Outdoor Wood Furnace Info

All-Purpose OWF Discussions => General Outdoor Furnace Discussion => Topic started by: automan77 on February 05, 2013, 04:42:29 PM

Title: Heat exchangers
Post by: automan77 on February 05, 2013, 04:42:29 PM
I"m looking into buying a heat exchanger but am not sure what brand of type to get. My plenun is 13 1/2 by 201/2.  Any info would be helpfull  thx
Title: Re: Heat exchangers
Post by: Scott7m on February 05, 2013, 05:07:56 PM
Sounds to me like you need a 12x18. 

It would have a slight crack on the sides daily taped and maybe a couple inches in the back..


I've used the same supplier for a while now...   
Title: Re: Heat exchangers
Post by: automan77 on February 12, 2013, 06:17:08 PM
need a 19x20  175,000 btu  to heat my home according to my sq footage. 
Title: Re: Heat exchangers
Post by: Scott7m on February 12, 2013, 06:22:09 PM
Wow, I'm heating homes over 4000 square feet on 12x18's sometimes


There is hardly any home that would require 175,00 btu an hour..  Most stoves couldn't produce that for more than 4-5 hours.... 

Where did you read that??
Title: Re: Heat exchangers
Post by: Scott7m on February 12, 2013, 06:24:46 PM
I see folks install monster coils all the time, for what reason I'll never know and the furnace air will be flowing through maybe half of it..

For example theyll mount on top of the plenum, it may measure 20x20 but the hole coming put is 12x18, the rest out of the air flow is wasted
Title: Re: Heat exchangers
Post by: Scott7m on February 12, 2013, 06:30:01 PM
Here is something to consider....

Wood is 8600 btu per pound

Let's deduct 20% for water content

Then say your furnace can reclaim half of that heat...   That means for every pound of wood you can capture 3,440 btu

So 100 pounds of wood would produce 344,000 btu...   That's less than 2 hours worth of wood if your home truly required that much heat

Title: Re: Heat exchangers
Post by: automan77 on February 12, 2013, 06:33:13 PM
question  MY house is 1,685 sqft. with basement. do i double the footage for the size of the exchanger for the basement
Title: Re: Heat exchangers
Post by: willieG on February 12, 2013, 06:38:51 PM
i filled my plenum..i had to pur 2 smaller exchangers side by side..i think they are either 2 12 x12 or 12 x14

if your original furnace and ductwork were professionally installed, the ductwork is the size it is for a reason. i dont think you should be choking it down with tin along the sides (at least not very much) i sure am no heat vac guy so i did not want to change what the pros had done when they installed my system?

now, both mys sytems work good and even if i put in too much exchanger....it works and so does my original heat (if i ever use it)

and then again...i also believe you should never  hoook your indoor boiler to yoru OWB directly...but many do it and they say it works great. i think ..why would you change a closed system to an open system when the closed  system is designed to be just that...closed
Title: Re: Heat exchangers
Post by: Scott7m on February 12, 2013, 06:39:21 PM
Playing with numbers here....   

A home requiring 175k btu would need 4.128 million btu per day

123,840,000 btu per month

6 month winter would require 743,040,000btu per winter

This is all just playing with numbers to realize how much wood it would take to produce that many btu per hour all winter...


At that rate and 50% efficiency, it would require 1200 pounds of wood per day

36,000 pounds per month

216,000 pound per winter.

Red oak is 3500 pounds per cord. 4x4x8

So if a home used that much

A cord of seasoned oak would last 2.9 days

10.28 cord per month

62 cord per winter



Interesting stuff, to me at least lol
Title: Re: Heat exchangers
Post by: Scott7m on February 12, 2013, 06:44:04 PM
i filled my plenum..i had to pur 2 smaller exchangers side by side..i think they are either 2 12 x12 or 12 x14

if your original furnace and ductwork were professionally installed, the ductwork is the size it is for a reason. i dont think you should be choking it down with tin along the sides (at least not very much) i sure am no heat vac guy so i did not want to change what the pros had done when they installed my system?

now, both mys sytems work good and even if i put in too much exchanger....it works and so does my original heat (if i ever use it)

and then again...i also believe you should never  hoook your indoor boiler to yoru OWB directly...but many do it and they say it works great. i think ..why would you change a closed system to an open system when the closed  system is designed to be just that...closed

