Central heating Q&A Archive

Why so little content about furnaces?

My husband and I are discussing a move to wood heat.  We wonder why there is so little information on wood furnaces compared to wood stoves.

Will we get best heat distribution thru the house with a basement furnace (blowing air through our existing ducts) or with a centrally located wood stove such as your site mostly describes? Are there any other reasons (besides looks) to prefer one over the other?

Laura

Hi Laura,

There is not much content on our site about central wood furnaces because:

1. Furnaces are exempt from the EPA emission certification regulations, so their development has not kept pace with stoves, fireplace inserts and specialized fireplaces.

2. As a result their efficiency is about 30% lower than stoves and their smoke emissions are about ten times greater.

3. Some are terrible, some are just mediocre, but in the absence of EPA certification, we can offer no criteria for purchasers to determine which is which.

4. Almost all furnaces operate on an on-off thermostat cycle, but no one has figured out how to cycle a wood fire without creating high emissions.

5. We are committed to promoting only low emission technologies because conventional equipment is difficult to justify environmentally without a large number of qualifiers.

6. Modern houses of moderate size don't usually need the power output found in most furnaces and where a good wood stove has enough power to heat a house, it can do it with so much less wood and pollution that the other options are not even in the running.

7. Advanced stoves and fireplaces are not only wonderful to watch operating, but having one in the living space permits better monitoring and management and we contend that a human being remains the best control system for a wood fire.

We wish it were otherwise but we find ourselves constrained by our mandate and the present state of the technology.

John

He built his own furnace and now he has problems

I built my own wood furnace and I have a question concerning the chimney I need for proper function.  The furnace I built typically exhausts the smoke between 250 and 300  degrees F.  Although the smoke normally travels through a system of heat exchangers, for tending the fire there is a by-pass baffle that lets the smoke directly enter the flue pipe above and behind the feed door.  The  flue pipe is 8" diameter and the door is 14" x 21", resulting in a ratio of  6:1 for door area to flue area.  

There are no restriction or bends that  the smoke must make to enter the flue with the by-pass open.  I currently have the stove connected  by 2 feet of 8 inch pipe and two 90 degree elbows to a masonry chimney that has an  8" square flue.  From inlet to outlet the chimney is about 20' tall.  The chimney is plenty high enough  above the roof line, and there are no hills or trees to the west of the chimney.  The house is an old leaky farmhouse, so there is no problem  with negative pressures inside the house.  Most of the chimney is inside  the house.  I looked up the chimney with the aid of a mirror and there is no blockage.  

The stove burns fine, but I can not tend the fire without a great deal of smoke entering the basement.  In fact, I can't open the door more than a few inches before smoke enters the house.  There is less than .02" of water column vacuum in the chimney.  I measured the temperature of the smoke exiting the chimney and it was 125 degrees F.  

Would an 8 inch insulated stainless steel chimney take care of my problem?  I  know that a round flue draws better than a square flue of the same area,  and by not cooling the smoke so much in the chimney,  I'm sure to get  more draw.  I don't want to spend the money on a new chimney if it won't  solve my smoking problem.  I was hoping you could make some suggestions.    

Tony

Tony, 
I think the problem is that your door is too large, you have too many restrictions in the venting system, and your temperatures are too low.  With a smaller door, say 12 x 12 (which is all that is really necessary), you might get away with two flue pipe elbows and another 90 degree change of direction at the chimney base.  Alternatively, you might get away with a big door if you had a perfectly straight system from the flue outlet up.  But the combination you have is guaranteed to spill smoke when the door is opened.  Also, with draft of only 0.02" and a flue gas temperature of only 125 F almost any system would spill.

Here are some suggestions, starting with the cheapest and easiest things to try: 

1. try starting your fires top down so you don't have to mess with the fire so much at start up.

2. try to get your flue gas temperature up higher; good systems need at least 200 F and 0.05 draft to limit spillage; you probably need double that considering your other problems. 

3. replace the two 90 degree flue pipe elbows with two 45 degree elbows to eliminate the horizontal run and reduce restriction 

4. since you built this thing yourself, you could modify the door to reduce its size (a lot) 

5. your 8 x 8 tile chimney is probably only 6 1/4 x 6 1/4 inside which is very marginal for such a large door opening; you could consider having a sweep or installer remove the clay liner and install a 7" stainless steel liner  

Hope this helps. 
John  

How to heat a large L-shaped bungalow

There was a brief mention of Tarm boilers as being the only boiler;/furnace to match the efficiency and emissions of wood stoves. Is this still the case, and if so, how does one find more information on this brand? (tarm.com didn't work; I'll try a search next) Also, do you know anything about Charmaster? They claim to have a high-efficiency furnace design that burns the hot gases. The problem I have with all these manufacturer's claims is that they don't give specifications for what high-efficiency means, so I don't know how to compare it to a good stove. I'm also concerned about the emissions and again, no one publishes figures for their products.

