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Heat storage device for car cabin heater Answered

I want to increase the heat storage capacity of the existing car heater so that I can run the heater (just the fan and a liquid pump) while the engine is off and so I can have a warm car as soon as I start on a cold day. The current heat storage is the coolant circulating in the engine. I want to increase the capacity of that.
Instead of simply attaching a liquid reservoir to the heater circuit (to increase the coolant volume), I was considering using a picnic cooler (insulated) box with a coper tube coiled in it. The box would be filled with oil and paraffin. Paraffin melts ≈ 40° C  and I can take advantage of the latent heat of fusion when the paraffin changes phase. The oil is a medium to suspend the paraffin.
I need a recommendation of an electric 12 volt pump to circulate the fluid.
I request any other thoughts or criticisms.



1 year ago

approx heat/fusion 200 J/g

J=1 watt second

Car heater: 1500 watts.

Assuming 100% melt, how much volume needed to equal an elect car heater?

~10 liters?


Reply 1 year ago

somebody check my mathh.

Also. What is density o parafin? I was guessing a wee bit lighter than h2o.


1 year ago

the easy solution to the same problem: 12v elect heat.

But why go with easy?

Jack A Lopez

1 year ago

That word, "paraffin", it has two effs.

Why use oil and paraffin both? You say the oil "is a medium to suspend the paraffin", but I say oil makes it too complicated. Suspend paraffin in oil will keep it liquid, and mess with phase change magic.


Just use paraffin alone.

Another why: why use "12 volt pump to circulate the fluid" ?

Is there not coolant pump, already built into your car, pushing hot coolant through heater core plumbing,


for to warm the car's cabin?

Just put your picnic-box-full-of-paraffin plus copper-pipe-heat-exchanger, in place in cooling circuit where heater core used to go.

Also be advised: liquid paraffin is somewhat flammable.
Does not Wiki article for, "Paraffin wax", linked previously, have pictures of burning candles and such?


1 year ago

In my home country people tried heat exchangers and storage to quite some extend.

Even if no frost is involved the time something keeps warm enough to be of benefit highly depends on the volume in comparison to the "room size" in need of heating.
And if only heated through a heat exchanger when the engine is running the time runs from the moment the engine is turned off.

Let's say you want to warm up a small family car on a cold winters morning.
From experience I would say it takes at least 10 minutes to fell comfortable and another 5 to feel warm.
that is with a pre-heated engine.
To do the same with a storage system means it has to provide sufficient heat for at least 15minutes of operation, minus if the car engine can take over fast.
If the engine was shut off 14 hours before that than your storage needs to be well insulated and charged very hot.
If you need a cheap pump for testing then try one from an old washing machine.
Create your setup in the shed or garage and use a normal heater to get your mix to the temp you expect to reach from the engine running.
Let it run and circulate with the fan active and check for how long you get sufficiently warm air out of it.
Repeat the test after your usual off time (for the car engine) on a cold day.
You might get far less time than what you might think...

A diesel heater only uses a few ml of fuel for the time required to heat your car.
Bit on the costly side to put in but well worth it in very cold climates, especially if combine with the cooling system of the car to pre-heat the engine while you have breakfast.


1 year ago

I've been considering a similar concept for years. However, I don't understand the reason you are pumping the paraffin. I would consider that to be stationary while another fluid (air, oil, EGW/PGW) flows through channels embedded in it. Note that the low conductivity of phase change materials is a significant challenge to overcome.

BTW, my idea was mainly to extend the range of electric vehicles in cold weather climates. The second use would be for energy discharge in case of crash (safety for first responders). I haven't run the calcs yet but I assume the weight/volume of this idea might negate the benefits. Feel free to PM me with detailed questions.