Where the flanges of your 2 smaller coils meet in the middle would probably equal the amount of resistance as a 1/2" flange on the side...   From my experience there I've never had any issues in restricting air to much and such

Your correct, one should never ever depressurize a closed system and tie it to an owb

Had a guy the other day do that and not run treatment in his stove cause it was stainless, his boiler was mild steel and likely ate up with corrosion after 6 years of abuse
Title: Re: Heat exchangers
Post by: willieG on February 12, 2013, 06:45:04 PM
i am under the understanding when you buy a furnace and if a heat loss is done on the house the furnace will be sized to heat yoru home on the average "coldest " day of the year in your area. if this works out to 150,000 btu then your furnace will be sizzed for that. so you will likely get buy 98% of the time with a much smaller btu delivery (and that means a smaller exchanger as well) but if you want to be sure you never have to have less heat than you set your thermostat at, you should size  your exchanger to match your existing furnace btu out put (at least that is the way  i was told furnaces are sized?)

like i said earlier, i am not a ehat vac guy but i have asked a few  and this is the away they described sizing a furnace to me?
Title: Re: Heat exchangers
Post by: Scott7m on February 12, 2013, 06:46:41 PM
question  MY house is 1,685 sqft. with basement. do i double the footage for the size of the exchanger for the basement

No, basement counts for less than half

Sometimes I do 2200 sq ft manufactured homes on 12x12's, because there is no way in the world to get bigger coils in them

I make up for it with fast pump speeds and keeping the stove 180 or higher as a set point

No complaints so far......   I've been in there homes too to see how they worked, air was over 105 out the vents, house was warm
Title: Re: Heat exchangers
Post by: willieG on February 12, 2013, 06:47:29 PM
i didn't meet my flanges in the middle scott, i set one up against teh other so i only have the thickness of 1 flange. so i have three flanges..one on each side and one in the middle that was the way i could do it to get the least "restriction" due to the flanges
Title: Re: Heat exchangers
Post by: Scott7m on February 12, 2013, 06:50:26 PM
i am under the understanding when you buy a furnace and if a heat loss is done on the house the furnace will be sized to heat yoru home on the average "coldest " day of the year in your area. if this works out to 150,000 btu then your furnace will be sizzed for that. so you will likely get buy 98% of the time with a much smaller btu delivery (and that means a smaller exchanger as well) but if you want to be sure you never have to have less heat than you set your thermostat at, you should size  your exchanger to match your existing furnace btu out put (at least that is the way  i was told furnaces are sized?)

like i said earlier, i am not a ehat vac guy but i have asked a few  and this is the away they described sizing a furnace to me?



The other day when we were discussing the empyre house on the video, it required 52000 btu per hour on the average coldest winter day in Ontario and was 5200 sq ft

Efficient home it seemed but still...

A lot of homes in my area have 120k btu furnaces, yet when I do the math, they would only require 40-45k btu an hour on our average coldest day

So I don't think that these guys get that technical
Title: Re: Heat exchangers
Post by: Scott7m on February 12, 2013, 06:52:33 PM
i didn't meet my flanges in the middle scott, i set one up against teh other so i only have the thickness of 1 flange. so i have three flanges..one on each side and one in the middle that was the way i could do it to get the least "restriction" due to the flanges


I see


I'm just not convinced a little bit of restriction amounts to much...
Title: Re: Heat exchangers
Post by: willieG on February 12, 2013, 06:58:07 PM
i amsure many dont and in older homes they are likley way over sized but if y ou  arein a fairly new house (at least hear in ontario) i think a heat loss is required by some  county laws...and i know when i put my inground water furnace in the company not only did a heat loss but did an infa red phot to see where the most heat loss was so i could use this info for future insulating as i tried to improve things

the first two years i used only the water furnace the heat coil (that i never installed becasue i had a fire place) has a light on it that tell you when the furnace can not keep up and it is using electricity to heat the house only came on 2 times..so their calculations i think were quite good

i think most calcualtions are better now than years ago...years ago the plumbing guy sol the furnace and he sold what ever he was getting a deal on

it is my belief you should still "fill your plenum"
Title: Re: Heat exchangers
Post by: Scott7m on February 12, 2013, 07:12:40 PM
Yep Ontario has far more regs according to the guy at empyre

From what he says they do mostly low fan speed settings that
Never shut off.

