Fan heaters on extension lead

[Thorfun]

I'm trying to put some heat in to our basement to dry it out and I have the following products to assist me.

 

2 x PTC 2kW heaters (https://www.screwfix.com/p/ptc-2000-freestanding-ptc-heater-2kw/9158t)

1 x dehumidifier (https://www.amazon.co.uk/gp/product/B0839M7VQT/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1)

1 x plug-in oil radiator (it's the wife's and I don't have any specification on it although I could climb down the ladder to the basement to find some details out if required!)

 

I'm wanting to run both 2kW heaters from the same extension cable (I have this https://www.mad4tools.com/masterplug-open-drum-40-metre-cable-extension-reel-240v-13a and this https://www.mad4tools.com/masterplug-open-drum-25-metre-cable-extension-reel-240v available to use) and the dehumidifier and radiator of the other extension cable.

 

I'm looking for some smart people to tell me if running the items off of those reels is an issue. I did A-level physics 30-odd years ago but spent more time mucking around that I did learning which would probably account for the 'E' grade I got. I do remember V=IR and P=IV but I'm not sure how that relates to running this stuff on a 13amp extension reel!

 

 

 

[markc]

2x 2kw heaters is over 16amp without any voltage drop over the long extension so 13amp is a definite no.

Running just one on a 40m lead is not good.

 

2x 2000w = 4000/240 is 16.66 amps

but on a 40m lead you may be down to 220v so current will be over 18amp

Edited January 18, 2022 by markc

[Thorfun]

5 minutes ago, markc said:

2x 2kw heaters is over 16amp without any voltage drop over the long extension so 13amp is a definite no.

Running just one on a 40m lead is not good.

 

2x 2000w = 4000/240 is 16.66 amps

but on a 40m lead you may be down to 220v so current will be over 18amp

oh dear. so I should stop using the one heater on the 40m lead then? I also have the dehumidifier running on the same 40m extension.

 

out of interest, how does the length of the extension make a difference? would the 25m extension be better?

 

I don't have electrics in the new house yet so I'm running everything off extension leads from the existing house.

[PeterW]

Drying out needs a dehumidifier not a fan heater - all you will do is increase humidity not remove it. 
 

Hire an industrial dehumidifier - £35/week and seal the basement up and let it do it’s job. 

[Thorfun]

1 minute ago, PeterW said:

Drying out needs a dehumidifier not a fan heater - all you will do is increase humidity not remove it. 
 

Hire an industrial dehumidifier - £35/week and seal the basement up and let it do it’s job. 

I looked at hiring an industrial dehumidifier and the specs on it just weren't very good! said it removed 20l/day and so I bought a dehumidifier that removed the same quantity and it is running but the trouble is I can't seal the basement very well as there's a massive void where the stairs will eventually go. 

 

so I thought heat the room and dehumidify it at the same time. I thought the heat would allow the air to hold more moisture that the dehumidifier could then remove.

[ProDave]

And if you are going to run a big load on an extension reel, then FULLY UNWIND the reel first or it will turn to a melted mass of plastic on the drum.

[Thorfun]

7 minutes ago, ProDave said:

And if you are going to run a big load on an extension reel, then FULLY UNWIND the reel first or it will turn to a melted mass of plastic on the drum.

yep. I have fully unwound it and run it out along and through the basement so it is unwound and not just off the reel in a heap on the floor!

[Temp]

45 minutes ago, Thorfun said:

I do remember V=IR and P=IV but I'm not sure how that relates to running this stuff on a 13amp extension reel!

 

Equations are correct.

 

P = IV

I = P/V

 

for a 2kW heater..

I = 2000/230

= 8.7A

 

Two of those easily over 16A as others have said.  The wire gauge of extension leads can vary a lot. +1 to what @ProDave said.

 

I cant see the power rating for the dehumidifier anywhere on Amazon. One person suggests 420W.

 

You should be OK if you put one 2kW heater and one 420W humidifier on each extension lead.  Ideally plug the extension leads into different rings or at least check if there is anything else that will take the ring over its rating (typically 30A). 

[Russell griffiths]

All I will say is ONLY run them when you are on site, I make sure every night that I have unplugged everything before I Leave, I had a heater running from an extension lead the other day and when I unplugged it the plug was unpleasantly hot. 

[Thorfun]

55 minutes ago, Temp said:

 

Equations are correct.

 

P = IV

I = P/V

 

for a 2kW heater..

I = 2000/230

= 8.7A

 

Two of those easily over 16A as others have said.  The wire gauge of extension leads can vary a lot. +1 to what @ProDave said.

 

I cant see the power rating for the dehumidifier anywhere on Amazon. One person suggests 420W.

 

You should be OK if you put one 2kW heater and one 420W humidifier on each extension lead.  Ideally plug the extension leads into different rings or at least check if there is anything else that will take the ring over its rating (typically 30A). 

thanks Temp. looks like I'll do that. sticker on the dehumidifier does say 420W and I can plug both extensions in sockets in the main house that are on different rings which is fortunate!

 

with the formulas correct I'm thinking that one heater and dehumidifier on one extension (2420/230=10.53A and even if the voltage drop is to 220V then that's still 11A) and the other heater on the other extension and things will be ok. 

[SteamyTea]

A 13A plug can only take a continuous 10A load.

1 hour ago, Thorfun said:

how does the length of the extension make a difference?

A wire has a resistance. The longer the wire, the larger the resistance.

As wire heats up, the resistance increases (basically how a heater works).

So fatter and shorter wires are best.

[Thorfun]

Just now, SteamyTea said:

A 13A plug can only take a continuous 10A load.

I didn't know this. how is that calculated? 

 

so with one heater AND the dehumidifier on one extension I'll be over the 10A continuous load? 

