Water to Air HX in existing forced air handler

[rkusek]

I have a Lenox air source heat pump forced air system (15kW emergency heat) in my new home because of the cooling needs (NE summers), no natural gas (rural), and didn't want to mess with propane since I have an endless wood supply. My next best option would have been closed loop geothermal system (~$25,000) but the EKO/Lenox route should cost me a little less (I hope) plus give me a nice heated pole barn to work in during the winter with only 1 fire to tend. The Lennox should give me a decent backup setup like the oil boilers most of the others here on the forum have. I actually put a decent fireplace (Heatilator) in the new house too mostly for ambience but could keep us warm should we lose electricity AND something fail miserably with the EKO or the piping to the house. My generator would be able to run the EKO, lights, fridge, freezer, etc. and I plan to have a couple batteries with a small inverter for the EKO and circs should I lose power with a full load of wood burning.

I have asked a couple of the heating techs from the company that installed the Lenox as well as a ex-plumber friend of mine and all seemed to be against putting a water to air HX in the existing furnace although I'm pretty sure most of those here with forced air were doing exactly that. They were worried that it make restrict the flow too much or mess with the balance throughout the house. If I place it in the cold air return just before the filters that should NOT hurt the balancing should it? Is there a concern that the blower motor would be subject to hotter air? At worst would I just need to up the speed on the blower. The last tech out here noticed it was wired for LOW and he changed it to MED and I believe there are still 2 more higher speeds. I didn't ask the tech but my ex-plumber buddy at work thought most are wired to run 1 speed faster in cool mode vs. heat mode. If I plumb it with PEX I could even pull out the HX during the summer months if the restriction really made that much difference. Any thoughts? I read the thread about the "custom made HXs" here in USA and Chinese made ones on Ebay. How low of water to the better ones work with? How much did it cost you? Is everyone using a second thermostat to activate just the blower and circ? Keeping the main system set for a lower temp as a backup when the water temp is insufficient. They were suggesting I use a separate air handler and maybe even separate ducting but that seems like a ton of extra work. Down the road I would like to add some radiant floor heat to the tiled areas and maybe the whole house but I think I still need the HX first. DHW and future hot tub are also planned down the road. The 350' (each way) loop of 1.5" foamed in PEX will probably be my primary loop and run continously, with separate circs for the boiler, storage, air HX, DHW, and eventual hot tub.

 

[sgschwend]

You are correct, folks do add a water to air heat exchanger to accomplish heating using the boiler output.

The drag of these exchangers are minimal, your system should not have a problem, unless you already have a problem. Put the exchanger in the plenum not the return.

 

[rwh442]

I installed a 16" x 18" water to air HX on the outlet side ducting (supply) of my propane furnace. I would not, and others suggest here as well, install the HX on the return side because as you stated you would be subjecting you blower and electronics to 140+ degree air temperatures.

I cannot tell a difference at all concerning the air flows through the ductwork with the HX staying installed year round. The propane furnace and air conditioner still heats/cools the house as before the HX was installed. I leave it in year round. Just remember to turn your circulator pump off if using the furnace or AC!

Concerning fan speeds - my furnace has a variable speed blower. I ended up using the AC circuit in the winter time to obtain the maximum fan speed which was needed. I just disconnected the AC compressor from this winterized circuit with a toggle switch.

I installed two thermostats in the house for the boiler thinking that the original furnace thermostat would kick in if the boiler would not supply enough heat by the time I got home. This never happened last year and it was a colder than normal winter here. So basically I would recommend trying your original thermostat first.

As far as lowest "usable" supply temperatures I found that my blower would start to run continuously, probably just recirculating the heat in the house, at water supply temperatures slightly below 100 degrees.

Duct temperatures above the water to air HX would read 140 - 145 degrees at a boiler supply temp of 180 degrees.

Hope this helps. Good luck.

