4000 sqft Home, 2 furances required?

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Old 09-22-11, 11:45 AM
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4000 sqft Home, 2 furances required?

We are in the planning stages of building a two story home with a walkout basement (so really 3), the total sq ft of all 3 floors is around 4000. The back of the house with most windows is facing North west, Front is south east, very few windows on sides.
We are in Winnipeg Manitoba so it does get very cold out.

Our general contractor just got back to us and said that the heating contractor says we will need two furnaces (natural gas) as well as two AC units. Apparently a large furnace will only cover about 3000 sq ft. We were going to be putting in a 3 zone system (1 per floor).

My question is does this make sense or are their larger furnaces available. Also what other options should I be looking at? Perhaps air handling units and a boiler?

Thanks
 
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Old 09-22-11, 11:49 AM
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Not my area of expertise but we have two of each in my office which is 2400 ft² and I know my boss would have gone with whatever was the cheapest option.
 
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Old 09-22-11, 02:14 PM
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Hi unique, that's a trick question . A 1,000 sq ft home with no roof (I'm exaggerating) could use 2 or 3 systems, while an 8,000 sq ft MC-Mansion might be heated with a water heater if it were insulated to the extreme. Since you are still in the planning stage, the size of the system is yet to be determined. IMO, 4,000 sq ft that includes a basement is not huge, that's a 1,300 sq ft foot print and with heat moving vertically you should be able to design it for one small to medium system.

First, if you read through this forum, one of the most difficult challenges we have in offering advice is working around a home that got off to a bad start. If you are still working with drawings you have a great opportunity to plan sealing for those basement walls and drainage and vapor barriers where needed, not to mention the right amount of insulation and air sealing. So tell us, how far along are you??

Bud
 
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Old 09-22-11, 02:40 PM
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We are still at the design phase, we have our floor plan pretty much done but haven't signed contracts to build yet. The builder is now getting pricing on some of the major items to get a reasonable estimate before we continue into more detail.

The walls will be 2x6 with fiberglass insulation, attic will be blown in R40 or R50, have to double check.
The house has vapor barrier which will be continuous from inside out around the sill for the second floor and back in, the joist cavity where the first floor meets the basement walls is spray foamed.

Windows are all triple pane Low E argon filled.

The basement is a structural wood floor, not sure if that's common where you are but there is basically a crawl space under the wood basement floor, not concrete. The house is on piles to allow that, and because Winnipeg is all clay.
The basement walls that are concrete (back wall is a walkout so its not) will have interior wood wall insulated, not sure R value here.

Any more details I can add?

I was thinking of finding a heat load calculator online to trying to put in all the data, any suggests on one to use? Preferably free or with a free trial.
 
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Old 09-22-11, 03:29 PM
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There is a load calculator floating around that is $49. Its a good deal and probably the best money you will spend.

The contractor should of done, I believe a manual J calculation, to determine the heating and cooling load. Has he done this?

Once you get that you can determine what size units you need.

I dont know how your layout will be but I would probably prefer 3 units. One per floor. From what I read and seen in the field zoneing off a hvac unit dont work too well. But they may have better technology now.

Whats your wallet allow?

Boiler with baseboard? Radiant floor heating throughout? Solar? How are you going to heat the water?

There is alot to consider. I myself would never have a duct heating system. A boiler and nothing else.

You should be thinking efficiency also, and dont just throw anything in there.

Ideally you would want two small boilers tied togther. Only one will fire, but when the demand gets higher the other will kick in. That would be the most efficient then having a big boiler.



Mike NJ
 

Last edited by lawrosa; 09-22-11 at 06:25 PM.
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Old 09-22-11, 06:10 PM
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Sounds like they are trying, but as an example, they use 6" walls in Tennessee. R-19 fiberglass is way below what you should be using in Winnipeg, BURRR!

There is lots of discussion here on the forum and on the web about fiberglass and how it does poorly with air movement and even loses R-value as it gets cold. Being in Canada I would certainly expect mineral wool, Mike H uses it all the time and it is finally finding its way down into the states. A far superior product. Think a minimum of r-30 walls.

