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HVAC electrical help needed

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Butch(OH)

05-23-2006 04:57:04




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I have purchased an outside wood boiler. The boiler will become my primary heat and my gas furnace, a 10 year old Amana, will used as back up. The same duct work will used for both heating systems as I will be adding a heat exchanger to the cold air return (per instructions with the boiler) Then two thermostats are used, the original conrolling he gas furnace and A/C and an additional one that will only control the air circilation fan common to both systems. The pumps from the boiler run continuously and do not need any control. The instructions say to wire the new thrmostat to control the blower(duh)and to not disturb the present control wiring (duh again) but offer no suggestions for doing so. The gas furnace is new enough that it has one of the processer boxes to control the furnace and fan and I dont want to burn it up by having something cross wired. The thermostat that controls the gas furnace has a "Fan-On" feature that allows the fan to run seperate of all other funtions, would it be prudent, proper or whatever to wire the new termostat in series with that "fan on" switch and leave that switch on while operating the boiler? Or would there a better way? Thanks in advance.

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mark lake

05-25-2006 19:27:20




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 Re: HVAC electrical help needed in reply to Butch(OH), 05-23-2006 04:57:04  
First I have aSuper WD6 (like the md). Anyway, the reason the stove makers want the water flowing all the time is to stop it from freezing. Stove maker instructions are for plane jane old single speed moters. Your Ammana has at least three speeds available.You don"t want to power more than one speed at any one time. You need to get somebody that knows what their doing! You cannot simply jumper R(24volts) with G(fan) as when you do this and you furnace thermostat switch is set to "auto" it will feed power out to the Y (AC) terminal. I used a Douple pole,double throw relay on the last one I done on a Carrier high efficiency to make it idiot prove as far as what the customer can control.If it"s done right you can have the wood stove set for twenty and the furnace set for 18 and the furnace comes on if the fire goes out.The heat from the house duct will keep the water in the stove from freezing but not very cheaply. Engineers make me laugh, what works great in theory or the lab doesn"t always work in the field. Chances are the wood stove company gave you a line voltage thermostat to feed power to the fan motor. Also these outdoor stoves are not a pressure vessel like a standrd boiler, don"t expect it to last like a boiler which circulates the same water under pressure. Expect lifespan to be closer to a standard water heater for domestic water.Good luck,I know in my area only 25% of the service guys could get it right the first try!

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evilboweviel

05-24-2006 12:04:22




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 Re: HVAC electrical help needed in reply to Butch(OH), 05-23-2006 04:57:04  
I work on hvac for a school system and before that Johnson Controls, before that Honeywell Inc before that electrican in highrise bldgs.

said all that to say I am in central ohio and willing to help you with this. send me an email to rselzer at columbus dot rr dot com and we can set up a look see. no charge as I enjoy working theese little problems out

Ron



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Butch(OH)

05-23-2006 19:30:20




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 Re: HVAC electrical help needed in reply to Butch(OH), 05-23-2006 04:57:04  
Thanks for all the input, sounds like I am over my head a bit with the controls. Just to clarify things for you that understand your HVAC systems yes the wood fired boiler (technicaly hot water not a boiler) will be my primary heat with the gas forced air unit becoming a back up for times when the fire goes out. The boiler contains its own pre wired digital controls for maintaining X water temp and the instructions call for constant flow through the heat exchanger. As designed by the Mfg the thermostat for that system will control the fan only as flow through the exchanger is contstant as is the temp of the water given fuel in the boiler. Call for heat, run fan, no call for heat fan off. The gas furnace would need to operate automaticaly at some setting below the wood boiler system. I used to have a wood fired forced air add on in the basement but it had its on controls and circulation fan and only shared the duct work with posible flow reversals handled by simple flap valves. B&Ds suggestion to control the flow of water to the exchanger sounds logical as does the dual function T-stat. I better call in a pro to do the control work, I surely dont want a "rigged' set up.

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T_Bone

05-23-2006 16:58:12




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 Re: HVAC electrical help needed in reply to Butch(OH), 05-23-2006 04:57:04  
Hi Butch,

The only condition you would want a gas fired unit on the HVAC system is for back up heat when the boiler was down for repair or your gone for a extended time beyond the boilers fuel source. Correct?

Then you need a two stage heating/cooling T-stat.

Stage #1 controls the boiler & HVAC system at all times satisfiying the heat load demand.

Stage #2 comes on when stage #1 can NOT satisfiy the heating demand. At this time you would have both Stage #1 and Stage#2 "on".

As the heating demand falls then stage #2 drops out and only stage #1 is "on". As stage#1 is satisfied then it shuts down.

What is most likely to happen is stage#1 will not shut off or will short cycle when Stage#2 is supplying all the heat load demand. As the heat load once again calls for heat then stage#2 will once again come on if stage#1 never shut off.

The t-stat has complete control over stage#1 and stage#2 as per code. You will want a battery back up t-stat so incase the line power goes out then the t-stat will remained programed for when the line power comes back on.

Do NOT jury rig controls for controlling the units.

Running a fan continously during heating demand will only cause the occupants to become cold caused from the skin effect, (the evaporation of moisture from the skin that causes cooling).

