Building house soon, Want wood furnace and heatpump...can it be done?

[hydroncollider]

Hey everyone, If you find me a way to do this I will post pic's the whole way.
Im building a house and would like to hook up a central heat pump and wood furnace to the same duct work.
I cant find any threads on this. Most people online just say dont do it because the wood heat will kill the heatpump. Can I not just hook up duct dampers at the output of each heating system? One normally closed and one normally open so the high heat cant backflow to the heatpump when the wood is operating.

I like the idea of using the heatpump during 8 months of the year and wood during the cold winter months when the heat pump is no longer productive (I believe central systems go full electric coil around minus 15)

I will be very grateful of any advice! Thanks!

 

[webbie]

I don't see why this cannot be done with a decent plan and a good installer....someone else can probably chime in with more specifics, but to me the main issue is to install the ductwork with the clearance for oil or wood heat. You can easily look up these clearance in some of the furnace manuals.

The easier way would seem to be one or the other - not set up as auto-backup. In that case, if your wood furnace has a fan (and make sure it's big enough!), then you could do as you mention and completely bypass the heat pump coils and air handler.

There are probably ways to do it using the heat pump air handler also...

An even better idea might be to use a wood boiler and a additional coil in the plenum. This is probably how I would do it unless I was on a really tight budget. That way you get the best of all worlds - even the ability to run a baseboard or two off the boiler if you add a room to the house or want to heat a room in the basement, etc.

 

[Floydian]

Hello and welcome,

Sort of a stock response but have run the heat loss calculation on the house? The is the foundation of designing any heating system.

Hopefully you are building something extremely efficient-lots of insulation, air tight as possible, quality triple pane windows.
If this is the case a ductless mini split or two and an efficient wood stove would about the best thing going IMO.

Heck, even if you are not super insulated you could still make a couple of the larger mini splits work along with a wood stove when it really gets cold. The mini's will seriously out perform any central heat pump system and there are units available that will provide rated output down to -13 and still operate at a COP of 1.8.

Worth considering at least.

Noah

 

[hydroncollider]

Hey webbie, you're getting me excited, hope i have more people chime in on specifics. I wanted to do a boiler origionally but theres no good brands(no gassers or high efficency) sold in NB,CANADA. and it cost too much to bring one in. I can get the heatpump installed with ducts for 10k and the furnace for 4k.

Hey Floydian, I looked into this, unfortunatly the layout is no good for minisplit. bedrooms on both sides and open in the center, im looking for something that will heat the whole house evenly.

 

[jebatty]

Look at my recent post in Major Remodeling Project. Same ideas for you.

 

[flyingcow]

Hey webbie, you're getting me excited, hope i have more people chime in on specifics. I wanted to do a boiler origionally but theres no good brands(no gassers or high efficency) sold in NB,CANADA. and it cost too much to bring one in. I can get the heatpump installed with ducts for 10k and the furnace for 4k.

Hey Floydian, I looked into this, unfortunatly the layout is no good for minisplit. bedrooms on both sides and open in the center, im looking for something that will heat the whole house evenly.

I know a gentleman that bought a econoburn in new brunswick. Just outside the woodstock area. I believe it was delaer from the province. this was about 2 yrs ago.

Also, I'd look again at the mini splits. The basic idea is to have a head in each room. Each head has it's own control.

 

[heaterman]

Are you talking an air to air heat pump or geothermal using ground source heat? If geo, is it open loop or closed?

The reality of the situation is that if you wrap your house up well, the payback on installing even a wood furnace along with chimney, extra ducting and controls, etc., gets pushed a long way into the future.

Personally speaking (from experience) if you were my customer i would advise that the two systems be kept discrete from one another for reasons of simplicity and also warranty on anything to do with the heat pump.
If you attempt to "twin" the two systems together you are introducing things into the mix that the HP manufacturer may take a dim view of in the event of problems down the road. Don't ask how I know that......

