surface area of the radiators or add some airflow to get more!

For increasing the surface area, I did a test where I used aluminium tape. I cut 5x5cm squares and just stuck them to the radiator with around 1cm strip from one side connected to the radiator and the rest hanging in the air. So far I'm not super impressed, the heat does transfer but the part of the tape that's hanging in the air only feels warm and not piping hot like the radiator. Perhaps the tape is too thin to conduct a meaningful amount of heat before it disperses into the air. Perhaps the glue is inhibiting it too much.

By my calculations, I could likely use up the entire 50m roll of tape on one radiator and increase its surface area from the current ~2.5m2 to 5m2 but I'm not sure it would do much given the result of my small scale test.

For adding airflow, I pointed a typical 40w desk fan at minimum speed at a radiator and closed the door to the room. The room did go from 19C to 20C over the course of an hour or so. I'd consider that a success but I'm looking for more than a 1 degree difference.

In actuality, I would like it to be quiet and look decent so my plan is to put a sheet metal enclosure around the radiator and fill the bottom with around 8 120mm case fans running on 5v. By my calculation, that should give roughly the same airflow as my 40w desk fan did at minimum speed. I'm hoping the enclosure will increase the efficiency of the airflow.

I realize this is a bit fuzzy kind of a question but I was hoping that there is somebody here who has done a similar thing before. Are there better methods of getting more heat out of a radiator like this? Any tips for my current plans?

I've already taken some steps to even get to 20C. So far I put insulating plastic on both sides of all my windows, added insulating strips around all external doors and windows, moved furniture against external walls, added heat shielding behind all the radiators and sealed a bunch of little cracks around where the walls meet the floor and the ceiling.

• I'm surprised websearch hasn't found you tips like putting some insulation/reflection behind the radiator so you don't waste energy heating the wall... Commented Feb 23, 2023 at 20:29
• Oh, I did not mention but I've already taken some steps to even get to 20C. So far I put insulating plastic on both sides of all my windows, added insulating strips around all external doors and windows, moved furniture against external walls, added heat shielding behind all the radiators and sealed a bunch of little cracks around where the walls meet the floor and the ceiling. Commented Feb 23, 2023 at 20:34
• Have you tried to go to a black radiator and or add another one in the room? The light colored paint on it does not help.
– Gil
Commented Feb 23, 2023 at 21:13
• I was in a similar boat last winter. Our upstairs heat pump needed replacement (downstairs furnace was fine), but I didn't want to deal with it in the cold season because I thought contractors would jack up rates, so I kept the master BR warm with a plug-in oil heater. I rigged up a computer fan to provide a little airflow to basically push the warm are away from the heater. I didn't really do any comparisons of fan vs. no fan. Commented Feb 24, 2023 at 13:21

There are lots of discussions on this topic to be found, here and elsewhere. Here's a summary of the more useful tips I recall as well as some insight from experience.

• Airflow is good, but only to a point. Drafts undermine comfort much more than the few degrees you seek to gain. Therefore, don't use fans.
• Instead, use a shroud to enhance convection. Seek to establish a chimney effect, where warmed air rises out of the compartment, creating low pressure below, and drawing more air in. This is effective at moving air without causing a drafty feel.
• Layers of paint act as an insulator. I'm not sure if you can go this far, but consider chemically stripping it. Bare metal will perform much better.
• An insulating and radiating layer behind the radiator would help conserve energy. A wall that's heated to a higher degree loses heat to the exterior more readily. A reflector directs that heat back into the room, warming line-of-sight surfaces and the air. Try foil on foamboard or corrugated board. It doesn't need to be fancy or expensive.
• In this century we use air flow (fans) (draft) to heat/cool Commented Feb 23, 2023 at 21:41
• Not across radiators we don't. Even you ultra-modern folk would find a fan chilly on a winter day. Forced-air systems aren't too bad because the output is 120 degrees or higher. That wouldn't be the case here. Nice snark, though. Commented Feb 23, 2023 at 21:42
• Now, now, @isherwood, those of us who live in this century are more than happy to burn electricity to move air when simple, old-fashioned physics will do the job. `</snark>` Commented Feb 24, 2023 at 15:09

There are a lot of factors that will impact how warm a room can get from whatever heating source is available to it and you may just be expecting too much from the system. How cold is it outside? How much insulation is there in your walls? Do you have single-pane or double-pane windows? If double-pane, do they have any sort of gas in them to improve their insulation ability? Are you on the top floor, loosing heat out through an uninsulated or poorly insulated roof? Is this room on a corner that faces the cold, prevailing winds?

Improving insulation, if that's a possibility for you, would likely be your best bet. However that may not be possible, so...

I would attach fins to the piping itself. This will help draw more heat from the pipes and give it extra surface area to flow into the room. This is what electric or hydronic baseboard heaters do, and you'd just be emulating that. It wouldn't be as efficient as if it were designed that way, but it may help.

You will probably have to scrape paint off the piping to make your attachments more effective, and it won't be pretty, but it could help.