 

[brad068]

Another thing that I have notice on several other hx in plenum setups is that they are placed horizontal. If you are running one main primary loop, this causes convection. If you can, place the hx vertical to minimize this or run a 3 way zone valve or secondary loop.

This can become a real problem in the shoulder seasons.You'll keep turning down the t-stat and wonder why it is still so warm in the house.

 

[dogwood]

Huskers, I don't have any answers for you but face a similar situation. My Lennox Pulse forced hot air furnace will not put out enough cfm of air even at its highest speed, which is used for cooling, to heat the house, even before the hx is added. There is a three speed blower in my Lennox. After much thought I am planning to replace the whole Lennox propane furnace with a new and higher capacity blower unit having an electric element for backup heat. The new blower should blow the air at a high enough cfm rate to blow the air through the water to air heat exchanger, overcome the resistance to air flow of the cooling coil too, and put out enough cfm from each heat vent. Restricting the existing inadequate air flow even further by putting a hx in the supply plenum above the Lennox below the cooling coil was not even an option.

My boiler will arrive next week and the next purchase will be a four row water to air hx ordered through Ross at Nationwide Coils, who is frequently recommended on this site. I imagine he could tell you what the lowest usable water temps would be depending on the hx size, gpms etc. Like you, I've learned on this site you have to watch out for heat exchangers that make extravagant BTU claims utilizing only highest water temp scenarios.

If I could switch the blower in my Lennox to a higher speed, as you seem to be able to, my heat exchanger would be going into the supply plenum above the Lennox and I would not have to get a new air handler There is a thread somewhere that said the hotter air created by a return air hx would mess up the blower in the furnace over time so I don't plan to go that route even though there is plenty of room there to install it this way. I couldn't retrofit a bigger blower into the existing furnace either. I was told by two professionals to ballpark a total of 100 cfm per heat vent in the house and am sizing the new blower fan output accordingly. Couldn't tell you if this is good advice or not and might find out the answer the hard way. Best of luck figuring this out. I hope someone here can help you. You can probably find the cfm ratings of your Lennox (listed at different static pressures) online along with the info on how many speeds you do have on yours. I was able to find these ratings for my 17 year old Lennox Pulse. I'll be watching your post to see if you get any helpful answers. Good luck.

Mike

 

[Tony H]

I am using a exchanger in my gas forced air furnace on the supply side with another thermo set to run the fan and humidification unit the blower is set one speed higher (same as a/c) and seems to have no problem pushing air thru the house. If you have an issue with air flow could you just increase to a larger blower motor ? When I put a/c in my last house we did that and I don't recall the motor being any larger but it moved alot more air.
There are many control systems but mine is basic the boiler thermo is set to 72 and when it calls for heat it kicks on does not matter if the boiler is running or what temp it is, if the temp drops to 67 the regular thermo kicks on the gas heat. If I am not running the boiler I just switch that thermo to off.
I do not pull out the hx for summer and the a/c runs fine . I did however put in shutoffs so I could run the boiler for hot water and bypass the hx in the summer if desired.

 

[rkusek]

I will get a picture of my air handler to post here since it may be a little different. I'm not sure there is enough room in the plenum to install a HX on the output side. This HX will have its own secondary loop and circ(w/internal flow control) tapped off the primary loop. I'm going to have to investigate the Lenox wiring more closely. I would like to have a NFCS type setup eventually but may need to come up with something simple to heat the house until that becomes operational. Maybe an aquastat on the primary loop set at 140* that would interrupt the signal from the main thermo to the furnace and drive only the blower and HX secondary circ. When water temp in primary loop falls below the 140* temp then relays would reconnect the signal wire from thermo back to furnace and blower (original connections). This would be assuming 140* and higher water would be sufficient to heat house in all conditions. Bad thing is 139* and less water would be useless in this setup since it would be using heat pump heat. I still think 2 thermos is the way to go with the heat pump set 5-8* less than the one for the hot water HX. That way as long as hot water maintains house temp heat pump would not run although blower may run more as the water temp falls.

