Wood Furnace Hot Water System?

[JRobyn]

Hi folks,

I'm putting a wood-fired furnace in the new house. It came with a domestic hot water coil and I am trying to decide if I want to use/connect it. I know of no one who has any experience with this type of system, but I bet many on this forum do! I'll need about $100 of misc plumbing parts and pipe, plus an old water heater to use as a "tempering" tank, so add'l cost is not large.

So are these system worth the investment? Are there any long term operational or maintenance considerations to be aware of?

- Jay

 

[beenthere]

Do you have hot water heat now, or forced air?

 

[rockinmywaypa]

How many people are taking showers throughout the winter,there might be advantages to preheating the water before it enters the actual water heater for all your hot water needs.

 

[inveresk]

I had a similar system in an old Victorian farmhouse I bought in the 80's. The stove worked like a charm and I never had any problems with it.

Electric hot water wasn't an option in the house because it was off grid. I lived there for seven months before I was grid connected. The stove had a heating coil which linked into a direct hot water tank that was located on the upper floor directly over the stove. The stove was in the kitchen which was at entry level. That tank fed wet accommodation which was all at entry level. Had to be that way - wet accommodation on the upper level wouldn't work because the system was gravity fed.

Although there were six open fireplaces in the house serving the various bedrooms and the sitting room, the stove was the main source of heat and the only source of hot water. It happily ticked over all day long. Even after getting power in the house, I kept the stove and it remained the main source for heating and hot water throughout the heating season. With no pumps and no electric motors, there's not much in such a basic system to go wrong.

 

[WayneB]

Hi folks,

I'm putting a wood-fired furnace in the new house. It came with a domestic hot water coil and I am trying to decide if I want to use/connect it. I know of no one who has any experience with this type of system, but I bet many on this forum do! I'll need about $100 of misc plumbing parts and pipe, plus an old water heater to use as a "tempering" tank, so add'l cost is not large.

So are these system worth the investment? Are there any long term operational or maintenance considerations to be aware of?

- Jay

Jay, just wondering what kind of furnace you are installing? Is it one of the new gasification units? If so you will have to really research "just adding a loop for domestic hot water as they burn extremely hot and a small tank will never be large enough to handle the temperature raise.

As for using a domestic hot water loop I would think it would be well worth the $100 in plumbing parts.

Although when we did ours I went ahead and just used a circulation pump and feed it into our regular gas fired hot water tank. I also added a small expansion tank, shut off valves and a over pressure relief valve. (I only added the valves so we could shut-off the loop during the months we were not using the wood furnace.)

This would an older model forced hot air furnace and we added the hot water loop. When we rebuilt the house and added on to it I went ahead and put in a hot water system and stopped using the hot air wood furnace.

We are now using a On Demand Hot Water system and for the past 7 months it cost us right around $9.00 a month for hot water (propane cost) so it would be hard for me to justify going with a new high efficiency wood furnace. We heat with wood up here and have an open concept house so our Vermont Castings defiant wood stove heats the 2500 house most of the year. We do have the oil back up but it stays turned off most of the year.

Few sites to take a look at:

Maine Wood Boilers - Reduce Oil Usage for Heating

Building a timberframe home from scratch.: Wood Gasification Boiler

Econoburn Wood Boilers

 

[DIRTROAD]

I know a guy who heats his water like this during the cold months. When it warms back up he turns a couple of valves and goes back to electric hot water. To hear him talk about it the savings are huge. The thing is that his outside woodstove is going to be burning anyway, he might as well get all of the goodie out of those BTU's and heat his water with it also. I am going to switch to this system as soon as possible.

 

[nybirdman]

Why not use it??It will pay for itself in no time..We just installed a Classic outside wood unit...to a hot water heating system...system already had a Super cell for domestic hot water..we run it for 10 months a year...saves greatly on domestic water.Make sure you have all safety devices in place,ie relief valves.

 

[qball98]

I have been using one for 11 years now. In the winter it preheat the hot water before in goes into my hot water heater. I kept track of it the first year I installed it saved about $20 per month which comes to about $100 per year during the winter. Since the stove came with the coil already it just made sense to run one extra water line to the hot water heater and take advantage of it. I am sure it save even more now since the cost of electricity goes up every year.

I am wondering what you need the tempering tank for? I run the cold water directly into a coil located in my stove and where it comes out as hot water and goes to my hot water heater to be distributed through out the house. My stove already has a pressure and temperature relief valve built into the coil just like a hot water heater. The only problem I ever had was having to replace the pressure valve because it started leaking. Other than that it has been great and well worth the money.

 

[JRobyn]

Hi guys - Thanks! Some replies to your questions below.

beenthere - all new construction, so nothing there now. Heat will be the woodfurnace plus dual heatpumps, plus a small "decorative" propane stove, plus fireplace. Conventional electric water heater.

WayneB - It's a Charmaster Chalet. They supplied the water coil. It's a 24" long u-bend of 1" galvanized pipe. Too much heat to the water coil is one of my worries. There's little control over too much heat to the water except a standard TP valve on the tempering tank. The Charmaster install instructions specifically say "no circ pump", so it's thermosiphon only. They do recommend having the tempering tank right next to the furnace, using a substantially sized tank (used 40 gal water heater) and using a TP valve on the tank.

nybirdman - I DO hope to use it, just not if it will be a hassle, or if I'll have constant over pressurization worries!

qball98 - The separate tank is recommended by the manufacturer - possibly to have it right next to the furnace for efficient thermosiphon, maybe because the recommended water heater will have a TP valve (the furnace coil does not have its own TP valve)!

Keep 'em coming! I've started to plumb in the coil but I'm not really convinced yet. I have to decide before next week when the HVAC guys install the plenum on the furnace. After that, the coil and connections will be a problem to get to.

- Jay

 

[OzGrasshopper]

Hi Jay, i have a wood fired room heater with oven & Hotwater tank/water jacket at rear of firebox. the HW is connected to a solar HWS tank & we have an electric booster in the tank. we have been in our new house 1 winter and the combined system works wonderfully.
BUT be careful, we had a simalar set up in our previous house but that was a coil in the firebox, not a water tank/jacket like the new one. the coil used to sometimes get airlocks when the fire was very hot - i recon this was becos the coil was poorly designed - i've seen better since that was made 20 years ago.

check with your plumber, but all those system in Oz work on a "convection" principal - cold water in at bottom of coil, hot water out on top pipe, then u need to have the pipes travel either vertically or on a increasing gradiant to storage tank - can't be flat or downhill from the top of the coil to storage as the convection flow won't work. i guess u could use a pump to get circulation but i've never seen that here.

Also all some units use "heat exchange" system where the water heated in the firebox continually circulates up & thru storage tank by a "heat exchange unit" so that water never flows into the the storage tank, only thru it in an exchange jacket. other system the water actually flows continually by convection, colder water from bottom of storage tank, heated water returns to the top.

Last winter we only used the electric booster once, when we returned home from being away for 3 or 4 days and the fire had'nt been lit. i am amazed at how good the system works. hope u have success. cheers OGH.