Wood Stove + condensing water heater?

Bicycle Bob · 07-06-14, 02:59 AM

Could I use a standard or even obsolete wood stove to feed hot flue gas into a condensing heat exchanger, preferably adapted from a gas-fired appliance, with draft provided by a fan on the exhaust side?

Would I be better off to spray water into the flue gas, since I only want it for a circulating hot-water heating system for the far room? The circulating pump could feed the spray head, with the ph controlled with ash or fresh water.

Daox · 07-07-14, 02:44 PM

You can do this, but I think it would be a maintenance nightmare. The soot will build up and create a mess. Even if you get the fire very hot, you'll still have soot build up issues I think.

AC_Hacker · 07-07-14, 05:53 PM

Quote:

Originally Posted by Bicycle Bob

Could I use a standard or even obsolete wood stove to feed hot flue gas into a condensing heat exchanger...

You would have produced a wood tar distilling apparatus.

Wood smoke has way too many particulates and gaseous tars to make it a good candidate for condensing. Nat Gas (CH4) is a very good candidate, as it produces CO2 and H2O... both easy to handle.

You are better off pursuing a small fire with forced draft & high oxygen... this is the Rocket Stove approach... also used in pellet stoves.

-AC

stevehull · 07-07-14, 06:47 PM

AC is exactly correct. It would be a daily maintenance nightmare and I can see creosote, etc, dripping out and making a huge mess.

Even a wood pellet stove has a lot of low temp condensing volatiles . . .

Great idea, but not going to work well with wood - even incredibly dry wood pellets.

Steve

Bicycle Bob · 07-08-14, 02:09 AM

Quote:

Originally Posted by stevehull

AC is exactly correct. It would be a daily maintenance nightmare and I can see creosote, etc, dripping out and making a huge mess.

Even a wood pellet stove has a lot of low temp condensing volatiles . . .

Great idea, but not going to work well with wood - even incredibly dry wood pellets.

Steve

Thanks, guys.
I was figuring on either replacing the water frequently, or adding ash to balance the ph and filtering out the sludge. Wood heat is a daily chore anyway, eh? I've got gas laid on here, but I think such a high-class fuel should at least be running a heat pump, but with fracking in the mix now, I'd rather quit entirely.

Any other options for super efficiency on wood, like an absorption heat pump?

AC_Hacker · 07-08-14, 11:11 AM

Quote:

Originally Posted by Bicycle Bob

...I think such a high-class fuel should at least be running a heat pump, but with fracking in the mix now, I'd rather quit entirely...

I agree with your reluctance to take part in the Great Aquifer Destruction that is known as 'fracking'. But just for information, there was a company that made a Natural Gas powered internal combustion engine driven heat pump. I'm not sure as to why it is no longer made.

There is also the possibility of Co-Gen where you have an engine that drives a generator, and you also harvest the heat from the engine.

BUT... You are no different from any other human whose first line of thinking on the subject of home heating, is the heat source.

Your greatest successes will be when your efforts are given over to preventing heat loss.

This begins with eliminating infiltration as much as possible, and then insulating as much as possible, and then window reduction/replacement with high performance windows.

-AC

Bicycle Bob · 07-08-14, 10:59 PM

I'm familiar with insulation, etc., thanks. Any other thoughts on the topic? Two other reasons it appeals to me are that it avoids awkwardness and expense on the chimney, and stops pollution at the source. The hot water for a remote radiator solves another common problem. I'm wondering about efficient ways to control the fan and pump motors.

BTW, my house started out as a 2-room shack. Each extension was bigger than the last, and the third one even added indoor plumbing, getting to 700 sq. ft. Everyone was pretty keen to add insulation along the way, though.

AC_Hacker · 07-09-14, 02:38 PM

Quote:

Originally Posted by Bicycle Bob

I'm familiar with insulation, etc...Everyone was pretty keen to add insulation along the way, though.

Just out of curiosity, how thick are the walls of your house?

-AC

Bicycle Bob · 07-09-14, 05:05 PM

The oldest walls are up to 22 cm, the new ones lagging around 16. I've had a blower door test, and done all the detailing. The foundation, or lack thereof, is discouraging major investments, but it might be wise to pull out the gas furnace and fill the crawl space.

AC_Hacker · 07-09-14, 06:58 PM

Quote:

Originally Posted by Bicycle Bob

The oldest walls are up to 22 cm, the new ones lagging around 16. I've had a blower door test, and done all the detailing. The foundation, or lack thereof, is discouraging major investments, but it might be wise to pull out the gas furnace and fill the crawl space.

Yeah, sounds like you've been there, alright!

-AC

07-06-14, 02:59 AM	#1
Bicycle Bob Suncatcher Join Date: Sep 2008 Location: Spiritwood, Northern Saskatchewan Posts: 42 Thanks: 0 Thanked 1 Time in 1 Post	Wood Stove + condensing water heater? Could I use a standard or even obsolete wood stove to feed hot flue gas into a condensing heat exchanger, preferably adapted from a gas-fired appliance, with draft provided by a fan on the exhaust side? Would I be better off to spray water into the flue gas, since I only want it for a circulating hot-water heating system for the far room? The circulating pump could feed the spray head, with the ph controlled with ash or fresh water.

07-07-14, 02:44 PM	#2
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	You can do this, but I think it would be a maintenance nightmare. The soot will build up and create a mess. Even if you get the fire very hot, you'll still have soot build up issues I think. __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

07-07-14, 06:47 PM	#4
stevehull Steve Hull Join Date: Dec 2012 Location: hilly, tree covered Arcadia, OK USA Posts: 826 Thanks: 241 Thanked 165 Times in 123 Posts	AC is exactly correct. It would be a daily maintenance nightmare and I can see creosote, etc, dripping out and making a huge mess. Even a wood pellet stove has a lot of low temp condensing volatiles . . . Great idea, but not going to work well with wood - even incredibly dry wood pellets. Steve __________________ consulting on geothermal heating/cooling & rational energy use since 1990

07-08-14, 10:59 PM	#7
Bicycle Bob Suncatcher Join Date: Sep 2008 Location: Spiritwood, Northern Saskatchewan Posts: 42 Thanks: 0 Thanked 1 Time in 1 Post	I'm familiar with insulation, etc., thanks. Any other thoughts on the topic? Two other reasons it appeals to me are that it avoids awkwardness and expense on the chimney, and stops pollution at the source. The hot water for a remote radiator solves another common problem. I'm wondering about efficient ways to control the fan and pump motors. BTW, my house started out as a 2-room shack. Each extension was bigger than the last, and the third one even added indoor plumbing, getting to 700 sq. ft. Everyone was pretty keen to add insulation along the way, though.

07-09-14, 05:05 PM	#9
Bicycle Bob Suncatcher Join Date: Sep 2008 Location: Spiritwood, Northern Saskatchewan Posts: 42 Thanks: 0 Thanked 1 Time in 1 Post	The oldest walls are up to 22 cm, the new ones lagging around 16. I've had a blower door test, and done all the detailing. The foundation, or lack thereof, is discouraging major investments, but it might be wise to pull out the gas furnace and fill the crawl space.