He was the biggest hvac guy in Canada for a long time

I put in as big of a coil as the plenum/duct work will allow

If they have a 14x14 trunk line and a heat pump will heat there home with 88 degree air,
I know my 14x14 coil will easily do it with hotter air


There is a huge difference to installing your own vs seeing a different situation every other day
Title: Re: Heat exchangers
Post by: willieG on February 12, 2013, 07:17:33 PM
I'm just not convinced a little bit of restriction amounts to much...
[/quote]
i agree with you 100% but if you restirct a plenum that is 20 inches high by 2 inches that would be 10% i think that is more than a little (but we all have different views of "little bit"
would a 10 percent blockage put more back pressure on your blower? would it cause any early failure of the blower? i don't know these things so that is why i chose to fill my plenum as best i could..i would think the exchangers them selves are causing some added restriction on the blower motor all ready

and i am not arguing with you either..just putting another view out there for interested parties to  sipher on (lol) i have no proof of any of this..just my twisted thinking. i always like your (and other) responses..give me (and others i hope) more things to consider when we are trying to decide
Title: Re: Heat exchangers
Post by: Scott7m on February 12, 2013, 07:25:55 PM
I'm not arguing either....

I jut know it's impossible in the real world to get things so precise.....  I used to freak over things like this.  I always do a pre run on the install doing the estimate where I see where I can install as big of a coil as possible...  Usually here it's a 14x18 or 16x18

I've also played with my own to see if allowing air gaps around the sides of the coil amounted to much, I allowed 1" gaps all the way around the sides of my coil and air temp out the vents only dropped 4-5 degrees. 
Title: Re: Heat exchangers
Post by: Scott7m on February 12, 2013, 07:57:18 PM
Hey Willie, help me figure this out

If your flowing 6 gpm, and you have a delta t of 20.   How many btu can you actually push through? 

360 gallons an hour, delta t of 20 degrees.........  I'm thinking
Title: Re: Heat exchangers
Post by: Scott7m on February 12, 2013, 08:36:51 PM
The results are very interesting, makes you think that the btu ratings we see on heat exchangers is worthless information...

They have no idea how many gallon your system will push, what your delta t would be and so on

For example the figures Willie confirmed me on was if you were pushing 6 gallon per minute and had a delta t of 20, the most btu's you could deliver is 57,000 per hour

You could speed the water up to let's say 10gpm but it wouldn't still get you anywhere near the ratings we see, and you really don't want the delta t more than 20 so...  You can easily see if your needing a lot of btu, big line is essential
Title: Re: Heat exchangers
Post by: willieG on February 12, 2013, 09:33:11 PM
the reason we see such high btu numbers on exchangers is the one we buy are normally for uch different applications. if you look on the tags tehy may say something like "Max pressure 300 psi" and "Maximum temp 300 degrres F) these exchangers are also used for steam pressure where temps can be much hotter  than we create and are capable of delivering the  btu they are rated at

with our little OWB we will never be close

the gpm  and the temp you deliver at AND your delta will tell you how many btu you are delivering to your house
 any change of those three things(or any change of any one of those three things)  will change the btu you are putting into the home




Title: Re: Heat exchangers
Post by: Scott7m on February 12, 2013, 09:36:51 PM
Yep.... 

So picking out heat exchangers based on there rated btu's is hokum
Title: Re: Heat exchangers
Post by: automan77 on February 13, 2013, 09:11:50 AM
Talked with a dealer/installer and he told me to go with the same btu as my propane furnace which is 70,000 btu
Title: Re: Heat exchangers
Post by: comnrailpwr on February 13, 2013, 11:59:59 AM
i didn't meet my flanges in the middle scott, i set one up against teh other so i only have the thickness of 1 flange. so i have three flanges..one on each side and one in the middle that was the way i could do it to get the least "restriction" due to the flanges


I see


I'm just not convinced a little bit of restriction amounts to much...
In heating, restrictions do not mean a whole lot, during heating the fan is run on medium speed unless heat source is a heat pump. Air conditioning and using heat pumps is where too much restrictions can cause problems. Coil flanges will make no difference in the operation of the original equipment, they wont cause enough restriction. HVAC systems should be designed off the cooling load. Its easier to heat a home than it is to cool it.
Title: Re: Heat exchangers
Post by: Scott7m on February 13, 2013, 04:46:28 PM
Talked with a dealer/installer and he told me to go with the same btu as my propane furnace which is 70,000 btu

Sounds far more reasonable....  The 12x18 will easily take care of you, with a proper pump and 1" lines you should be able to push that

Title: Re: Heat exchangers
Post by: automan77 on February 13, 2013, 06:28:53 PM
anyone ever buy a heat exchanger off ebay, there seems to be some good prices on there but not sure of the quality.
Title: Re: Heat exchangers
Post by: Scott7m on February 13, 2013, 06:34:14 PM
anyone ever buy a heat exchanger off ebay, there seems to be some good prices on there but not sure of the quality.

