(I'm not sure if this is the best place to discuss this... but here goes anyway... )

As part of my windscreen project I want to fit some form of demisting system. I know people have said that I won't need one - but I'd prefer to have it available.

I've looked at those CBS electric fans, and read some of the reviews, and decided that they aren't what I want (they're a bit bulky, there's not a lot of space, they consume a lot of power - nearly 15A each - and the general opinion is that they don't work very well).

The CBS heater & demist system that's plumbed into the engine's cooling system is just too expensive - it'd be around £200 once I'd bought all the bits needed.

So - what's the alternative? Passenger heating is not required (I've managed so far) so a Polo heater might be OTT (and probably a bit bulky).

Has anyone tried to make their own? I was thinking of a small-ish fan, a home-made heat exchanger matrix, a few water pipes and a bit of duct work. I'm not afraid of the work involved, but it would be nice to know that it has a chance of working if I did make one.

All bright ideas and opinions gratefully received!

I don't really have an answer but I'm intrested, I hope to build a car with a screen and a hood so I can use it in the rain.

I would have thought the pluming it into the engine heating stuff would be easiest and £200 doesn't sound like alot of money for the result. Personally I'd go with the polo heater option for the luxury of cabin heat.

Have a word with your local friendly radiator specialist , they may have a matrix that's suitable .A heater box should be difficult with a couple of outlet to some demister ventsand a fan should be easy possible an MG Midget ? Reliant Robin heater may be suitable if you can find one? Did you sort out a water outlet when you made your inlet manifold?

as the previous post buy a small matrix make your own box, you could consider using a pc fan to draw the air through a pipe I have used hoover pipe previously on my Austin a35 found it to be more manageable than the plastice piping and realy lo cost as I got if from a Knackered dyson

Macspeedy used a Sierra one and just made a box out of ali for it.
U2u him for the details

12volt ceramic heater? You could hide it away behind the dash and make some ducting - link and it's only a tenner so if it doesn't work you've not lost a lot!

Wyn

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Originally posted by rusty nuts
Reliant Robin heater may be suitable if you can find one?

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That's a thought - there's a good radiator place in Ipswich so I might have a word.

I've still got the original place to plumb in the heater, between the water pump and the inlet manifold - there's just a plain hose between the two at the moment, so that's easily sorted out.

My current thought is an aluminium box containing the matrix, 'snail' fan bolted on, and air outlets on top. This can be bolted to the passenger side of the firewall with the water pipes poking through to the engine side - this should reduce the risk of scalding if the hoses fail (as has happened to a few forum members, including a couple just the other day - very nasty).

As for the electric jobs - the one mentioned is 150W, so that's around 12A current. The average water-powered car heater is 4 or 5 KW, and that's only using waste engine heat, so there's no comparison (if you ignore the few Amps for the fan).

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Originally posted by rusty nuts
Have a word with your local friendly radiator specialist , they may have a matrix that's suitable .A heater box should be difficult with a couple of outlet to some demister ventsand a fan should be easy possible an MG Midget ? Reliant Robin heater may be suitable if you can find one? Did you sort out a water outlet when you made your inlet manifold?

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Originally posted by Dangle_kt

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Originally posted by rusty nuts
Reliant Robin heater may be suitable if you can find one?

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I'd leave it if I was you...crapist heater on the planet, or at least it was in both of mine...

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Unless you want the heater for heating as well - and I am guessing most of the heat disappears into the sky anyway - what about a heated screen instead? You can find the odd Caterham one for nto too much money.

I went from aeroscreen to full screen and have fitted a Caterham heated screen. It'w wired up, but I just need to wait for a cold morning to try out the screen

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Originally posted by speedyxjs

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Originally posted by Dangle_kt

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Originally posted by rusty nuts
Reliant Robin heater may be suitable if you can find one?

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I'd leave it if I was you...crapist heater on the planet, or at least it was in both of mine...