My concern is if your builder isn't picking up on these items, that's a red flag. MANY current builders still want to build them the way they always have. Unfortunately, that doesn't cut it any more and they need to be dragged into the 21st century.

I can't comment on the issues with your clay soil, but I'm certain there are energy related professionals in your area who could jump in at this stage and help you make a ton of affordable improvements.

I agree with lawrosa, I would prefer a boiler system. But I think you will find your heat loss when you are ready to build low enough to get by with just one. Of course, I always like a back-up heat source just in case.

You say the house is on piles, but then you say the basement walls are concrete, help me.

Bud
 
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Old 09-22-11, 06:11 PM
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Every penny you spend now in air sealing and good insulation will pay you back dollars over the years. I would NEVER use fiberglass insulation in 2X6 walls in Manitoba. I recommend nothing less than a two-pound density closed cell foam. Ideally you would use double wall construction to avoid the thermal transfer through the studs but that would up the cost considerably.

Mike is correct about using multiple furnaces for multi-level houses. Zoning of forced air residential systems is usually a mistake and often a HUGE mistake. It works well for commercial only because of some fairly sophisticated (compared to residential practice) control systems. Further, residential forced air systems are rarely designed properly and even if they are they are rarely installed correctly. Ducts are far too often made smaller to allow for easier installation or for more usable space in the house. You CAN have a fairly decent multiple zone system but you WILL pay for it. Most residential heating/cooling contractors don't have a clue as to what is REALLY needed and are simply pushing the ill-designed equipment they get from their suppliers.

That doesn't mean that you can get away with just a radiant heating system either as the cooling will need ducts and air handlers. If anything, residential cooling is even more critical as to design when it comes to total system operation and comfort. Whatever you do, do not skimp on insulation and air sealing and do not skimp on the mechanical equipment and controls.
 
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Old 09-22-11, 08:25 PM
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Two story's = two units. This will be cheaper to run comfort will be better and u have back up
 
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Old 09-23-11, 05:45 AM
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I agree with the others. You are WAY under-insulated.
I've never seen a zoned warm air system that worked well in a residential application.
Lawrosa mentioned a boiler. You could use a zoned hydro-air system with hot water coils in 2 or 3 air handlers, probably not the best but far better than using a furnace with zoned duct work.
The load calculation previously mentioned is from HVAC Software, HVAC-Calc for Heat Loss, Heat Load Calculations.
Before downloading I suggest you contact them to make sure Winnipeg design conditions are in the program. I have personally used this program & it was right on the money.
 
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Old 09-23-11, 07:21 AM
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I am going to double check the insulation values, I must have something wrong if everyone thinks that. Perhaps its 2x8. I know my current house is for sure 2x6 but its 25 year old, perhaps I am mixed up. I will ask the builder the R values for the walls.

As for the zoned system the vast majority of houses in Winnipeg are forced air gas furnaces with no zones, the entire house is one zone. I figure adding zones could only make it better, my current house in the summer basement is freezing and upstairs is still to warm so I leave the furnace fan on continuous to mix the air.
I am really confused as to why the prevailing opinion is that forced air is bad. 99% of the new houses here are forced air. If you put in a boiler and radiant are you adding an air handling unit then for AC?

Bud
The house is on poured concrete piles and it does have concrete walls. Piles and concrete walls is normal is Winnipeg now due to the clay, the difference here is we have a wood floor instead of pour concrete. I found this image that depicts it.
http://www.cornerstone-inspection.co...ural-floor.jpg

Thanks everyone for the all the great replies, this is why I love doityourself.com
 
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Old 09-23-11, 07:43 AM
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With single, or even 2 stage, furnaces you have a fixed firing rate & fan speed. They have no way of adjusting the firing rate or fan speed based on how much heat you need. For all practical purposes they are on or off. If you only have one zone calling for heat the furnace is grossly oversized for the amount of air you can move. For example if you have a furnace sized for total heat loss of 90,000 btu/hr & only one zone with a capacity of 40,000 calling, the furnace is going to overheat unless you dump the extra 50,000 somewhere.
 
