OWB Tweaking or Modifying

Junior437t · February 05, 2010, 09:20:27 PM

I have a Free Heat Machine OWB. It is right at 100 feet from my house. I have been thinking about trying a modification to use less wood. The pump on this unit circulates the water constantly, even when there is no call for heat. There has to be some heat loss just from circulating the water, or at least I would think so. I have a heat exchanger in my ductwork. I had a forced air oil furnace before I got the OWB. The existing blower on the oil burner blows the heat into the house. What I am considering is adding a timer and only run the pump when there is a call for heat. I would use an "On delay timer". I would wire it so that when the thermostat called for heat, the pump would kick on and maybe 30 seconds later, the blower would kick on. It could be set up so that the blower and the pump kicked off at the same time or could use an "off delay timer". If I used that, I would set it so that the pump would kick off and a few seconds later, the blower would kick off. Has anyone done anything like this? What drawbacks are there that I do not anticipate? I have experimented manually a few times by turning the pump off with the breaker and it seemed to use much less wood. This might not save much wood when it is extremely cold but when mild, I believe it will save a lot of wood. I have not kept track and timed it, but the blower on the furnace actually runs very little of the time. I can get the timers for cheap or free. I have the wire that I would need, so really the only cost would be some labor. Thanks in advance for ideas or suggestions.

Gary_C · February 05, 2010, 11:51:59 PM

I am not sure where significant heat savings would come from on the changes you propose. I don't believe the heat loss in the pex is significant. Plus I think you will cause thermal stresses in the OWB if the fire starts up with no water circulation.

Others have looked at the electricity for the circulation pump and found it to be rather low.

Here is another idea that I doubt also.

https://forestryforum.com/board/index.php/topic,41470.0.html

woodmills1 · February 06, 2010, 08:23:46 AM

I thought that the constant circulation was needed to insure that the stove water does not freeze in the pex from the back of the stove to the ground

My free heat machine is closer to my house, but I have a nearly 60 foot run to the furnace inside the house. I see less than a 10 degree drop in water temp from the OWB furnace to the hot air furnace, and that is after it goes to the sidearm on the hot water heater.

The one thing I would like to try, but have not due to warrenty concerns, is to drill a hole in the plate the opens by solenoid when the booster fan comes on. As it is now when the booster fan on the OWB is off, the solenoid completley closes the air pathway to the stove, so when the fan is off the only air that gets drawn into the firebox is what can leak around the plate. My thinking is with the right sized hole the fire could smoulder, burning less wood overall but keeping the temp up with using the booster fan as much. What stops me from trying this is if the hole allowed too much air I could overfire the furnace

bandmiller2 · February 06, 2010, 10:34:47 AM

junior I'am no heating engineer but it seems to me just a heat exchanger in the ducting can't be that efficient.Myself I ran slantfin baseboard hydronic heat and some radiant floor heat.The baseboard drops the water temp so its suitable for the radiant.Its not hard to run baseboard in addition to your heat exchanger.That way you could utilize the constant heat from your OWB ,would not be good form to stop the circulation.You need to get more heat from your system and possibly lower the water temp and save wood.Frank C.

Junior437t · February 06, 2010, 06:28:25 PM

Thanks for the ideas and thoughts. The heat exchanger seemed to be the best option since I already had the existing forced air furnace and ductwork. With the heat exchanger, basically all I had to do was cut a 4 inch section out of the duct and slide it in. It would be worthwhile for me to research adding the lines to the bottom of my floor and work from there. I would think that would allow me to lower the water temperature. I would be able to lower the temperature considerably. I will also research baseboard heaters also. I have not adjusted the water temp so it is still on at 150 and off at 185. Are there any thoughts on what would happen if the water temperature was lowered? I realize it might take a little longer for the thermostat to be satisfied so it might not save anything. I am not considering the power usage as I am sure it is basically nothing in the long run. My lines are pretty well insulated so I think I am in good shape there. I have foam insulation over the line, that is inside 1 1/2" conduit and that is inside 4" sewer line. I suppose part of my aggravation is that I have burned way too much wood this winter and the stove has never been as efficient as I was told when I bought it. On a normal day, I have to load it early morning, again early evening and again before bed time. This year I had mostly dry oak cut 20" long and only split enough to handle it. I have burned a lot more wood than I ever have before. I have cut 6 pickup loads since Christmas and I am out again. We have had more snow than normal but it hasn't really been any colder. Thanks