 

[sloeffle]

I have a wood furnace hooked into the same duct work as my geothermal furnace. As others have eluded to, you will need a damper system setup to keep the hot air from the wood furnace off of the coil in the furnace. I had to put about 500$ worth of dampers in to accomplish this.

I bought my wood furnace when you could still get a 30% rebate back from the government so the cost was a little more bearable. As heaterman said, if you are going to install a GSHP the pay back for a wood furnace, dampers, flue pipe etc is way out in the future. If you have frequent power outages or just like the idea of being self sufficient then I would buy a wood furnace or install a backup form of heat. You would need at least a 10KW generator in order to begin to think about running a GSHP ( at least the model I have ) during a power outage.

 

[wardk]

If you are building a new house I would install waterlines in your basement floor, it's a small investment in new construction and gives you more options for heating your home. No cold floors.

 

[hydroncollider]

Hey everyone,

Thanks for the replies, I want to user a Trane air to air central with a napoleon wood furnace( I can get both locally for a good price) each would have its own air handler and duct damber(to protect the trane from heat and to protect the napoleon from AC thermal shock) Im ok spending the extra $$ on dampers for the convenience of using the same duct work.(if I get your approval ha ha)
I have a young family in a rural area so I like the fact that if the power goes out I can still use the wood furnace as power is not required (nice and simple)

Regarding what dampers to use……ive seen mechanical ones online I can buy one “normally open” for the wood furnace and “normally closed” for the heatpump, that way if the power goes out they will default to the correct position to heat the house. Outside of a power outage, the on/off functions of the thermos-stats would need to control the dampers im assuming. Does this make sense? What else do I need to consider with this setup?

If that’s too complicated I may have to do manual dampers?

I would also like to use the NEST thermostat K he he I know Im not making this easy on you guys, but Im confident Ive come to the right place.

(p.s. I built an electric car with no automotive experience with help from the forum at diyelectric.com----forums like these can accomplish great things)

 

[Ashful]

Have you discussed Trane's recent troubles with a few of your local HVAC installers. Most shops around here seem to consider "Trane" a bad word, since they started having so many evaporator coil (and other) troubles, spring 2011. It turns out there IS a penalty for moving all of your production to a country with cheap and un-trained labor.

I had a Trane system installed in 2011, then fixed, then pulled out and replaced, then repaired again, then pulled out a second time and replaced with another brand. That installer has since dropped Trane, having had the same trouble on more than 20 systems installed that summer. Speaking with three different installers for another job just last month, two of the three told me, "stay away from installer xxx, they still use Trane."

 

[hydroncollider]

Have you discussed Trane's recent troubles with a few of your local HVAC installers. Most shops around here seem to consider "Trane" a bad word, since they started having so many evaporator coil (and other) troubles, spring 2011. It turns out there IS a penalty for moving all of your production to a country with cheap and un-trained labor.

I had a Trane system installed in 2011, then fixed, then pulled out and replaced, then repaired again, then pulled out a second time and replaced with another brand. That installer has since dropped Trane, having had the same trouble on more than 20 systems installed that summer. Speaking with three different installers for another job just last month, two of the three told me, "stay away from installer xxx, they still use Trane."

oooo this is the first Ive heard of it. I first asked my installer about Goodman because of the good price, but then he recommended Trane. I will have to ask him.

 

[maple1]

I'm a life-long hot water guy - can wood fired hot air furnaces really function OK with no power? Seems to me you could get into some serious heat in short order in places you don't want it with no fans pushing air through the ducts?

Yes, it is quite frustrating living in this corner of the country (continent?) with the shortage of locally available MODERN wood burning technology. It did cost me quite a bit to bring mine in from 'outside', but so far it has been well worth it. You can get Econoburns & Empyres in the area, but I'm not sure on their cost. I think when I was looking it wasn't any more to buy & bring mine in than it was to buy one of those here.

