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Old 03-12-2014, 12:05 PM   #1
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First Post-Help with Custom HVAC System?


Hey All, This is my first post on this site, so please be gentle

I Stumbled upon this forum while doing some research on a brainchild project I have in mind.
For starters A little background info:
I live in 120yr Old Farmhouse that my wife and I have renovated/are still renovating. One of our first projects we completed on the house was to install a hvac system as ALL of the 25 radiators in the house had blown up one winter while it was abandoned before we bought it. Along with that, the oil tank in the basement was wrecked (had holes in it) and the boiler was beyond repair.

Needing heat and also wanting AC we opted for a heat pump/AC unit with electric strip backup heat (our first choice was hydronic coil backup but as just mentioned the dead boiler put a damper on that)

anyways...Im sure some of you know where I'm coming from here with a drafty ol' farmhouse...they sure do look cool but MAN do they cost a fortune to heat!!! We recently installed some woodstoves and that seems to help a lot, however the layout of the house and fact that we aren't home for a lot of the day doesn't really help maintain the heat, which Finally leads me to my crazy idea...

I was looking at installing a wood fired boiler in our basement, and installing a hot water coil in the air handler plenum (or maybe return air side??) I want to still keep the electric backup heat though on the chance that I have to be away from the house for several days, however I want the hot water coil to be the main backup when the heatpump can't do it's thing.

A few of my comments/questions:
- Would most likely need glycol in the lines as the air handler is in the attic

- Is having a second backup system feasible/possible?

- Anyone have a setup similar to what Im describing?

- Any thoughts on controls? Would I need a second thermostat to control the wood boiler's circ pump and air handler blower and set the existing thermostat maybe 2-3 degrees lower so that it doesn't kick on while wood boilers going?

- Am I COMPLETELY Crazy!?! I do tend to get a little nuts with my ideas but love when I can get them to work...

Any input/info/help is GREATLY appreciated....I haven't done anything with this idea yet except try and lay it out in my mind

Thank you in advance

Dan

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Old 03-12-2014, 12:15 PM   #2
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First Post-Help with Custom HVAC System?


It is an idea but a very difficult one to accomplish. My first concern is the extra coil will add resistance to the airflow thru the airhandler and if it is too much then the AC can freezeup and get damaged in the Summer. No way to find that out until the glycol coil is in and then it may be too late. The controls and thermostat required is not easy to do and rarely done so you may need to invent that system. Most airhandlers use a integrated circuit board and there are no provisions for homemade add on units later.

If you have space in the basement then I would get a wood furnace and run a few vents to the main floor and let it run on it's own thermostat. Need a couple return vents also. If you have a closet that can be used as a chase then they can run a duct upstairs.

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Old 03-12-2014, 12:19 PM   #3
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Your plan doesn't sound completely crazy. There are many similar type systems out there that are working to varying degrees of satisfaction. you can get 3 stage heating stats that could control all 3 heat sources at once if that is what you desire to do.

One thought would be to make sure the heat source coils and elements are in the proper configuration. Ideally you would want to have the HP coil first in the airstream, then the hydronic one and finally the electric heaters if you have the option.
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Old 03-12-2014, 12:22 PM   #4
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It may be do-able but if you don't have enough airflow then later your electric elements can overheat and burnout. Not saying don't try but it all depends on the size of ducts and there is no scientific way to know the airflow issue ahead of time. These systems are custom built and later if the installer disappears or goes out of biz then you are stuck with no one who knows how or wants to service it. I run into all kinds of weird scenarios like that.
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Old 03-12-2014, 12:28 PM   #5
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If you have space in the basement then I would get a wood furnace and run a few vents to the main floor and let it run on it's own thermostat. Need a couple return vents also. If you have a closet that can be used as a chase then they can run a duct upstairs.
This was another Idea I was Kicking Around....The locating of the wood burning unit would be right below one of the main cold air returns to my air handler. Do you think I could duct into that? And when you say "run a duct upstairs" I'm assuming you mean on it's own and not into the air handler plenum. I've seen the latter done via wood furnace manuals, but they are almost always right next to the air handler which is not attainable in my situation
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Old 03-12-2014, 12:28 PM   #6
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Agreed, airflow is key in this type of adaptation, one option there would be to get ahold of a fan coil unit which would then have the Hp coil built into the suction side of the fan instead of in the discharge airstream. Have seen that unit oversized by 1 coil size to accommodate higher airflow through the ducting system to compensate for added resistance.

