Central Air and Wood Stove as primary heat

[Nostromo]

I did a search on central air and didn't find much relevant...anyway, I hope this topic hasn't been done before, if so, sorry in advance.

Does anybody have any success stories using a combined Wood Stove as primary heat but also using the forced air return (no furnace or heat pump turned on just the fans) to circulate the hot air (from the wood burning stove) to the rest of the house?

The sales guy I talked to asked me how far away my 'air intake vent' was located from the installation site of the stove. I was curious and asked him why it mattered and i guess he was really trying to sell me on a wood stove that could be used as a primary heat source. I went in just looking for a casual wood stove that i could kick on a few times a year. But I think he was trying to use some sales tactics to get me to buy on the spot...essentially he was saying if my air intake vent was 15-20 feet away that if you keep the fan going for your central air system the wood stove can distribute the heat to the rest of the house.

Has anybody tried or done this? Is it effective...seems to me, by the time the hot air from the stove went up the vent, throught the filter system, down through the duct work in the crawlspace it would be cold by the time in got to the back rooms.

Just for details:

Installation site to Air Uptake Vent is 12 Feet (so pretty close according to the sales guy that says it would work great in my house)
Insulation on all crawlspace Ducts but NOT on the Return Ducts in the attic.
2000 SQ Ft house...stove is centrally located to major living spaces (kithcen, living, family) but have standard ranch where rooms are 'down the hall'.
Avalon Olympic to be installed...

Any thoughts--do you think the central air system can deliver wood stove heat to the 'back rooms' of the house?

 

[madison]

IMHO, ducts in an unconditioned space (ie attic) are at best R8 and depending on your attic temp, leaks in attic air handler, length of runs of the ducts in the attic... to name a few, is a waste of money running the air handler fan, and a waste of heat to the attic via heat loss of the ducts and handler.

I experimented with multiple thermometers throughout the house and the use of the a/c air handler fans was futile. Though I live in a much colder climate than Seattle.

I go so far as to plug the AC ducts during the heating season, (ie next weeks chore) with insulation to limit the passive loss of heat to the attic air handler and ductwork.

Ceiling fans seem to do a decent job of moving the air.

 

[laynes69]

Madison, I would take batts of the insulation and stuff them in small cheap plastic garbage bags then plug the ducts. The bags will stop the airflow that can go through the insulation. Plus it keeps the fibers out of the ductwork. If heat is wanted through ductwork, then a woodfurnace would be the way to go.

 

[vvvv]

Madison, I would take batts of the insulation and stuff them in small cheap plastic garbage bags then plug the ducts. The bags will stop the airflow that can go through the insulation. Plus it keeps the fibers out of the ductwork. If heat is wanted through ductwork, then a woodfurnace would be the way to go.

wonder if balloon might be cheaper

 

[Pagey]

Trying this had zero effect for me other than increasing noise/electricity consumption.

 

[freeburn]

I would echo what has been said already. All the fan does is create drafts and because it is moving so much air it actually cools the air as it sucks it through the cold air return. Get a furnace, you'd be better off if you want even heat distrib. Otherwise, get a space heater = wood stove.

 

[Nostromo]

THanks for the replies guys...that's what I thought...it seemed a little bogus. Looks like I should turn off my central fan when i used the wood stove. Gets installed in 2 weeks, yay!

 

[Pagey]

I will add that adding a blower to our Endeavor has made a significant difference in how well its convection heating functions. I keep it on the lowest setting, and I am impressed with how much air it moves and how well it moves the heat.

 

[madison]

Madison, I would take batts of the insulation and stuff them in small cheap plastic garbage bags then plug the ducts. The bags will stop the airflow that can go through the insulation. Plus it keeps the fibers out of the ductwork. If heat is wanted through ductwork, then a woodfurnace would be the way to go.

Good idea I will try that next week.

Last yr, I actually cut ~ 12" squares of insulation that fit into the area where duct connects to register, and to be totally honest, went totally nuts and covered the inside of the register with saran wrap.

The balloon idea sounds good as well, if you could find a material that would not leak....

The HVAC guy at the counter suggested wrapping the filter at the air handler with saran wrap to prevent convection loops ...

 

[madison]

I will add that adding a blower to our Endeavor has made a significant difference in how well its convection heating functions. I keep it on the lowest setting, and I am impressed with how much air it moves and how well it moves the heat.

Ditto, adding the blower to our T6 made a significant improvement to heat output.

 

[Slow1]

The balloon idea sounds good as well, if you could find a material that would not leak....

The challenge I see with a balloon is that as it cools (one side at least will be exposed to cold, right?) the volume will decrease and it may shrink enough to either leak or fall out of place. Thus you will likely need to over-pressurize it enough to account for this loss in volume when temperature falls. This then lends to two risks when temperature rises - over-pressure and popping or stress damage to ductwork (most ducts aren't exactly the strongest design - especially if they are rectangular. Then of course the balloon material itself needs to be fairly tough and gas-tight (not your standard latex party balloon by any means) in order to stay inflated for a whole heating season.

Not to say balloons can't be done, I just expect that stuffing with something with a lower expansion sensitivity to temperature would be a better choice - insulation in a bag seems the better option of what has been offered as it would appear to conform to the shape, stop airflow, and have reduced conductive heat loss to boot.