 

[Medman]

I also use the W-A HX in my home, but I replaced everything at the same time.
I replaced a 30 year old single speed electric downflow furnace with a new variable speed air handler with backup electric heat.
I installed a w-a hx in the supply side of the ducting. My advice here is to get the biggest hx you can fit in the duct space, and get the best one you can afford. Cheaper units on ebay and elsewhere can restrict the airflow considerably or may not have enough coils. the better ones are more expensive, but worth it in the long run.

Remember to install the hx in a counterflow position, so that the hottest water is seeing the cool return air first. this will maximize heat transfer in the coil.

I used a single Honeywell IAQ thermostat to control the system; it works as follows:

System fan runs at low speed at all times to circulate air.
Boiler sends hot water to house, through sidearm on DHW tank, and back to boiler any time boiler is firing.
Snap-disc sensor on boiler supply lines closes at 120*, powering circulator circuit.
When thermostat calls for heat, first stage, the circulator turns on, sending boiler water to w-a hx in plenum. Fan remains at low speed.
If house does not begin to see a rise in temp after set time, second stage, the blower fan speed ramps up-from 30% slowly up to 80% of full speed.
If, after set time, house does not see a rise in temp, third stage, the elec. backup elements energize to heat house.
As a backup, if boiler supply temp is below 60*, the electric elements come on first stage. This is for the times when I am not home for extended periods and there is no fire in boiler.

I purchased the air handler, which also has the AC coil installed, and the thermostat from Alpine Home Air online. I found their service and products to be great, and they were considerably cheaper than my local dealer for the same equipment. If you are considering changing your air handling equipment I would recommend going this route. Get an ECM variable speed motor as well, the cost savings in electricity are huge.

I am changing the configuration a bit this year to add storage (zone valves and different circ), but the control is basically the same. Hope this helps.

 

[dogwood]

Medman, I've been looking on the Alpine site and planned to get a multiple speed blower from them rather than an air handler unit since I already have the cooling coil in my plenum. You mention considerable electricity cost savings with a ECM variable speed motor. Could you approximate what the savings are in dollars as the variable speed costs considerably more. I'd like to approximate its payback time, or at least ratiionalize the added expense if I were to go to a variable speed ECM blower unit. Also, how do you ramp up the blower speed from 30% to 80%. I assume the ECM variable speed feature enables you to do that somehow.

Which of Alpine's Air Handler Units did you go with? And if you happen to know, how many cfms did you require from the blower (fan) for your application, and how did you figure out how many cfms you needed prior to purchase. Its real interesting how you got the stages of heating and electric backup heating set up and sequenced. I'd like to replicate that. And if you don't mind, what is a snap disk sensor? You've obviously put a lot of thought into this system. My compliments.

Mike

 

[deerefanatic]

I have a thermalzone hi efficiency propane furnace in our house.... I installed the 20x20 ebay heat exchanger horizontally in the plenum..... I do not run the pump all the time though..... The thermostat's call for heat turns the pump on... Then I have a small digital temperature controller (available all over ebay for like $25) that turns the furnace blower onto it's highest speed only after the heat exchanger has reached 125F...... Then, when the thermostat turns the pump off, the blower continues to run until the heat exchanger has cooled to 80F to extract all remaining heat.....

Also, counter flow is important....... Being my furnace is an updraft unit, my hottest water goes to the top of the heat exchanger and travels downward.... This way, the water that has cooled somewhat preheats the cold air..... In this way, the air is preheated from the cooled water before getting to the hottest water..... Basically, you want your water and your air going in opposite directions.....

One last note. If you have underground lines from some outdoor location, having your thermostat operating your pump can be risky vs running the pump all the time and just turning the blower on and off..... For me, I found that it worked great, BUT, my lines are buried 5 feet down and insulated with 4" off Corbond.... I have a 0F temp drop in my lines when running.... Now, if you have some poorly insulated lines, or they are buried very near the surface, you may have problems with freeze up if only flowing water when demanding heat...... Especially if your house is very well insulated such that the heat demand is low....