Control can also be tricky, but is doable if you have an adaptable type of thermostat.
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Old 03-12-2014, 12:31 PM   #7
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Be somewhat cautious about ducting hot air into returns of your 2nd system ( if that is what you are thinking), I know insurance companies here would not approve of that method.
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Old 03-12-2014, 12:38 PM   #8
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Originally Posted by DIY_DAN03 View Post
This was another Idea I was Kicking Around....The locating of the wood burning unit would be right below one of the main cold air returns to my air handler. Do you think I could duct into that? And when you say "run a duct upstairs" I'm assuming you mean on it's own and not into the air handler plenum. I've seen the latter done via wood furnace manuals, but they are almost always right next to the air handler which is not attainable in my situation

I cannot see what you have but running ducts upstairs I have seen on This Old House Hour or Holmes on Homes. Usually it is to add AC to a hot water heated house. You can pipe some heat into the return duct of the airhandler but it would have to be interlocked and in such a way that it could not cut the heatpump or strips in or they would overheat as the return temp would be way too high. LIke I said it is all custom wiring which us techs could do for ourselves but I would not do for the public. Did a system for a co-worker where he had a separate wood and electric furnace married in the same duct and wanted separate tstats and a 2 speed blower etc. Took 4 hrs to figure it out and wire it and I think we used 11 control wires etc. He is no longer around and I hate to think of who may have to figure that beauty out now.
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Old 03-12-2014, 02:49 PM   #9
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I You can pipe some heat into the return duct of the airhandler but it would have to be interlocked and in such a way that it could not cut the heatpump or strips in or they would overheat as the return temp would be way too high. .

I was more thinking of sharing the return duct above as a return to the wood furnace...although as I wrote that I could probably get into trouble if both attic air handler and wood furnace are running at the same time. Wouldn't they fight each other?


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Old 03-12-2014, 05:18 PM   #10
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What controls the wood fire when the thermostat is calling for heat?

What you want to do is possible. But somewhat involved. Most wood boilers are outside.
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Old 03-12-2014, 09:39 PM   #11
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What controls the wood fire when the thermostat is calling for heat?

What you want to do is possible. But somewhat involved. Most wood boilers are outside.

I have researched a few indoor wood boiler units, I'm not sure what you mean by controlling the wood fire? I basically would have a wood boiler burning as often as possible, I know of a few with very large fire boxes so the burn time would be close to 10-12 hours constantly heating my water so I'm thinking I need to turn on a circ pump and the air handler when calling for heat. If the fire dies there's controls on the wood boiler unit to cut off the circ pump, and I'm guessing I either get a second thermostat or use my existing Honeywell prestige to kick on the heat pump/electric backup when the wood boiler gets too cold.


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Old 03-13-2014, 04:57 AM   #12
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Sorry. I meant what happens when the house is warm, and no more heat is called for by the thermostat. A hydro coil holds very little water, so where will the excess heat go.
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Old 03-13-2014, 08:01 AM   #13
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Quote:
Originally Posted by DIY_DAN03 View Post
I live in 120yr Old Farmhouse (in Eastern PA)....
Needing heat and also wanting AC we opted for a heat pump...
Gotta ask... why not an oil or gas fired furnace?
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Old 03-13-2014, 09:05 AM   #14
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A wood furnace will radiate the excess heat into the basement when the thermostat is satisfied. Not sure how well that wood work with a wood boiler in the basement and only one coil. Could put a radiator in the basement to help out.
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Old 03-13-2014, 11:24 AM   #15
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Gotta ask... why not an oil or gas fired furnace?
First off, $$$, I get a permit for $15/cord per household to cut my own wood. My father in law helps out and he only needs 1 cord himself...There's a 3 cord limit so i take my 3 and the other 2 from my father in law, I can heat the house for less than $100 in fuel...
Granted it's quite a bit of work, but I must be sick in the head or something...I kinda like it

Plus, where I live Nat-Gas isn't available, and don't want to incur the cost of setting up a propane system.

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