Heating hot water with exhaust

[LT_Rooster]

has anyone been successful in heating hot water with the exhaust from their pellet stove? If so, how much water do you get and at what temp do you get? What does the system design look like?
Regards,
LT

 

[ivanhoe]

any help to raise the temperature on the cold water to the hot water tank is a saving. the only drawback is the insurance not willing to insure, need a approved system!

 

[orangecrushcj7]

interupt the supply to the water heater with some of the thinwalled copper pipe used in baseboard hydronic heat, and wrap it many times around your vent pipe. not a whole lot of surface area of contact though for any effectiveness.

 

[Czech]

If you lower the temp of your vent doing this, you risk having exhaust gases condense on the inside of the vent which will casue you problems (rot, creosote). The stoves are not designed to do this, and the pay back is neglegable.

 

[LT_Rooster]

Well, I was thinking of designing a simple heat exchanger for inside the hearth. Say, start with a section of sched 40 stainless pipe, maybe a long pipe nipple and cap the ends. run some stainless coil through, in the top of the pipe and out the bottom. Let it run all night, might be able to get 100 gals. of water after 8 hrs.? The acid wouln't eat the ss, and I could just drain it off or neutralize it then drain.

I'll have to talk to the insurance company... may be able to get my PE buddies to sign it off... They would probably be ok if the system drains back and it is pressure relieved in two places.

I figure during the cold months, that stove is going full tilt all night... I'll have to do a heat balance to figure how much hot water I can really get out of it.

Regards,
LT

 

[OU812]

I like that idea - I keep wondering how to use the clothes dryer exhaust as a source of heat myself. Let me know if you come up with anything that works.

 

[orangecrushcj7]

Home Depot and Lowes as well as others sell what is called "extra heat", it is a diverter that redirects your ELECTRIC clothes dryer exhaust into your house. I use one. It is great, because it also adds the needed moisture to your interior.

(broken link removed to http://www.deflecto.com/OMS/tier2_template_air.aspx?ProductID=918)

 

[PunKid8888]

I would only use that product on an electric dryer

 

[cac4]

I tried one of those, too, and it filled my basement with lint.

dryer exhaust filtering is really minmal; they're really designed to just dump all those tiny particles of clothing fiber outdoors.

 

[alexdrozd]

The lint is bad and the humidity is ridiculous. I've tried it in my garage. Went back to a kerosene heater.

 

[orangecrushcj7]

I don't have any issues with the lint. It has it's own filter on it, so you have a double filter. the one on the actual dryer, and the one on the deflecto thing. You need to clean the filters. Unless you are dumping the ELECTRIC dryer exhaust into a space heated with a wood stove or pellet stove, the humidity will be too much. The wood burning stoves really dry out the air, so the humidity is usually welcome. I don't even get condensation on my windows. However, my situation may be unique, in that my stove and laundry equip are in the same location, my back hall.

 

[LT_Rooster]

I installed one on my dryer (elect) this year. Seems to work fine. It's an extra lint screen. I noticed home depot also sells one with a water lint trap. that might work better.

Back to the hot exhaust recovery, does anybody have the CFM rating of the combustion blower and the steady state temperature? Figure I'd try to calculate how much heat is available before I order my parts.

 

[Dr_Drum]

Back to the hot exhaust recovery, does anybody have the CFM rating of the combustion blower and the steady state temperature? Figure I'd try to calculate how much heat is available before I order my parts.

I wouldn't bother with the CFM of the blower, too many variables. Stick an exhaust temp guage in the fire box and get a base line temp at a given stove setting. Calc the amount of coiled copper pipe needed in the fire box based on incoming water temp and the delta T, change in temp you want to get out of it, and the velocity. Camerons Hydraulic Data book has heat transfer coefficients per materials, and the formula (I forgot it). This will give you an equivalent length of pipe. Doubtful you will get it perfectly balanced at your desired temp so use a gate valve or something to throttle the water velocity. I did something similar to this years ago adding a coil in an old coal stove. I used my electric hot water heater (disconected) as a holding tank and a small circ pump controlled by the aqua-stat in the bottom of the hot water heater. Worked great.
Mike -

 

[MCPO]

I don't have any issues with the lint. It has it's own filter on it, so you have a double filter. the one on the actual dryer, and the one on the deflecto thing. You need to clean the filters. Unless you are dumping the ELECTRIC dryer exhaust into a space heated with a wood stove or pellet stove, the humidity will be too much. The wood burning stoves really dry out the air, so the humidity is usually welcome. I don't even get condensation on my windows. However, my situation may be unique, in that my stove and laundry equip are in the same location, my back hall.

If you are running a stove of any kind the dryer exhausted in the house is a great idea especially on the colder days . Matter of fact I always remind my family to not turn the bath fans on when showering as the house benefits from the moisture.
I don`t see any condensation on the windows either.

 

[LT_Rooster]

Back to the hot exhaust recovery, does anybody have the CFM rating of the combustion blower and the steady state temperature? Figure I'd try to calculate how much heat is available before I order my parts.

I wouldn't bother with the CFM of the blower, too many variables. Stick an exhaust temp guage in the fire box and get a base line temp at a given stove setting. Calc the amount of coiled copper pipe needed in the fire box based on incoming water temp and the delta T, change in temp you want to get out of it, and the velocity. Camerons Hydraulic Data book has heat transfer coefficients per materials, and the formula (I forgot it). This will give you an equivalent length of pipe. Doubtful you will get it perfectly balanced at your desired temp so use a gate valve or something to throttle the water velocity. I did something similar to this years ago adding a coil in an old coal stove. I used my electric hot water heater (disconected) as a holding tank and a small circ pump controlled by the aqua-stat in the bottom of the hot water heater. Worked great.
Mike -

I looked in my (whitfield) manual and they disclosed that the exhaust flow rate is approximately 100 cfm. I'll see if I can shove a t/c in there to get an approx. exhaust temperature running on different settings, and estimate the heat availability. Maybe I can just call their engineering dept. and ask them so I dont' have to punch a hole in my exhaust pipe.

I don't want to take any heat from the firebox as I need all I can get in the room. Copper would probably be ok but the condensate might eat it up over time. Don't want to end up with a puddle in my living room. Shrapnel is bad too.

I usually run the stove(s) only when I'm home, so the concept is to use the water as a pre-heater for the electric hwh. So as I use hot water, it is replenished with hot and I don't have to pay for the electricity to heat it up (only the losses). Of course, I could run solar in the warm months in the same system. I'll try to get something on paper over the weekend, and post it if the system allows.