 

[Medman]

Lets see...

My old furnace was a single speed Chromolox with a multi-tap motor; at 1700 rpm it used 11 amps at 240 v. The new ECM is a variable speed DC drive motor, which consumes less than 1 amp at 240 v at full speed. So I estimate a savings of about 90% on fan power - significant in my case since I run continuously on low speed.
Fan speed is a function of settings on the control board inside the furnace. There are jumpers IIRC, that set the minimum speed based on your set maximum. In heat mode, max fan speed is 80% of maximum cooling speed (set with jumpers). Minimum speed is just a percentage set by the control board.
I started with a max CFM of 1700 - the same as the old furnace. I think I had to increase it slightly (moving one jumper) to get a max heating speed that would get the heat to the house. However, most of the time the fan only runs on low speed, with just the circulator turning on and off. Only on the coldest days did the thermostat reach second stage and call for an increase in fan speed.

Ramping of fan speed is a function of the control board in the furnace based on the thermostat status. If the tstat calls for second stage, fan speed increases. the longer the second stage call lasts, the faster fan speed becomes, to a max of 80%. If tstat returns to first stage call or is satisfied, speed ramps down.

The air handler I chose was the 20x20 with 3 ton cooling coil - I chose for the plenum size since I could not increase the size of the ducts.

Snap disc sensors are fixed temp thermostats - either normally open or closed- that actuate at a set temp. You can buy them in temps from 60* up to 210*. They are not the most accurate but are the simplest way to control the system when combined with a 24 v transformer and a few relays.

 

[dogwood]

Thanks Medman. I'll try to find your AHU on the Alpine site and look at its specs. What does "IIRC" stand for, as in "jumpers IIRC"?. And if you don't mind, how many square feet are you heating? And what thermostat (or kind of thermostat) are you using?

Mike

 

[Duetech]

My oil furnace plenum has a water/air hx just above the oil furnace hx. there is a separate T stat for the blower so I can utilize my air/water hx that is set about 10 degrees F above my oil T stat. The actual result is that my blower comes on more frequently but the air temp in my house is equalized throughout the house because the air/water T stat responds to a 1/2 to one degree swing where the T stat for the oil furnace is usually around eight degree swing. Two heat sources. one blower and one filter. No known problems. Though there is a perceived elongated run when the oil side is running solo (as it would be heating water and air exchangers) I have no hard data to verify it and I am always glad to have the boiler going instead. Reduces much of the heating costs per year.

 

[stee6043]

Remember to install the hx in a counterflow position, so that the hottest water is seeing the cool return air first. this will maximize heat transfer in the coil.

Medman, you prolly just slipped in the typing here but counterflow piping on your HX causes the cool air to hit the cool part of your HX first. Not the other way around. Counterflow piping should have your hot water supply going in the top (exit for air) of your HX and the cool water return coming out of the bottom (inlet for air).

This is the most efficient setup as it allows the air to see the hottest part of the HX right before it leaves the HX...

 

[Medman]

IIRC - if I recall correctly

I am using a Honeywell IAQ 4 stage cool/3 stage heat thermostat also purchased from Alpine. I needed this unit since I have no option to run a new wire to the tstat location through cement walls, so I only had three wires available. There may be cheaper options if you can run a six or eight wire cable to your tstat location. I purchased the Goodman AEPF313716, and I am heating 2400 sq. ft.

Stee, there was much discussion about the counterflow arrangement last year at this time. It was shown by experimentation as well as thermodynamic principle that heat transfer is best when the coldest returning air meets the hottest water in the coil first - greater delta t at the interface, resulting in the greatest heat transfer. I think others found a 6-10* increase in supply duct temps using counterflow. Please jump in here if anyone has better numbers.