jackpine · February 06, 2010, 08:58:36 PM

Woodmills
You are right, a small hole will allow the fire to smoulder and require the blower to cycle less often but it will also generate more creasote inside the boiler that may or may not burn off at the next cycle. The new owb I installed this year has an air leak I have not been able to find and does exactly what you want and has not overheated yet but I cannot burn pine slabwood without the temperature continueing to rise. I would prefer to see the unit sut down as it should, in fact I have the factory tech coming on Monday to troubleshoot the unit. I also do not think you will save any noticable amount of wood usage with a continuos smoldering fire. My main reason for wanting the unit to cycle normally, besides being able to burn slabwood, is with a smouldering fire there is a loke of smoke all day long, not just when the unit cycles.

Bill

woodmills1 · February 06, 2010, 09:56:12 PM

I will say my free heat unit hardly smokes at all

Junior, how large is your house, and check my OWB experiment post. that wood is over 2/3 gone.

bandmiller2 · February 07, 2010, 07:29:21 AM

Junior,you need the high temp water for your heat exchanger and even baseboard that will cycle on and off.My system runs between 130 and 140 but its always circulating and thus the lower temp works.Believing OWB manuf. about wood useage is like believing politicians.Read up on radiant floor heat its comfy but you cant let the water get too hot I use the return water from the baseboard.It takes a give amount of wood to keep a fire going might as well utilize as much of the heat as possible.Frank C.

red oaks lumber · February 07, 2010, 01:47:10 PM

junior,
you might close the gap on your temp, mine kicks on at 170 and shuts off at 185. by keeping your water warmer you'll use less wood always bringing it up to temp.

LAZERDAN · February 07, 2010, 06:57:07 PM

Junior I had been thinking the same thing for years, my neighbor just installed a new outdoor boiler and it shuts down like you want. You can do the reasearch under installation or call them , it must work i'm jealous of him very little smoke and uses very little wood. Best Outdoor Wood Furnace
Enjoy Wood Burning at it's Best. Choose a Shaver Outdoor Wood Furnace today! ... Shaver Outdoor Wood Furnace: An outdoor wood furnace is as the name implies ...
www.outdoorwoodfurnaceboiler.com/ - gota go games on . Lazerdan

Junior437t · February 15, 2010, 06:34:34 PM

I am heating about 1280 sq ft, (32x40), 6 inch thick hemlock log walls. I have 4 inches of sytrofoam insulation in the roof. I have 1 inch sheeting, the insulation and then 1 inch sheeting for metal roof. The floor is 1 inch poplar, 3/4 plywood and the 3/4 oak flooring, ran into a deal for the 3/4 inch plyhwood and bought it for less than price of 3/8. I have 4 inches of fiberglass insulation under the floor over a crawlspace. I like the idea of radiant heat on the floor. I have about 500 feet of 1/2 inch pex and 200 feet of 3/4 inch. I have read that 1/2 inch may not be the best size to use. I bought the 1/2 when I bought the furnace. I was hoping to use it when I pour cement for my garage floor. That is what they told me I needed. The way my house is laid out, I thought 3 or 4 "zones" would be the best setup. Would it work if I bought a manifold for the number of zones and then installed and used the zones as I go? Would it be logical to have the water circulate through the heat exchanger and then out to the floor heat? Would if be worthwhile to have a thermostat in each zone and have that control a solenoid? Would I have problems with the higher water temperature it runs at? I am not sure If I can tighten up the on and off temperature on the existing thermostat. I realize I have lots of questions and that I could call somebody like Radiant Floor Company with them. Sometimes the practical knowledge that is in a forum like this is more accurate than the advice from someone trying to sell components.
I realize I would have to remove the insulation under the floor, install the "plates" with the line and then I could put the insulation back in place. I appreciate the advice offered here. Thanks

woodmills1 · February 15, 2010, 09:43:11 PM

If your furnace is like mine take the cover off the retangular control box, you can then change the shut off temp and the drop range. I set my off temp a 160 for early and late in the heating season, with like a 10 degree drop to kick on, and 185 on for the cold season with a 15 degree drop

BBTom · February 15, 2010, 09:57:47 PM

Been running Taylor OWB since 88 and have never had full time circulation. Always turn on the circulator when the thermostat calls for heat. Always wondered why some stoves had that extra pump on them. Now I know.

