Is indoor training without a fan drastically limiting my FTP?

I currently do not train with a fan. All training is done in my basement at temps never exceeding 70°. Most of the training is done around 65°. My current FTP is 213. I just completed a 60 mile charity ride on Saturday. The ride had about 2600 feet of climbing, and 3 SAG stops. I never stopped for longer than 10 minutes. For the 60 mile ride my stats were as follows:

Avg speed 17.0
Moving time 3:32
Avg power was 154
Normalized power was 210

The NP is the metric I might be misunderstanding. Is it possible for me to have an NP for a 3.5 hour ride that close to my FTP? Or is my FTP actually higher, but since I’m not using any cooling during training, I can’t actually get to what it should be.

My wife had a similar trend:

FTP 154
NP for the ride was 150

If we were using fans, what increase in FTP would I likely see? The problem is if my FTP isn’t accurate, it’s hard to pace longer rides and I’m basically riding on RPE.

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Yes you need a fan or 3.

Evaporative cooling makes a huge difference.


Yes, the lack of evaporative cooling will typically reduce power for any given RPE. This will lead to a lower test FTP, and lower power levels indoor without a fan.

Generally, you should do most of your indoor training with a fan - the increased power levels will lead to better training results.

Of course, there is an argument for heat acclimatisation without a fan closer to your target event, but that is another discussion.


Your body will limit the power you can produce to protect itself from overheating internally. The by-product of power is internal heat. Your body uses evaporating cooling to cool itself. Your blood is naturally routed away from your muscles to the surface of the your skin. Training indoors you are not moving so there is no air moving over your skin to aid in evaporative cooling. You basically heat soak until the body’ internal temperature raises to the point it goes into protective mood. Fans are a must regardless of the temp of the room. I normally warm up a few minutes before turning on the fans.


As said above, not having a fan is certainly limiting how hard you can go indoors.

There are other factors to consider though:

  • Are you using the same PM both indoors and out, and do you always calibrate it? If you’re getting indoor power from a smart trainer and outdoor power from a PM, then there could be significant differences. My PM reads consistently about 30W lower than my Wahoo Kickr, I’m not sure which one is accurate or whether the real number is somewhere in the middle, and it doesn’t really matter too much since the difference is consistent and therefore I can allow for it in my training
  • Even if power readings are consistent, many people find they can push higher watts indoors than out. Reasons for this can include better heat distribution, better motivation (hills to get over, other riders to chase or hang onto, etc) or improved comfort and muscle recruitment from being able to move around more on the bike. After allowing for PM differences above, I suspect my FTP outdoors is anything up to 20W higher than I get from testing indoors.
  • Those 3 stops could have a significant impact on your NP since you effectively got 20-30 minutes of complete recovery that aren’t accounted for in the numbers. Could also be worth checking your bike computer settings, there is an option to “ignore zeros” which would also give your numbers a big bump if you’re on a hilly course where you’re freewheeling the descents. Basically like doing interval training where your average power ignores the rests between intervals
  • And lastly, it’s possible your FTP is wrong! When did you last test? What test did you use?

Re your last sentence, nothing wrong with pacing on RPE! Altitude, temperature, state of recovery/fatigue, nutrition and other factors can all have a big impact on what watts you’re capable of holding on any given day. I find FTP to be a very useful number for tracking fitness improvements and for setting training intensities, but in races RPE is at least as if not more important. Pretty useful in TTs and long steady climbs where you can pace yourself, not so much if you’re riding in a group on flat or rolling roads.


I agree that a fan will come in to play for trainer rides, but I’m not sure the difference over the course of a 15 minute ramp test would be that great.

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I’ve been asking myself a similar question:
Suppose the power you could produce for your FTP is 15watts lower indoors (200) vs outdoors (215). If you then train indoors to 200, wouldn’t you be hindering your training? Because for example: indoor threshold intervals might be in the sweet spot zone of your (actual?) outdoor FTP. Would you get the same/maximum benefit?

You can certainly try, but I think you’ll find that whatever the reasons are that stop you from testing higher indoors (heat, airflow, position, etc) will also make it impossible to complete the workout.

Personally I try not to overthink FTP. It’s a useful test of progress, and it’s a useful benchmark for setting training intensity, but that’s it. At best anything short of a full hour test (and who wants to do those on a regular basis?!) is only an estimate, and test results are going to vary by at least a few % on any given day depending on temperature, fatigue, nutrition, time of day, etc. And then everybody has a different power curve anyway, so although FTP (if accurate) is pretty good for setting SS and Threshold intensity, it becomes much less so at higher intensity levels.

It’s not unusual for one person to have different indoor and outdoor FTPs. Likewise, people often have different FTPs on their road bike, compared to their TT position. I think it’s fair to say that, assuming you’ve conducted reliable FTP tests, sticking with the FTP value that matches your environment is still going to give you the intensity and therefore results that you’re looking for

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Not having a fan likely does lower your indoor FTP.

The TR crew have said in past podcasts that their indoor and outdoor FTP are the same - in large part by having sufficient cooling.

It’s also much more pleasant to not be sweating everywhere. At home, no sweat drips off me as my fan evaporates it all. At the gym with no fan, there’s a pool of sweat beneath me after a ride.

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My own experience (n=1).

I trained for a few years without a fan. At first I had a cooler place in veranda (could be 13°C in winter) without any negative effect from lack of fan. But last few years I had a smaller room which heated up during a 60 minute workout. It was harder to do the workouts but sill manageable. I left a puddle of sweat after each workout and my heart rate crept up as intervals went by.

It got too hard as I approached 4 W/kg. I found this deal for a carpet dryer on forum and it was a great choice.

The only issue I experienced was catching cold after a few sessions. You should keep you paincave clean from dust and position your fans to not blow in your face.

Probably limits your FTP, but also probably limits the life of your bike - I sweat quite a lot, and it took me a number of years to realize that maybe, just maybe, I should get a fan rather than just overheat and drip all over my bike. My older bike that I used on the trainer then still has corrosion marks to show for it. And that seat post is never going to move again. It’s welded into the (steel) frame.

I wouldn’t be able to ride the trainer for more than 20 minutes without a fan…who are you maniacs who do this!?!


I usually leave the fan off while I warm up because my basement gets pretty cold, but leaving it off for 10 minutes is already a stretch for me!

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You don’t miss what you don’t have - until you have it.

I don’t understand this. How does a fan evaporate sweat? I could understand it if the fan keeps you so cool that you sweat less but don’t know how it just stops the sweat dripping

Basically, if the air is still, there is a concentration of water vapour around you. The air gets saturated with water vapour and no more sweat can evaporate into this air and it just hangs out on your skin. Once a fan starts blowing, the layer of water vapour is moved away from your body and replaces the saturated air with new air, allowing for more evaporation of sweat.


Fascinating! Makes a lot of sense

Also - I use a lasko max performance fan. Blows at close to 40mph. Placed above + in front of my front wheel so it hits my head and torso.

The overall consensus seems to be I need to get some fans. I’ll order some this week and see what effects that will have.

The bike is covered in a towel anywhere that would be in a sweat path, so I’m not concerned with bike damage.

To answer a couple of the consistency questions

Power meter is the same indoor and out - stages FSA-K light (both mine and wife’s)
Power meter zero reset is performed prior to every ride

As far as the counting 0s, my understanding is that the TR analytics automatically does that which is why there is the drastic difference between my avg power 154 (counting 0s) and the NP, which was 210 (not counting 0s) Am I misunderstanding this?

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