> What is a Trombe Wall and how can you use one?

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What is a Trombe Wall and how can you use one?
Last updated 7:22 am, Wednesday 18th October 2023

Trombe Wall, what is it?

A Trombe wall simply put is a very thick, south-facing wall (or North facing wall if in the Southern Hemisphere), which is painted black and made of a material that absorbs a lot of heat (say concrete, stone or brick). A pane of glass or plastic glazing, installed a few inches in front of the wall, helps hold in the heat. The Trombe wall heats up slowly during the day. Then as the wall cools gradually during the night, it gives off its heat inside the building.

Trombe walls like this work via the basic greenhouse principle that heat from the Sun in the form of higher-energy ultraviolet radiation passes through glass largely unimpeded to heat up the material behind it. 

Trombe walls are a great 'passive' (as in no mechanical parts) way of providing heat to a room or space. plus they are completely silent in operation. They are often easily built from readily available materials, very reliable, and of course cheap to operate. Trombe walls can successfully contribute to reducing heating and cooling costs all year round if set up correctly. As a result they are one of the core techniques used in Passive Solar Architecture.

Trombe Walls have an extra benefit, in that the heat is radiated in the infra red, which is more penetrating and pleasant than the traditional convective forced air heating systems.

Trombe Wall, who invented them?

Trombe walls are named after the French inventor Felix Trombe, due to his work on them in the late 1950s.

Trombe Walls, how do they work?

Trombe WallWith reference to the diagram on the right. The simplest form of Trombe wall consists of a glass pane held against a wall with an air space behind it. Connecting this air space with the inner room are two vents, one at the top and one at the bottom of the air space. During the day the Sun heats first the air in this space, then the solid wall behind. Once the air is heated it rises and enters into the room, giving it additional heat. Also the rising air pulls in cooler air from the room below to then be heated. The real trick with this though, is that for sometime after the Sun goes down the now hot wall will still keep heating air and exchanging that heat into the room.

Though once the wall is cold you need to stop the cold of the outside interacting with the inside of the property, so a one way flap is used on the bottom vent to stop the cold coming back into the room and creating a cooling cycle with the room.

The great thing with a Trombe Wall, is if you have an existing solid wall in the right place, then it can be converted to a Trombe Wall by the addition of vents and external glazing - so this is great energy saving improvement to an existing building. Although remember the wall has to be solid, this won't work with double brick walls, they will require extensive modification.

Note: There is of course an assumption here that the wall is facing directly to the Sun and has good Solar access (i.e. no trees, building or structures that obstruct access to the Sun as it tracks across the sky).

So how do you stop the Trombe wall heating the room in Summer?

This is where the roof overhang comes in - if it is deep enough the higher Summer sun will be able to heat the glass. Although by doing this you a missing a cooling trick...  Basically if an opened vent to the outside is put at the top of the outer side of the air space and you only open that and close the top wall vent in Summer, you create a Solar Chimney that sucks air out of your house to the outside, giving you ventilation for free!

Trombe wall design, variations

There are several ways you can change or improve on the simple Trombe Wall design to suit your circumstances:
  • Use double glazing - basically this makes the solar collection of the wall a lot more efficient as more heat is trapped in the inner air space.
  • Use low-e glass - this is special glass which has a lower rate of heat transmission, similar in effect to double glazing. Although do check that you still get a usable level of solar transmission through it for your purposes; this could be a useful trade off if you find yourself loosing heat at night.
  • Forced fan - basically using a fan to drive air through the air space, this improves the rate of air exchange. Often controlled by a timer and a thermostat.
  • Dark colour - if you paint the inner wall black or a dark colour its heat gain potential will improve drastically.
  • Movable blinds - these are placed over the glass and used to limit solar gain and can help with reducing heat loss at night.
  • Tubes or water tanks as part of a combined solar hot water system.
  • Fish tanks used as a form of additional thermal mass.
  • Insulation - if the wall areas not behind the glass are insulated on the outside it avoids heat loss at night, improving the longevity of heat gain after dark.
  • Sunspace (conservatory) - in effect the glass area in front of the Trombe Wall is sloped to create a space with two surfaces, the Trombe Wall itself and the floor area in the Sunspace. They can heat spaces both through radiation and convection.
  • Half-height Trombe Wall - there is no requirement that a Trombe Wall must be full height; rather you can have a Trombe Wall be half height to allow light and direct solar gain into the adjacent living space. A half-height Trombe wall is a simple way to increase solar storage capacity in a passive solar home, whilst still allowing views of the winter Sun. Such half-height walls are usually constructed 4 to 6 inches (100-150 mm) from the inner window surface, such a gap allows blinds or curtains to be used to reduce heat loss on Winter nights and heat gain during the Summer.
  • Underfloor ventilation - the air flows through channels in a floor, which warms the floor and then the building. This also makes good use of the thermal mass of the floor to even out temperature changes. See Barra System .

