BK Princess Fan and Runtime

[twd000]

I am the proud new owner of a Blaze King Princess Insert - thanks for all the helpful discussion and research around Hearth.com

This thing is the real deal; I have been burning 24/7 since Sunday on a pretty steady 12-hour reload cycle. I'm not heating my house 100% as I left the upper floor furnace zone on so my wife and new baby don't get frozen out.

The house is a fairly standard 1970s colonial, with the stove at the center of the main living floor, and 4 bedrooms on the second floor. I've been pleasantly surprised that the main floor is maintaining within 3-4 degrees of the stove room at 72 F. "Some" heat is naturally convecting up the stairwell up to the second floor, but it's hard to say how much. Thermostat upstairs is left at 67 and kicks on periodically but certainly much less often than before the stove.

So my question is about the fan on the insert. I know the manual states to match the fan speed to the thermostat setting, but I've never been one to follow the manual . I have experimented with turning the fans on for a 12-hour cycle, but mostly I have left them OFF, with the thermostat between 30-40% open. A 400 F stove top temperature seems about right in the current weather (20s-30s). The fans definitely blow air around the stove room, and shorten the burn cycle (by maybe 20%?), but I don't notice them putting more total heat into the house. Of course, I would prefer to leave the fan off, even though they are pretty quiet on LOW, silent is even better.

Do you think the fans increase the efficiency of the insert, of just the heat output rate? In other words, for a given load of wood, do you think the fans increase the amount of heat going into the room (not lost to the masonry fireplace)?

The automagical thermostat damper is so effective that I can hold the stove top temperature anywhere from 400-600 without engaging the fan, so what is the fan doing for me?

 

[jetsam]

So my question is about the fan on the insert. I know the manual states to match the fan speed to the thermostat setting, but I've never been one to follow the manual . I have experimented with turning the fans on for a 12-hour cycle, but mostly I have left them OFF, with the thermostat between 30-40% open. A 400 F stove top temperature seems about right in the current weather (20s-30s). The fans definitely blow air around the stove room, and shorten the burn cycle (by maybe 20%?), but I don't notice them putting more total heat into the house. Of course, I would prefer to leave the fan off, even though they are pretty quiet on LOW, silent is even better.

Do you think the fans increase the efficiency of the insert, of just the heat output rate? In other words, for a given load of wood, do you think the fans increase the amount of heat going into the room (not lost to the masonry fireplace)?

The automagical thermostat damper is so effective that I can hold the stove top temperature anywhere from 400-600 without engaging the fan, so what is the fan doing for me?

The fan gets heat out from the stove into the room. The PI has a small surface area as compared to a freestanding stove. You'll hear princess freestander owners saying "meh" about the fan kit, but the insert needs it to blast out the BTUs in cold weather. Note that BK didn't give you the option to buy the insert with no fan- not an accident.

I don't use my fan in shoulder season (maybe 5-6 months a year), but I use it all the time in winter.

The fan cools the firebox right above the cat when it runs. This means the magic thermostat cools down faster and opens up the air more often, which means less burn time. On low burn, I can expect 20-24 hours with no fan, or 10-12 on the lowest fan setting. (Note that the lowest thermostat setting that I can burn at is a lot lower with the fan off, so that's not a really fair comparison.)

Efficiency-wise it is tough to tell what we're sending up the flue since not many insert owners run a flue probe thermometer. I have to imagine that you are wasting a lot of wood if you burn on high (>40%) thermostat settings without the fan.

Be alert to the fact that the fan is not always your friend, too. If the fan is set higher than the thermostat setting can support, the cat will cool down out of its active zone, and you will have a large drop in heat output and efficiency.

My general rule of thumb is that if it's below 40 outside, the fan is on. Your stove will burn differently and your heat needs are not the same, so you have to play with it and find your own happy spot.

I don't ever do what manuals tell me to do either, but the 'match fan speed to thermostat' rule is actually a pretty good guide for new owners. It stops them from burning on high with no fan and sending all the heat up the flue, and it stops them from burning on low with a high fan and killing the cat.

