Does DC motor allow more flexible placement of furnace

[dpkform]

Planning to install all new furnace/AC/ductwork as part of our TOTAL gut interior renovation on our old home in central Toronto, Canada. Only the inside of the double brick exterior walls remain. We have had three professionals HVAC contractor sales persons through the house, plus have had a design (J/D) done by a pro, for our HVAC permit.

I would like a second opinion on some of the things I have heard.

I have five questions - and thank-you very much in advance, for reading this long post.

Here are some quick picture links to our floorplan. The top of the pictures (back of the house) faces West. Click the pics for a full size view.

http://i67.photobucket.com/albums/h307/dpkform/reno/th_Basement.gif (http://i67.photobucket.com/albums/h307/dpkform/reno/Basement.gif)
http://i67.photobucket.com/albums/h307/dpkform/reno/th_second_floor.gif (http://i67.photobucket.com/albums/h307/dpkform/reno/second_floor.gif)
http://i67.photobucket.com/albums/h307/dpkform/reno/th_main_floor.gif (http://i67.photobucket.com/albums/h307/dpkform/reno/main_floor.gif)

1) The rep who came to my home on referral by Home Depot, told me that if I go with a DC motor based furnace, I can place the furnace in a far corner of the house (SE - or bottom left of floorplan) without any significant impact on efficiency - unlike other types which should be close the center of the home to work well. This of course, gives me the possibility of larger rooms/ more flexible layout for future basement finishing. I'm having a bit of a hard time believing this - especially as most of the exterior windows, a larger portion of the exterior walls are at the back (west) of the house. Is he correct?

2) What I do seem to like about above contractor is he says, despite the HVAC plans drawn by our licensed HVAC engineer, the rear (west) bedrooms should definitely have their own returns - a large return in the upstairs hallway will not work well. I am inclined to agree with him on this - is he correct?

3) I have purchased and used the residential version of HVAC calc. As we are undergoing a total interior renovation, we can choose how many windows to add/move, what R-value to insulate to, and even how "tight" to make the house. We could make it as tight as new construction by using top quality spray foam everywhere (then needing an ERV/HRV), or typical old-home loose, by using crappy old fibreglass batt.

I understand that typically a furnace should be no more than 20% oversized, but if I model our house, as "tight", I can get the heat loss down to about 37,000 BTU - it seems that pretty much any furnace would be quite oversized, and that the benefit of a multi-stage or modulating furnace would be mostly lost - as only the lowest stage would ever be needed to maintain heat. Would I still benefit from a multi-stage/modulating furnace in this case?

4) I'm confused about duct length and transitions. Let's say two identical rooms call for the same CFM. Room A can be served by a nearly straight duct only a couple feet long, while Room B is served by a long duct run, with a transition to and from round/square (through interior 2x4 walls), and several changes in direction (elbows). In HVAC calc - it would seem to call for the same duct size for Room A and B, yet to me it would seem Room B would at least initially need a larger duct size to compensate?

5) I understand it would be advantageous to do hi/lo returns - with top and bottom vents, and a damper to close off the bottom return vent while using AC in the summer. Would it be just as beneficial to run a hi/lo ducts for the supplies, where the heat comes from the bottom in winter, and the cold from the top for AC?

Surprisingly, the Home Depot guy is the only one to call back with a quote - even though I did not set a budget limit to the reps. I'm rather shocked - considering this job with all ductwork is worth about twice as much money, as someone who simply wants a new high efficiency furnace and A/C unit on their existing ductwork. All 3 reps claimed they were capable of replacing all ductwork.

If anyone knows some good HVAC contractors in Toronto, I would appreciate a few more recommendations. I'm particularly interested in the Rheem/Rhud modulating furnace, as we have had old fashioned radiators for heating our previous home, and came to love the consistent, even heat they provide. Unfortunately, hydronic floor heating + mini-duct AC would likely be way too expensive for us.

Many thanks again for reading all this, and for sharing your professional knowledge and experience!

[Freezeking2000]

No safety factor in HVAc calc so add 20%+ then go to the next higher furnace. I would go 50-60K 2 Stage with ECM motor. You could just run the duct around the entire perimeter of the home............!

[dpkform]

No safety factor in HVAc calc so add 20%+ then go to the next higher furnace. I would go 50-60K 2 Stage with ECM motor. You could just run the duct around the entire perimeter of the home............!

