Storing Heat from a Radiator

[some bloke]

Hello all,

I suffer from having a very cold house - as it is rented, we cannot put insulation in or change the windows (single glazed!), so I am looking for non-permanent options to maximise the warmth we can get from it.

We have a log burner, and I have found that it is still kicking heat out long after the fire has died - due to the mass of cast iron which holds the heat.

Does anyone know whether it will work to stand a sheet of something dense, such as cast iron or ceramic (paving slab) in direct contact with the radiator, with a view to store the heat from it and slowly release it into the room - essentially functioning as a mass heater. Currently the heat is all produced quickly, rises to the roof and disperses, which is no use to us inside!

Am I on the right train of thought here? I know that having a towel on the radiator makes it less effective, but I'm not sure if having a mass on the face of the radiator will be beneficial or detrimental.

I will be supporting the mass by the floor, for anyone worrying about me ripping the radiator off the wall!

Cheers,

 

[Rive]

change the windows (single glazed!)

A thin sheet of transparent plastic (thicker than just a foil) would help a lot. You should use a glue which you can remove easily, without any (!) traces.

Am I on the right train of thought here?

My humble opinion is that not likely. Higher temperature will require more wood to be burned: the mass can help only by releasing the heat slower, so you can have short, intensive bursts instead of continuously fed fire. With other words, it makes a better average.

Is it an internal stove or something with a radiator&water circulation? It is not exactly clear.

I would try to improve the feeling first. Rugs & drapes, if possible. Try to check the air circulation if there are leaks you can patch with some textile.
(Be careful: internal stoves requires air, so you can patch only the excess holes). You can try to aim a fan on the radiator, that might help spreading the heat (stoves are not advised to be used this way).

 

[anorlunda]

A so-called thermal wall is a frequent feature in houses that have more heat source daytime than night. Stone is the primary heat storage medium.

I used to heat my house with a wood stove. It worked fine, but most nights I was unwilling to get out of bed to stoke the fire, so the fire went out. But the stove was close to a massive brick and stone fireplace, and the stone helped.

 

[berkeman]

as it is rented, we cannot put insulation in

Depending on how long you are going to live there, you might ask the landlord if it would be okay if you added insulation to the attic and left it behind when you are done renting the house. That's a win for the landlord (free insulation job), and it's not very expensive if you do the work yourself.

 

[phinds]

we cannot put insulation in or change the windows (single glazed!)

https://www.amazon.com/dp/B00002NCJI/?tag=pfamazon01-20

goes on easily, comes off less easily but not impossible

 

[russ_watters]

Am I on the right train of thought here?

I think you are. It's just I suspect you need a lot of mass to store enough heat to matter. And it won't be released as fast as the radiator heats it, or allow control. So it isn't a perfect solution unless you create a heat-storage-water-tank-radiator system.

I know that having a towel on the radiator makes it less effective...

That's because the towel insulates the radiator and blocks heat transfer. The boiler in such a case will throttle back to compensate. But your system is all-in one, in the room, and will not change its heat output by adding additional mass to absorb the heat.

...but I'm not sure if having a mass on the face of the radiator will be beneficial or detrimental.

My experience with wood stoves for heat is thin, but my recollection is they give off way more heat than needed and the usual problem is overheating and waste. Having something to absorb some of the heat would probabely be a net improvement when it is on.

 

[Ketch22]

Two immediate thoughts come to mind. One you are definitely on the right track to introduce some thermal mass. As noted earlier a thermal wall of some type is of great use. It will warm when it is cooler than the space it is in (which should be close proximity to the burner and flue). Often these take the form of a masonry or stone wall near the stove which also can be a fire preventive feature. Be careful as the more mass you have the greater the heat stored but also the more the structure must support.

The second is your comment of the heat rising from your "log burner." The heat does rise to the ceiling but is still present in the room unless you also have high ceilings which would make it unavailable. Are you speaking of this challenge or is it the one of the large amount of heat that goes up the flue? The burner (if it is a typical woodstove type) generates its airflow for combustion from the flow of heated air up the flue. When the stove is at proper operating temperature this can create significantly more airflow than is needed.