How big a place are you planning? I'd be hard pressed to go with anything but a mini-split system & wood stove for something small-ish & modern-built. Something big or possible added out-building heating I would definitely go with a hot water system for heat - maybe add a mini-split for a/c (seldom needed where I live) & shoulder season. The two years we did live in a forced hot air (oil) apartment, I didn't like it.

 

[hydroncollider]

I'm a life-long hot water guy - can wood fired hot air furnaces really function OK with no power? Seems to me you could get into some serious heat in short order in places you don't want it with no fans pushing air through the ducts?

Yes, it is quite frustrating living in this corner of the country (continent?) with the shortage of locally available MODERN wood burning technology. It did cost me quite a bit to bring mine in from 'outside', but so far it has been well worth it. You can get Econoburns & Empyres in the area, but I'm not sure on their cost. I think when I was looking it wasn't any more to buy & bring mine in than it was to buy one of those here.

How big a place are you planning? I'd be hard pressed to go with anything but a mini-split system & wood stove for something small-ish & modern-built. Something big or possible added out-building heating I would definitely go with a hot water system for heat - maybe add a mini-split for a/c (seldom needed where I live) & shoulder season. The two years we did live in a forced hot air (oil) apartment, I didn't like it.

Hey Maple, I have looked into all of the hydronic options, even got a quote on shipping an effecta.... i would love to get my hands on those lamda controlls. Ive also looked into empyres..... they are all mostly out of my budget and I also dont want to deal with the wood all year round, thats why a 3 to 4 thousand dollar gasification furnace seemd like a good alternative for me. ive also considered the minisplits but im thinking 4 heads would be 20k and i still dont have the wood backup. the way im planning it now is 10k for central heatpump which includes ducts and 3 or 4 k for furnace.

The house will be 30x54 pure rectangle foundation with clight overhang in the frame
http://s1027.photobucket.com/user/scottarseneau/media/house/housepic_zps816fd00d.jpg.html

its not the plan to run the furnace with out the fan, infact if there was a power outage i would grab some big batteries and an inverter to run it, i have lots of that stuff sitting around. i just like that if my wife was home with the kids she could throw a log in without complications and no tweaking required

 

[rkusek]

Congrats on the new home and you have a few ways to go the way I see it. I'm using a Lennox 5 ton air source HP with electric backup and a water-to-air HX in the same plenum which I did myself afterward. Since I had an outbuilding I wanted heated the boiler made sense to me. Because of the cheap winter electricity here right now (roughly 5 cents, I think) my boiler setup will take several years (>10) to break even. The HP is a lot cheaper to operate than what I thought it would be. Our worst bill before wood boiler was $257 if I recall. My in laws have a 25yr old 2 story with the original HP and Clayton (now US Stove, I believe) wood furnace still working fine. His manually changes his damper and only uses the HP for vacations or cooling in the summer. They have a lot of southern glass exposure that generates quite a bit of warmth even in winter. He lets it burn out during the day while they are at work and I can only recall one time (-20F) when he did have a water line freeze in the basement before they got home. I think you are correct in thinking a damper with normal spring loaded position for wood furnace and a powered switchover to HP when the temp drops below a certain threshold would give a more automatic changeover using separate tstat for the HP. The mini-splits and wood stove with a well insulated home sound good too if you can make that work. The ground source HPs using 2 wells start out at about $25k around here. My sister built in a more rural area that allowed only 1 well GSHP (pump & dump) and that is about the same as an air source. Her bills are about $250 in the heat of summer and middle of winter. Like many have mentioned good windows, and plenty of insulation make all the difference. Are you using conventional "stick built" contruction or the SIP insulated panel type?

 

[Ashful]

oooo this is the first Ive heard of it. I first asked my installer about Goodman because of the good price, but then he recommended Trane. I will have to ask him.

Maybe they've gotten past some of those problems, but it seemed that they could not make an evaporator coil that would last 3 months, back in summer 2011.