I have before in a pinch, I just don't trust everything I see on there

The 12x18's I carry I sell for $151 w/free shipping...  I trust them and have sold hard telling how many wih no problems

Title: Re: Heat exchangers
Post by: ghitch75 on February 13, 2013, 06:55:12 PM
Quote
In heating, restrictions do not mean a whole lot, during heating the fan is run on medium speed unless heat source is a heat pump. Air conditioning and using heat pumps is where too much restrictions can cause problems. Coil flanges will make no difference in the operation of the original equipment, they wont cause enough restriction. HVAC systems should be designed off the cooling load. Its easier to heat a home than it is to cool it.

thats all good with gas and oil but electric air handlers with heat strips if you stick a water/air coil in the supply air it will burn the heat strips up from to much restriction and turbulence........i always put the coil in the return.....
Title: Re: Heat exchangers
Post by: Scott7m on February 13, 2013, 06:59:43 PM
I never install in the plenum


I always try to install in the main trunk line supply

If that don't work I'll go to the return side and make a new filter space.

If you install in the supply side of the main line the air is already filtered
Title: Re: Heat exchangers
Post by: ghitch75 on February 13, 2013, 07:03:02 PM
yes filter is a must or the coil turns into the filter :thumbup:
Title: Re: Heat exchangers
Post by: willieG on February 14, 2013, 03:28:51 AM
I never install in the plenum


I always try to install in the main trunk line supply

If that don't work I'll go to the return side and make a new filter space.

If you install in the supply side of the main line the air is already filtered
my mistake on referring to plenum...i also installed in the main feed trunk after the filter. just after the furnace itself (very sorry for error)
Title: Re: Heat exchangers
Post by: automan77 on February 14, 2013, 05:01:01 AM
I have a buddy that has a 18x20 in a 1,800 sq ft home. Would that be like 140,000 btu
Title: Re: Heat exchangers
Post by: WoodMOJoe on February 14, 2013, 08:00:27 AM
Great thread here.

I (for some reason) had assumed that the heat exchanger needed to be in the plenum over the A-coil (upflow propane-fired)furnace).

That was going to be a difficult trick in my situation, installing it in the main trunk line will be a breeze.

I'm learning.   8)

Thanks!
Title: Re: Heat exchangers
Post by: automan77 on February 14, 2013, 08:22:14 AM
Who has the best price on a 12x18 heat exchanger
Title: Re: Heat exchangers
Post by: Scott7m on February 14, 2013, 08:58:25 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
Title: Re: Heat exchangers
Post by: willieG on February 14, 2013, 10:48:02 AM
the real pros can straighten me out here if i am wrong but here is something i always think and i could very well be wrong...so here goes

lets take your house and a water hose...you house us putting out 40 pounds pressure, you have a outside tap with a y on it..youhave a 50 foot garden hose on one side of the y and the other side shut off. you open the tap and lests say for fn you are getting 3 gpm out the hose....now you open the other side of the y with another 50 foot hose on it,,,because you have now given that 40 pounds pressure some where else to go so you have eased the head pressure  in the first hose and added head pressur in the second hose,,but you have likley reduced the velocity at which the water is moving so in fact it is moving slower but it will not be half or what it was so lets say now it could be moving 2 gp in each hose so now you have 4 gpm...i think a larger heat exchanger may do this as well...you are capable of moving say 6 gpm through an exchanger that has maybe 8 tubes but your pump is capable of 10..so you are pushing with the force of ten but due to friction you can only get 6 through the exchanger...add now, an exchanger with 16 tubes you are  adding length to the pipiing and you think it would add double the ehad but becasue you are lowering the velocity of the water the resistance is much lower so you get more gpm through the larger exchanger

the pros can step in and tell me if i am on the right track or not i  hope i am typing what i am thinking...lol
Title: Re: Heat exchangers
Post by: Scott7m on February 14, 2013, 10:57:16 AM
I think the plate exchangers are more restrictive than the coils though, I know if u run 10 plates you have to be careful and keep the flow up
Title: Re: Heat exchangers
Post by: Jd79 on March 02, 2014, 03:18:00 PM
Quote
In heating, restrictions do not mean a whole lot, during heating the fan is run on medium speed unless heat source is a heat pump. Air conditioning and using heat pumps is where too much restrictions can cause problems. Coil flanges will make no difference in the operation of the original equipment, they wont cause enough restriction. HVAC systems should be designed off the cooling load. Its easier to heat a home than it is to cool it.