Holmes · February 16, 2010, 11:17:09 AM

Junior Your house needs over 60,000 btus to heat it make sure your heat exchanger is large enough. If not put in a bigger 1 ,or add baseboard heat. Figure about 400 btus per foot of baseboard heat, and if you can, install it in the colder areas. You can install it after the heat exchanger. Radiant is very nice but it is difficult to drive the heat thru your 21/2" thick floor, adding baseboard will be cheaper and easier.The more heating element you install the easier it is to make your house warm. Like Frank said if your burning it you should use it. Try to keep all the pipes in the warm area to avoid freezing problems. Holmes

splitter · February 16, 2010, 11:59:29 AM

I have a Heatmor my circulating pump is controlled by a thermastat in the house and my water temp. is controlled by a aquastat, only circulates water when you need heat. A aquastat is on the pipe that goes into the heat exchanger making sure the water temp. is up before the fan cuts on. This way you won't get cold air blowing in your duct work. I also have a aquastat on my domestic water tank that circulates water when the temp. drops, works great. Splitter

Junior437t · February 16, 2010, 09:57:40 PM

Quote from: woodmills1 on February 15, 2010, 09:43:11 PM
If your furnace is like mine take the cover off the retangular control box, you can then change the shut off temp and the drop range. I set my off temp a 160 for early and late in the heating season, with like a 10 degree drop to kick on, and 185 on for the cold season with a 15 degree drop

I took the cover off and found the adjustment. I adjusted it to close the gap. I am only burning enough this week to keep it going. I am pretty well out of wood so I am trying to m ake it to the weekend and will plan to cut some more then. I will have to deal with the snow and cut it. Nerly everyone I know that burns wood is out. Of course that has made the price go up, supply and demand system. We have 6 or 8 inches of snow on the ground right now and they are calling for 12 to 15 between now and Thursday. Supposed to get above freezing for Friday and Saturday. I will look into the baseboard heat. The reading that I read about it indicated that it wasnt too bad expensive. Thanks for the ideas.

woodmills1 · February 17, 2010, 10:57:05 AM

the other thing I don't think that has been asked is about your pex size. How large are the pipes to and from the stove through the heat exchanger. I use hot air with an exchanger in the plenum on a much larger house and it works well.

About the pipe size.....for example if you are using 1" and one of your exchangers is only half inch..the flow is cut to 1/4

Junior437t · February 17, 2010, 04:17:38 PM

The lines from the burner are 1 inch. The connectors on the heat exchanger are both 1 inch also. The sales order from the manufacturer lists the heat exchanger as 140,000 btu.

woodmills1 · February 18, 2010, 06:53:43 AM

OK a couple of other things

fan speed on your furnace....if it is too high..it might be cooling off your air too much
I checked my air temp at some of the floor registers and it is only a few degrees below the water temp, at least in the registers close to the furnace

and......filters.......I find I need to be religious on changing the filters in my return system....and when it is really cold I cannot use the pleated kind as they restrict the air flow enough so the outdoor furnace needs to work too hard to keep up

remember though my house is nearly 3 times the floor space and we have weeks of -10 nights and 10 above days

trapper · February 18, 2010, 01:30:37 PM

on the pipe size. I put a kickbox heater in the new bathroom. It uses half inch copper pipe. the rest of my loop is three forth copper. I put in a three forth tee reducing one side to one half for the kickbox heater and added three forth pex to the other side of the tee in the loop. pex having the fittings on the inside as opossed to fittings on copper being on the outside seems to force water to both lines without restricting flow in the loop.
If some one sees an error with my thinking please reply