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Old 09-23-11, 08:10 AM
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Thank you that makes a lot of sense and I see why it would be an issue. I work for an automation company and I guess I assume the control is more inelegant than it is.
I would think if the basement required heat but the other floors didn't yet you would run the basement damper wide open with the other two open just enough to keep airflow up. That or wait until at least two floors are calling for heat, but I guess their not designed like that.

I also figured out why everyone has forced air here, in our climate you need to have the air moving around the house in the winter for health reasons (mold, air exchange etc) so even if you put in radiate you still need an air handler unit and an HRV for air exchange/movement as well as AC. For most houses why put in the extra cost of a separate radiant heat system.

I am definitely getting why we need two furnaces but I want to review all my options. As an alternative are perhaps 1 smaller air handling unit per floor with a hot and cold heat exchanger in each. A boiler and AC unit that heats and cools some glycol or water tanks and circulation pumps to each heat exchanger. My uncle has this type of system but he has geothermal for the heating and cooling.
 
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Old 09-23-11, 09:10 AM
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One of the items I see, the picture is great, is your exposure to ground conditions. When you say the homes around you like to circulate a lot of air for air quality and health reasons, I can see why. The relative recent move to tighter homes has created a greater awareness of moisture and related problems. To solve those issues they now have the ability to install a water resistant barrier on the outside of the concrete and carry that function down under the footings (around your piles) and over that dirt (or whatever) floor. Not shown in the picture but I'm sure it is there would be the use of drainage next to the foundation and the extension of that to some place well away from the house, hopefully to daylight. Once the foundation is properly protected from ground moisture your indoor air quality becomes a much easier issue to deal with. And don't forget the Radon mitigation.

Also, don't forget a substantial layer of rigid insulation on those concrete walls.

Remember, most if not all of the above must be done during construction. There is no whoops and going back to add a complete WBR (water resistant barrier).

Bud
 
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Old 09-23-11, 09:40 AM
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My understanding is the moisture isn't mainly from the ground while it does make a difference, its from living in the house, showers, cooking and breathing put a lot of moisture into the air and if your house is well sealed it has nowhere to go unless you have an air exchanger. The outdoor temperatures in Winnipeg winter are -20 to -40 C and will cause condensation if you have too high of an indoor humidity, condensation unchecked will cause the mold. But I know I am preaching to the choir.

The dirt in the crawl space is covered with a thick poly, then a layer of sand and then gravel so the soil is separate from the air in the crawl space. There is a weeping tile system around the house that runs to a sump pump in the crawl space, sump is sealed from the air as well. My understanding is their is also an air exchange system for the crawl space to remove excess moisture and possible radon leakage.
 
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Old 09-23-11, 10:09 AM
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Going back to my alternatives here is what I am currently researching, comments are appreciated

Either 3 small air handlers or 1 larger one, with 4 speed variables fans, The units come with a water heat exchanger.
AH-95 Air Handler - 106,241 - 90,014 Btu's smaller one
AH-220 Air Handler - 233,373 - 197,884 Btu's larger one

A boiler capable of providing heat for the house, or possible two boilers with the second only kicking in as required. Even better option would be electric heat in each air handler. Electric could be used spring and fall when you just need a bit, boiler for winter and boiler and electric when its really cold out

An AC unit that cools water/glycol in a tank that can be circulated through the coils in the air exchanger, preferably the boiler and cool tank would have the same liquid so I can switch hot and cold with solenoid valves and not need two heat exchangers.

I could control the fan speeds, valves, circulation pumps, call the AC and boiler to run etc all from a PLC. I'm assuming their isn't a great control system for this type of system out there?
If I put on modulating valves I could controls the system to run continuously and hold a temperature instead of cycling on and off.
 
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Old 09-23-11, 10:21 AM
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There should, from my understanding, be a separate radon collection system under that thick poly with a 24/7 fan venting to the outside. A quick search indicates Manitoba has a definite Radon concern. Be sure to consider a back-up system for the sump. There is so much that is so easy when planned before construction begins.

