Woodburning stove in new home construction

[Leef]

Hi all,

Today I signed on with a general contractor to build a new home on our acreage this spring [img]/forums/images/icons/smile.gif[/img] . We have lots of timber and would like to put in a woodburning stove in the basement family area. I kinda liked a cast iron stove by jotul, but my wife likes what she's read about soapstone. We've never owned one and have no experience.

We have plenty of wood in the timber but only young children and me to do the cutting and splitting. That should change as the kids get older and can help safely. For now I think the stove will be used only occasionally.

Unfortunately, the jotul stove doesn't a "fresh air kit" which may be a problem in a tightly built home. I do want to have a fresh air heat exchanger installed in the HVAC system but don't really know exactly how they work and if that compensates for the deficiency in that stove.

Any advice from those familiar with stoves and efficient use?

Leef

[GaryM]

I have a Vermont Castings airtight stove at my place. It has a fresh air inlet via a 3" pipe that draws from the chimney chase.

It's red enamel and looks really pretty against a brick base and wall.

I also have a fantech energy recovery ventilator that draws from the bathrooms and dumps the incoming air into the furnace cold air return. So I'm not at all concerned about using up "house air".

The soapstone stoves do look very nice though. And they are supposed to hold the heat and radiate for a long time after the wood's been used up.

[Pat]

I have a very similar setup to the one Gary has for the ERV (Energy Recovery Ventilator.) It is a multi speed unit and we let it run 24/7, on low speed. It revs up under the control of a humidistat and slows back down when the humidity drops to the set point. The humidistat is located in the master bath near the shower. We have a "booster" fan on the exhaust side of the ventilator system with a screwdriver adjustable humidistat in the exhaust duct. If the relative humidity exceeds the setting on that humidistat the booster kicks in and really moves some air. Doesn't run very often.

You can have a cast iron stove AND the heat holding attrubutes of the soapstone. There are accessory water tanks for wood stoves. Some are toroidal (doughnut shaped) and have the flue pipe through the "doughnut hole." The hot water gives off a significant quantity of heat to a room long after the fire goes out. This is a ready source of hot water for beverages as well. One system I saw put together had a coil of pipe in the stove and the water thermosyphoned to a tank above and behind the stove. This reservoir of hot water kept the room fairly warm for a long time after the fire went out.

If your house is really tight there is a danger of sick house syndrome from all the man made materials that give off formaldehyde and other pollutants. A ballanced ventilator such as Gary and I use is way more important than you might think as relates to health issues. They are very cheap to operate. Mine uses less than an amp on low.

Likewise a tight house has problems with vent free appliances as well as B-Vent appliances. Fire places and wood stoves need a ready and dependable source of combustion air for proper safe operation and have a hard time getting it unless you open a window or have a vent to the outside to bring in air. Why build a tight house and then have to leave a window open? Tight houses really need to only have direct vent appliances, units whose internal volumes are sealed off from the house's air.

I have 4 propane gas logs. Three are parlor stoves and one is a large fireplace and all are direct vent. They can not back draft into the house. None of the products of combustion end up in the house. None of these fires compete with people for the oxygen supply.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[Leef]

Thanks guys,

You both give examples of both direct venting and energy recorvery units. We will definately put in ERV or HRV but the Jotul stoves don't offer direct venting. Should I look for another brand or will the ERV compensate adequately?

Pat, since you mention a water resevoir as a heat sink: have you seen any way to transfer the heat from a woodburning stove to a radiant floor system in the concrete floor of the basement? That would be ideal for us.

Leef

[GaryM]

Pat's an expert on a lot of things, and I'm not being sarcastic, so he might have a more informed opinion than mine.

That said, if you really want the soapstone, go for it. Just be sure you have an energy recovery ventilator to make up the air loss to the fire. A stove with an outside air vent would be better, but unless it's going to be your main heat source, I don't think it will matter too much in the long run.

Not too nice to sit there and look at a wood stove with a fresh air intake and wish it were one of those pretty soapstone units.

Sometimes the most efficient isn't the right choice. We all make decisions based on looks. Fortunatly for me my wife didn't do that when I asked her to marry me! [img]/forums/images/icons/grin.gif[/img]

[egon]

In colder climates the heat exchangers may have a tendancy to frost up.

I have seen house pressure equalizing systems that are simply a six in. flex aluminum hose coming from outside into the basement and terminating in a five gallon that is set at an elevation lower that the inlet.

Gary: I asked

You may have asked but was it under your own initiative or was it controled by "She who must be obeyed"??

Egon [img]/forums/images/icons/grin.gif[/img]

[Chillimau]

My first thought is you don't want to use a decorative woodstove as a boiler for radiant heat. More controls and plumbing are required than you might want to see sitting in your living area. Maybe the controls and plumbing could be hid on the back side.

They make boilers, indoor and outdoor, (wouldn't recommend the outdoor) that can be fed wood. A wood boiler will be a commitment that you should consider very carefully. Do you want to or can you be around to feed it regularly? Some wood boilers have a oil or gas backup, so when the wood fire goes out, the oil or gas will take over if the call for heat still exists.

My understanding of wood boilers is that they typically produce heat faster than the distribution system needs it. So you need to slow the fire down but, doing so kills the effiency. You could make small fires to keep the firing rate down and the effiency up, but may need to build them more often.

To keep the efficiency up you want to burn the fire at a high rate of burn and not let it smolder away while waiting for the call for heat. In other words, built a roaring fire and let it burn itself out to get the effiency up. So a secondary storage tank is recommended to store the excess heat for later use by the radiant or Domestic Hot Water, DHW. More plumbing and cost. Not trying to discourage you from using a wood boiler but there are many points to consider and $$$$$...