Trombe Wall design challenges

  • Low Thermal Resistance: During period of low solar availability, heat is transferred from the inside to the outside.
  • Reverse thermal flow: Designs that lack controlled vent systems will experience reverse thermal flows during the Winter, night or non-sunny days. When the wall temperature is less than the interior, reverse air circulation from the upper vent to the lower vent reduces the interior room temperature. The remedy is automated or one way-ventilation systems that prevent the reverse flow.
  • Uncertainty of heat transfer due to unpredictable air movement.
  • The convection process is influenced by the channel width and inlet or outlet dimensions, causing variation in overall heating performance
  • Low aesthetic value.

Trombe wall construction guidelines to remember

  • The space between the thermal mass wall and the glass should be a minimum of 4 inches;
  • Vents used in a thermal mass wall must be closed at night;
  • Trombe wall thickness should be about 10-14 inches for brick, 12-18 for concrete, 8-12” for adobe or other earth material and at least 6 inches for water. For a 16 inch thick brick wall it will take about 8 to 10 hours for the heat to reach the interior wall surface.

Trombe Walls alternative uses

Trombe walls can also be used to create ventilation in sub floor spaces. If you have the height in the sub floor space set it up so that the top vent goes into the sub floor space and that the bottom is open to the outside (instead of the inside). In effect you have made a solar chimney feeding into the sub floor space - this will raise the average temperature in the sub floor area that should lower the relative humidity. Also you can use a basic Trombe wall as a solar chimney to "suck" air out of a space, basically bottom goes into the sub floor space and the top vent is outside. These are not true Trombe walls, but essentially use the same principals to do the work for you.

We hope this article has given you a good insight into how Trombe Walls can be useful and save you money in keeping your house comfortable. Please look at the articles below for additional information related to Trombe Walls.

Trombe Wall Related Articles


BTW if you are reading this page and know of any equations or formula that can be used to work out how to dimension/design a Trombe Wall - please let us know via the contact page - thanks!

Related Tags: trombe wall, solar heating, solar cooling, solar gain, passive solar, solar house, solar wall

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What is a Trombe Wall and how can you use one?
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Comments left

  • Andy Zaugg said:

    You mention the use of low-e glass for a Trombe wall. Do you have data? Even with the latest, high-transmittance versions of this glazing system, the SHGC drops so far that I am not at all clear that this is a good idea. Any references to projects would be helpful. If not, This may not be good advice to publish. Thanks, Andy

    ON Tue, 23 Mar 10, 3:29pm probably from United States  Reply to this comment

  • Rod Hyde said:

    Question: Living in the southern hemisphere (Australia) the sun does not shine from the South. I rises in the East and sets in the west. Does this mean the the Trombe wall would be best located on the North side?

    ON Mon, 10 May 10, 12:07pm probably from Australia  Reply to this comment

    • Eco Guy said:

      Yes, in the Southern Hemisphere the solar 'character' of the North and South walls swap when compared to the Northern Hemisphere - so yes you would put a Trombe wall to the North.

      ON Tue, 11 May 10, 5:28am probably from Australia  Reply to this comment

    • Gary Little said:


      ON Fri, 26 May 17, 6:25pm probably from Australia  Reply to this comment

  • Samar said:

    Can a Trombe wall be built on the Sill (resting wall of the window) below a window facing south? The height of the sill (resting wall) is 1 meter approximately.

    ON Thu, 13 May 10, 6:13am probably from India  Reply to this comment

    • Eco Guy said:

      In principal yes; but a Trombe wall is meant to act as 'time delayed' heating - so you will only get the area under your window acting as a storage heater that will give heat into the room beyond - assuming that the wall is brick of course. This also assumes the night thermal loss through the window will be less than that gained through the Trombe Wall. if I was you I would look for a full height wall to the side of the window to use instead, that way you can use curtains to cut out the night time heat loss by the window.

