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#450443 - 01/18/09 04:50 PM Re: Furnace sizing [Re: jtheile]  
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bradyf Offline
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lakeville, mn
We did all kinds of these to seal up bypass areas and stuff.

We had new windows installed about 2 years ago but I still put on window film to stop any drafts or heat loss. caulking where the siding meets the windows and doors is another area to look at as well as any through wall penetrations. You'd be surprised about the oulets. You might not even be able to feel any drafts or cold air but I can almost assure you that there is heat loss there. We even went so far as add caulking and minimal expansion foam where the flooring meets the outside wall under the base trim.
In attics, the biggest areas are the flue pipe hole, main stack (sewer) hole and any hole where wiring goes in. I havent gone so far as to caulk the holes in the junction boxes in the attic (light fixture boxes too) but we did caulk the areas where the recessed lights are at, from the attic above you could litterally feel warm air coming from below.
There are TONS of websites that tell you where to look for attic bypasses and heat loss areas too.

Heres one that I used, its a PDF file.
Dept of energy air bypasses - PDF

Also, when you tackle the fireplace insulation and air leak issue, as stated above, make sure that you know the clearances. I believe that the clearance for a gas fireplace is about 1 inch along the sides and bottom (dont quote me on that). You may be OK if you use Fire retardant foam which is made by the same company that makes the expanding "great stuff", but I would check.


I dont have a boat frown


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#450457 - 01/18/09 07:27 PM Re: Furnace sizing [Re: bradyf]  
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Frantically Relaxing Offline
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The tiles are icing up? That means they're cold enough to gather condensation AND freeze it, even while inside the house. That's cold. It's a safe bet that there isn't a stick of insulation around the fireplace inside your "bump", or anywhere between the slab and where the tiles are mounted. Being that cold, any tiny space where air can get thru is going be like a mini hurricane.


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#450469 - 01/18/09 09:03 PM Re: Furnace sizing [Re: Frantically Relaxing]  
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firecadet613 Offline
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Indiana
Originally Posted By: Frantically Relaxing
The tiles are icing up? That means they're cold enough to gather condensation AND freeze it, even while inside the house. That's cold. It's a safe bet that there isn't a stick of insulation around the fireplace inside your "bump", or anywhere between the slab and where the tiles are mounted. Being that cold, any tiny space where air can get thru is going be like a mini hurricane.


True on that mini hurricane FR, before the towels were put in place. If you look close at the picture of my fireplace I posted, you can see the two verticle black/dark brown metal strips between the tile and the fireplace itself, its the fireplace assembly. That is what ice up, you can see in the picture it is white from the frost, the tile was just VERY cold!


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#450485 - 01/18/09 11:10 PM Re: Furnace sizing [Re: firecadet613]  
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bradyf Offline
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that space has problems then


I dont have a boat frown


#450685 - 01/20/09 06:31 PM Re: Furnace sizing [Re: bradyf]  
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firecadet613 Offline
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Had a guy out today to give me an estimate on what size furnace/AC I should have, and I'm not suprised with what he came up with. If I stick with an 80% efficiency furnace, I need a 90,000 BTU unit. If I moved up to 90%, I can do fine with 80,000 BTU. A far cry from the 44,000 BTU unit I have. He said when they spec out equipment, it is done in a house that is "super sealed," and of course all the houses they build are loose. Made a lot of sense...

He did note poor vent placements in the bedrooms, and gave me quotes on that as well as adding an additional return in the master bedroom, and blocking one off in the living room. I learned a lot, not just on what I need to change, but also in what this tract builder (Centex) did wrong. They took a LOT of shortcuts. All my vents are located in the central part of my house, none of them are out on the outer edges of the rooms where the should be.

I can fix the upstairs vents easily, and plan on doing that shortly. Shouldn't take much money at all to buy an additional vent for each room, and some flexible ducting. On the first floor I'm stuck with the three poorly placed vents I have.