I think Pat has a ground source heat pump for his "boiler" and AC. No worries about feeding it unless the electricity quits flowing and very efficient.

My ramblings are spotty at best, but...

As the other "Gary" said Pat is very knowledgable and will point you in a good direction.


Gary

[GaryM]

Egon, it was my idea. Must have been a good idea as our 36th anniversary is in March. [img]/forums/images/icons/grin.gif[/img]

[Leef]

Gary,

That answers my question exactly - since the stove will be for occasional use and the house will have an ERV, I can shop for a stove without fresh air venting for combustion whether it's soapstone or not. Actually, the Jotul stove we like (based on appearance) is cast iron - not soapstone.

The complexity of a woodburning boiler probably isn't what we are looking for but it sounded like a good idea.

Leef

[Pat]

Leef, ERV vs HRV was a wash in my climate. No real incentive for going with a way to handle latent heat as well as sensible. Not sure what your situation is but suspect you may be deeper into the envelope where ignoring latent heat is the right thing to do. What I said was: you probably would do fine with HRV in place of ERV. The HRV works with sensible heat while the ERV also transposes moisture between the exhaust and intake air streams thus working on latent heat as well.

I have read the pitches for various soapstone stoves as well as Jotul (don't know how to make the Scandinavian characters) and I think you should avoid letting advertising hyperbole make your decisions. Not that Jotul isn't a good brand, it is, but I STRONGLY urge you to consider the reality of your situation. If you make the structure as tight as you would probably want (not a lot of infiltration in a basement!) then you really don't want a furnace/stove drawing a vacuum on your living space. It is a situation ripe for back drafting. You will be forced to open something up and let air in.

In my opinion an ERV or HRV works best when operated as designed as a ballanced ventilation system, i.e. exhausting a volume equal to what you are taking in. Pulling the CFM required to feed a wood stove through your "ballanced" ventilation system will certainly unballance it. Thast may not be a catostrophe but I would hate to see you go with the traditional type stove and end up with fumes and CO in the house. There are wood burning stoves that duct outside air into the fire box to support combustion and these are not effected by nor do they cause imballances between indoor and outdoor pressures. They absolutely will not back draft and put fumes, smoke, or DEADLY CARBON MONOXIDE into your living space.

To rephrase the ERV/HRV comment: The ERV/HRV will not compensate for the stoves draft requirements but the stove's draft requirements will interfere with the ERV/HRV ballanced airflow.

In-floor hydronics basically does not care how you get hot water just if you get hot water. Water heating coils can be used in wood stoves/furnaces to heat water for hydronic heat. It is likely that you will need at least a small insulated storage tank to buffer the system. Due to the volume of sales it is virtualy impossible to find an insulated pressure vessel to use as a hot water storage tank for a better price than buying a conventional electric hot water heater and just not hooking up the heater elements. (This is what I did.) You will probably not want this storage tank particularly near the stove for aesthetic reasons so run a chase (sleeve) under or in the slab to accomodate pipes to allow you to remote locate the tank to an equipment space or closet or... You use a small circulator pump to circulate water through the stove, to the storage tank and back in a loop. A second circuit with a second circulalting pump circulates water from the storage tank through the loop(s) of PEX in the slab whenever the thermostat calls for heat.

A simpler system would use just one pump and directly circulate water from the stove to a supply manifold thence through the in-floor loops to a return manifold and back to the stove. You would want a small header/expansion tank in the circuit for either version. You put an air sepearator on that tank and locate it at the highest point above all other components of the system. A drawback of the simple version is that you have to circulate water all the time the fire is lit to avoid building up steam pressure, even if you don't want the slab any warmer.

You will want to insulate the basement's slab floor whether or not you go with in-floor hydronics. Additional insulation would be placed around the stem wall to give a thermal break that decouples the slab and stem, if any, from the outside soil. I used R-11 rigid foam insulation on the outside of my basement walls to thermally decouple the concrete walls from the earth. I used a product called InsulDrain. It has grooves in it on one side and the grooves are covered with Tyvek filter cloth. I never have a head of water on my walls as any water goes through the filter cloth and falls to the bottom of the wall where the French drains are located.

I have no other water proofing system. No membranes, no elastomeric coverings, no penetrating sealers. Nothing, nada, zilch! My average ground water level is a few feet above the basement floor. I have cracks in my basement walls. I have holes where the SnapTies went through to space the forms. I have taped impermeable plastic over the walls and floors in 3 ft by 3 ft squares and left it for a week or more. When removed there is not even a slight discoloration on the concrete to show a trace of moisture. My French drains have been running a constant stream of water for 3 years but the walls and floors of the basement are very dry so the humidity in the basement is not particularly different that the rest of the house.

If any of this approach is of interest to you I'd be glad to share what details I can still remember.

back to in-floor hydronics: You absolutely can do in-floor hydronic heat using a wood stove as a heat source. It is a good plan. It will allow you to store lots of heat in the slab to be "time released" long after the wood fire has gone out. Think of the slab and walls as a huge thermal flywheel.

My basement walls have stayed at about 70 degrees all winter. I have not run heat in the basement. I get enough heating from the mechanical space where there are two storage tanks and lots of pipes with hot water. I insulated most of the pipes and still the basement zone stat is left turned off. Mild winter this time. Maybe another year will require me to add some heat to the basement.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]