Thanks Freezeking

I assume you are saying that with the ECM motor that I can place the furnace at the front of the house, and that heating/cooling to the back of the house would be just as effective with the same duct sizes, as if I placed the furnace in the middle of the house?

[beenthere]

Thanks Freezeking

I assume you are saying that with the ECM motor that I can place the furnace at the front of the house, and that heating/cooling to the back of the house would be just as effective with the same duct sizes, as if I placed the furnace in the middle of the house?

Doesn't matter if its an ECM, or PSC blower, the ducts have to be sized for the TEL.

In reality the duct size is about the same for either type blower. The ECM will use alittle less electric then the PSC, if the duct is sized right.
Done wrong, the ECM will use morre.

A duct that moves 200 cfm of air at 500 fpm is the same size no matter which blower motor is moving that air.

[dpkform]

A duct that moves 200 cfm of air at 500 fpm is the same size no matter which blower motor is moving that air.

thanks beenthere

does that mean duct size for a given cfm/fpm at the register says the same, or is duct sizealso influenced by

1) length of run?
2) number/degree of transitions (round to rectangle) and elbows?

thanks again

[propmanage]

The duct size and shape has a given design flow .Each elbow, transition or length will create static if the duct exceeds 25’ or has excessive transitions increase to the next size.
The right or wrong diffuser can increase or decrease velocity

[dash]

1.)A variable speed indoor fan can deliver the same cfms ,at a much higher static presuure(resistance of ducts,filter and A coil).So he's correct ,however the watts used by the indoor fan will increase,so there is a penalty that should/could be avoided since it's almost like a new construction job.

2.)All rooms ,except kitchen and baths,that have a door that will be closed ,should have a return duct,or a return path.A return path can be a thru the wall or door,or a "jumper" duct,from the room to an area that has a retun that is sized to include the cfms from that room.

Undercutting the doors on baths is a good way to provide return.

3.)Tight construction ,and controling where the fresh air comes from,is the best way to go.

4.)If your example is correctly designed ,the shorter run would call for a damper.It sounds like improper design.HVAC Calc,is not a Manual D(from www.acca.org ),which is what needs to be done,it simplisticly select duct sizes assuming a certain FR(Friction Rate),which is not likely to be the true FR ,that Man> D would determine.

5.)Manual D tells us that the location of retuns,high versus low,has very little effect on comfort.The location and correct selection of supplies ,has a lot to do with comfort.

Your duct system needs to be designed using Manual D ,by someone knowledgable.Better insulation,etc.,will get you a smaller system,which will use smaller ducts ,that cause less of a problem with your availabe space.

To keep the ducts as small as possible ,all returns except one ,could be "return paths",the one return would need to be close to the furnace.Doing this will help to reduce the space required for supply ducts,and no need for return ducts.That said a return on each floor would be better.

[dash]

The duct size and shape has a given design flow .Each elbow, transition or length will create static if the duct exceeds 25’ or has excessive transitions increase to the next size.
The right or wrong diffuser can increase or decrease velocity


That's just another "rule of thumb" ,what size would you increase from,and how do you come up with that size in the first place??.

[dpkform]

Thanks for your detailed and informative replies Dash. They are very, very helpful.

Can anyone recommend excellent contractors in the Toronto area?

I realize that a quality installation is more important than brand/model. That said I am particularly interested in the Rheem/Ruud modulating furnaces.



2.)All rooms ,except kitchen and baths,that have a door that will be closed ,should have a return duct,or a return path.

If returns near kitchens are supposed to be avoided to prevent sucking kitchen smells into the system, how do you deal with an open concept main floor? Here is a thumbnail of our proposed main floor - click on it for a larger picture.

http://i67.photobucket.com/albums/h307/dpkform/reno/th_main_floor.gif (http://i67.photobucket.com/albums/h307/dpkform/reno/main_floor.gif)

[
]A return path can be a thru the wall or door,or a "jumper" duct,from the room to an area that has a return that is sized to include the cfms from that room. Undercutting the doors on baths is a good way to provide return.

If I am interested in reducing sound transmission between rooms, would it be best to have individual returns for each bedroom? I have read that if using "jumper ducts" between rooms, sound transmission can be lessened if the duct path switches directions, rather than simply being a "hole" in the wall with return path registers on either side. For example: vertical to ceiling from Room A register, then horizontal through ceiling, then vertical back down to room B's register.


