Any help is appreciated..... We bought my grandma's house not sure who installed everything but this has been used this way for the last 10 years or so. The problem is with my wood furnace I'm not getting very warm air out of my ducts. The fan from my oil furnace is kicked in once the wood stove reaches temp. The cold air return for the house is ducted into the oil furnace(blue). The oil furnace is ducted into the cold air return on the wood furnace (red). All warm air produced by both furnace passes through the plenum on the wood furnace into the ducts and it's distributed through the house (yellow). When the oil furnace runs by itself the plenum gets very warm to the touch and I get 100° heat out of my vents upstairs. When I run just the wood furnace I only get 82-84° heat out of the vents and the plenum isn't even warm to the touch. My chimney is approximately 36' tall and is 6" stainless steel lined inside the original brick with clay flue. I have a damper installed the the connecting pipe from the furnace to the chimney. That pipe is only 30" long because the chimney is right behind the wood furnace. The wood furnace is a Clayton 1600. I use a natural air draft on the wood furnace. I'm heating about 2300 square feet including the basement.
Not getting much heat
- Thread starter 53ksm
- Start date
Help Support Arborist Forum:
Gabriel1982
Addicted to ArboristSite
Oil has a higher kwh per unit lbs or kg than wood! Some temperature measurements should be taken in the stove and outside of stove in the exhaust pipe right near the stove(s). For the oil and wood stove! If that's ok, not a big difference ,then problem is elsewhere! A good fresh air supply for the wood is a must or wood won't burn well with less oxygen,not giving up all kwh heat and burning with a lot of smoke!
Also chimney must be clean,from top to right near the stoves!
If still there's not enough heat compared to oil stove,try drier wood with lots of fresh air draft!
Temperature measurements are essential,or else you will blindly look for the "problem"!
Also chimney must be clean,from top to right near the stoves!
If still there's not enough heat compared to oil stove,try drier wood with lots of fresh air draft!
Temperature measurements are essential,or else you will blindly look for the "problem"!
Your not running both off the same chimney are you? If so that's most likely effecting your draft of the wood furnace. I have no issues getting 100*f+ plenum temps from my wood furnace. The fan kicks on when the bonnet hits 90*f and doesn't shut off till the bonnet temp hits 70*f. Grate temps depend on how long the furnace has Been running and the closest to the furnace can get quite warm. Really it's all about moving air efficiently, you can barely feel the air coming out of the grates but the house is always nice and warm, too warm sometimes.
Doubt it, if tour return air is plumbed right it will also keep getting hotter as it's drawn through the furnace over and over again. I'm assuming a reasonably tight house that isn't loosing heat fast.
samaritan
ArboristSite Operative
I've worked on oil heat for many years. either check it's fire or have someone do it, the air temp should be about 140 degrees, maybe it needs a bigger nozzle or just an air adjustment. And be sure the chimney's are clean!
Thank you for the response. I'm very happy with the oil furnace. It is the wood furnace that seems to be underheating.
Both furnaces don't running off the same chimney do they?
Yes they do. The wood has an elbow immediately then about 24" of pipe straight into the mason chimney with stainless liner. The oil furnace has about 7' of pipe. It T's into the same mason chimney with stainless liner. It's a Mickey mouse thing. There is a barometric damper installed in the oil furnace pipe.
There's your issue. I doubt your wood furnace is getting the draft it needs as it can pull cold air from the oil furnace. Really each appliance needs its own dedicated chimney. I can't comment for your area, but here it's against building code for 2 appliances to share a common chimney. My dad found this out the hard way in his shop. It had an oil furnace and a wood furnace. He didn't use the oil furnace when we still lived at home, so the wood stove was hooked up and the oil burner went unused. After we all grew up and moved out, there wasn't 3 boys tending the fire. Dad got a T and hooked up the oil furnace to the chimney in conjunction with the wood stove. Creosote city and hardly any heat out of the wood stove. The oil furnace has a forced draft so it didn't seem to care.
Ok. Could I put a damper in the oil furnace pipe to close things off more or would that be pointless?
Without digging into too many details, I believe that there is a serious mismatch between the two heat sources, and they should probably not be mixed.
