Add on wood furnace to forcer air system

[CowboyAndy]

Okay, with the predicted fuel prices, we are seriously thinking about a wood furnace to suppliment our heating.

Currently we have forced air, not sure of the size but I was told by the guy who does our annual service that it is a bit undersized. The house is roughly 1900 sq ft and the furnace is 105,000btu.

I have been looking on the net and found these...

http://www.vogelzang.com/Norseman2500.htm

http://www.barbecues.com/web/catalog...spx?pid=187795

http://www.englandsstoveworks.com/28-3500.html

What exactly would be involved in installing something like this? Is it something that would be worth installing?

FWIW, we will have all the hardwood we could want from my father in law.

 

[offroadaudio]

Take a good look at the Charmaster also.

 

[CowboyAndy]

Take a good look at the Charmaster also.

Thanks, I will look into it.

 

[johnsopi]

Yukon/eagle the Big Jack. I'm on my third winter with mine love it.

 

[Ken45]

Check out your furnace. I was told that connecting a wood furnace to a heat pump/AC furnace would void the warranty (and I assume do damage).

We just ducted ours directly to a new register in the floor and it works well. There is enough convection that the blower stays off most of the time.

Ken

 

[CREEKY]

As a dealer of wood furnaces we install about 30 systems each winter that are added to existing forced air furnaces. The comment was right that some heat pumps can't handle the heat of a wood/coal furnace. Sometimes we design a damper plate in the supply plenum of the oil furnace so we aren't sending heat thru it. It is easy to install and can be removed easily. The only downfall is that you must turn off the oil furnace while damper is in place. Sometimes the heat from the wood furnace turns the oil furnace blower on and you can have to much heat. This could be another reason for the damper idea.

 

[offroadaudio]

As a dealer of wood furnaces we install about 30 systems each winter that are added to existing forced air furnaces. The comment was right that some heat pumps can't handle the heat of a wood/coal furnace. Sometimes we design a damper plate in the supply plenum of the oil furnace so we aren't sending heat thru it. It is easy to install and can be removed easily. The only downfall is that you must turn off the oil furnace while damper is in place. Sometimes the heat from the wood furnace turns the oil furnace blower on and you can have to much heat. This could be another reason for the damper idea.

The Charmaster has this damper built in.

 

[begreen]

Do some research and investigation into this. Besides stout, efficient and safe furnace construction, you'll want a very safe and controllable installation. Do you have an independent flue for the wood burner? Adequate clearances for the supply plenum? Adequate air supply?

FWIW, this is not something I would buy from an online barbeque shop.

 

[solarguy]

I know many people that have installed warm air wood fired units & although they are cheaper to purchase when compared to a wood fired boiler the installation can be expensive.

There are always issues with clearances from the supply air pluenum & the automatic control dampers. One down side is they do radiate a ton heat when the unit is in idle mode becoming one big wood stove.

I would suggest you also look at wood boiler & weigh the costs of both installations. With a wood boiler all you need is a hot water coil & some control wiring. We've found that many times a boiler installation ends up being cheaper. Plus a boiler will last longer.

 

[JustWood]

Check out Meyer Mfg. I love my Woodchuck. Installed it myself with little effort.

 

[BrownianHeatingTech]

Currently we have forced air, not sure of the size but I was told by the guy who does our annual service that it is a bit undersized. The house is roughly 1900 sq ft and the furnace is 105,000btu.

Does it heat your house on the coldest day of the year? If so, then it's not undersized.

Actually, though, even figuring that the output of the furnace is probably 75% of the input, you're still at over 41 btu per square foot, which is rather high. So I would say that your furnace is almost definitely oversized, not undersized. If you are having any lack of heat, I would look at the ductwork before thinking that the furnace was too small.

Joe

 

[CowboyAndy]

Check out your furnace. I was told that connecting a wood furnace to a heat pump/AC furnace would void the warranty (and I assume do damage).

We just ducted ours directly to a new register in the floor and it works well. There is enough convection that the blower stays off most of the time.

Ken

It's not a heat pump, just a standard forced air furnace so I don't think that would be a problem.

Do some research and investigation into this. Besides stout, efficient and safe furnace construction, you'll want a very safe and controllable installation. Do you have an independent flue for the wood burner? Adequate clearances for the supply plenum? Adequate air supply?

FWIW, this is not something I would buy from an online barbeque shop.

I am not sure about the flue issue, that is one thing we need to figure out before proceeding with this. I can say for sure that our chimney has 2 seperate flues, one for the funace and one for a fireplace that has never been used.

Also, we probably wouldn't buy from an online bbq shop, that was just to show one of the stoves we were interested in.

I know many people that have installed warm air wood fired units & although they are cheaper to purchase when compared to a wood fired boiler the installation can be expensive.

There are always issues with clearances from the supply air pluenum & the automatic control dampers. One down side is they do radiate a ton heat when the unit is in idle mode becoming one big wood stove.