By the way, the reason we ruled out a stove is that our house is a 1 story on an L-shaped plan and is 2500 sq. feet, with a lot of hallways and doors, so there doesn't seem to be a good place to put a stove. Furthermore, David thinks a furnace in the basement will help dry out the large unfinished basement (which I hope someday to use for yoga classes) and keep the floors warm on the main level. The house already has 2 electric furnaces with heatpumps (noisy, inefficient things, don't know why anyone would put them into a house in central Ohio); we would connect a furnace to the existing ductwork and also pre-heat our hot water which is also quite expensive and inefficient.

Any other suggestions for heating this space efficiently will be greatly appreciated.

Janis

Hi Janis

I imagine your search on Tarm would yield this: http://hearth.com/tarm/hs.html

I have corresponded with the company lately and found them friendly and helpful.

You wrote:
They claim to have a high-efficiency furnace design that burns the hot gases. The problem I have with all these manufacturer's claims is that they don't give specifications for what high-efficiency means, so I don't know how to compare it to a good stove.

Exactly, which is why we think all wood burning equipment, including fireplaces and furnaces, should be regulated under the EPA certification program. If you check the promotional literature put out by manufacturers of EPA certified stoves and fireplaces you will see very little hype about combustion systems with made-up names. They concentrate on other features that are a lot harder get away with lying about.

I've heard of Charmaster, but I don't know their products. Probably the best advice I can give is to find a good, trustworthy dealer and installer.

John  

Combination wood/gas furnace??

Hi,
My wife and I are building a new 2000 sq. ft. home this spring.  We are thinking about installing a dual fuel heating system.  We want thermostatically controlled forced air heat.  This system will use LPG (Propane) as well as wood.  We would not want a pellet stove as the home is on forty acres of hardwoods that need thinning badly.  We figured we could cut and split our own firewood and use the LPG when necessary only.   Is there such a system out there?

Thank you,
Marty & Suzanne  

Hi Marty and Suzanne,
I don't know of a combination wood/gas furnace.  In fact, in Canada such combinations have been deemed incompatible by safety code committees.  Even if you select separate furnaces and have them sharing the same ductwork (which I think is the only viable option) do not attempt to vent them through the same chimney.  Gas and wood venting requirements are not compatible at all.  

Are you aware that a well-constructed 2000 sq. ft. house can be heated effectively with a single wood stove or heat producing fireplace?  These are much more efficient than furnaces (about 70% vs. about 55%), cleaner burning (about 5 grams of smoke per hour vs about 40g/h) and you get the bonus of a spectacular fire to watch all winter long.

Regards,
John

Wood burning to heat several rooms

I am looking for a fireplace design that will send hot air to several rooms as well as have a nice living room view of the fire burning in a typical fireplace. I have seen something like this on THIS OLD HOUSE or one of Bob Villa's programs. Can you lead me to such a product? Thanks!      
Hopeful  

Hopeful,    
There are only a few fireplaces like this: Security BIS II, RSF series of fireplaces, Regency WarmHearth, Fireplace Xtrordinare, Vermont Castings WinterWarm are about it. Check with the specialty fireplace shops in your area. They will carry one or more of these. 
John

Do central systems get a bum rap?

I know this website is about woodstoves and fireplaces but I think central wood heating is getting a bum rap from some of the writers.  I have a Tarm boiler and it is very efficient and very clean ( 1 gram emissions per hour ).  Not all central heaters are dirty and wasteful.
Ross

Hi Ross,
I agree completely with your assessment of our site and with the frustration I sense regarding the treatment of central heating systems.  The fact is that I started my wood burning career in a wood furnace factory and was a true believer in central heating for several years.  You are quite right that not all central heaters are low-tech and that the Tarm is a fine example of what is possible. 

Our problem is that one model of one brand (Tarm) that is not widely known or available in North America does not constitute a class of appliance we feel comfortable recommending.  We cannot tell everyone who asks to go and buy a Tarm because we would then be criticized for promoting one commercial product.  We would prefer that central heating appliances, including outdoor boilers, be required to meet the same EPA emission requirements as stoves and fireplace inserts.  Then we could freely advise people to look for that class of appliance.