Some observations:
1. Most stoves have a lower heat rating than a house furnace. I'd guess 35,000 btu to perhaps as high as 60k. Most home furnaces have 60k to 120k btu output. The difference, of course, is that furnaces run only intermittantly, and their air flow is generally much higher. The largest stove in quadrafire's lineup comes in at 72k btu. https://www.quadrafire.com/products/5700-step-top-wood-stove
Their smallest fireplace insert comes in at 37,000 BTU.
2. In light of #1, you should expect a serious mismatch in what is called the temperature rise. Wood stoves are engineered around keeping the firebox hot, and producing a steady (but low volume of air) stream of continuous heat. Turning a high capacity air handling system loose on a low air volume system is going to guarantee a lower temperature rise, as the firebox of the stove was never engineered to lose that much heat to high air flow.
3. You need to measure the temperature rise of each heating source, not the final output. Measure the temperature of the air going in, and then the air coming out. This is the temperature rise, and it will tell you a lot about how each device is working, especially if you can figure out how to...
4. Measure the air volume moved through each heat exchanger. Get a cheap spirometer and measure the air flow. Then multiply by the duct diameter coming out. With a little bit of math, you can figure out whether your devices are really producing enough heat for the house. Kinda complex, but anything less is just guesswork.
5. 140° exhaust temperature would be WAY too high for a conventional forced air furnace. You would be at risk of burning up the heat exchanger from inadequate cooling, and that much heat going through the ducts would be kind of dangerous, as well. Most people signal acute pain at temperatures above 120°, tissue damage occurs at 140° and up.
6. Any draft problems you might have will not probably influence the air temperature rise, except that a fire not making enough heat won't have a significant temperature rise. If the furnace and wood stove share a common exhaust up the same chimney pipe, I would expect any fireplace to burn a bit cooler when the furnace fires up. That might be causing a bit of back-pressure on the stove exhaust, with a subsequent reduction in heat.
7. You should avoid any scenario where the stove feeds warmed air into the furnace. Remember my remarks about temperature rise? When all other factors remain the same, feeding warm air into the furnace heat exchanger causes it to run hotter, and it's lifetime is thereby made shorter.
8. Any reduction in air flow over the furnace's heat exchanger will cause the same problem: hotter air, shorter lifespan, with the production of holes that leak CO2 and carbon monoxide into the house. This is always a bad result.
9. If you are having heating problems in general for a system that formerly worked, check all your ducts for having adequate air flow. In my experience, ductwork never gets any better than the day it was installed, so find any problems. Really dirty vanes on the blower are the most likely source of low air flow, providing that you at least don't have an obstructed air filter.
10. I can easily imagine that the air passages of a wood stove could become lined with ash, dust, or rust, and then the temperature rise will be too low, regardless of how well the wood fire is producing heat. Clean if possible!
Some observations:
1. Most stoves have a lower heat rating than a house furnace. I'd guess 35,000 btu to perhaps as high as 60k. Most home furnaces have 60k to 120k btu output. The difference, of course, is that furnaces run only intermittantly, and their air flow is generally much higher. The largest stove in quadrafire's lineup comes in at 72k btu. https://www.quadrafire.com/products/5700-step-top-wood-stove
Their smallest fireplace insert comes in at 37,000 BTU.
2. In light of #1, you should expect a serious mismatch in what is called the temperature rise. Wood stoves are engineered around keeping the firebox hot, and producing a steady (but low volume of air) stream of continuous heat. Turning a high capacity air handling system loose on a low air volume system is going to guarantee a lower temperature rise, as the firebox of the stove was never engineered to lose that much heat to high air flow.
3. You need to measure the temperature rise of each heating source, not the final output. Measure the temperature of the air going in, and then the air coming out. This is the temperature rise, and it will tell you a lot about how each device is working, especially if you can figure out how to...
4. Measure the air volume moved through each heat exchanger. Get a cheap spirometer and measure the air flow. Then multiply by the duct diameter coming out. With a little bit of math, you can figure out whether your devices are really producing enough heat for the house. Kinda complex, but anything less is just guesswork.
5. 140° exhaust temperature would be WAY too high for a conventional forced air furnace. You would be at risk of burning up the heat exchanger from inadequate cooling, and that much heat going through the ducts would be kind of dangerous, as well. Most people signal acute pain at temperatures above 120°, tissue damage occurs at 140° and up.
