Using central air fan to move heat

[gixxer340]

So I finally pulled the trigger on a Jotul c550cf last night. While I was at the stove shop I was talking to the owner about my fear of not being able to move the heat around the house effectively and somehow the fact that I have central air came up. He said that this is a great way to get the air moving around the house and move the heat. Just put it on fan only and the heat will be pumped into each room through the vents. In theory this seems like a great solution but I just wanted to get opinions here as to whether or not this is true.

I have a raised ranch and I am basically looking to heat the main house with the insert. The intake for the central air is on the ceiling about 15-20 feet away from the unit and a few feet down the hallway that has the bedrooms that I am concerned about heating. Every room has a vent in the ceiling that can be selectively opened or closed as necessary.

Thanks in advance for any input and opinions

Jeff

 

[prezes13]

I have a raised ranch built in 1994 fairly well built. My insert is in my living room, runing central fan doesn't work for me. Where is your stove going to be? Wherever you gone put it I think you will have a better chance of distributing the air by putting a small fun on the floor by the bedrooms and pointing it towards the stove. That way you will influance the convection effect. My insert in living room heats the house nice. Bedrooms stay a bit cooler but that's how I like it. Sometimes I even close the doors to keep them cooler.

 

[Nick Mystic]

I have tried circulating stove heat from our lower level stove to the rest of the house via the central forced air duct system with little success. Too much heat loss during transport seems to be the consensus on this idea. It's easy enough to test in your home by just doing it. Get some good temperature readings and then turn on the fan and monitor the temps for several hours. No discussion or debate needed.

 

[Hickorynut]

Didn't work for me either. By the time the heat went out to the ac/propane unit and then back it was cool

 

[gixxer340]

Thanks for the input. I am thinking that I may be over worrying about this anyway. I am only trying to get this thing to heat 1200 sf at most. If I get any more than that I will be very happy. I just hope I can get a decent balance between the temperature i the living room (where the insert is) and the kids bedrooms down the hall. We shall see, I guess.

Thanks again
Jeff

 

[BurningBrutus]

I have experimented greatly with this and I have found out it does not work for me. The reason is my insert is on the first floor, the furnace is in the basement, and the basement is very cool, so what happens is all the hot air get sucked into my ducts, cools the hot air in the basement, and just blows cold air back out. I have seen a 2 degree loss of heat while using my fan only option.

 

[BurningBrutus]

The only way i see this working is if my stove/insert was in my basement it would heat up all the ducts and then blow the hot air up stairs to both floors.

 

[daleeper]

I tried using the central air fan, and felt like it was costing more than in benefited. I didn't like the fan running all the time, as it cooled off the house, rather than warming it up. I tried a controller on the fan to kick it on intermittently, and that was better. It seemed that both levels of our house were more the same temperature, but still didn't like the fan running that much, so I removed it. I can't remember what the name of that little control box was, but it was a fair compromise. There are thermostats that will turn the fan on for a few minutes and off for a while, you might try that.

I am using duct booster fans now with an on/off thermostatic switch above the stove, and they kick on when the stove gets warm enough. They are small and quiet fans, cheap enough to replace when needed, and do the job pretty good, and shut off automatically when the stove room cools down.They pull heat away from the stove room, we leave the basement door open, and the cooler air returns back down the staircase. Not perfect, but is working better than anything else we have tried, cheap enough to maintain, and don't cost much to run.

Find out how your air is flowing through the house with and without the fan with smoke sticks or incense sticks. You might be surprised how the air moves in the house. Then try to figure out how you can improve upon that.

 

[akbear]

You can certainly try and see how different scenarios work, but it's always more efficient to blow cold air (which is denser) than it is to blow hot air (which is expanded and contracts as it cools). While it may not be exactly what your intentions were, the likely greatest advantage would come from closing off vents to the point that the air is pulled into the system at it's farthest or coldest points, blown out nearest to the stove, and the heat from the stove allowed to expand naturally through the space.

 

[Lumber-Jack]

As others have said, give it a try and see if it works for you.
I am one of rare ones that it does work well for. Some of the contributing factors to my success is that all my ducts are all located within the insulated envelope of the house, and there are 3 duct vents in the room where my wood stove is located and they blow down from the ceiling, so the cooler air (relatively speaking) is being blown into the room where it is always the warmest. This helps that room from getting too hot and helps force the warmer air out to the rest of the house.
I usually just set the controller on circ which intermittently turns the blower on low speed. Unless it's dead silence in the house it's hard to detect when the fan is actually blowing or not.

