Fuel Oil Furnace not Cutting it - Outdoor Wood Furnace Almost Helps - Air Flow Issue?

[usergray]

I started heating my home with an outdoor wood furnace this year. The home is old and drafty. When storms come through the area my furnace just can't keep up and the fan in the basement runs constantly. My guess is that the air temperature is lower with the OWF than with the fuel oil and the ducts can't move the proper volume of air. Does that sound right? Correcting this is a big job and I'm not up for that just now.
Another idea I have is to allow outside air into the home to reduce the pressure changes from high and low pressure systems moving through the region. How does this idea sound?
Has any one else had this type of trouble converting from fuel oil to an OWF? Were you able to resolve the issue? How did you do it?
Thanks!

 

[blakey]

Check the belt on your fan, I have had to tighten it a bit which speeds up the fan.

 

[Cedar-Acres]

Did you get a heat exchanger that was rated at least as much BTU/hr as the oil furnace produces? When I got mine I figured the electric furnace I have produces a nominal 75k BTU/hr. I got a heat exchanger rated for 95k BTU/hr and have much warmer air out of the ducts with the OWB than with the electric heat. Electric heat gives me an air duct temperature of about 110 degrees and the OWB setup gives me 140 degrees at the same air duct with the OWB tank temp holding at 160 degrees.
You might check the heat exchanger inlet and outlet temperatures to see how much of a temperature drop it produces. If you see a large drop then I would suspect your heat exchanger is undersized for your system.

 

[coalman]

I had the same problem with a customer last year he had a big heat exchanger and the pump wasn't big enought we changed the circulator pump and he has more heat now than with the oil furnace

 

[Cedar-Acres]

Coalman, that sounds right. If the inlet and outlet temperatures show a large drop in temperature then there is insufficient water flow to provide the BTUs the system needs. A larger pump would solve the problem. On the other hand, if there is sufficient flow and the heat exchanger is too small then there would be very little drop between the inlet and outlet temperatures.

 

[jcappe]

Coalman, that sounds right. If the inlet and outlet temperatures show a large drop in temperature then there is insufficient water flow to provide the BTUs the system needs. A larger pump would solve the problem. On the other hand, if there is sufficient flow and the heat exchanger is too small then there would be very little drop between the inlet and outlet temperatures.

What would you is an acceptable temp drop from the inlet and outlet sides of the hx? I'm still trying to figure out why I can not get a good air temp out of my registers. Water going in to hx is 170 air temps at closest register is 110ish.

 

[Cedar-Acres]

I will measure actual inlet and outlet temps on my system and post them when I get home this evening.

 

[laynes69]

Bringing outside air into the home will increase heat loss. If your home is old and drafty fixing those drafts would be the first thing to do. The stack effect in a home causes pressure differences. If you have an outdoor furnace pushing heat you need returns also. Air sealing in the attic and working your way down will save alot of money in the long run and increase comfort. I still have a little ways to go, but just airsealing alone we have cut heat loss by at least 25%.

 

[Cedar-Acres]

Ok, here are the actual numbers:

HX inlet temp : 161 degrees
HX outlet temp : 137 degrees
Air duct temp 14 feet from the HX : 136 degrees

These temps were taken with an IR thermometer. I had spray painted the spots I took the temps with flat black paint when I installed the system. That gives a more accurate reading. This is at the tail end of a long run. The system had been running awhile and warmed the house from 65 degrees to 72 degrees after the setback thermostat bumped the temp up prior to me coming home.

 

[nt3041]

Hi;


I would speed up the fan as much as possible without overloading the motor. You might need an adjustable sheave on the motor so you can make the adjustment. Check the motor amperage with an amprobe. and adjust. Try a larger pump that gives you approximately 20* F difference between the inlet and outlet temperature.

Good Luck

 

[mtfallsmikey]

Did you get a heat exchanger that was rated at least as much BTU/hr as the oil furnace produces? When I got mine I figured the electric furnace I have produces a nominal 75k BTU/hr. I got a heat exchanger rated for 95k BTU/hr and have much warmer air out of the ducts with the OWB than with the electric heat. Electric heat gives me an air duct temperature of about 110 degrees and the OWB setup gives me 140 degrees at the same air duct with the OWB tank temp holding at 160 degrees.
You might check the heat exchanger inlet and outlet temperatures to see how much of a temperature drop it produces. If you see a large drop then I would suspect your heat exchanger is undersized for your system.

That is a splendid idea...Your supply temp. from the OWB can vary greatly, so oversizing the HX makes sense, with it you will get enough heat output, even with water temps down to 155-160, with proper airflow. My supply air temps are 130-140, a 20-25 deg. temp. drop across in/out piping is normal. Need to seal up/insulate, best money you can spend.

 

[usergray]

Wow. Thanks to everyone for your ideas. I have lots to try but I'm on a $0 budget right now. I will totally be adding insulation to my house when I can. I'm sure the heat exchanger is big enough but going bigger wouldn't be too hard so maybe I'll do that. I don't know enough about the fan to change the speed or whatever. It would probably work but the thing is so old I'll just wait until it dies and then upgrade.
What has worked these past weeks is that I've cracked the basement window in the furnace area. It's just a small opening but what I think has happened is that my furnace doesn't have to fight the cold air getting sucked into every room of the house, especially the living room where the thermostat is. Instead the air is sucking into the furnace and being pulled directly into the cold air return. This, in-turn, is being warmed and fed into the rest of the house. My wood consumption has dropped a small but noticeable amount; even with the extreme cold of the past few weeks.
I know this isn't a great solution but it seems to be working. What are your thoughts guys? I really appreciate being able to bounce ideas off the community.
Thanks!