thats all good with gas and oil but electric air handlers with heat strips if you stick a water/air coil in the supply air it will burn the heat strips up from to much restriction and turbulence........i always put the coil in the return.....

Is this a big concern?  I've always noticed when my backup heat strips come on, the variable speed blower ramps up to high speed.  I never thought about the heat exchanger causing too much restriction that it could potentially burn out the backup strips if they did come on.  Can anyone elaborate more or have specific examples?  I know this is an old thread, but I've been trying to decide where to put my hx if/when we ever get this OWB built and I was pretty well set on placing it in the supply above my updraft air handler.  I have read that in the return ductwork, you risk overheating the blower and electronics in the air handler.  That's not really much of an option anyway due to space restrictions.  I don't think I could get an exchanger into my return ductwork anyway.  I've heard mention of using the main trunk line (after the furnace) but that would mean my heat exchanger would be put in the attic.  I suppose that's possible, but it would still create a restriction after the heat strips.  What sayeth the experts?
Title: Re: Heat exchangers
Post by: Sloppy_Snood on March 02, 2014, 03:55:51 PM
I never install in the plenum

I always try to install in the main trunk line supply

If that don't work I'll go to the return side and make a new filter space.

If you install in the supply side of the main line the air is already filtered

I am thoroughly "corn-fused" here...  :bash:

Why is it that you don't install a water-to-air heat exchanger in the plenum of a home's existing forced air furnace?  :-\

What the heck is a "main feed trunk?"  Isn't that a plenum?  :-\
Title: Re: Heat exchangers
Post by: Scott7m on March 02, 2014, 04:25:40 PM
I never install in the plenum

I always try to install in the main trunk line supply

If that don't work I'll go to the return side and make a new filter space.

If you install in the supply side of the main line the air is already filtered

I am thoroughly "corn-fused" here...  :bash:

Why is it that you don't install a water-to-air heat exchanger in the plenum of a home's existing forced air furnace?  :-\

What the heck is a "main feed trunk?"  Isn't that a plenum?  :-\

It's the main duct that comes out of the plenum where the fan itself is located.   I have no desire to mess with that big metal box that has very little space to work with when I can accomplish the same thing by installing in the duct board or main trunk line right above it.

Title: Re: Heat exchangers
Post by: ffbare on March 02, 2014, 08:08:45 PM
 :post:
Title: Re: Heat exchangers
Post by: mtoll on March 03, 2014, 04:19:32 PM
So does it really matter if the heat exchanger is above the furnace fan so the fan sucks air through it or below so it blows through the HE even if there is some small restriction below the fan 
Title: Re: Heat exchangers
Post by: mlappin on March 03, 2014, 04:36:31 PM
So does it really matter if the heat exchanger is above the furnace fan so the fan sucks air through it or below so it blows through the HE even if there is some small restriction below the fan

If you pull air thru the HX then you might have the possibility of overheating the motor on the blower. Others that install for a living would know for sure.
Title: Re: Heat exchangers
Post by: Scott7m on March 03, 2014, 04:42:12 PM
So does it really matter if the heat exchanger is above the furnace fan so the fan sucks air through it or below so it blows through the HE even if there is some small restriction below the fan

If you pull air thru the HX then you might have the possibility of overheating the motor on the blower. Others that install for a living would know for sure.

We have done a lot on return side and never seem it be an issue.