 

[pybyr]

... there was much discussion about the counterflow arrangement last year at this time. It was shown by experimentation as well as thermodynamic principle that heat transfer is best when the coldest returning air meets the hottest water in the coil first - greater delta t at the interface, resulting in the greatest heat transfer. I think others found a 6-10* increase in supply duct temps using counterflow. Please jump in here if anyone has better numbers.

Medman- no disrespect intended, but you're remembering it backwards. I remember it clearly in part because, in at least one of those discussions, I was the one to mention the importance of counterflow through an air-water HX, and to explain the how and why - the whole point is to keep the maximum possible temperature differential [between water and air] through/across all of the multiple layers of the coil. The only way to do that is to feed the hottest water into the area of the coil that is the last to contact the air on the way to the heated space, and to draw the coolest water from the first part of the coil to contact the air. "Counter" refers to the physical directions of the flows (which side is in and which out) on the two separated sides of the HX. See folks' discussions and explanations at:

https://www.hearth.com/econtent/index.php/forums/viewthread/28535/

 

[Duetech]

Remember to install the hx in a counterflow position, so that the hottest water is seeing the cool return air first. this will maximize heat transfer in the coil.

Medman, you prolly just slipped in the typing here but counterflow piping on your HX causes the cool air to hit the cool part of your HX first. Not the other way around. Counterflow piping should have your hot water supply going in the top (exit for air) of your HX and the cool water return coming out of the bottom (inlet for air).

This is the most efficient setup as it allows the air to see the hottest part of the HX right before it leaves the HX...

Hooobooy.. If I understood correctly what Medman is describing is standard flow and what stee6043 is describing is counterflow. Counterflow was found to give hotter air exiting the hx..........

In any event my air/water hx completly fills the plenum area above my oil burner so there is not way for air to go around the hx and when needed the oil burner has worked well.

 

[stee6043]

The simplest explanation I've come acrossed of why counterflow is allegedly better:

If air meets the hottest part of the HX "first" it has no chance of getting any warmer while it passes through the HX. If the air hits the hottest part of the HX right before it leaves the HX it is receiving more btu's the entire time it is passing through the HX.

Medman - I think I've seen posts where you described counterflow correctly in the past. No lie!

 

[pybyr]

I have asked a couple of the heating techs from the company that installed the Lenox as well as a ex-plumber friend of mine and all seemed to be against putting a water to air HX in the existing furnace although I'm pretty sure most of those here with forced air were doing exactly that. They were worried that it make restrict the flow too much or mess with the balance throughout the house. If I place it in the cold air return just before the filters that should NOT hurt the balancing should it? Is there a concern that the blower motor would be subject to hotter air? At worst would I just need to up the speed on the blower. The last tech out here noticed it was wired for LOW and he changed it to MED and I believe there are still 2 more higher speeds. Down the road I would like to add some radiant floor heat to the tiled areas and maybe the whole house but I think I still need the HX first. DHW and future hot tub are also planned down the road. The 350' (each way) loop of 1.5" foamed in PEX will probably be my primary loop and run continously, with separate circs for the boiler, storage, air HX, DHW, and eventual hot tub.

I have a 24x24 HX with 4 rows of 1/2 copper tubing. It's wider than the actual plenum outlet of the preexisting furnace, but manages to sit/ seal over the furnace, and then I reduce from the outlet of the HX to the preexisting ductwork. This reduces air backpressure for the furnace's blower to completely acceptable levels. One thing to be especially aware of is that "regular" hydronic design for usage of a water to air HX assumes a fixed and relatively high water temperature (180 F or so) of water entering the HX from the boiler system-- whereas with a wood boiler + storage, you may often (depending on your system and type of storage- perhaps "always" rather than merely "often") be seeking to deliver heat using water lower than 180F.