 

[Hiram Maxim]

If the furnace has an outside air intake for combustion you will fight a loosing battle :-/

 

[begreen]

Numerous folks here have good success moving the heat in their ranch houses by placing a table or box fan, on the floor at the end of the hallway, pointing towards the stove. The idea is to work with natural convection and blow the cold air towards the heat. The fan can be run on low speed. Put a thermometer in the hallway and try it!

 

[madison]

The balloon idea sounds good as well, if you could find a material that would not leak....

The challenge I see with a balloon is that as it cools (one side at least will be exposed to cold, right?) the volume will decrease and it may shrink enough to either leak or fall out of place. Thus you will likely need to over-pressurize it enough to account for this loss in volume when temperature falls. This then lends to two risks when temperature rises - over-pressure and popping or stress damage to ductwork (most ducts aren't exactly the strongest design - especially if they are rectangular. Then of course the balloon material itself needs to be fairly tough and gas-tight (not your standard latex party balloon by any means) in order to stay inflated for a whole heating season.

Not to say balloons can't be done, I just expect that stuffing with something with a lower expansion sensitivity to temperature would be a better choice - insulation in a bag seems the better option of what has been offered as it would appear to conform to the shape, stop airflow, and have reduced conductive heat loss to boot.

slow1, thanks -- Charles Law in action.

I'll stick with the insulation

 

[burleymike]

The single return on my HVAC system is in the living room ceiling right above the entrance to the hallway 20' from the fireplace. If I keep the ceiling fan in the living room off I can circulate the heat pretty well around the house. However at night it is a waste to keep it running. I just keep all the bedroom doors open and the heat travels fairly well into the bedrooms.

The other reason I run the blower on the air handler during the day is we get a ton of south sun that makes the front half of the house too hot. The duct work is very well insulated as well as the air handler and it is all sealed with mastic.

 

[SWNH]

Trying this had zero effect for me other than increasing noise/electricity consumption.

+1

 

[Gridlock]

Running the central air fan can significantly increase the air quality in the house, especially during the heating season and in a tight, well insulated house. Allergy and asthma sufferers can especially benefit as there are filters available for central systems that trap very small particulate matter. Any smoke leakage or smell can also be filtered through the system.

 

[begreen]

That really depends on the heating system. You're not going to be trapping very much other than large dust particles with a standard 1" fiberglass filter. But if you have a 4" pleated filter or an electrostatic filter and the system has some fresh air makeup, then yes, it may make a nice difference in air quality. However, if electricity costs are high this will bump up the bill noticeably.

 

[Gridlock]

That really depends on the heating system. You're not going to be trapping very much other than large dust particles with a standard 1" fiberglass filter. But if you have a 4" pleated filter or an electrostatic filter and the system has some fresh air makeup, then yes, it may make a nice difference in air quality. However, if electricity costs are high this will bump up the bill noticeably.

I've used the 1 inch 3M Filtrete 1900 'maximum allergen' filters, which has made a very big difference. My girlfriend had a hard time last season with some smoke and cat dander (she has allergies and asthma), which was mostly alleviated (thank goodness!) after installing the 1900 rated filter. There is a 2200 'elite allergen' filter as well that appears to get good ratings which I'll try this season. I agree that a standard fiberglass filter doesn't make much of a difference with smoke or pet dander.

 

[begreen]

Good tip, thanks.

 

[madrone]

I was advised not to use those micro allergan 1" filters in my newer furnace, as they're too restrictive for the higher flow fan. I've got 2" filters in now, a compromise between air flow and air cleaning. I sometimes run the fan during winter to remove dust from the air, but I've found it doesn't circulate heat well. The ceiling fan does a better job of that.

 

[op_man1]

Really, if you are concerned about air quality in a modern, tight house during the winter, an air exchanger (heat recovery ventilator) is the way to go, although filters are better than nothing, I suppose.

In my application, running the central ventilator in the winter had the effect of cooling the main floor but keeping the basement from getting too cold (this was in below freezing weather but not in extreme cold). It actually can work, depending on how you are set up. All my duct work is within the building envelope (i.e. within an insulated space) and I would think that this would certainly be one of the requirements for this to work.

 

[burleymike]

You also need to be careful using those pleated filters during the A/C season. If the circumstances are right you will have a frozen evaporator coil due to the reduction in air flow. I do however use them in the winter months and they do seem to make a difference in the amount of dust we have.

 

[Bubbavh]

+1 on the ceiling fans.

I've had good luck with running the fan in the room with the stove blowing down and all other fans reversed.

Good luck!

 

[soupy1957]

We have a forced hot air furnace system and only two years ago had a new furnace installed.

We have Central Air, installed last Fall, utilizing the existing duct work.

We use only the blower in the furnace during the winter, to level off the air temps throughout the house. It doesn't transfer heat much, but it balances out the temps to a 75ºF on the upper level, (we have 3 floors) and a 65ºF down in the family room, below grade. (By the way, I set my furnace thermometer to 45ºF for those times when the fire goes out because we leave town........to keep the pipes from freezing).

The heat from the wood stove DOES transfer, but not much.........

The fan in the kitchen (ceiling type) in conjunction with the blower in the furnace, help things balance out even better!

As for the pleated filter in the system, I take it out in the winter to reduce heat absorption.

-Soupy1957