You really need a local sharp HVAC control person to look at your units as it's possible that a isolation relay will be needed.

T_Bone

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Joe in MN

05-23-2006 16:25:01




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 Re: HVAC electrical help needed in reply to Butch(OH), 05-23-2006 04:57:04  
I have the same set-up you have, and I'm a Heating Engineer, all you are asking is how to wire up the Thermostate for your wood boiler just like your back-up heat is, right ???? Well, just wire a second thermostate in series with your first thermostate, and turn down your first thermostate as far as it will go, and use your second thermostate, that will do it, mine works GREAT, WE LOVE IT, AND IT WORKS GREAT... GOOD LUCK AND KEEP UP THE GOOD WORK, JOE

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Butch(OH)

05-23-2006 19:37:39




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 Re: HVAC electrical help needed in reply to Joe in MN, 05-23-2006 16:25:01  
Thanks Joe, Yes you have the system right. After a long struggle with stainless 304 vs stainless 309 vs carbon steel and forced draft vs natural draft I went with a carbon steel Woodmaster with forced draft for no sound engineering reason just gut instinct.



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Bob

05-23-2006 06:54:47




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 Re: HVAC electrical help needed in reply to Butch(OH), 05-23-2006 04:57:04  
I'm sure there is a more elegant way to connect the thermostat for your outdoor boiler to the existing furnace using a fan conrol relay.

However, if you are willing to manually set the fan to run all the time, and have the new thermostat wired in series with the existing manual fan control wire, there's no reason that wouldn't work, with the new thermostat for the outdoor boiler then controlling the fan as needed..

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Butch(OH)

05-23-2006 07:08:18




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 Re: HVAC electrical help needed in reply to Bob, 05-23-2006 06:54:47  
"elegant" LOL, now thats a word that should not be applied to my electrical talents. I dont want the fan running all the time as that would send heat all the time, I was thinking that since I cant read and electrical print very well that I could "fool?" the system by using that fan on switch wired to a thermosat.



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buickanddeere

05-23-2006 07:50:01




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 a$$ backwards Re: HVAC electrical help needed in reply to Butch(OH), 05-23-2006 07:08:18  
You are trying to steer the horse by beating it on one side of the backside or the other. The fan should always run in order to even out the air distribution cold/hot spots in the structure. And to provide continous filtration of dust/dirt from the air. What is required is a three way water valve on the water line into the hot water HX. When home heat is required the water flows into the valves #1 inlet and out the #2 port which opens when energized. When no heat is required the hot water still flows into the valve's #1 inlet. But the port to the #2 HX port has closed and the #3 port has opened. #3 is connected to the line returning to the boiler.

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Butch(OH)

05-23-2006 08:23:04




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 Re: a$$ backwards Re: HVAC electrical help needed in reply to buickanddeere, 05-23-2006 07:50:01  
Daggonit B&D your throwing a crowbar in my gears, LOL. Your way goes against the way the Mfg (Woodmaster) says to do it but sounds logical. I assume that the three way valve you mention is a commonly used item and available from a good heating equipment supplier?

Good thing I have 4 months to figure this out.



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Bob

05-23-2006 07:29:06




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 Re: HVAC electrical help needed in reply to Butch(OH), 05-23-2006 07:08:18  
I guess I didn't make myself clear...

All you have to do is figure out which of the wires to the existing thermostat is for the existing "fan on" function, and splice a simple 2-wire heating-only thermostat into that wire, and the new thermostat will then control the fan, as long as the existing thermostat's fan switch is set to "fan on".

Likely, the fan control terminal on the existing thermostat will be marked "F" or "G".

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Kevin Bismark

05-25-2006 17:50:14




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 Re: HVAC electrical help needed in reply to Bob, 05-23-2006 07:29:06  
Yes, this is the way it is done, you leave your old T stat alone, run 2 wires up to your new one, connect in the furnace to the "R" and the "G", and in the T stat hook the one from "R" to "R" and the one from "G" to the "w" terminal, works great will turn on the fan when it calls for heat, pretty easy to do..
Kevin



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Oliver Power

05-23-2006 06:34:58




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 Re: HVAC electrical help needed in reply to Butch(OH), 05-23-2006 04:57:04  
I wouldn"t think you would want the fan on all the time. Seams like it would get too warm in the house. Go to this site (http://hvac-talk.com). I"m sure someone can help you out.



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TimS

05-24-2006 11:23:18




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 Re: HVAC electrical help needed in reply to Oliver Power, 05-23-2006 06:34:58  
We have the same setup you are putting in, but ours is made by Hardy.

We have two thermostats, one heat only for the Hardy, one normal one.

The Hardy comes with two relays, one is wired up with the existing thermostat wiring so the Hardy thermostat can switch the fan on when heat is needed.

The other relay is used in the outdoor unit to turn on the pump out there to move the hot water into the heat exchanger in the furnace air plenum.

When we moved in, ours was hooked up wrong, when it tried to turn on and heat, the Hardy thermostat turned the a/c on, haha.

Anyhow it works now.

Can you get a hold of your manufacturor or distributor and get an example wiring schematic?

Link

That is a link to the hardy installation manual, page 32 shows the schematic for hooking up the two thermostats.

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