Assuming at some point you or the next owner may want to finish that basement, then the WRB on the exterior will permit insulation and finishing with minimal concerns about moisture. The detail about moisture is it will seek a balance. If the concrete is exposed on the inside and the air is dryer than the soil outside, there will be a constant flow of moisture through the concrete from moist to dry. The typical tar coatings on the outside have proven to be less than what is needed to stop this action, thus the WRB.

The space below the basement floor, I'll call it a crawl space, is unique, but it does have a potential for moisture issues and it doesn't look like a place you would want to access to do over. A HRV would be a possible winter solution, but not a summer one. Cool ground temperatures and humid summer air will deposit condensation down there, the very problem you are wanting to prevent. Crawl spaces or basements need warm dry air in the summer, specifically the output of a dehumidifier. Some duct provisions to provide that would be nice.

I apologize if I'm bringing up details beyond your question, it is simply as an energy auditor I deal with 90% plus of my work being done to compensate for these details that were not addressed during construction. Frankly, it is fun being able to talk to someone in the planning stage, no matter what you finally decide.

Bud
 
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Old 09-23-11, 11:25 AM
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For the radon I'm not sure how you would put a fan under the poly as under the poly is soil, there is no air gap to get any flow. Does the poly not stop the radon from entering the crawl space. My understanding is that houses where no poly was put under the poured basement floor end up needing radon systems but most houses that have poly don't have radon showing up and don't need a system.

I will ask about the sealing on the outside of the concrete. I know there is some kind of coating put on, I think a spray on rubber coating but I will double check. Were you suggesting insulation on the outside of the concrete as well? On the inside there will be an internal 2x4 wall and insulation vapor barrier etc added to that.

For the crawl space I am not sure how the exhaust works but it seams to be ok. Both my in-laws and uncle have the structural wood floor and crawl space and have no issues so whatever they are doing is working. I think they may draw air from the crawl space into the cold air on the furnace and treat the air down there as part of the house, but I am not sure.

I do appreciate all the details you are providing and the time you are taking to reply. Everything I learn makes me more educated when discussing with the builder.
 
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Old 09-23-11, 01:10 PM
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The Radon systems create a negatives pressure below the barrier so in the event of any leaks, the leak goes the other way. Usually a network of pipes embedded in gravel so the system can protect the entire floor. Sump is then sealed and left below the barrier. It is one of those things that comes up during the final inspection when selling, "do you have a working radon system?" If the answer is no, it complicates the sale and gives the buyer more leverage. It is also an unknown and only after the home is completed will you be able to get a reading. If everything is great, turn the system off. Some even wait to install the fan (somewhere outside of that crawl) until after the test. Pass/fail determines if you put one in. But in any case, the pipes and such are already there to eliminate any future concerns.

"On the inside there will be an internal 2x4 wall and insulation vapor barrier etc added to that." See, that's the type of description that concerns me. That's becoming old school. Modern thinking is to ensure the basement wall has a direction in which to dry. Since it can't dry to the outside, it should be able to dry to the inside. Here is a building science link that does some explaining.
BSD-103: Understanding Basements — Building Science Information

The spray on rubber coating is part of the process, but adding an insulating panel to protect that coating during backfill is the second half. Search on "Waterproofing Foundations" and you should find some options.

Bud
 
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Old 09-23-11, 01:40 PM
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Until you get the insulation issues straightened out it's premature to be talking about which size air handler to use. Some of the new air handlers have true variable speed (ECM) motors. With this type of air handler & a boiler you could modulate the boiler temperature & blower speed (air volume) to match the outdoor temperature. I don't know how compatible the new boilers are with glycol since many of them are aluminum. I'll let some of the guys over on the boiler forum know about this thread. They may have some valuable input.
 
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Old 09-23-11, 01:52 PM
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Thanks for the reply Grady

I know your right about not being able to determine which air handler to use, I think one larger air handler with a variable speed drive and dampers is probably the most effective way to go but I its all very preliminary, I was just putting out some examples of what I meant.

I was more looking for a validation of concept that what I am thinking of doing is feasible. I know the boiler and heat exchanger would work its more the AC I am not sure about, the air handlers I found as examples probably don't have a way to deal with condensation, If it just contained an AC coil if I slowed down the VFD when one floor is calling for cooling it could possible freeze up the unit, which is why I was looking at a cold tank that the AC could cool down a volume of water during one cycle and the air handler slowly heat is up again.