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You have obviously never used (more like tried to use) the heater from an mg midget. You would be better off with a passenger breathing on you!

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I stripped down the mx5 and mondeo heater boxes. the 'radiator' part in the mx5 is actually only about 8"*6"*1.25", and the mondeo one is only slightly larger. Quite difficult to get out of the car usually, but only £2 from your local scrappy! I plan to use a couple of 12V PC style fans and some aly duct

Regards
Hugh

I'm using an oil cooler. PC fans are rubbish, they hardly flow and cfm.

Centrigual fans are much better as they'll cope better with back-pressure than axial fans.

Just out of intrest, does anyone make a windscreen with all the ancillaries atatched that could be bolter on and plugged in as a unit?

Modyfied Hairdryer???

I have been wondering if air ducted from around the exhaust would be more efficient.

The exhaust gets hot before the water system does.

Cheers
Paul G

I think that an old-style VW used to do that - Kamffwagen (or some such name).

I'd be concerned about exhaust leaks - but in an open top car that's less of an issue! Apart from that, I'd guess that you'd have to blow cold air into the heat exchanger, rather than suck hot air out...

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Originally posted by 907
I have been wondering if air ducted from around the exhaust would be more efficient.

The exhaust gets hot before the water system does.

Cheers
Paul G

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How about this one then?
Ebay linky

That looks ideal - apart from the price!

What about a VW polo heater.
Small, cheap and proven.

See this thread
http://www.locostbuilders.co.uk/viewthread.php?tid=21377

and ayoungman's photo archive for pictures of the bare heater.

Second heated screen. Wire it in with a timer relay from CBS and bingo.

But where would you get a heated screen made to measure?

I'm getting fed up with this windscreen project!

Fitting the windscreen is going OK, doing the wipers and screenwash should be fine, and I have no worries about the extra switches and wiring.

However, I had a good look under the scuttle over the weekend - and if I want to fit any sort of fan-driven water-powered heater for demist then I'm going to have to move a load of wiring, relays and my Megajolt unit. This work would involve a LOT of rewiring.

The CBS electric units are actually quite bulky and will get in the way.

In all honesty, do I really NEED demist (I've done SVA)? Would I be OK with a regular dose of Rain-X Anti-Fog instead?

You could get your self a wiping pad and just wipe it clear when you get in and when it needs it but its dangerous, do you really want to risk your life?

I was under the impression that if you clear a screen and then leave the windows open it wouldn't mist up again because it would be the same temp both sides and the water vapour would not be trapped. All said, I'd want a demister of some sort.

http://shop.ebay.com/?_from=R40&_trksid=p3907.m38.l1313&_nkw=12v+hair+dryer&_sacat=See-All-Categories

This one is 360 Watts.
Pricier though.
http://www.1-800-espresso.com/hair-dryer-12v.html


[Edited on 12/2/2009 by Angel Acevedo]

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Originally posted by morcus
You could get your self a wiping pad and just wipe it clear when you get in and when it needs it but its dangerous, do you really want to risk your life?

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Rain X might keep the mist off? Might be worth a try.

Can't see the need for demist in an open car - the air 'outside' is basically the same as the air 'inside'.
In a closed car or convertible with hood & sidescreens in place, the conditions differ on each side of the screen and it is the difference that can lead to misting - such as cold outside -> cold glass; breath/humid air inside leads to condensation.
Just my 2p.
I have a flyscreen on my MK but haven't yet been out in really cold weather...
I've run convertibles in the past (MG Midget and Dellow Mk VI) and don't recall misting with the hood down, whereas the Midget with hood up was susceptible to misting up.
John.

I was assuming you'd be using a roof aswell.

Maybe, in the dim and distant future, I might fit a 'Flintstones' hood. Until then, if it rains I'll just get out and put a cover on the car... Yes - I am that fair weather driver!

I don't plan to fit a proper hood - last time I tried to get in a seven-style car with a hood on I nearly gave myself a hernia - and and I've passed a lot of water under the bridge since that time!