 

[heaterman]

Have you discussed Trane's recent troubles with a few of your local HVAC installers. Most shops around here seem to consider "Trane" a bad word, since they started having so many evaporator coil (and other) troubles, spring 2011. It turns out there IS a penalty for moving all of your production to a country with cheap and un-trained labor.

I had a Trane system installed in 2011, then fixed, then pulled out and replaced, then repaired again, then pulled out a second time and replaced with another brand. That installer has since dropped Trane, having had the same trouble on more than 20 systems installed that summer. Speaking with three different installers for another job just last month, two of the three told me, "stay away from installer xxx, they still use Trane."

The coil problems are not isolated to Trane. It's an industry wide issue and every manufacturer is dealing with it from what I have heard from various reps, parts counter talk between contractors and tech line calls that I have made. There are boat loads of unhappy customers, installers AND manufacturers over this problem. Google "formicary corrosion".

Here's one link talking about the problem. http://www.achrnews.com/articles/troubling-pinhole-leaks-in-evaporator-coils-cause-corrosion-issues

Not saying that particular issue is the cause of all the evap coil leaks but it could very well be a factor in many of them.

 

[Ashful]

That sounds like a failure that occurs over some period of time, "Eventually, these etched areas of the copper become thin enough to start leaking as the copper becomes so thin that it becomes porous." I'm talking about three coils that were all DOA, right out of the box, from the manufacturer. All three leaked. According to the installers, they had at least 20 - 30 other customers that month with the same problem, and they state this suddenly started when Trane moved the manufacturing of their coils to another country.

Like I said, I'd be amazed if they're not past this issue, after more than 2 years, but according to an installer who was working in my house just three weeks ago, Trane is still having manufacturing problems.

 

[Fred61]

If I were building new right now, in no way would there be a need nor would I want a wood fired boiler or furnace. A large 50K or 80K BTU heating unit would never pay for itself. It is, of course "personal preference" but I would build incorporating the highest insulation standards and then plunk a high mass masonry fireplace (aka Russian) in the middle and design the house around it. Then add a couple mini-splits.
The company in Quebec that supplies Woodstock Stoves with their soapstone had a nice masonry stove on display in the plant when Woodstock had their open house in 2011.

 

[sloeffle]

My HVAC installer had only installed a wood furnace one time before and he said it was probably 30 years ago. Originally we had a manual damper between the wood furnace and the GSHP. However that manual damper leaked like sieve. I was pushing a lot of heating and cooling into my wood furnace.

The damper between the GSHP and wood furnace is normally closed. On my Caddy their is a box on the side of the furnace with a basic Honeywell thermocoupler. The thermocoupler also drives when the fan will kick on. I figured out which wire runs the fan and wired up a 120V - 24V AC relay off of that wire. I then wired the damper between the two furnaces to this and I also wired the zoning damper that sits on top of GSHP to this. When the motor for the wood furnace turns on, the damper between the two furnaces opens and the damper sitting on top of the furnace closes. The only issue I have ever had is when my wife decided it would be a good idea to run the GSHP and furnace together because she wanted the house heated up ASAP. When I got home I thought she cooked a two year old GSHP.

We generally only use the wood furnace during the really ( Jan, Feb ) months of the year. The GSHP is so cheap to use during milder weather that it does make sense to burn wood. During these few months I am thinking about setting the damper between the two furnaces to normally open and then wire that damper to the GSHP furnace to close it, if it kicks on.

I can take some pictures if you want and post them.

 

[sloeffle]

The coil problems are not isolated to Trane. It's an industry wide issue and every manufacturer is dealing with it from what I have heard from various reps, parts counter talk between contractors and tech line calls that I have made. There are boat loads of unhappy customers, installers AND manufacturers over this problem. Google "formicary corrosion".