Many of the low-cost water-air HXs' specifications are arrived at assuming high/ fixed temperatures of water, and flows of both air and water, that are not very representative of what you'll have with wood/ storage, and also if you want gradual airflow of warm air through your house and not loud billowing blasts of air.

I worked with the supplier of my coil (Ross, of Nationwide coils) to make sure it was sized to actually be able to move the needed # of BTUs under my particular furnace's blower specs (1600 CFM) even with relatively low water temperatures (from partially-depleted storage) feeding the coil, and without introducing unacceptable levels of backpressure for the blower.

In my opinion, this area- sizing of a water-air HX for use with a wood system that includes heat storage- is a place to be especially careful not to penny pinch. The amount initially thought to be "saved" by using a lowest-priced HX with unrealistically optimistic specs/ assumptions will quickly go out the window if one finds oneself with a system that heats poorly, is unable to make useful use of heat storage, and/ or one has to pull it all apart again (and end up buying additional/ different items).

I did not run my storage yet last heating season, but the coil I have could begin to deliver noticeable heat to the house on a cold day even as the boiler was first coming up to temp, when the water being fed to the coil was still in the 150s F temp range.

 

[Medman]

Sorry for the confusion - you guys are right as usual! I just checked my original diagrams for the plumbing and I do have it plumbed for counterflow - hottest water at the air exit. Thanks for being on the ball.

 

[dogwood]

Trevor, any chance of getting a picture and maybe a cross section diagram of how you have the plenum ductwork sitting/sealing over your furnace and then reducing around the hx again. I am getting ready to order my water to air hx through Nationwide Coils following your lead, and have the same furnace plenum outlet size installation issue. I've been wondering how to solve the problem of enclosing a hx bigger in size than the blower plenum outlet. Seems like you solved that problem.

Do you have a cooling coil in your plenum too, or located elsewhere? I've got one in the plenum over my existing furnace now and would like to place the w/a exchanger under it after the blower. The blower unit installation guidelines on Alpine recommend that the cooling coil go under the blower. That would be a real hassle to reinstall the cooling coil, I don't know how to do it anyway, and hope it is not absolutely necessary. What do you all and Trevor (Pybyr) think? Do I have to move the cooling coil underneath the blower?

Mike

 

[pybyr]

Trevor, any chance of getting a picture and maybe a cross section diagram of how you have the plenum ductwork sitting/sealing over your furnace and then reducing around the hx again. I am getting ready to order my water to air hx through Nationwide Coils following your lead, and have the same furnace plenum outlet size installation issue. I've been wondering how to solve the problem of enclosing a hx bigger in size than the blower plenum outlet. Seems like you solved that problem.

Do you have a cooling coil in your plenum too, or located elsewhere? I've got one in the plenum over my existing furnace now and would like to place the w/a exchanger under it after the blower. The blower unit installation guidelines on Alpine recommend that the cooling coil go under the blower. That would be a real hassle to reinstall the cooling coil, I don't know how to do it anyway, and hope it is not absolutely necessary. What do you all and Trevor (Pybr) think? Do I have to move the cooling coil underneath the blower?

Mike

It's all in a spot where it'd be hard to get intelligible photos, so I'll try to describe, and please feel free to ask questions.

The outlet from my furnace is about 21x22, but there is room around it, in that the furnace body is almost 27 inches across- and there is some room to spare around the outlet towards fore and aft, too. I had the 24x24 coil made with part-inverted flanges on the bottom, which allows it all to sit over/around, and center on, the furnace's "outlet bonnet." Then a large rectangular bent duct fitting usually used for cold air returns into furnaces, with some extra galvanized metal, serves to transition from the top of the water-air HX to the main heat trunk duct.

In effect, the box body of the HX becomes its own oversized duct section directly over my furnace outlet, and since it is no wider than the furnace body, and weighs a lot, it's self-locating and close to self-sealing

 

[Medman]

dogwood, if you are buying a new air handler from Alpine it is easy to change the blower/cooling coil locations. I had to do it because my furnace is downflow, so I had to put the blower on the bottom and the cooling coil on the top, which is the return side. My w-a hx is under the whole unit, encased in a frame that holds the hx, carries the weight of the furnace and seals to the supply duct in the floor.