You'll work out the nuances as you get to know your stove; nobody can tell you "set the fan to x and the thermostat to y for success" because they might have the same stove, but they have a different thermostat calibration, different wood (huge influence there), different draft (large influence, just ask @Ashful), different burn practices, and different requirements for heat output.

 

[Blazing]

I find it only necessary to run my fan if the temperature is below 15 degrees. In short yes they provide more heat do to better convection but I don't care for the sound and a cool bedroom is good with me. I guess it's a choice of do I want 20+ hour burn with my bedroom at 68-70 or 12-14 with a 70+ bedroom. It's all about comfort vs how much wood you want to feed the stove.

 

[jetsam]

That little insert kept my house at 70 all day today without a fan. Shoulder season is just around the corner here!

I would also like to take a moment to assure you that even though Blazing and I have the same stove and what appears to be the same dog in our profile pictures, we are not in fact the same person.

 

[twd000]

so if the lowest fan speed cuts burn time by 50%, wouldn't you expect the heat output rate (BTUs/hour) to double? But it doesn't double the heat output rate, otherwise you would overheat your house. So where is that extra heat going? There should be LESS heat lost to the masonry firebox, not more...

 

[Highbeam]

so if the lowest fan speed cuts burn time by 50%, wouldn't you expect the heat output rate (BTUs/hour) to double? But it doesn't double the heat output rate, otherwise you would overheat your house. So where is that extra heat going? There should be LESS heat lost to the masonry firebox, not more...

I'm with you here, assuming the efficiency is the same then a halving of burn time means a doubling of output rate. You won't necessarily overheat your house though, doubling a small number is still a small number. Using the fan makes more hot air so that parts of your home that would otherwise be cool are now being warm, that consumes more heat. In other words, you aren't losing the heat up the stack but to the home.

 

[Tar12]

I have found that it doesn't matter one bit to me what setting the fan is on in regards to wood consumption as I load twice a day regardless.Air control is everything to me about burn times...With out the fans the rear of the house stays a lot cooler so they do in deed work.

 

[jetsam]

Fan cools the firebox, magic thermostat calls for more air, fire burns hotter.

I agree that on a high thermostat setting, you won't see too much difference in burn times between the fan being on low or off. At a very low thermostat settings, you see a dramatic difference.

The heat that the fan removes from the firebox all goes into your house. The fan is external to the stove and doesn't add or remove combustion air.

 

[twd000]

I can understand the heat distribution improvement. But my main floor (where the stove is ) is pretty uniform , even without the fans. Its my second floor that's not getting the heat. I'm trying to scheme up a way to get more heat up the stairwell, which would draw more heat off the stove, and shorten runtime.

 

[jetsam]

I can understand the heat distinction improvement. But my main floor (where the stove is ) is pretty uniform , even without the fans. Its my second floor that's not getting the heat. I'm trying to scheme up a way to get more heat up the stairwell, which would draw more heat off the stove, and shorten runtime.

Try putting a fan on the floor upstairs and blow cold air down the steps towards the stove.

 

[James02]

I've always wondered, instead of the fan on the stove, why not have a small fan pointed at the stove to distribute the heat... I think I've read it weakens the steal, can somebody confirm?

 

[jetsam]

I've always wondered, instead of the fan on the stove, why not have a small fan pointed at the stove to distribute the heat... I think I've read it weakens the steal, can somebody confirm?

The built in fan blows right through the convection deck which is right on top of the cat. If you have a small surface area and need to get heat put to the room, this is where you want your fan to blow.


As far as an external fan weakening the steel, that sounds silly unless you're suddenly blowing a hurricane of cold air onto a red-hot steel surface.... I am no metallurgist though. We could ask @CheapBassTurd !

 

[Blazing]

Using a fan to move cold air to the stove works better for some than others being house layouts are different. With the stove fan running be it high or low you can't get around improving convection in the house. The higher the fan speed the more cool air will pass around the stove and be warmed at ### temp. I can see the issues that one with a two story would encounter trying to keep the upstairs warm without overheating the downstairs. As said above the best bet is play with floor fans and the one on the insert itself. That said gotta love my bk it's 67 outside stove is running and 74 in the house.