 

[sigepsb]

I originally wanted to do this using my new zoned system to move heat from the end of the house with the insert, to the far end. After seeing so many people unsuccessful on here I checked the temperature drop to see if it was feasible. The plenum has a temperature sensor for the zone controller. A typical reading from this in mild (50's) weather is about 135 degrees when the heat is running. I checked the output at the registers during the same conditions and its about 120 degrees. So, with brand new insulated ducting, I'm losing about 15 degrees and this is in a mild California climate. My ducting runs under the house, through the crawlspace. If you had interior ducting I could see better results, but it sounds like they're in the exterior unconditioned space like mine. I'll probably just stick to a floor fan and my ceiling fans.

 

[RSNovi]

It didn't work for me. Actually makes it worse for getting heat from my basement to the 1st floor. Natural convection works better in my house.

 

[JA600L]

I've been experimenting with this as well.

My stove is in the basement, ducts in attic, rancher with bedrooms above the garage.

This summer I re- insulated the attic and air sealed everything. The ducts are all covered with 8" of blown in. I built a raised floor and added 10" on top of 8" to the attic floor. Then I insulated the air handler.

Last night it was 40 degrees outside and 71 inside when I had the stove running. I turned on the fan and measured the register temps with infrared.. I saw 71 degrees.

At this point I went to sleep and woke up an hour later. The thermostat still read 71 degrees and the registers read 70. All of the rooms were comfortable.

I believe it will be effective if I get a thermostat that circulates the fan then shuts it off. The problem with letting it run constantly is 70 degree air feels cold to your skin when a heat pump puts out 100+ degree heat which is comfortable. So you are indeed evening out the house temps but the fan running feels cold.

So you let the stove build heat, fan circulates and evens out house, stove builds up heat, and repeat!

 

[begreen]

Sounds like you need a thermostat for the thermostat! LOL

 

[Rossco]

The only way i see this working is if my stove/insert was in my basement it would heat up all the ducts and then blow the hot air up stairs to both floors.

This.

I find you need to create a heat sink to get any heat out of duct work. I have a stand alone that pumps heat like crazy ONCE the duct and everything around the duct is up to temp.

 

[Lumber-Jack]

I believe it will be effective if I get a thermostat that circulates the fan then shuts it off. The problem with letting it run constantly is 70 degree air feels cold to your skin when a heat pump puts out 100+ degree heat which is comfortable. So you are indeed evening out the house temps but the fan running feels cold.

So you let the stove build heat, fan circulates and evens out house, stove builds up heat, and repeat!

I know what you are saying. Sometimes heat pumps only warm the air by a few degrees and people feel it is blowing cold air, but in fact it is warming the house, just more slowly than a electric or gas, etc,,, furnace. And of course if the house is cold, the metal ducts will take a while to warm up, but once they do there is no more heat loss.
My system is to get the stove hottest at night just before going to bed, which makes that room uncomfortably warm, but nobody is in it anyway. Then during the night the excess heat slowly dissipates throughout the rest of the house and bedrooms via the central air ducting. By morning the other rooms are just starting to cool down again and the stove room is tolerable again at which time we may or may not reload the fire again, depending on the outside temps.

 

[fossil]

The air coming from the central heating unit, be it oil, propane, electric, whatever is HOT (way above comfortable room temperature) when it begins its journey through the duct system to its destination living spaces. The ducting is typically insulated, but insulation isn't magic...heat loss still occurs, so the heated air inevitably drops in temperature on its travels, because most often the ducts run through unheated (cold) areas of the structure (attics & crawl spaces), but it starts out hot enough that it's still nice and toasty warm when it arrives (or at least it should be). By running the system fan in the hope of evening out temps in the home, or redistributing warm air from the stove room to remote spaces, you simply can't expect the same type of performance. Air that starts out comfortably warm as it begins its journey through the duct work is likely to exit at its destination as cool air. Some few folks have reported good results, but the vast majority of members who have commented about it here have concluded that it just seemed to be a waste of power to run the fan, and all it accomplished was throwing heat away to the unoccupied spaces through which the ducts run. Rick

 

[akbear]

The thing people tend to forget about forced air heating systems is that they are a two way nearly closed system unless one has a single point air return as was common in mobile homes which required doors to remain open or doors that did not reach the floor. So in trying to circulate heat using the blower only, one can't forget how cold air returns factor in (and while they rarely have dampers on them, they still can be closed off with magnetic sheets or of course plastic). In a sense one could attempt to do the reverse of the mobile home situation only worrying about pulling the colder denser air to feed it as close to the stove as possible, which would take much less of an effort than a total rebalance of the heating system to ensure not only is the system pulling enough from the area of the stove to counter both what's also pulled in from returns of the other rooms and pushing expanded air that is losing volume the farther and colder it gets.