Tight construction ,and controling where the fresh air comes from, is the best way to go.

Our before renovation blower test measured a whopping 9.5ACH@50Pa, 361 inch sq ELA. The infiltration was the largest source of heat loss, much more so than even the all the uninsulated double brick exterior walls :) The house is 102 years old. It is a semi-detached (duplex). Some indistinguishable part of that infiltration figure is from the conditioned space of the adjacent unit, and not from the outdoors.

With the interior gutted, a liberal application of spray foam insulation on all walls, joist headers, and ceilings should change that figure dramatically. We'll have the home re-tested after renos are done.

Perhaps we'll need an HRV/ERV when done?. I may add an air cleaner in the future - not ready to do so now. Would the added static pressure of an an air cleaner, or the HRV/ERV possibly change the overall duct design/sizing requirements for individual rooms throughout the house?


The location and correct selection of supplies ,has a lot to do with comfort. Your duct system needs to be designed using Manual D ,by someone knowledgable.

I have had a couple Manual J & D designs done by a licensed professional. They are required for our HVAC modification permit. For the most part, I have no problem with the placement of registers.

I'm not yet too happy with with how the ducts themselves are being run. I think our engineer would probably shoot me, if I asked him "hey what about this idea" 20 more times :D Wish we could afford hydronic floor heat/miniduct AC :p

The best way to come up with a duct layout I can live with, would be if I could "play" with various duct layouts/design modifications to the engineers existing Manual D based suggestions, then present my preferred layout to the engineer for suggestions and approval.

I had hoped the duct sizing option in HVAC-calc residential would allow me to do this - but as you pointed out, it does not. It does work great though for showing how various decisions would affect heat loss/gain.

Is there any inexpensive "homeowner" version of manual D software, or at least some sort of manual D guidelines I can use to play with various layouts?

[dash]

Thanks for your detailed and informative replies Dash. They are very, very helpful.

Can anyone recommend excellent contractors in the Toronto area?

REPLY:Call around ,asking "Can you provide a Manual J,S and D"if they can't keep dialing.

I realize that a quality installation is more important than brand/model. That said I am particularly interested in the Rheem/Ruud modulating furnaces.

Reply:From those who know furnaces much better then this "Florida Cracker",I've been told that's a great choice,when using the control/stat that's made for it.



If returns near kitchens are supposed to be avoided to prevent sucking kitchen smells into the system, how do you deal with an open concept main floor? Here is a thumbnail of our proposed main floor - click on it for a larger picture.

Reply:Although no one here argees with me,it's my contentionthat returns are not located in kitchens and even baths,more to insure the exhausts work,more then for oders.We know that the exhaust do not remove all the oders ,in most cases.In our area with open kitchens,code offficals require the return to be 10' from the kitchen ehxhaust hood.

http://i67.photobucket.com/albums/h307/dpkform/reno/th_main_floor.gif (http://i67.photobucket.com/albums/h307/dpkform/reno/main_floor.gif)

[

If I am interested in reducing sound transmission between rooms, would it be best to have individual returns for each bedroom? I have read that if using "jumper ducts" between rooms, sound transmission can be lessened if the duct path switches directions, rather than simply being a "hole" in the wall with return path registers on either side. For example: vertical to ceiling from Room A register, then horizontal through ceiling, then vertical back down to room B's register.
Reply:Jumper ducts with 90° turns ,greatly reduce sound transmission,using ductboard or lined metal helps when using jumper ducts as well.Jumper ducts are much more restrictive due to length and turns,as compared to thru the wall,so they ned to be much larger.Wall spaces are seldom large enough.If you undercut the doors ,you can count that space in determining the size required.Jumper reurn have near zero static pressure to move the air ,hence they need to be sized carefully.



Our before renovation blower test measured a whopping 9.5ACH@50Pa, 361 inch sq ELA. The infiltration was the largest source of heat loss, much more so than even the all the uninsulated double brick exterior walls :) The house is 102 years old. It is a semi-detached (duplex). Some indistinguishable part of that infiltration figure is from the conditioned space of the adjacent unit, and not from the outdoors.

With the interior gutted, a liberal application of spray foam insulation on all walls, joist headers, and ceilings should change that figure dramatically. We'll have the home re-tested after renos are done.