 

why do they say a 13A plug then if it will only take 10A? isn't that dangerous and confusing?

[Thorfun]

11 minutes ago, Russell griffiths said:

All I will say is ONLY run them when you are on site, I make sure every night that I have unplugged everything before I Leave, I had a heater running from an extension lead the other day and when I unplugged it the plug was unpleasantly hot. 

yeah. I saw this thread. devastating. we live on site in the existing property so there is always a sense of over-confidence as we're always here if things go wrong. but even living on-site wouldn't really help if a fire like that breaks out.

 

[Temp]

3 minutes ago, Thorfun said:

so with one heater AND the dehumidifier on one extension I'll be over the 10A continuous load? 

 

But not by much. I suspect old sockets with weak contact springs might be more of an issue for overheating. 

 

I probably wouldn't leave everything running while you are all out.

[Adrian Walker]

1 hour ago, Thorfun said:

I don't have electrics in the new house yet so I'm running everything off extension leads from the existing house.

 

Not sure where abouts in the build process you are, but I would run a dedicated spur from your existing house your new build. 

[Thorfun]

1 minute ago, Adrian Walker said:

 

Not sure where abouts in the build process you are, but I would run a dedicated spur from your existing house your new build. 

that is a damn good idea! I will speak to my sparky about this.

 

I think we're still about 4 - 6 weeks away from starting 1st fix, the bloody insulating is taking me bloody ages. ?

 

[saveasteading]

1 hour ago, Thorfun said:

it just weren't very good! said it removed 20l/day

Getting 20 litres out every day should make a huge difference.

 

What is the cause of the dampness? Building works (which you can resolve with 20l/day) or groundwater seeping in which needs another solution.?

[SteamyTea]

22 minutes ago, Thorfun said:

I didn't know this. how is that calculated? 

 

so with one heater AND the dehumidifier on one extension I'll be over the 10A continuous load? 

 

why do they say a 13A plug then if it will only take 10A? isn't that dangerous and confusing?

Not sure how it is calculated, probably in BS 7671 somewhere.

Reason it is 13A is so that a 3 kW load, like a kettle, can be used for a short time.

Most 3 kW domestic stuff is usually 2.8 kW, which is 12.2A. So a little safety margin built in.

I also suspect that if you tried to start a loaded 3 kW motor, the fuse would blow.

[Thorfun]

8 minutes ago, saveasteading said:

Getting 20 litres out every day should make a huge difference.

 

What is the cause of the dampness? Building works (which you can resolve with 20l/day) or groundwater seeping in which needs another solution.?

definitely not groundwater! it's more just a case of rain getting in to the building and through the block and beam before we put the windows and doors in. and it's cold down there (about 6°C) and so I just wanted to warm it up and get it dry.

 

I looked at the dehumidifier sticker and they're a bit cheeky with their 20l/day. that's at 30°C/80% humidity! it's 10l/day at 27°C/60%. so at 6°/90% I'm probably not getting much water out at all. which is confirmed by how little I'm having to empty the tray. ?

 

I'll stick with my current plan though and I will get it dry.

[Thorfun]

7 minutes ago, SteamyTea said:

Not sure how it is calculated, probably in BS 7671 somewhere.

Reason it is 13A is so that a 3 kW load, like a kettle, can be used for a short time.

Most 3 kW domestic stuff is usually 2.8 kW, which is 12.2A. So a little safety margin built in.

I also suspect that if you tried to start a loaded 3 kW motor, the fuse would blow.

thanks. so that makes me feel a bit better about running heater and dehumidifier on one extension during work hours. will turn the heater off overnight though.

[saveasteading]

I have had a new basement with 1m standing water in it*. So yours is not so bad.

 

Really, don't bother yet, if it can get soaked again,  until you close the walls.

 

Close the windows off with stud and polythene and it will not get worse.

 

*Coming from rain and I was pleased to see that it was completely watertight.

Once the envelope was completed and the pumping was done , it was 2 weeks of dehumidifier and no further problems.

[SimonD]

I've tried heat & dehumidifier strategy before and it was dissappointing. Better off not heating the air at all. Overall, you'd be much better served by using fans to create plentiful airflow especially if there's a big void for the staircase and supplementing this with a dehumidifier if needs be.

[Radian]

2 hours ago, markc said:

2x 2000w = 4000/240 is 16.66 amps

but on a 40m lead you may be down to 220v so current will be over 18amp

 

There's always a smart arse, and today it's my turn!

 

In the interests of there being no false information on the internet, I have to mention that the current won't increase as a consequence of using a long extension lead. It will be reduced. What has been assumed is that the power will remain constant. It won't, not for dumb resistive loads like these heaters. At 240V this total resistance looks like V/I or 240/16.66 = 14.4 Ohms. This resistance will remain constant, so at 220V the current would drop to 220/14.4  = 15.27A and the power would drop to 220x15.27 = 3361W

 

Of course we would have to take into account the resistance of the cable that's causing the 20 volt drop, something like 20/15 = 1.33 Ohms and this would dissipate 300W of its own which is the real reason this would be a very bad idea!

 

I hate myself now.

[Conor]

We bought three £100 dehumidifiers from screwfix and hired two "commercial" ones from local firm. The cheapies were extracting as much as the commercial ones so sent them back and bought two more 12l Screwfix ones.

 

They work brilliantly and only a couple hundred watts so you can have multiple off the one extension. 

 

At the start they were drying about 25l a day between them. Now, it's more like 10l now that we've dried out.

 

I know from searching gumtree, we'll be able to sell them on for £80 each. Bargain.

[SteamyTea]

15 minutes ago, Conor said:

We bought three £100 dehumidifiers from screwfix

How noisy are they, and do they chuck out warmed air, and how warm is that air.