I know what your probably all thinking, just put in 2 furnaces and AC units.
 
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Old 09-23-11, 03:59 PM
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There are variable capacity A/C units available such as these: http://www.nordyneliteraturelibrary....a-80f79d425168

Even with these, you are still dealing with a single air handler. The heating & cooling of a structure having more than one level with a single system is a no win situation. Plain & simple.
 
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Old 09-24-11, 01:40 PM
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I have completed putting all the information I have into the Hvac calculator and this is what I have come up with

Main floor Heat gain 10324 Heat loss 34814
2nd floor Heat gain 9249 Heat loss 30186
Basement heat gain 4300 heat loss 27944

Total heat gain 23874 Heat loss 92944

So while I understand the argument about better control with multiple units I don't know of a single house that has multiple furnaces, if one furnace is so bad why is it that everyone does that?

That being said I only need the 92944 BTU/hr on the coldest days of the year, if I change the outdoor temperature from -27F to be the average low for January of -13F the program says I only need 24495 BTU

So my thought is if the concern with running a zoned system off of single furnace is the inefficiency of running a single zone off of a 100,000 BTU furnace. What about if I put in a smaller furnace that is capable of of handling the average outdoor temperature and supplement the gas furnace with an electric in duct heater, say put in a 50,000 btu gas furnace and a 50,000 (14.6kw) electric heater. The gas furnace would be smaller and during the majority of the winter would have much better run time without short cycling while with electric would still have enough power to keep the house warm on the coldest days of the year.

FYI in Manitoba the difference in price per BTU between a 96% gas furnace and electric heat is not very much so I am not worried about using electric axillary on the coldest days of the year.

Your thoughts, I appreciate all your help everyone.
 
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Old 09-24-11, 01:58 PM
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The reason so many people have forced hot air is because it is the cheapest system to install. When you say you only know of homes having one furnace, are any of them 4000 sq ft?

I don't see why having one air handler for the whole house can't be balanced out to provide even heating and cooling.

How much do you pay per therm of gas and per kwh of electricity? I find it hard to believe that the cost to heat with either is close, but I could be wrong.
 
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Old 09-24-11, 02:08 PM
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My in law is around 4000 and they only have one furnace. Like I said my heatload calculation is 93000 while carrier makes a 120,000 model so I don't think it is a total size issue.

$0.2913 per cubic meter of gas
$0.0662 per kwh of electricity.
http://www.hydro.mb.ca/your_home/hea...omparisons.pdf
Actually on second look its not that close per BTU but since the electric heat will only kick in a 10 or 20 days a year the improved efficiency of running the smaller furnace more continuously instead of shorter cycling it all but 20 days a year should help offset the difference.
 
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Old 09-24-11, 02:47 PM
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For those saying zone systems wont work could you look this system and tell me what the problems are. I realize years ago the systems weren't very good at zones but technology has come a long way.

http://www.docs.hvacpartners.com/idc...858-502-25.pdf
The furnace is variable speed and variable gas so it is designed to run continuously without cycling just by varying the flame and fan speed, IE it should be able to throttle back enough to only heat 1 zone at a time.

Infinity® Control - Carrier
Thermostat to control the furnace, has capacity for 8 zones and controls the furnace speed and flame.

Infinity Heat Pump With Greenspeed Intelligence - Carrier Heating and Air Conditioning
Heat pump for AC and heating in the fall and spring. Variable speed based on demand.
 
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Old 09-24-11, 03:20 PM
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Your climate is too cold for an air source heat pump. Ground source would be the way to go.
 
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Old 09-24-11, 03:37 PM
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drooplug
I figured that would be the case, it would only be effective a few months out of the year, I was going to crunch the numbers and see if it was worth it to use it for the 4 months a year or just go straight AC and Gas

Any reason the zoned unit wouldn't work well, 1 zone per floor. the furnace would have more than enough BTU for my house.
 