I would suggest you also look at wood boiler & weigh the costs of both installations. With a wood boiler all you need is a hot water coil & some control wiring. We've found that many times a boiler installation ends up being cheaper. Plus a boiler will last longer.

Would a boiler system work with an existing forced hot air system? We have no intention at this point of changing our entire system, we just don't have the $$$.

Currently we have forced air, not sure of the size but I was told by the guy who does our annual service that it is a bit undersized. The house is roughly 1900 sq ft and the furnace is 105,000btu.

Does it heat your house on the coldest day of the year? If so, then it's not undersized.

Actually, though, even figuring that the output of the furnace is probably 75% of the input, you're still at over 41 btu per square foot, which is rather high. So I would say that your furnace is almost definitely oversized, not undersized. If you are having any lack of heat, I would look at the ductwork before thinking that the furnace was too small.

Joe

It heats the house okay, but we go through fluel like crazy. We have recently insulated the whole house, sealed air leaks, new window and doors, etc. During the coldest months we average about 150-175 gallons of oil a month. Our main problem is the upstairs. There is no ducting going up there, except one bedroom. Our thinking was that if we could afford to turn the heat up at night, then the upstairs would be warmer.

 

[BrownianHeatingTech]

Would a boiler system work with an existing forced hot air system? We have no intention at this point of changing our entire system, we just don't have the $$$.

Yup. You install a heat exchanger in the airstream. Basically, think of an automobile radiator - lots of small tubes and fins to transfer heat from the water to the air. Of course, the ones used for heating are made a bit differently than a car radiator, but that should give you the basic image.

It heats the house okay, but we go through fluel like crazy. We have recently insulated the whole house, sealed air leaks, new window and doors, etc. During the coldest months we average about 150-175 gallons of oil a month. Our main problem is the upstairs. There is no ducting going up there, except one bedroom. Our thinking was that if we could afford to turn the heat up at night, then the upstairs would be warmer.

I doubt your furnace is oversized. Typically, undersized furnaces run less efficiently and waste fuel.

If you have no heat upstairs, a boiler may be a better plan. That way, as funds allow, you could install baseboards, radiators, or fan convectors up there using the hot water system directly. No need to try and run ductwork - 1/2" or 5/8" pex can be snaked through walls or otherwise hidden on its way from the basement to the second floor.

Extending heat to the second floor may generate a high WAF, as well!

Joe

 

[CowboyAndy]

Yup. You install a heat exchanger in the airstream. Basically, think of an automobile radiator - lots of small tubes and fins to transfer heat from the water to the air. Of course, the ones used for heating are made a bit differently than a car radiator, but that should give you the basic image.



Joe

Can you point me in the right direction for something like this?

If we were to go with the water system, can we get domestic hot water off it too?

 

[BrownianHeatingTech]

Can you point me in the right direction for something like this?

The best heat exchanger will depend upon the heat demand for your house, and the physical dimensions of your plenum and ductwork. There are a number of manufacturers of heat exchangers, and we typically specify them based on what fits, not the brand name of the coil, since most are of similar quality.

If we were to go with the water system, can we get domestic hot water off it too?

Yup. A heat exchanger can be added to your existing hot water tank, or a completely new tank can be installed.

Joe

 

[CowboyAndy]

Can you point me in the right direction for something like this?

The best heat exchanger will depend upon the heat demand for your house, and the physical dimensions of your plenum and ductwork. There are a number of manufacturers of heat exchangers, and we typically specify them based on what fits, not the brand name of the coil, since most are of similar quality.

If we were to go with the water system, can we get domestic hot water off it too?

Yup. A heat exchanger can be added to your existing hot water tank, or a completely new tank can be installed.

Joe

I tried a quick google search, but all I could come up with were the outdoor wood boilers. Can you suggeest where to look and more specificly what TYPE I am looking for?

 

[BrownianHeatingTech]

I tried a quick google search, but all I could come up with were the outdoor wood boilers. Can you suggeest where to look and more specificly what TYPE I am looking for?

You're looking for a water to air heat exchanger.

http://www.heatexchangersonline.com/airtowater.htm shows some examples. (not an endorsement - I've never done business with them - just the first thing that showed up on my quick web search)

I tend to err on the side of making heat exchangers a bit large. That reduces the airflow requirements, which saves energy. Using the charts on that site, I would suggest the 16x18 or 18x18 for your system. That's based on guessing that your 105kbtu furnace really only produces about 80kbtu (listed input, multiplied by probable efficiency).

The 18x18 is more than you need, which means you could run with a lower fan speed and a smaller circulator pump, and still get the required output, which in turn means better efficiency. Of course, whether you could (mechanically) fit that large of a heat exchanger in your ductwork is another question. Heat exchangers always go on the supply side of the furnace, by the way. And hot water heat exchangers are typically installed after A/C coils.

Joe