On the issue with the drafty fireplace, there is two big return vents for the furnace on the wall next to it. He recommended sealing those off, and adding an additional one upstairs. The furnace is going to get the air it needs, and right now its getting it from the outside via the fireplace. He also said that the direct vent fireplace is notorious for letting outside air in through its vent, since you can't fully close it off.

We did feel up next to my outlets and light switches, and there is still a small draft coming in, even with the foam insulation in there that I installed. Can I take the covers off and spray any of that expanding foam insulation in there, not in the box itself, but the area around it if it needs it?

He did say I should also add some cellulose insulation, about 3-4" in my attic is all I need, on top of the 2' or so of the pink blown insulation I have, since that isn't really good as a blown in.

I haven't gotten the thermal imaging camera yet, but I still plan on doing that shortly.

Thoughts on this?


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#450687 - 01/20/09 07:08 PM Re: Furnace sizing [Re: firecadet613]  
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jtheile Offline
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When my house was built, they sprayed a squirt of the foam where the wires come into each outlet and switch box that is on an exterior wall.


Joe
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#450712 - 01/20/09 10:38 PM Re: Furnace sizing [Re: firecadet613]  
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bradyf Offline
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lakeville, mn
sounds like you got it figured. 90K BTU's output is about right. it also sounds like this guy that came out knows what he's talking about. From what you described, the supply registers are on the "interior" walls and not on the exterior walls? thats goes against every single home builder's "standard" for HVAC!!! If you can, I would check into the home warranty you have and see if ANY of this is covered. A new heating plant isnt going to be a mere $200 - start checking the interweb for class actions too, you may be surprised what you find out. I am not saying go after them and sue them, just to find out if you could very well be protected against this kind of thing. I would think that there is a "lemon law" for homes out there.
If I may offer a word of advice on the flex duct - keep the run as straight as you can and dont go over 8 feet if at all possible. On the return side it wont matter quite as much, but on the supply side it matters alot.
I will assume that the duct chase's are in the walls and ceilings as you are on a slab and that the furnace is on the 2nd floor? just being curious there..
Yeah, dump the returns near the fireplace and in the spring check out the insulation issue. The furnace isnt going to starve for combustion air but he was right to tell you to replace them with additional returns, furnace can only push what it can pull.
Take the outlet and switch covers off and shoot some foam around the box, then buy outlet gaskets and "babyproof" oulet plugs - if you have a "slight" draft around the outlet, you will be surprised at what you might find.
Seeing as you are going to be cutting a hole or two in the walls due to the return/supplies, stay aware as to the insulation in the walls. You may want to cut a couple more after you get the camera.
Anywhere you can add insulation or foam (or caulk) to stop leaks is going to help the bigger picture. If the foam expands beyond the wall, it trims off pretty easy.


I dont have a boat frown


#450714 - 01/20/09 10:50 PM Re: Furnace sizing [Re: jtheile]  
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Frantically Relaxing Offline
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My thoughts---stick with an 80% furnace, our new one works great... any higher than 80% and you're looking at condensation that needs to be drained, the plumbing to drain it, possible corrosion problems because the condensation is acidic (I did some web research awhile back, and the majority opinion was that the higher initial cost and the possible costs of maintenance and repairs of a high efficiency furnace can override the energy savings--do some googling and see what you find!)

As for your current furnace heating OUTSIDE air, good grief! That's like boiling ice cubes for your hot cocoa instead of starting with hot tap water! Sheesh!

As for your vents, before going to a great deal of work, I'd leave them be and see how well the new furnace--drawing INSIDE air instead of OUTSIDE air--heats the place, it may do just fine...
<<edit>> for what it's worth, our new furnace was less than $2200 installed...

Last edited by Frantically Relaxing; 01/20/09 10:51 PM.