Here's one link talking about the problem. http://www.achrnews.com/articles/troubling-pinhole-leaks-in-evaporator-coils-cause-corrosion-issues

Not saying that particular issue is the cause of all the evap coil leaks but it could very well be a factor in many of them.

I know that Waterfurnace was also having issues for awhile a few years ago. Hopefully they got those issues resolved before they built my furnace.

Sometimes the simplest ( woodstove for heating ) solutions are the best.

 

[slowzuki]

Hello Hydroncollider - also in NB. Heat pumps operate at lower temps so need higher air flows than a wood furnace so the ducts need to be upsized to move this extra air. Once sized like this a wood furnace can be connected for sure with precautions about backflow between applicances. Problem with a wood furnace in power outage is they need to be idled way down or you will warp the fire box. They also barely deliver any heat without power for the blower fan, and have to be in the basement to deliver any heat in power failure. My sisters has the automatic damper propped open usually so you have to be very careful during power failures in cold weather as the damper won't close.

I honestly think I'd consider a wood stove in the centre area of house if there is a large room and avoid the furnace. The heat pump air handler can circulate the heat from the wood stove well with the large ductwork and an override on the fan. Even without power its still about 3/4 good at making the place comfy.

 

[hydroncollider]

Hello Hydroncollider - also in NB. Heat pumps operate at lower temps so need higher air flows than a wood furnace so the ducts need to be upsized to move this extra air. Once sized like this a wood furnace can be connected for sure with precautions about backflow between applicances. Problem with a wood furnace in power outage is they need to be idled way down or you will warp the fire box. They also barely deliver any heat without power for the blower fan, and have to be in the basement to deliver any heat in power failure. My sisters has the automatic damper propped open usually so you have to be very careful during power failures in cold weather as the damper won't close.

I honestly think I'd consider a wood stove in the centre area of house if there is a large room and avoid the furnace. The heat pump air handler can circulate the heat from the wood stove well with the large ductwork and an override on the fan. Even without power its still about 3/4 good at making the place comfy.

oh nooooooo......that sounds just like a very logical idea. now you have me thinking of changing everything. now im thinking about how to make space in the living room.
what does everyone think about wood inserts? where are the pipes and how big are they?
http://www.regency-fire.com/Products/Wood/Wood-Inserts/CI1250.aspx

thanks slowzuki, now im opening my cad program ha ha

some more info for those who asked...this is a stick build, mainly friends and family doing the work, with run of the mill new windows.(yes i know thats not what you want to hear) im considering blowing in the insulation. this is a low cost build probably $150k for the whole thing 1620 sqft

i was quoted 100k more from a builder so before you all bash me for going cheap and loosing money in heat loss, consider the savings in my mortgage ha ha

 

[flyingcow]

look at cutting sheet foam and inserting it between the studs. Your labor is free? Just look at everything.I understand about mortgages, but run the numbers on 15 yrs with a reduced cost for heating. Help pay a bit of the loans I would think.

 

[jrod770]

Hydroncollider, It's no big deal, I am currently running the set up you are asking about. I built my house 4 yrs ago myself, installed a propane furnace, heat pump, and a Clayton wood burning furnace in the basement. I went with a cheapo furnace and heat pump, since I can buy them at cost, I don't really care how long they last. Last year, we burnt $67.00 worth of propane, that was mainly from the gas range. I know the Clayton gets a bad rap on here, but to be honest, I would continue using it if I didn't think it was causing breathing problems with my daughter.

No need to upsize ducting. Just normal size ducting to and from wood burner. Mine has a 8 x 24 return dropping down to it and a 14" round off of the top of it feeding back to just above the a-coil on the furnace. At that point on the 14", I installed a simple manual damper that only gets shut off during the summer, air conditioning time. That's it. Nothing fancy. You put wood in it and it heats the house. I spent $1500.00 on the Clayton, brand new and burn about 4-5 cord of wood a year with it. If we have a power outage, I can just run it off the generator and keep on heating. My 2 cents.