Perhaps we'll need an HRV/ERV when done?. I may add an air cleaner in the future - not ready to do so now. Would the added static pressure of an an air cleaner, or the HRV/ERV possibly change the overall duct design/sizing requirements for individual rooms throughout the house?

Reply:The ERV/HRV has it's own fan and ducts,which need to be sized correctly,I like to use them as the bath exhaust when possible,so when the bath exhaust runs it has makeup fresh air replacing the exhausted air.One HRV can serve more then one bath.



I have had a couple Manual J & D designs done by a licensed professional. They are required for our HVAC modification permit. For the most part, I have no problem with the placement of registers.

I'm not yet too happy with with how the ducts themselves are being run. I think our engineer would probably shoot me, if I asked him "hey what about this idea" 20 more times :D Wish we could afford hydronic floor heat/miniduct AC :p

The best way to come up with a duct layout I can live with, would be if I could "play" with various duct layouts/design modifications to the engineers existing Manual D based suggestions, then present my preferred layout to the engineer for suggestions and approval.

I had hoped the duct sizing option in HVAC-calc residential would allow me to do this - but as you pointed out, it does not. It does work great though for showing how various decisions would affect heat loss/gain.

Is there any inexpensive "homeowner" version of manual D software, or at least some sort of manual D guidelines I can use to play with various layouts?

When they did the manual D,did they give you the ASP(Available Static Pressure)?If not I'd ask to see the worksheet(s).

To do a correct manual D,they need to know the following;
Exact indoor equipment that will be used
Man. J results
Man. S results
Then the TEL(total equivelent length of the duct)
All other PD(pressure drops,from devices,coil,grilles,etc.)

Can you post their duct system layout?

[dpkform]

Can you post their duct system layout?

A little explanation required. We had a different floorplan for our layout 6 months ago, and had an HVAC design done for that. I have electronic versions of the worksheets and duct layout for that original design. Other than the changes in our floorplan, we had to reject this first version as the interior walls that run front to back of the house are load bearing - and the proposed ductwork too severely compromised the structure.

We changed the 2nd floor layout - and shortened the north wall of the hallway in our subsequent plan. I have an electronic version of a proposed duct layout for that plan, but no worksheets.

Hope this at least gives an idea - sorry for the small print, I had to use screen captures. Make sure you view the images at their actual size or larger. If the pictures open up in Windows default Image and Fax viewer, there is an "actual size" icon at the bottom, 4th from the left.

Old Layout Plan and Worksheets
http://i67.photobucket.com/albums/h307/dpkform/heatcalcs/th_Old_Second_Floor.gif (http://i67.photobucket.com/albums/h307/dpkform/heatcalcs/Old_Second_Floor.gif)
http://i67.photobucket.com/albums/h307/dpkform/heatcalcs/th_Old_Main_Floor.gif (http://i67.photobucket.com/albums/h307/dpkform/heatcalcs/Old_Main_Floor.gif)
http://i67.photobucket.com/albums/h307/dpkform/heatcalcs/th_Old_basement.gif (http://i67.photobucket.com/albums/h307/dpkform/heatcalcs/Old_basement.gif)
http://i67.photobucket.com/albums/h307/dpkform/heatcalcs/th_Duct_Calculations.gif (http://i67.photobucket.com/albums/h307/dpkform/heatcalcs/Duct_Calculations.gif)
http://i67.photobucket.com/albums/h307/dpkform/heatcalcs/th_Heat_Loss_Calcs.gif (http://i67.photobucket.com/albums/h307/dpkform/heatcalcs/Heat_Loss_Calcs.gif)

Current Layout Plan (actual final plan slightly different - see notes below)
http://i67.photobucket.com/albums/h307/dpkform/heatcalcs/th_Newer_Layout.gif (http://i67.photobucket.com/albums/h307/dpkform/heatcalcs/Newer_Layout.gif)

I think some of his room measurements are slightly off - I could email my file generated in HVAC-calc - it is correct. I believe he assumed R20 walls - not sure about that yet - don't know if we have space enough for that. That's one reason I have been playing with options in HVAC-calc.

We are currently rennovating the basement and main floor and living on the second floor. When that is done, we will move down to the main floor, and rennovate the second floor. Our new plan for the second floor essentially leaves the existing layout alone, and will convert 1 bedroom to an ensuite.

