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Author Topic: Heat exchangers  (Read 13365 times)

Jd79

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Re: Heat exchangers
« Reply #45 on: March 03, 2014, 05:50:45 PM »

I would like to know if anyone has seen cases of it burning out the heat strips on electric backup due to reduced airflow.
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jtepn87

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Re: Heat exchangers
« Reply #46 on: March 03, 2014, 06:23:47 PM »

Scott. How do you put the hx in the main trunk? I live in a mobile home, and this method seems like it would be a lot easier than trying to fit one in the plenum.
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Scott7m

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Re: Heat exchangers
« Reply #47 on: March 03, 2014, 06:35:57 PM »

Never seen it cause any issues period

I had 1 guy have is ac unit freeze solid and it burst his coil,  it just seeped but needed to be replaced

This is 1 our of a PILE so no real concern for me

A twisted dead short wire ain't much to go wrong tho


in a mobile home, installing in trunk line I'd impossible, or next to it

The biggest u can install in trunk line in a double wide is 12 12 directly under the unit

Is your unit gas or electric

That will tell me where ur coil will go

Is the cabinet fans in open on top?
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jtepn87

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Re: Heat exchangers
« Reply #48 on: March 03, 2014, 07:23:13 PM »

It's gas and the fan sits at the top of the unit.
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Scott7m

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Re: Heat exchangers
« Reply #49 on: March 03, 2014, 07:42:18 PM »

Poor u

I hate those


Under ur home between the floor joist is ur only place to put it

It has to be before the crows over duct or you'll only heat half of it

You have room for a 12 x12 under there

if you need a bigger one you may have to re design the box under floor

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jtepn87

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Re: Heat exchangers
« Reply #50 on: March 03, 2014, 08:17:19 PM »

Gee thanks! If only I had a dollar for every time I heard "sucks to be you". Anyways, I was thinking about making a box to put the hx in. The box would have a coupler on top and bottom, to connect into where the duct comes through the floor and then to the insulated duct truck. Would this work, or would it slow the air flow too much.
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Scott7m

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Re: Heat exchangers
« Reply #51 on: March 03, 2014, 09:50:25 PM »

That's basically what you have to do to get a good sized coil in there

I've got 12x12 coils heating a couple double wide homes but it's hard for them to keep up real well if it's -15
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Sprinter

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Re: Heat exchangers
« Reply #52 on: March 03, 2014, 10:07:32 PM »

It doesn't cost much to have a HVAC guy bend up or fab you a section of duct or box that will slide right in, sometimes if there's room well put the Furn on a riser instead of sitting on the floor. Similar to setting an air bear or upgraded air filter. Cash motovates guys if you find them on a job site if possible.
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Scott7m

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Re: Heat exchangers
« Reply #53 on: March 03, 2014, 10:19:08 PM »

It doesn't cost much to have a HVAC guy bend up or fab you a section of duct or box that will slide right in, sometimes if there's room well put the Furn on a riser instead of sitting on the floor. Similar to setting an air bear or upgraded air filter. Cash motovates guys if you find them on a job site if possible.

Slide right in where? 

On the gas furnace like he has there isn't enough room to get half of a coil in the plenum, there jam packed from ceiling to floor and are usually in a space or closet built just for them. 

Then where it comes through the floor you have a 12 x12 or so square box inside an aluminum duct that runs full length of one side, from that duct is a cross over duct to the other side of house

The bad thing is this,  that aluminum duct is up in the insulation and very odd ball stuff.  It's likely 14x4 or a similar odd shape

The box below floor level is great if you have room between it and ground but it has to incorporate that odd duct too

Sometimes you have to cut floor joist and box them back in, it's a mess
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Sprinter

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Re: Heat exchangers
« Reply #54 on: March 03, 2014, 10:50:38 PM »

I have a buddy that has a 18x20 in a 1,800 sq ft home. Would that be like 140,000 btu

No...  The numbers on the box are worthless

How can the manufacturer know how much water will be flowing through the coil?  They don't

Do they know if we installed 3/4" lines or 2" lines, they don't.   

What I'm saying is there is no way to determine what size coil you need by simply looking a a btu rating on the box.  I can take the same coil, put it in my system and get 60k btu an hour, take it to another stove, another system, and it make 110,000 btu an hour.....  Same coil, different system design

Don't the ratings figure the surface area of the HE and how it's designed for a specific GPM , delta T and spec supply temp. Sure you can change the flow but won't this also change delta T with little change in output. I guess I'm looking at them like regular fin tube baseboard, increasing the GPM by double only increases output by a few btu's , less than 5%. Water temp makes a much larger btu change. Only way to come close to doubling output is to raise specified supply temp 50-60 degrees.
Supply pipe size has zero bearing on output, surface area, Delta T and supply temp are the big variables, or variables that can make output btu changes. Slowing the fluid down increases BTU output more than increasing flow.
I don't deal with a lot of air handlers or water to air exchangers, so correct me if I'm wrong.
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Sprinter