Alpine's Goodman units are configured for this change. Simply slide out the cooling coil, unscrew the coil frame, remove the blower and reinstall in the correct spots. The cabinets are pre-drilled for the new screw locations and have ports for the refrigerant lines in all the right spots.

You could then put the w-a hx above the furnace on the outlet, as Trevor has done, and adapt the sheet metal to fill in any gaps. Alpine sells sheet metal pieces and tools to do small jobs, or you could call a local guy who wants a small cash job to help you out. I had a local shop make up the sheet metal for the frame I needed. Cost was minimal and it fit like a glove.

 

[dogwood]

Medman, the problem I am looking at is that I have a cooling coil in place in the plenum above my existing furnace. Because I have that in place already I was not going to purchase an entire AHU, just a modular blower unit, which is considerably less expensive, roughly $550 dollars if I recall. There is no place for a cooling coil in the blower unit although it will accept an electric heating element which will provide my backup heat once my propane-fired Lennox Pulse is history. If there was a AHU that came without the cooling coil it might be possible to relocate my existing coil into such an AHU, as you suggest, but I have not come across a coiless AHU for sale. The course of least resistance for me is to put in an 2100 cfm max, up-flow blower, followed by a w/a hx, and next the cooling coil. I'm thinking others may have this arrangement and it may be workable. If I have to though, I will have to figure a way to extend the copper tubes going into the cooling coil , extend the tubes and refill them with whatever they contain (freon?) and put the cooling coil beneath the blower. I would love to do as you suggest and scrap the modular blower only idea, and get an entire AHU, but I am trying to limit cost after the humongous expense of purchasing a Solo Innova 50. And I am going to follow Trevor (Pybyr's) advice and not skimp on the hx, which will add more, but well justified expense. Do you think the arrangement described above would work as opposed to the more ideal arrangement you have in place with your AHU?

Trevor, I mostly grasp what you are saying but am unsure of what you mean by the furnaces "outlet bonnet". Are you describing the whole top surface of the furnace or just the 21x22 opening? On re-reading your post, what I am picturing is a 24x24 water to air hx sitting over the smaller 21x22 opening, with the hx having a flange sticking outwards, that sits on the flat top of, and is screwed or duct-taped to, the furnace top. I already have the reducer plenum piece you describe in place over the existing plenum piece containing the existing cooling coil. Does this sound like what you have? I wish I had a side-view drawing (hint) of what you ordered from Ross at Nationwide Coils so I could better visualize what the part-inverted flanges look like so I could order the same. Are the outside edges of your hx exposed and functioning as the plenum enclosure for the width of the hx? Did I ask you enough questions? Thanks for your help. Maybe Nationwide Coils will have your order on file and adapt it for me size-wise. I've got 3000 sq. ft. home with 10 ft. ceilings to heat. Probably calls for a similar in size hx to what you've got.

 

[Medman]

OK, I get it now. I see how it could be difficult to install the HX below the cooling coil in the plenum. I think you are on the right track, though, and maybe you can get the flange on the HX to be custom bent to meet your needs, as Trevor has done. The flange on my HX is about 1" wide, and the listed dimensions are 20x20. The actual dimensions were about 20.5"x21" on the in/outlet side.

It will work, and there is no issue I can see with the configuration you suggest as long as you can get the CFM's you need. Remember to have a clean-out so you can vacuum the hx and cooling coils, because even with good HEPA filters I am seeing a buildup of fine particulate on the coils. Not enough to cause a restriction, but enough to limit heat transfer (I think).

Maybe you could post a pic of your current configuration and list some of the dimensions - particularly the plenum piece that has the cooling coil in it. This would help us get a handle on exactly what you need.