larobj63, many thanks for your advice again. Upgrading is not a good solution because of limited budget. Compromised portable heaters might make more sense economically.
Only 10 feet of the main duct are exposed; the rest is between downstair's ceiling and upstair's floor. All the ducts are not exposed either. If the main duct were to upgrade to accommodate with the 60k btu, so were the branches as they are only 5" ducts and the smallest bedroom is 120 sf. It would not be a small retrofit, would it? I will ask a contractor later on about this; just wondering if it would cost a few thousands for this retrofit?
58 MVB infinity 96 efficiency
Finally I got Sears to do the install for me. The sales rep did the heat loss mainly based on the geographic area, the house's age as well as square footage of the house, which is 52 000 BTU. My heat loss Cal is 35000 BTU with more detail of the structure of the house, windows... He recommended 60,000 BTU but agreed that with the my duct system (plenum size 14 x 8 inches) capable of handling 40,000 BTU. So Sears will install a 40,000 BTU furnace for me.
I learn from one of the posts in here that the BTU output = temp rise x airflow (CFM). Based on the 40000 BTU MVB infinity 96 spec (attached) from Carrier in high fire, the airflow is 800 CFM. If the output BTU is at 38000, the temp rise = BTU output / airflow = 38,000 / 800 = 47.5 deg temp rise.
The would-be installer informed me that he would set up the furnace to the manufacture's temperature spec, which is in the range between 30 to 60 F for the high fire stage. He said if the furnace is installed and measured to be 40F, he is happy with that because it is in the manufacture's range. However, the BTU output would be 800 CFM x 40 F = 32,000 BTU and the efficiency would be 32,000 / 40,000 = 0.8 or 80%.
Does this low temp rise happen often when a furnace is installed? Do you often need to make adjustment to get the efficiency to 90+% (equal to 45 deg F temp rise)
Should I have to pay extra money for the installer to adjust the furnace to get clost to 47.5 deg temp rise as calculated above?
Thanks a lot.
Your fixed on 800 CFM.
He said he's happy if its 40°, as an example.
Not, that he is setting it there period.
Also, your only using part of the formula.
800CFM 40° rise=34,560
800CFM 45° rise=38,880
750CFM 45° rise=36,450
Been there, Thanks again for clarifying the airflow. So, both air flow and temp rise will vary.
From the conversation with the installer, I assumed that he would install and fire up the furnace and as long as the temp rises for both stages within the manufacture's range, he's done his job.
If for some reasons, the temp rise comes in after install at 40F on 800 CFM airflow, the efficiency will be 34560 / 40000 = 0.864 or 86.4%.
as a consumer, is it too much to ask him to adjust the temp rise to 43 - 45 F range to get close to 96 % efficiency?
If he does a proper commission/start up.
You don't have to ask him
From what you posted. He doesn't do much in the way of set up.
If it comes out low, you can ask hm. he may tell you no, its good enough.
Or he may check and see what needs adjusted, to improve its efficiency.
Did you place an order and schedule your install yet?
If not, see if you can get a quote for an automated zoning system and zone you’re upstairs and downstairs separately.
It should consist of a zoning panel, motorized dampers and separate thermostats.
This could solve several potential problems.
By implementing an automated zone panel with dampers and separate thermostats for upstairs and downstairs, you can have a much smaller HVAC system installed.
This is because you won’t be constantly conditioning the upstairs and downstairs to the same temperature simultaneously.
The savings of the smaller system can help to offset the cost of zoning.
The smaller HVAC system could help with your undersized duct work (if they are undersized).
Installing a smaller HVAC system is equivalent to increasing the size of your duct work. As a result, no noisy ducts.
Zoning can also make your home more comfortable. You don’t have to worry about uneven temperatures between floors (unless that’s what you want).
Best case, you should save on energy costs as well since you will have a much smaller HVAC system.
Hope this is helpful. If you do this, let us know the results.
Been there, the installer is not Sears’ employee; all I can do is to communicate with Sears though phone or email. Sears replied to me today that the installer will do according to the manufacture’s spec and Sears does not warranty any efficient performance – not even 80% AFUE for the 96.6% furnace.