 

[James02]

@jetsam, so a small desktop desktop fan in front of the stove blowing on it might be a good option for people without a fan attachment I'm thinking...

 

[jetsam]

@jetsam, so a small desktop desktop fan in front of the stove blowing on it might be a good option for people without a fan attachment I'm thinking...

BK doesn't offer the Princess Insert without a fan.

I've heard a lot of freestanding stove owners say they had better results putting the fan in a cold area blowing towards the stove than they did having the fan blow on the stove, but I imagine that your house's layout will determine what works best for you.

 

[CheapBassTurd]

I like to just feed mine while hanging at home in the stoveroom with wife, laptop,
kids, etc. Easier to toss on a couple of splits every hour to keep a very steady temp.

At night we load the stove and run the "quiet on low"fan pushing air down towards the
bedrooms with a 1/2 full firebox damped down low. Each bedroom door becomes a thermostat.

I'm no mettalurgist, either. lol Robotics operator now.
Only specifically in Fe. Gray iron=softer and machines easily, and deadens sound vibrations. (Engine blocks.)
Ductile=Much harder and tougher but transfers mechanical noises loudly. (Engine heads)
That's really 95% of my knowledge, and the thousands of things that can be made with the two.
If ya ask me about titanium or aluminum I'll look at ya as dumbfounded as the next guy. LOL

 

[jetsam]

I like to just feed mine while hanging at home in the stoveroom with wife, laptop,
kids, etc. Easier to toss on a couple of splits every hour to keep a very steady temp.

At night we load the stove and run the "quiet on low"fan pushing air down towards the
bedrooms with a 1/2 full firebox damped down low. Each bedroom door becomes a thermostat.

I'm no mettalurgist, either. lol Robotics operator now.
Only specifically in Fe. Gray iron=softer and machines easily, and deadens sound vibrations. (Engine blocks.)
Ductile=Much harder and tougher but transfers mechanical noises loudly. (Engine heads)
That's really 95% of my knowledge, and the thousands of things that can be made with the two.
If ya ask me about titanium or aluminum I'll look at ya as dumbfounded as the next guy. LOL

It's a (contaminated) Fe question!

I've always wondered, instead of the fan on the stove, why not have a small fan pointed at the stove to distribute the heat... I think I've read it weakens the steal, can somebody confirm?

 

[drstorm]

Has BKVP chimed in on whether or not the fans actually are cooling the cat,or just the cat probe?
I have no doubt they are cooling off the firebox,but is it as drastic as stated on the probe?
Basically giving a false reading due to the part of the cat probe extending through where the fans pull off heat before it hits the coil.
Just curious as to the actual science/lab findings.

 

[jetsam]

Has BKVP chimed in on whether or not the fans actually are cooling the cat,or just the cat probe?
I have no doubt they are cooling off the firebox,but is it as drastic as stated on the probe?
Basically giving a false reading due to the part of the cat probe extending through where the fans pull off heat before it hits the coil.
Just curious as to the actual science/lab findings.

It is very significant.

Say I put my thermostat on 40% with a fresh load- at 0% fan the cat glows like a light bulb, at 50% it maybe glows a little, and at high fan there is no glow.

 

[shoot-straight]

My fan reduces my burn time sometimes by 50%, depending on speed and stat setting.

Someone on here used a timer to kick his fan on and off. I tried it and it works well to lengthen the burn.

 

[jetsam]

I toyed with the idea of having a room air temp thermostat turn the fan off and on, but while that's a great idea with a fresh load of wood, it also killls the cat early at the tail end of the burn, so I decided not to mess with it.

Someone who is available for more frequent reloads might find it to be a better idea.

 

[twd000]

My fan reduces my burn time sometimes by 50%, depending on speed and stat setting.

Someone on here used a timer to kick his fan on and off. I tried it and it works well to lengthen the burn.

And would you say it's heating your house at twice the rate?

Interesting about the timer. Is it basically equivalent to a "lower than low" fan setting?