 

[akbear]

We actually had a similar (though opposite) situation many years ago in my mother's house when we relocated the furnace (new) to the garage her first winter in it as well as eliminating the wood stove (with her advancing age and cognitive abilities declining it was warranted). The original furnace was a single point return, plus the plumbing was in an unheated crawlspace that relied upon a rat's nest of heat tape that needed to be activated when needed. We had to not only do the changeover in a way that reused as much of the existing system as possible, but without an interruption of heat as we were experiencing an extended cold snap with temperatures cold enough that the then soon to be abandoned propane tank needed to be bundled up and heated and at the same time doing it in a way that kept the plumbing from freezing or needing attention.

The similarities of course are the relocation of the heating source, but also the part of the equation where the cold air returns are actually part of what powers the warm air ducts, which is why I keep bringing up the issue about cold vs warm. For instance, in putting in the new system we also added a heating vent into the arctic entry (a large one), by not putting a cold air return in that room it only received enough gentle flow to keep that room just slightly warm, without that, the room at times could actually be colder than the outdoor temperature by being completely shut off to any possible air movement or migration, having 5 exterior surfaces (roof, floor and 3 sides) and a well insulated house that didn't bleed heat into it (which kind of negates the usefulness of an arctic entry if it's 30 below outdoors, 40 below in the entryway and above 70 in the rest of the house). As I say, it's quite a balancing act, but especially if you want it to do different things from different sources at different times.

 

[Sconnie Burner]

Another thing to remember is if you have a cold air return or 2 that are near the floor where your natural draft is being sucked towards the stove it is pulling the coldest air back into the ducting and negating heat from a ceiling level return.

With the stove in the basment living area I have found a system of shutting off vents on the upper level and opening the lower level ones that works pretty well for me. I turn the circulating fan on and off randomly mainly wheb the stove area starts to get uncomfortabley hot. It pushes air into the warmer stove area dispersing the volume of heated air out into the lower bedrooms and up the stairs (verified by thermometer). I do also have a fan at the bottom of the stairs pointed at the stove. Like mentioned I am one of the few that it works for.

I don't think its so much moving the warm air THROUGH the ducts but more pushing the air into the stove area forcing the warm air out of the area.

 

[bbeals]

The air coming from the central heating unit, be it oil, propane, electric, whatever is HOT (way above comfortable room temperature) when it begins its journey through the duct system to its destination living spaces. The ducting is typically insulated, but insulation isn't magic...heat loss still occurs, so the heated air inevitably drops in temperature on its travels, because most often the ducts run through unheated (cold) areas of the structure (attics & crawl spaces), but it starts out hot enough that it's still nice and toasty warm when it arrives (or at least it should be). By running the system fan in the hope of evening out temps in the home, or redistributing warm air from the stove room to remote spaces, you simply can't expect the same type of performance. Air that starts out comfortably warm as it begins its journey through the duct work is likely to exit at its destination as cool air. Some few folks have reported good results, but the vast majority of members who have commented about it here have concluded that it just seemed to be a waste of power to run the fan, and all it accomplished was throwing heat away to the unoccupied spaces through which the ducts run. Rick

Glad to be back on the forum, have had a busy summer but happily burning tonight. While I don't disagree with most I have read on this topic, I do however; have a couple of thoughts. We have a 2800 sq/ft colonial and heat it primarily with a Jotul 550C and it works really, really well. We also have tried in the past to "even out" the temperature with the furnace blower running, however, it is loud, inefficient and seems to make the room feel colder. Now, if you have upgraded or are planning on upgrading your home heating system, please do your self a favor and go the the high efficiency models that have and ECM blower (Electronically Commutated Motor). It is a 24VDC motor that is variable in speed, costs pennies to operate (less than a 60 watt light bulb) and is completely silent. While we rely on our Jotul as our primary heat source, our blower turns on for about 20 minutes per hour, per zone and keeps each room the same temp and the beauty is, we don't hear it, or feel it, other than each room is enjoying the same comfort that we have in our living room (where the stove is blazing). You can do it with a standard blower, however; they are loud, not efficient and the circulating fo that much air may make it feel colder. For the record, we run a Trane XV95 for our furnace (only used when were out of town, or circulating woodstove heat).