Even when the inlet air is regulated this can significantly reduce the burn time which also reduces the amount of heat input to your space while throwing large amounts of heat away "up the pipe." This is typically controlled with a damper in the flue which can easily double the burn time for the same amount of fuel. If you are trying to increase your heat input I would be curious if the flue is equipped with a damper and are you effective at using it. This is the quickest method to increase how much heat you utilize.

 

[Tom.G]

A friend who lives in heavy Snow Country is using another approach for the windows. He bought some 'insulation board' at the local building supply store. The stuff is Styrofoam (foamed plastic) coated on each side with metal foil. He cut pieces to fit in the window frames and puts them in at night. It is easy to cut with any mostly-sharp knife. Admittedly a slight nuisance each night and morning, but extremely effective.

If you decide to add some thermal mass:

• you can speed its heating by using a fan to blow the hot air on it.
• perhaps use hollow concrete blocks layed on their side for maximum surface area access
  - watch out for floor loading, 12 inch blocks weigh 80 pounds per cubic foot, bricks and rock are 120 - 150 pounds
  floors are strongest at the walls

Cheers,
Tom

 

[hmmm27]

Weatherstripping for the doors/windows. Also, if your roof has icicles, mentioning to the landlord that adding insulation to the attic will extend the life of the roof by a few years might win them over.

General assumption : you want thermal mass to buffer the heat for when you're sleeping or out.

A few years ago an ice storm knocked out the mains power for a few days : no furnace fan = no furnace, but the NG water heater was still operational. We kept a few rooms at 60F+ for the duration using buckets/saucepans of water. Noticeably humid, though. Very apocalyptic.

 

[jim hardy]

A friend who lives in heavy Snow Country is using another approach for the windows. He bought some 'insulation board' at the local building supply store. The stuff is Styrofoam (foamed plastic) coated on each side with metal foil. He cut pieces to fit in the window frames and puts them in at night. It is easy to cut with any mostly-sharp knife. Admittedly a slight nuisance each night and morning, but extremely effective

Excellent idea. Try the little adhesive backed Velcro buttons from any craft store for attachment.
Duct tape the edges to prevent little styrofoam balls from detaching.:.
I used 1" styrofoam on a metal door in Idaho , worked great and was immediately noticeable. I hung a thrift store quilt over it for aesthetics - the aluminum looks too "industrial" (but you might affix some MC Escher prints and call it Steampunk).

A few years ago an ice storm knocked out the mains power for a few days : no furnace fan = no furnace, but the NG water heater was still operational. We kept a few rooms at 60F+ for the duration using buckets/saucepans of water. Noticeably humid, though. Very apocalyptic

Yes, once is enough.. No furnace, no electric blanket, no coffee...
One of these

would sure be nice to have stashed away for "just in case"
they run on little propane cylinders

i think i'd get the adapter on right so i could run it for several days from the barbecue tank..

 

[johnbbahm]

You might try finding a 30 gallon barrel and filling it with rocks and water, and placing it in contact with the radiator.
(Perhaps do not seal the barrel) The mass of the rocks and water would warm up with the radiator,
but then take several hours to cool down after the source of the heat stops.
It may help flatten out your duty cycle.

 

[OmCheeto]

You might try finding a 30 gallon barrel and filling it with rocks and water, and placing it in contact with the radiator.
(Perhaps do not seal the barrel) The mass of the rocks and water would warm up with the radiator,
but then take several hours to cool down after the source of the heat stops.
It may help flatten out your duty cycle.

After some research and calculations, I don't think adding rocks to the barrel will add anything to the system, aside from weight.
Common rocks(basalt in my neighborhood) have only 63% of the volumetric heat capacity of water.
If the barrel is filled to the 26 gallon level with water, it will have a heat capacity of 400,000 Joules/°C, and weigh 100 kg.
With a 50/50 mix, by volume, it will have a heat capacity of 320,000 Joules/°C, and weigh 200 kg.

But I do like this idea. From further calculations, such a system could comfortably store 50% of my excess wood stove energy, when burning a 10 kg log for 21,600 seconds.