      ON Thu, 13 May 10, 10:48am probably from Australia  Reply to this comment

      • Samar_thapa2005@yahoo.co.in said:

        Dear Keith, Thank You for your mind opening suggestion. Infact the side of the window can be made a trombe wall. However, in my case, this is school building working only during day time, so neglecting the thermal storage required for night time use, I wish this can be done to heat the room air passing naturally through the vents on the Trombe wall. Further, since the purpose is just for heating the air during day, only a single glaze would work I presume? Thank you

        ON Fri, 14 May 10, 7:10am probably from India  Reply to this comment

        • Eco Guy said:

          Hi Samar, for what you want I'd suggest going under the window and painting the wall surface black. if you have a thermometer check the inside and outside temperatures first thing in the morning when the sun strikes where the Trombe wall would be - if the inside is warmer have the lower vent feed from the inside, if the outside is warmer on average, feed from the outside. This way you don't waste heat. Also try to cut down drafts in the room itself, especially at the higher levels, this encourages the heat to stay inside the room.

          I take it you must be in a colder region of India then is perhaps the norm?

          ON Fri, 14 May 10, 11:24pm probably from Australia  Reply to this comment

          • Samar said:

            Hi Keith, Thank you for the suggestion. For, what your suggestion may be right especially for the first few hours. Then is there any possibility of having a (or two dampers) opening in both the direction( outside and inside)? Yeah.. I am from Darjeeling in India.

            With regards, samar

            ON Sun, 16 May 10, 10:38am probably from India  Reply to this comment

            • Eco Guy said:

              You could certainly put in dampers, but if you add them in you need to be very careful to make sure they are air tight. Think of them as doors, in that they will need a lip to seal against with a 'lock' (usually a piece of wood that turns to hold shut) and make them sturdy enough not to warp. You won't need to cover the whole width of the wall with vents, just vents that are roughly in cutout area the least cross sectional area of the air behind the glass, as that will limit the flow possible.

              ON Mon, 17 May 10, 12:02am probably from Australia  Reply to this comment

  • Pete Lovett said:

    I'm thinking of using a trombe wall as the common wall between the house and an attached (north facing - I'm in Australia) greenhouse to transfer heat into the house. Will the wall work with relatively diffuse sun coming through the greenhouse roof or does the sunlight have to be direct?

    ON Thu, 24 Jun 10, 2:30pm probably from Australia  Reply to this comment

    • Eco Guy said:

      I'm assuming you are looking to provide heating in winter.. If so first check how warm the greenhouse gets and how warm the wall you intend use gets as well. Also check throughout the day to see how much actual sunlight makes it onto the wall. You will get some energy transfer loss from the greenhouse glass, but that would be minor, the fact the greenhouse is also acting as another layer of insulation should make up for that. Although do make sure when doing the Trombe wall in this situation that it is only cycling air from the room - the greenhouse air will quite likely be rather humid; which is not good for you and makes you feel cooler.

      ON Fri, 25 Jun 10, 12:25am probably from Australia  Reply to this comment

      • Vision said:

        Actually the humid airwill make it feel warmer and using a green house is a great idea. use a shadehouse on the south side of the house. in summer open a vent to the outside of the greenhouse and the air will be cooled by the shadehouse and then drawn through the house.

        ON Sat, 10 Sep 11, 5:59am probably from Australia  Reply to this comment

  • Bahaa Al Hariri said:


    ON Tue, 2 Nov 10, 7:10pm probably from Pakistan  Reply to this comment

  • Trevor Boughen said:

    presumably this could also be linked to a heat recovery system to provide heat and power.

    ON Thu, 3 Feb 11, 10:56am probably from United Kingdom  Reply to this comment

  • Scott Shackleton said:

    I'm looking for a US source for automatic opening vents for the top and bottom of the trombe wall. I'm designing a cabin that will only be used weekends in the winter, but I want it to stay warm all the time. Nobody will be there to close vents at night to prevent the heat from reversing out of the cabin. Thanks for any help.

    ON Sat, 4 Jun 11, 7:04pm probably from United States  Reply to this comment

  • Gaurav Gupta said:

    this one treatment is nice but how can its managge for west facing wall in summer

    ON Mon, 26 Sep 11, 1:07am probably from Australia  Reply to this comment

    • Eco Guy said:

      A West facing wall will work, but not as well as a full Sun facing wall (i.e. North or South depending on which hemisphere you are in). Also with a West facing wall the geography and ground features (such as trees and other buildings) will play a large factor on whether it will work. A West facing wall should work if it has clear view to the Sun, you just won't get the full effect.

      ON Mon, 26 Sep 11, 1:48am probably from United States  Reply to this comment

  • Allen Sinclair said:

    I have a plastic enclosed 100 ft long greenhouse with the 100 ft facing South. Would a 4 ft high trombe wall be cost effective? Would appreciate suggestions re: venting structure, circulating fans, ideas to stop venting when wall begins to bring in cold air during night.