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Old 09-24-11, 04:41 PM
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You are correct that the problem is not one of finding a large enough furnace, the problem is the zoning. Hot AIR rises and if your downstairs zone has a fairly high heat loss while the upstairs zone(s) have lower losses then the result is going to be an overheated upstairs. This will work in reverse during the cooling season. There is also the problem of heat loss during transport...the heat lost in the ductwork running from the furnace to the terminal register. The longer this duct the cooler (or warmer in cooling season) the air exiting the register. This means that larger ducts need to be installed to get more air at a cooler temperature to the room it is supposed to be heating.

Now I'll throw out some IFs. IF you can properly design the ductwork for the anticipated loads, IF you can actually get the properly designed ductwork properly installed in the structure and IF you can get a properly designed zone control that interfaces with a variable speed blower / variable BTU output furnace then you could have a good system. It will be a one-of-a-kind system and getting people that are knowledgeable to install and service it will be a problem and because of its complexity it will be expensive to purchase and expensive to repair.

But it CAN be done.

I haven't looked at your links so it is certainly possible that there are some positives among them. Still, without the LOCAL people with expertise you are taking quite a chance in my opinion.
 
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Old 09-24-11, 04:44 PM
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I may be way off, but this is what I assumed about the zoned type systems and why they dont work well. Its the cfm and ductwork size needed if all zones were on. Now you damper two zones off and the whole thing is unbalanced...etc Something like that.

Also through out my plumbing career I have seen probably every zoned system ripped out and replaced with multiple units. I have never heard good things at all about them. Just my experiences.


Just want you to be an informed consumer and weigh all your options. IMO what everyone else has in thier home does not mean its what should be installed. Its really a cost thing I think.

Possibly the pros can clarify...

When my parents house was built in a retirement village all they put in is HVAC units. Everyone has them so it must be right? 600 homes were built. I suggested to my parents that they should install a boiler why they have the chance. Well we brought it up to the builder and the silence in the room.... you could hear a pin drop. They could not understand why we would want that. It was not offered they said. And not one homeowner brought it up before so they did not really know how to act. Everyone assumes that thats what your supposed to have. In the end they quoted us an outragous price, like $20,000 or so extra.


What am I trying to say? I dont know. I forgot where I was going with it.

But anyway, I will shut up. The guys responding are much more seasoned them I am.

Good luck with your home.

Furd just posted what I was trying to say.

Mike NJ
 

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Old 09-24-11, 05:02 PM
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I think the fact that the heating and cooling contractor quoted a system that was to be more than twice the size you need says a lot about their abilities. I advise finding a better one to help you sort things out.
 
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Old 09-25-11, 10:28 PM
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If the duct system is designed correctly (all rigid metal, ducts sized based on room by room load calculation, return air in every room with door except for bathrooms) you won't have any trouble with a single furnace, even without zoning.

To improve the performance of your house...

- Make sure that the basement vents are brought down to the floor
- Floors over unheated areas should be sprayed with closed cell foam insulation.
- Window openings should be spray foamed under trim
- The basement sill plate should be spray foamed; conventional stapled on vapour barriers tend to come off between the joists, allowing indoor moisture to move through the insulation and condense when it hits the cold sill plate/concrete
- If the house will be tightly built, get an HRV installed. (duct intakes to bathrooms in lieu of exhaust fans if allowed by code
- Do not any under circumstances allow the builder to install ductwork or hvac equipment in the attic

- R19 sounds a little low for winnipeg; once thermal bridging (google it) is taken into consideration, the effective r-value of r19 batts is far lower than that
- A good practice is to put a layer of foam on the exterior of the house (see http://www.cmhc.ca/en/co/maho/images...Figure-1_E.gif)

- Make sure that the furnace has a 2-stage gas valve and variable speed blower motor. Also insist that it be connected to a 2-stage thermostat
- Variable speed blowers can be left on continuously for even distribution without incurring high hydro bills
- Insist that all duct joints are sealed with duct mastic or foil tape
- Have the ductwork balanced based on the room by room load calc

The impact of the stack effect (warm air rising up) on heating is greatly over-rated.

What design temperature was used on the load calc?

Garbage in = garbage out
 
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