6. Any draft problems you might have will not probably influence the air temperature rise, except that a fire not making enough heat won't have a significant temperature rise. If the furnace and wood stove share a common exhaust up the same chimney pipe, I would expect any fireplace to burn a bit cooler when the furnace fires up. That might be causing a bit of back-pressure on the stove exhaust, with a subsequent reduction in heat.
7. You should avoid any scenario where the stove feeds warmed air into the furnace. Remember my remarks about temperature rise? When all other factors remain the same, feeding warm air into the furnace heat exchanger causes it to run hotter, and it's lifetime is thereby made shorter.
8. Any reduction in air flow over the furnace's heat exchanger will cause the same problem: hotter air, shorter lifespan, with the production of holes that leak CO2 and carbon monoxide into the house. This is always a bad result.
9. If you are having heating problems in general for a system that formerly worked, check all your ducts for having adequate air flow. In my experience, ductwork never gets any better than the day it was installed, so find any problems. Really dirty vanes on the blower are the most likely source of low air flow, providing that you at least don't have an obstructed air filter.
10. I can easily imagine that the air passages of a wood stove could become lined with ash, dust, or rust, and then the temperature rise will be too low, regardless of how well the wood fire is producing heat. Clean if possible!
user 184817
ArboristSite Lurker
- Joined
- May 10, 2022
- Messages
- 9
- Reaction score
- 11
Both flies going together are fine there is no issue with poor drafting. Unsure of what the problem is but oil and gas flues are joined all the time. Can’t mix natural gas or propane with wood or oil.
Is the fire big enough is your wood wet? Is the damper for the fire box working. The wood should be hotter than the oil.
Is the fire big enough is your wood wet? Is the damper for the fire box working. The wood should be hotter than the oil.
Thank you for the detailed write up. I will start trying to gather some of the weekend to look at the different things you mentioned. To be clear the furnaces are never fired at the same time. The oil furnace simply draws cold air through the return ducts. That cold air then passes through the unfired oil furnace and into the cold air return on the side of the wood furnace. That same air blows the hot air out of the plenum on top of the wood furnace. The ambient air in the house is typically between 68-70 depending on outdoor conditions. With the wood furnace fired the heat coming out of the register is 82-84. I know these measurements aren't taken where you asked for them but it's all I've got for now. There are only 2 runs off duct work carrying hot air, each run has 2 outlets into the house. The blower on the oil furnace is on its lowest setting and the hot air coming out of the ducts had plenty of speed to it.
Just because bad installation habits are normal doesn't mean they are right, nore does it mean they are up to building codes. Oil and wood furnaces have different draft requirements. Hooking up 2 appliances causes cold air to be drawn into the chimney from the unused appliance. This effects draft.
Took some temps with an temp gun from my furnace. Room temp in the basement is about 65*f I started the fire about an hour ago. Fan just kicked in. Bonnet it running 95*f flue temp 12" from out let is 550*f furnace feed door is running around 287*f. Register temp in the middle of the house is 87*f. Main house temp is 68*f and rising. In about an hour or so I'm sure I'll be cutting the furnace back. Outdoor temp is 28*f. Heating 2600 Sq ft.
Attachments
user 184817
ArboristSite Lurker
- Joined
- May 10, 2022
- Messages
- 9
- Reaction score
- 11
Since I am a licensed wood burning inspector I can say that that most building codes don’t cover wood burning systems. In Canada it is a separate licence to inspect and install wood burning systems. The system appears normally installed unless it is two separate units then there can be some issues but they would be seen on the oil side as well.
To the OP is the a combination furnace or two separate units.
To the OP is the a combination furnace or two separate units.
No offense mate, we're in the states, not Canada. NFPA sections 31 and 211 cover this here. As well as state and local laws. His first picture shows its an add on unit.
user 184817
ArboristSite Lurker
- Joined
- May 10, 2022
- Messages
- 9
- Reaction score
- 11
And the world doesn’t revolve around the US how are we supposed to know where this is? This is the internet and this site has members from around the world. The pictures are also not clear that’s why I asked for more info.
Just giving advice based on my location. And after 20 years of inspecting buildings in North America the codes are not that much different.
Cheers.
Just giving advice based on my location. And after 20 years of inspecting buildings in North America the codes are not that much different.
Cheers.
As to location? Most members post their location under their avatar. In this particular conversation, that is "MN", presumably for Minnesota.