Rdy2zone, I have until tomorrow night to make up my mind if I like to order this furnace along with the Infinity Control and Electronic Air Cleaner.
I thought about the zoning for upstairs and basement before and was advised by one contractor that due to the runs going upstairs and basement come from both sides of the extended plenum, it is not easy to do zoning without changing the duct system. Only 1/3 to ½ of the extended plenum is exposed in the furnace and laundry rooms.
When I was doing the heat loss cal, the result was 36,700 BTU for the house (not 35,000 as I indicated before) and annual energy consumption from the summary will be 130-135 MMBTU. I’ve been in this house for 3 and half years and 110 MMBTU were the highest number in 2007. Therefore, I believe that 36,7 is closer to my real heat loss compared to Sears (52,000). The 40,000 BTU furnace would be good for my house unless this new furnace turns out to be less than 80% efficient after installed.
I really like your idea about this zoning. I like to be able to run the blower in low speed all the time. It should still be ok in that case, isn’t it. Since I am planning to use the infinity control with zoning capable, do I need 2 infinity controls or 1 infinity control and one generic single stage programmable thermostat are good enough?
Then expect a minimal set up.
It fires up, it has a temp rise some where within factory printed allowable rise.
And maybe, a your new furnace runs, thank you, have a nice day.
There are some contractors on this board. That do installs for Sears. They pretty much all say the same thing.
Sears doesn't really paying them enough to do the job right.
And is not covering extras.
So they barely break even.
So cross your fingers, you get an installer that cares about system performance.
And not leaving at quiting time.
Not sure how you can install a new HVAC system if the duct is too small without either replacing the duct or installing a smaller HVAC system. If I read your thread correctly, it sounds like this is the problem you have.
It also sounds like you have a single trunk with several seperate runs coming off of it for both upstairs and downstairs floors. And, much of this trunk is concealed in finished areas.
This doesn’t have to prevent you from Zoning. Retrofit dampers for the individual runs can be installed close to the trunk by cutting relatively small holes in the dry wall. Dry wall repair isn’t major surgery.
For areas that can’t be accessed to install retrofit dampers, your contractor can install motorized vent registers in place of the motorized dampers.
A barometric bypass duct and damper may need to be installed between the supply and return as well to relieve pressure when conditioning the smaller of the two zones.
Replacing your HVAC system is the perfect time to install zoning. The additional cost of zoning is offset by installing a lower cost (much smaller) HVAC system in combination with the lower energy cost of running the smaller system and energy savings as a result of zoning. For example, it should take less energy to condition only the upstairs while you are sleeping (with a properly sized and zoned system). You also end up with a much more comfortable home.
It’s important to identify a contractor that is comfortable with installing a zoning system and appreciates what it will do for you. A contractor that is not comfortable with this may talk you out of it.
I don’t know much about the reputation of Sears HVAC install services, but I don’t think I would hire an organization or a person to install my HVAC system if they are merely going to sell the job (or sub it out) to someone else.
I suggest asking the experts on this site what they think would be a good replacement HVAC manufacturer that will support zoning with retrofit dampers and motorized vent registers. Then, call the manufacturer and ask them to recommend some local contractors that can properly size and install the entire system.
Hope this helps.
I just noticed your other questions.
Yes, a zoning panel should work with a variable speed ECM motors for continuous air circulation (but double check with your conractor).
Basically, when neither zone is calling for conditioning, all zone dampers should open to cirulate air.
I'm not familiar with the infinity controlls, so I dont know how many controls or type thermostats you would require if you plan to zone. Perhaps someone else here can help.
beenthere and Rdy2Zone, I was seriously thinking about looking for another contractor when Sears indicated that they do not care much about the performance efficiency; however, Sear does not want me to give it up yet.
Yesterday, the Sales rep informed me that he was sending another installer, who was forwarded all my concerns. Although I was willing to work with the old installer as we might have misunderstood each other, working with another installer might be a better solution.
Basically, I am having the furnace, Electronic air cleaner and the infinity control installed in a few weeks, not touching much to the duct system. Can i upgrade to the zoning system later on without touching the equipments that are already installed?
Pretty much so.
Have to add the dampers, and zone panel.
But the furnace doesn't eally need anyhing done to it.
As long as proper air flow is maintained.