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Re: Heat exchangers
« Reply #55 on: March 03, 2014, 10:56:34 PM »

I've seen many different set ups, not all of them are crammed into a closet floor to ceiling. As long as there is enough exposed duct to slide it in, or whether it be a 24"-30"-36"-42" etc... Long Section of trunk. Its nothing for a tin knocker , even with small access.
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Scott7m

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Re: Heat exchangers
« Reply #56 on: March 04, 2014, 06:36:07 AM »

I have a buddy that has a 18x20 in a 1,800 sq ft home. Would that be like 140,000 btu

No...  The numbers on the box are worthless

How can the manufacturer know how much water will be flowing through the coil?  They don't

Do they know if we installed 3/4" lines or 2" lines, they don't.   

What I'm saying is there is no way to determine what size coil you need by simply looking a a btu rating on the box.  I can take the same coil, put it in my system and get 60k btu an hour, take it to another stove, another system, and it make 110,000 btu an hour.....  Same coil, different system design

Don't the ratings figure the surface area of the HE and how it's designed for a specific GPM , delta T and spec supply temp. Sure you can change the flow but won't this also change delta T with little change in output. I guess I'm looking at them like regular fin tube baseboard, increasing the GPM by double only increases output by a few btu's , less than 5%. Water temp makes a much larger btu change. Only way to come close to doubling output is to raise specified supply temp 50-60 degrees.
Supply pipe size has zero bearing on output, surface area, Delta T and supply temp are the big variables, or variables that can make output btu changes. Slowing the fluid down increases BTU output more than increasing flow.
I don't deal with a lot of air handlers or water to air exchangers, so correct me if I'm wrong.

Yea totally different concept

Base board rads are radiating heat into the room where this coil has forced air rushing through it. 

You can cause big increases in heat output by the rate at which the fan blows, a fan may be set on low at 800 cfm for heating purposes, but often times if you run it on high as it would during ac season the fan may produce 1300cfm. 

All of this will be taken into consideration but with proper sized pumps and plumbing all of it can be worked with. 

But if is far different than radiant baseboard designs where heat can only radiate so fast.
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Scott7m

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Re: Heat exchangers
« Reply #57 on: March 04, 2014, 06:40:59 AM »

I've seen many different set ups, not all of them are crammed into a closet floor to ceiling. As long as there is enough exposed duct to slide it in, or whether it be a 24"-30"-36"-42" etc... Long Section of trunk. Its nothing for a tin knocker , even with small access.

Sprinter, he said he lived in a mobile home, I have never seen any exposed ducts in a mobile home besides the cross over tube.   

All of the duct work is ran inside of the plastic lined insulation that covers the under side of the home. 

For example when u look under there u see nothing but black plastic and one 12-15" crossover duct

To even see the duct that comes from below fan you have to cut out a big section of plastic and then start pulling out all the fiberglass insulation, it's a mess

Also in all mobile homes I've seen,  all of them were installed in closets where they simply studded the walls against the unit itself to save room, maybe you've seen something different but out of all I've seen, they were all like this
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slimjim

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Re: Heat exchangers
« Reply #58 on: March 04, 2014, 07:00:41 AM »

  Perhaps the ones you have seen Scott are different but the ones that I have done all had room enough to install the Rad right at the bottom of the unit just above the floor, the biggest issue here is that unless the water flow is controlled by TT or a bypass loop is installed, the Rad puts out enough convected heat up through the hot air unit that the snap disc turns the fan on even when there is no call for heat
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CountryBoyJohn

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Re: Heat exchangers
« Reply #59 on: March 04, 2014, 07:10:50 AM »

I hope I can add some insight to the "mobile home" situation.  I have 2 experiences with this. 

1.  I have an electric "mobile home" type furnace in my modular constructed home.  The underside of my floor is all sealed and wrapped just like Scott says.  I do not have a return on my furnace, just the filter on top and vented doors.  I was able to disconnect the furnace from the floor (no easy task) and build a wood frame for the furnace to sit on and house the heat exchanger.  With Mr. jtepn87's gas with fan on top, he may not be able to lift his furnace up like I did. Which brings me to my second experience.

2.  My cousin has a true double wide with a gas furnace with the fan on top.  I imagine it's just like Mr. jtepn87's.  He did not have the clearance to raise the furnace, nor did he have a good spot to "slide" it in there either.  He contacted an HVAC guy and he constructed a new distribution box for my cousin to insert into his ductwork below the house.  He'll have to pull back the insulation around the main line under the furnace, but they took lots of measurements and this box looks AWESOME!!  I think it set him back $200-$300.  But, I think it'll work well for him.  He will have to do some duct work under the house to route his existing lines through this heat exchanger box.

Neither of these 2 methods are easy.  But, it's all worth it to get your home heated!!  Good Luck!  Let me know if you want pictures of either setup.
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