Also - the rear bonus rooms. Note the basement fixtures will ALL be demolished. The main floor bathroom is being kept temporarily, so we can use it when we renovate the 2nd floor bathroom. After that, the main floor rear bonus room will be open concept to the kitchen dining area, and filled with large windows to overlook our backyard, which is well shaded by many very large old trees. The rear of our home faces west.

The second floor sunroom is also likely to have more windows on all 3 sides, not just the one as in the plan.

Thanks for any comments - and again - if I there was some sort of homeowner version of Manual D software - that would be great.

I did find this great article online - 25+ years old, but still gives a great comprehensive layman's overview of forced air HVAC.

Residential Duct Systems - Selection and Design of Ducted HVAC Systems (http://www.toolbase.org/Design-Construction-Guides/HVAC/ducted-hvac-selection)

[dash]

Looks like they did a great design job.

Suggestions;

1.)Insulate and seal to the max.,best windows and doors.This saves money forever,reduces the system and duct size,to help with space constriants.

2.)Once the design and factors in #1 are set,decide the register locstions,provide the designer the space available ,floor joists ,beam ,etc.,so the can do a new load and duct design.

3.) Have them consider using a return drop that's closer to sq,so turning vanes can be installed,and using turning vanes where the supply Tee's (if they didn't already)or makes a 90° elbow,should up decide to move it to one end of the basement.These things can lower the TEL of the duct system,which will allow smaller ducts,and/or the install of a better filter.

4.) Have them consider using custom sheet metal were space is a problem for round pipe.Example a 6" round is equivalent to a 8X4,11X3,6X5,etc..a 14X8 ='s a 20X6,etc..

For your planning ,I'd assume that the FR(friction rate) will be .05 to .06,you can use a ductlator ,there are some online .

I think you and your designer will have a great design and top system performance when it's all completed.

BTW ,consider using a variable speed fan,furnace,but keep the static at .5 per their design,no more then .6 ,if you have to ,to be able to use smaller ducts.

[propmanage]

That's just another "rule of thumb”, what size would you increase from, and how do you come up with that size in the first place?

Just trying to help a home owner out with the question. Maybe you would be able to give him some exact shapes and sizes. I would like to see what you recommend.
Thanks,

[dpkform]

Dash

just wanted to say thank-you again for such a great, detailed reply

I'm trying to get some actual quotes on spray foam insulation, see how expensive it really is. It's the only way to really make a 100 year old double brick exterior wall house "tight". Hope we can fit it into the budget. :)

I would like to get the variable speed (ECM?) fan - will keep in mind your helpful suggestions.

Thanks again!

Cheers

Dave



sorry for the slow reply - was away for the weekend


Looks like they did a great design job.

Suggestions;

1.)Insulate and seal to the max.,best windows and doors.This saves money forever,reduces the system and duct size,to help with space constriants.

2.)Once the design and factors in #1 are set,decide the register locstions,provide the designer the space available ,floor joists ,beam ,etc.,so the can do a new load and duct design.

3.) Have them consider using a return drop that's closer to sq,so turning vanes can be installed,and using turning vanes where the supply Tee's (if they didn't already)or makes a 90° elbow,should up decide to move it to one end of the basement.These things can lower the TEL of the duct system,which will allow smaller ducts,and/or the install of a better filter.

4.) Have them consider using custom sheet metal were space is a problem for round pipe.Example a 6" round is equivalent to a 8X4,11X3,6X5,etc..a 14X8 ='s a 20X6,etc..

For your planning ,I'd assume that the FR(friction rate) will be .05 to .06,you can use a ductlator ,there are some online .

I think you and your designer will have a great design and top system performance when it's all completed.

BTW ,consider using a variable speed fan,furnace,but keep the static at .5 per their design,no more then .6 ,if you have to ,to be able to use smaller ducts.

[cem-bsee]

read lots at BUILDINGSCIENCE.com

undercutting doors= poor choice == most are blocked by carpet -- use "jumper" over or staggered inlet | outlet --

consider tight packed blown cellulose--
dbl bricks should have minimum infiltration -- leakage is where framing meets brick, around openings.

got gutters & wide overhangs to keep roof moisture from brick?
how much moisture is coming in thru brick?
set doors & windows into ledges --