If you go to return side tho u must install a filter on upper side of coil or it will become the filter
Title: Re: Heat exchangers
Post by: Jd79 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.
Title: Re: Heat exchangers
Post by: jtepn87 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.
Title: Re: Heat exchangers
Post by: Scott7m 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?
Title: Re: Heat exchangers
Post by: jtepn87 on March 03, 2014, 07:23:13 PM
It's gas and the fan sits at the top of the unit.
Title: Re: Heat exchangers
Post by: Scott7m 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

Title: Re: Heat exchangers
Post by: jtepn87 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.
Title: Re: Heat exchangers
Post by: Scott7m 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
Title: Re: Heat exchangers
Post by: Sprinter 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.
Title: Re: Heat exchangers
Post by: Scott7m 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
Title: Re: Heat exchangers
Post by: Sprinter 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.
Title: Re: Heat exchangers
Post by: Sprinter 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.
Title: Re: Heat exchangers
Post by: Scott7m 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.
Title: Re: Heat exchangers
Post by: Scott7m 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
Title: Re: Heat exchangers
Post by: slimjim 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
Title: Re: Heat exchangers
Post by: CountryBoyJohn 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.
Title: Re: Heat exchangers
Post by: jtepn87 on March 04, 2014, 07:39:10 AM
The only time I ever get called Mr. is when I'm in trouble, I guess I really am getting older. LOL. Did they cut the hole under the furnace bigger to allow more air to flow, or did they just leave it and butt the box against the subfloor?
Title: Re: Heat exchangers
Post by: CountryBoyJohn on March 04, 2014, 08:38:30 AM
Ha!  Well, I just call everyone on here Mr.  It works for me.   :)

He hasn't installed the box yet.  But, I'm sure he will just connect the main trunk into the top of the box with the same size it comes out of the hole as.  I'm sure he'll connect flexible duct to the floor, run it to the box, then he'll tie the other end of the box to the other branches. 
Title: Re: Heat exchangers
Post by: jtepn87 on March 04, 2014, 11:47:36 AM
Sounds similar to what I'm wanting to do, only I'm going to put the box below the floor insulation.  I cut that stuff once to work on water lines, and its a pain to get that stuff to stay in place after that. This post is full of redundancy. :bag:
Title: Re: Heat exchangers
Post by: cantoo on March 04, 2014, 06:08:45 PM
I just installed one in my mobile home. It was an electric furnace in a small closet. All I did was built a tin box for the exchanger and moved the furnace up that amount. Lots of room to raise it. Not sure about the gas but I bet it's a lot of empty space I would start removing stuff and take a look. I would do any cutting underneath if you don't have too. And it actually is easy toi fix if you buy the proper insulation and belly tarp to install it. The insulation is available in 48" wide batts by as long as you want, same stuff as used on ceilings and walls of steel commercial buildings, belly tarp backing material is already glued to it. just cut the material to length and there is a 1x4 piece of wood screw nailed to the bottom of the floor joists that you can screw nail it to. If you do a search on utube for trailer floor repair there is lots of videos of what you can do to repair the floor insulation.
Title: Re: Heat exchangers
Post by: jtepn87 on March 04, 2014, 08:39:36 PM
I would have to change my cold air return and something else to raise the furnace. And i ended up using black plastic, gorilla tape, and 1x4's on the insulation under the house last time
Title: Re: Heat exchangers
Post by: Scott7m on March 04, 2014, 08:49:00 PM
I just installed one in my mobile home. It was an electric furnace in a small closet. All I did was built a tin box for the exchanger and moved the furnace up that amount. Lots of room to raise it. Not sure about the gas but I bet it's a lot of empty space I would start removing stuff and take a look. I would do any cutting underneath if you don't have too. And it actually is easy toi fix if you buy the proper insulation and belly tarp to install it. The insulation is available in 48" wide batts by as long as you want, same stuff as used on ceilings and walls of steel commercial buildings, belly tarp backing material is already glued to it. just cut the material to length and there is a 1x4 piece of wood screw nailed to the bottom of the floor joists that you can screw nail it to. If you do a search on utube for trailer floor repair there is lots of videos of what you can do to repair the floor insulation.

Yep those are the easiest.......   
Title: Re: Heat exchangers
Post by: Sprinter on March 04, 2014, 09:57:40 PM
Thanks for the info,

I also came across this water to air heat exchanger sizing data and specification charts that shows what you're saying.
http://www.firstco.com/getattachment/Products/Multi-Family-Residential-Products/Miscellaneous/HWC/hwc209.pdf (http://www.firstco.com/getattachment/Products/Multi-Family-Residential-Products/Miscellaneous/HWC/hwc209.pdf)

And some braztek plate and finned water to air exchanger sizing and specs
http://www.brazetek.com/finned-coil-water-air-heat-exchangers (http://www.brazetek.com/finned-coil-water-air-heat-exchangers)