However, we know that many people have had bad experiences with dirty inefficient conventional furnaces and boilers and we don't want to be responsible for leading more people to get burned.  We feel somewhat between a rock and a hard place on this one.

A couple of questions for you:

1. Do you know of any other central furnaces or boilers that are clean burning and efficient?  Maybe if we could come up with a short list we wouldn't feel so bad about making recommendations.

2. What advice do you have for us to correct the apparent bias in the site?  We don't particularly want to be seen as promoting just stoves and efficient fireplaces.  Our mandate is to promote responsible wood burning, not just a couple of classes of appliance.

Thanks for your input on this troubling issue.
Regards,
John

Ross responds:
John, you are not the only one frustrated.  I'm a large animal veterinarian in northeastern Wisconsin.  I spend my day working with farmers - one quarter of whom still heat with wood.  When I tell them about my Tarm I get one of three responses.  

1. Hey, that sounds good.  Where is the nearest dealer? 
2. Hey, that sounds good.  When my current furnace wears out I'll look into that.  Where is the nearest dealer? 
3. If I knew about them earlier I wouldn't have bought that XXX!!! outdoor wood boiler. Where is the nearest dealer?  

I have to tell them, of course, that there is no nearest dealer and they would have to order them from the distributor and then find a qualified installer.  At that point their interest usually ends.  Tarm boilers are expensive units and with past low sales Tarm USA has been unable to maintain a dealer network.  Now that fuel prices are up more units could be sold but they don't have the network in place to do so. Most people have never heard about Tarm's so never consider getting one.  Everyone has heard of or seen an outdoor wood boiler so that is what ends up getting bought.  This is a Catch 22. 

To maintain your non-commercial basis in the face of central heating questions I would suggest a response like this.

"We at woodheat.org recommend only clean burning wood heating appliances.  The EPA has defined clean burning as those woodburning units that emit less than X.XX grams per hour.  The only wood fired central heating units that currently meet this standard are those that employ wood gasification.  At this time all commercially available wood gasification units are manufactured in Europe. Only one that we are aware of (HS Tarm) is imported into North America. We hope that more central heating manufactures will have their units tested so consumers can have a wider choice of heating units and companies."  

Keep up the good work
Ross

A comment from Tarm USA

Well, I can't stay on the sidelines "lurking" any longer so here are some comments from our perspective at Tarm USA, Inc. But first, Ross, I'm glad to know what your profession is. In all of our discussions during your purchase and installation of your Tarm boiler I never knew about what you did to make a living. You might find it interesting that my wife and I ran a small Qtr. horse breeding farm for 10+ years in Calgary Alberta until 1986. I've supported a vet or two in my earlier life!

Regards your email to John and the problem of "Where's the nearest dealer?" it is a serious problem for us. In fact, finding a competent, available heating system installer to do any installation is a problem in most parts of North America because the economy has been so strong for the past few years. As far as dealers for Tarms is concerned, you're right; cheap oil has made the market for wood boilers too small to keep the interest up by former dealers who used to sell and install a lot of units in the 70's and early 80's. Currently, our hopes are being buoyed up by a renewed interest because of the higher oil prices that seem to be holding up. We are getting calls from installers and plumbing supply houses who used to be active and who are starting to get inquiries. We have invested a lot of time and money on the belief that the situation would eventually turn and sales would justify our commitments. Maybe this is the start of something new. The fact is that there are a lot of installers with past Tarm experience and if the demand comes back they will become interested again. Just today I spent time with a heating contractor who fits this category exactly and who has 2 very strong prospects who have stated that they want Tarm boilers. We are seeing this scenario repeat itself frequently now. We'll see where this goes over the next few months and years.

One of the things we've done recently to help spread the information accurately about the gasification wood boiler technology and the many benefits of the heat storage technology we've been developing over the last two years is to make a new video. This video shows boilers operating in numerous homes and it shows several installations with heat storage systems. We send these out to anyone who shows interest. This helps a little to make up for our lack of knowledgeable dealers, we feel. At least we know that the information being given is accurate and true.

Ross, we think we're making progress here. We agree it is not as fast as we would like but we don't control oil prices. We hope to be ready when the interest is rekindled. If you know any good installers in your area let us know and we'd be happy to contact them so we could work on building a relationship. We have gained a number of really good installers the last two years but we need many more.

We sincerely appreciate your interest, concern and input. We always want feedback, good or bad, so we can get better. We know we have a long way to go but we're way ahead of some of the "smokers" that are being sold. "STAY WARM"

Lloyd Nichols , Tarm USA, Inc.