    ON Sat, 1 Oct 11, 2:31pm probably from United States  Reply to this comment

  • Bob in Ar said:

    Thx for this great explanation. I am planning a small, offgrid cabin for a 3 yr Buddhist retreat, NW Ark Ozarks. full time occupancy. needs to have a cistern for water catchment. would like to consider trombe wall design using mix of cinderblocks and pvc pipe, or maybe even PVC alone! PVC would hold non-potable water, could even gradually fill with graywater over season. am considering all passive solar technologies, may mix with a micro photovoltaic system for lighting and fans. because of meditative activity planned, all uses should be down-scaled: less water, less heat, less energy consumption. also looking for less complexity in activity and building design (you can see the challenge as I begin to think with complexity about this). summer is humid, winters can be cold but lots of winter sun, so a Trombe wall seems a great idea. any references for experience with Trombe walls in Arkansas or similar partly arid, partly cold, partly humid climate, and for use of water as Trombe wall, either active or passive? thx!

    ON Wed, 25 Jan 12, 3:23pm probably from United States  Reply to this comment

  • Carlos said:

    Can this same effect be accomplished with translucent metal building panels rather than glass?

    ON Thu, 23 Feb 12, 8:36pm probably from United States  Reply to this comment

    • Eco Guy said:

      all depends on the metal used and its specific heat transfer properties. Also on the surface of the metal and if its painted. Its not the light as such that is important its the heat (infrared) that gets into the bricks..

      ON Sun, 11 Mar 12, 10:52am probably from United States  Reply to this comment

  • Shraddha said:

    Thanks for this very useful information. A house I am designing in Rishikesh, India- the living room and master bedroom face the south. I am planning to have the bedroom wall as a trombe wall. The size of the wall is 7'9 long and 10'3 high. There is a yoga hall above the residence. 1. Can I have only the bedroom with the trombe wall. 2. What should the size of the vents inside the room and outside be?

    ON Wed, 28 Mar 12, 6:50am probably from India  Reply to this comment

    • Eco Guy said:

      Hi Shraddha, the vents do not need to be that large - think of the horizontal cross section area between the wall and the glass - that determines the absolute maximum air flow possible as you have no pressure fans 'driving' the air just the heat gain (i.e. making the vent areas in total on inlet and outlet bigger than that won't do anything). You can have the bedroom just have the trombe wall - but be sure of solar access.

      ON Wed, 28 Mar 12, 8:07am probably from Australia  Reply to this comment

  • Lj, said:

    Great article, thanks! Q. Any experiences re condensation inside the glass? i imagine it can be minimised in cold damp weather by closing all vents..? Am hoping to work a cob trombe wall into strawbale house, but have to control moisture.

    ON Sat, 14 Jul 12, 7:56am probably from Australia  Reply to this comment

  • Kent Gallaway said:

    in things to remember it says close the vents in the thermal wall at night they must be talking of vents to the outside as you want the heat to exchange at night for warmth.

    ON Tue, 12 Feb 13, 1:05pm probably from United States  Reply to this comment

  • Esra said:

    Hi , Im from europe,my question is gonna be different from the others. Im a student at universty and ı m working on a project about trombe wall. I need a catalog and it should imply the trombe wall capacity datas.But I couldnt find a supplier name on internet. How can I learn it or could u give me a few name please? thanks..

    ON Sat, 23 Nov 13, 9:45pm probably from Turkey  Reply to this comment

  • Jeff B said:

    In the above information it states the Thermal Wall should be "X" thickness for a particular thermal mass substance. Is this referring to the overall thickness of the wall or the thickness of that particular mass substance?

    ON Sat, 11 Oct 14, 10:56pm probably from United States  Reply to this comment

  • Steph said:

    Hello. Can you help me with the calculus regarding the dimension of the trombe wall? I work on something related to that and I don't know how to start properly. Thank you!

    ON Mon, 13 Oct 14, 8:39am probably from Denmark  Reply to this comment

  • Gordon said:

    Looking for some feedback.....I'm building a 6 metre x 3.5 metre hothouse in Tasmania...southern hemisphere that is. I have a north, east and west walls in glass windows (roof in laser light) and I am considering building a cob or straw bale or earthen or stone....southern wall. Could I build a glass wall (trombe style) inside the hothouse next to the southern wall (with gap) and have the bottom vent accessing air from outside into the gap and having the top vent opening from the gap into the hothouse....would this work for maintaining heat in the hothouse into the evening. Appreciate any advice you can provide...Regards Gordon

    ON Tue, 9 Aug 16, 11:32am probably from Australia  Reply to this comment

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