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#450719 - 01/20/09 11:18 PM Re: Furnace sizing [Re: Frantically Relaxing]  
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bradyf Offline
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lakeville, mn
FR, he's not talking about just a new furnace but supply and return issues as well.
"new" high effiency units need "fresh" outside air for combustion. You can burn air from inside the house, but then all your doing is drawing the house into a negative as its trying to pull air from the home. Its not good on the blower motor.
Now I will agree that trying to "heat" outdoor air is as ridiculous at ***s on a boar, but its whats needed to make the system more efficient.
I also agree that the condensate is coorisive due to the exhaust out the "flue" BUT, high efficiency units use PVC or ABS for intake and exhaust and utilize a condensate pump to move the fluid - no corrosion, no plumbing, just a simple 1/2 drain vinyl tube to the sink.

yes, stay at 80%, 90% isnt needed in your climate.

In any case, yes, firecadet should go with an 80% as opposed to spending the extra few thousand on another 10%


I dont have a boat frown


#450721 - 01/20/09 11:22 PM Re: Furnace sizing [Re: Frantically Relaxing]  
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Justification Offline
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What are the tax implications for increasing the efficiency of your furnace? Since you're having to replace the old unit you might save a few bucks that way. Seems like last year you could get a tax CREDIT for 10% of the cost of energy efficiency improvements.


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#450722 - 01/20/09 11:25 PM Re: Furnace sizing [Re: Justification]  
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bradyf Offline
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Originally Posted By: Justification
What are the tax implications for increasing the efficiency of your furnace? Since you're having to replace the old unit you might save a few bucks that way. Seems like last year you could get a tax CREDIT for 10% of the cost of energy efficiency improvements.


depends on the state/county or fuel company. some offer tax rebates and some offer refunds in dollar amounts (or credits) on your fuel bill.
I think that federally there might be some too, but you's have to go with a pretty large scale (wind, solar, geothermal) system...
Again dont quote me on that


I dont have a boat frown


#450723 - 01/20/09 11:35 PM Re: Furnace sizing [Re: Frantically Relaxing]  
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track75 Offline
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There's a more technical way to determine proper furnace sizing called Manual J.

From the DOE gov't website:

Quote:
Manual J and Manual D: The Correct Way to Size a System

Correct system sizing requires considering many factors other than simply reading the nameplate of the existing unit. Key factors for correctly sizing a heating and cooling system include the following:

* The local climate
* Size, shape, and orientation of the house
* Insulation levels
* Window area, location, and type
* Air infiltration rates
* The number and ages of occupants
* Occupant comfort preferences
* The types and efficiencies of lights and major home appliances (which give off heat).

Homeowners should insist that contractors use a correct sizing calculation before signing a contract. This service is often offered at little or no cost to homeowners by gas and electric utilities, major heating equipment manufacturers, and conscientious heating and air conditioning contractors. Manual J, "Residential Load Calculation," published by the Air Conditioning Contractors of America (ACCA), is the recommended method for use in the United States. There are also many user-friendly computer software packages or worksheets that can simplify the calculation procedure. You should make sure that the procedure used by the contractor follows Manual J.

If ducts are part of the installation, they should be sized using the ACCA's Manual D, "Residential Duct Design." The ACCA also offers a comprehensive guide for choosing home heating and cooling systems, called Manual S, "Residential Equipment Selection."


http://apps1.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12340

In my experience, most contractors stick to rules of thumb since the Manual J calculation involves some data collection and input to a computer program. A good contractor should be able to perform it for you. Probably at no cost if you're buying a new furnace but for a couple hour charge if done as a stand alone service.

If you get into a dispute with the builder a Manual J computation would go a long way to supporting the correct position on furnace size.

On the insulation and weatherization front, Taunton,the Fine Homebuilding and Fine Woodworking magazine publisher has a good book on the subject. I picked up a few others from them recently since some (including the insulation/weatherization one) are 50% off.



http://store.taunton.com/onlinestore/ite...ley-070649.html


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#450743 - 01/21/09 08:39 AM Re: Furnace sizing [Re: track75]  
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2Suns Offline
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As to the 80% vs. 90%- IF your water heater is vented with your current furnace, and you go 90% and side wall vent, your flue may be too big for just a water heater, leading to a condensing flue. On the other hand, if you stay 80% and double the furnace btu, your flue may not be big enough for that. Make sure your flue is properly sized or abandoned when done.

Here is an interesting column that talks about what Bradyf touched on:

http://contractormag.com/columns/yates/cubic_feet_infiltration/


By the time they had diminished from 50 to 8, the other dwarves began to suspect "Hungry.-Gary Larson
#450767 - 01/21/09 02:23 PM Re: Furnace sizing [Re: 2Suns]  
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bradyf Offline
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lakeville, mn
Great article!

Good call on the flue sizing too!


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#450806 - 01/21/09 06:32 PM Re: Furnace sizing [Re: bradyf]  
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Frantically Relaxing Offline
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It's okay to BURN outside air, but it's not okay to HEAT outside air. And--just to play devils advocate wink -- a blower motor 'drawing negative' will work LESS hard, as it will have less air to push. (there's no air resistance in a vacuum).


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#450807 - 01/21/09 06:38 PM Re: Furnace sizing [Re: Frantically Relaxing]  
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2Suns Offline
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Originally Posted By: Frantically Relaxing
....but it's not okay to HEAT outside air.


In essence, that is what you are doing with an 80% furnace.


By the time they had diminished from 50 to 8, the other dwarves began to suspect "Hungry.-Gary Larson
#450811 - 01/21/09 06:42 PM Re: Furnace sizing [Re: Frantically Relaxing]  
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2Suns Offline
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Originally Posted By: Frantically Relaxing
-- a blower motor 'drawing negative' will work LESS hard, as it will have less air to push. (there's no air resistance in a vacuum).



OK then. Take out your furnace filter, cut a piece of plywood 3/4 the size of your filter and put it in the filters place. Now turn on the blower, let it run and check amp draw with all covers in place.


By the time they had diminished from 50 to 8, the other dwarves began to suspect "Hungry.-Gary Larson
#450812 - 01/21/09 06:42 PM Re: Furnace sizing [Re: 2Suns]  
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firecadet613 Offline
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Thanks for all the tips thus far. I plan on sealing up all the switches and outlets tomorrow, and looking into a new return this weekend hopefully. I'll probably have to get some normal ducting and not just flex ducting to get the vents where they need to go on an exterior wall.

Any idea who I would call or where I should look to find out about the building codes/vent placements?


2008 Four Winns V318 T-5.0 DTS
#450814 - 01/21/09 06:43 PM Re: Furnace sizing [Re: firecadet613]  
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firecadet613 Offline
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Indiana
Almost forgot. They quoted me at 4400 for just a properly sized 80% AFUE furnace, a 90k BTU unit, and a bryant one at that. I did find out I could get any Carrier stuff at dealer cost, I'd just have to pay someone to install it.


2008 Four Winns V318 T-5.0 DTS
#450843 - 01/21/09 09:11 PM Re: Furnace sizing [Re: Frantically Relaxing]  
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bradyf Offline
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lakeville, mn
Originally Posted By: 2Suns
Originally Posted By: Frantically Relaxing
....but it's not okay to HEAT outside air.


In essence, that is what you are doing with an 80% furnace.


pretty much, of course with any newer furnace you have to have outdoor air for combustion and proper operation - even 90%.
Commercially we do it all the time with the economizer packages and a heating coil.

Originally Posted By: Frantically Relaxing
And--just to play devils advocate wink -- a blower motor 'drawing negative' will work LESS hard, as it will have less air to push. (there's no air resistance in a vacuum).



you devil you.. wink

See 2Suns comment about the filter, ya gotta remember, its a BLOWER, not a pump. Its not designed to run that way - electically it will overheat and *poof* you just smoked your motor.

Firecadet:
Did they give you a price for a 90% ? I would be curious just to see.
Stop in to the city and see what the building inspector has to say. Or ask the guy that came to give you the quote where he would plan on placing them.

Supply registers should be on the outside walls and returns should be on interior walls. Like I said before, you can use flex on the return but advise against it on the supply side as you wont get the static pressure you need.


I dont have a boat frown


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