[dannieboiz]

While I'm shoping for a new furnace, I'm thinking how can I improve the efficiency and comfort of my home that would not break the bank. Installing a dual zone HVAC is out of the budget so the only 2 solution I can think of is dampers and inline fans.

Was wondering which route should I go with? During the summer, upstairs is always hot. Additionally on very hot nights I'd like to be able to redirect all the cold air upstairs and shutting off downstairs completely.

My home has an automation system which the thermostat is already communicating with. I can have remote temp sensors to trigger the thermostat on and off. Like wise, I can also have the dampers open and closed based on set temperature and at the same time have a fail safe where if one damper is closed the other must be open etc...

Question is, do I want 2 dampers 1 for downstairs vent the other for upstairs?

Or the easy route is just to add an inline fan to the upstairs duct and have it turn on as needed?

 

[supers05]

Your ductwork won't be big enough to redirect all of the cooling/heating like that. You'd need at least 2 stage for both cooling and heating. (even with a bypass damper you need at the very least dual stage)

You can increase the static pressure to help a bit, if you like the sound of air rushing through your vents. In commercial, the main truck would be high static, with each zone branch low static. We make sure that there enough ductwork after the damper to muffle the noise.

Can you let us know what kind of hvac that you currently have? Regular furnace? Ac? Heat pump? etc.

Cheers!

 

[dannieboiz]

The furnace I'm looking to put in is a Goodman NG 80k BTU 2 stage with a 96% efficiency, the AC is a 3.5 tons 13 seer unit (current and not replacing)

I don't mind the sound of air as much as I mind the heat :devil3: Just think of it as a little white noise.

 

[beenthere]

What your describing that you want to do, is a dual zone set up.

What model Goodman furnace. If a GMH, you could end up with problems zoning it without a bypass.

 

[roughneck]

Do you really need 80k BTU?
Booster fans are an entire waist of money, energy and time.

 

[yuri]

To do it properly you would need a zoning panel AND a bypass damper system. When one zone closes ( downstairs ) you need to be able to relieve the excess pressure and airflow amount back into the return duct. If you don't then not enough air may flow across the AC coil if the motor is overloaded and it may freeze up. It will be noisy and the extra speed of the air can lift off the water from the coil and the motor could be overloaded.

Honeywell makes a good system and if you view some of the install videos they will show you the bypass damper and proper duct setup.

https://forwardthinking.honeywell.com/products/zoning/truezone/truezone_feature.html

 

[dannieboiz]

What your describing that you want to do, is a dual zone set up.

What model Goodman furnace. If a GMH, you could end up with problems zoning it without a bypass.

Exact model is GMEC960803BN.

Yuri, I'll check out the HW panels. I did see it yesterday while I was browsing but didn't look in depth

 

[dannieboiz]

Was reading the HW panel manual and it shows it needs 2 T-stat. Running a T-stat wire to the upstairs isn't a huge problem but is it possible to use a T-STat with a remote sensor like a NEST or Ecobee3?

 

[yuri]

In the real world there is no cheap easy workaround quicky zoning system or to do what you want to do.

If it was myself I would buy a Goodman GMV or whichever model has a ECM variable speed fan and get the Honeywell zoning and a bypass.

That way you have something which will work. Any other DIY idea will never work properly and could overheat your furnace or damage the AC and may void the warranty of the new furnace.

Duct boosters are a joke in the industry and never work. Like trying to push air thru a straw it does not have enough power and uses a lot of elec which is $$ and they vibrate and are noisy.

The ECM Variable speed fan is very important because it can alter it's speed when 1 zone closes and will work 100X better with a zoning system than a fixed speed PSC fan. You can also run it on slow speed 40% of full for air circulation which may help also.

Honeywell is very clever and the largest maker of HVAC controls and put a lot of [email protected] $$ into their redline resi products and they are very good. Before they were mostly into industrial and commercial automation controls and the rest was not their main interest. Now they realize there is big $$ in resi it seems.

 

[yuri]

Was reading the HW panel manual and it shows it needs 2 T-stat. Running a T-stat wire to the upstairs isn't a huge problem but is it possible to use a T-STat with a remote sensor like a NEST or Ecobee3?

Personally I don't like Nest or Ecobee. I sell Lennox and their thermostats are made by Honeywell . I would stay with Honeywell tstats and whatever they recommend. Once you start re-inventing the wheel or going against what they recommend problems usually happen. They designed that system for their products and to be installed exactly like they show.

 

[dannieboiz]

Personally I don't like Nest or Ecobee. I sell Lennox and their thermostats are made by Honeywell . I would stay with Honeywell tstats and whatever they recommend. Once you start re-inventing the wheel or going against what they recommend problems usually happen. They designed that system for their products and to be installed exactly like they show.

THe T-STat I use now is a HW rth8580wf but it does not have the option for remote sensor.

The Goodman furnace GMEC960803BN that I'm looking at does have an ECM motor. However, it only have a 1200cfm blower, my ac unit is a 3.5 ton 13 seer unit. On another thread it was said that I should have 350 to 400 cfm per ton. I choose that model due to feature and price. 2-stage burner and high efficiency. I'm in Northern California so the extra money spent on a high end furnace isn't a wise investment. We use our heater 3 months out of the year.

 

[yuri]

There are 2 types of ecm motor.

x13 which is 4 fixed speeds but constant torque ( to a point ) and variable speed ecm. The GMV is variable speed.

A high efficiency in Cali may be overkill and it needs to vent out the side of the house or roof. They make a GMVC8 series, 80% which uses a chimney which may be a better value. The $$ saved may buy you a better variable speed motor. You can run 350 cfm/ton or as low as 325 if you have LARGE free flowing ducts which most people don't. Otherwise get a bigger blower and go with 400 cfm/ton.

 

[dannieboiz]

Going with an 80% efficiency unit the GMVC81005CX seems to fit the bill.

The price difference is only a few dollars.

on the same note, which unit will be more efficient dollar wise?

just looking at raw #, a 100k btu unit @ 80 % will use more energy than a 80k btu @ 96%

 

[roughneck]

Why would you need a furnace that large in CA?

 

[yuri]

OK. HVAC 101

You buy a furnace and AC to fit the size of your house. Heat loss and heat gain (AC). Has nothing at all to do with efficiency or dollar cost.

If it is too small your house will be cold or too hot with a undersized AC.

If the furnace is too big it will overheat as the ductwork will be too small.

You need to do a heat load calc and find the right size.

I would not recommend a 96% efficient furnace in Cali. A higher SEER AC would be a better choice. If you burn a LOT of gas like in Canada then yeah we want 96% efficient.

If you use a lot of expensive AC electricity like in Cali then a more efficient AC saves a lot of $$.

You would never burn enough gas to notice the difference anyway. A mid efficiency furnace has less to go wrong/is simpler and in the long run may require less repairs.

http://www.hvaccomputer.com/gtarget1.asp?kwx=6&adx=3&gclid=CMjGvu7Kw7UCFe4-MgodPF4AoQ

 

[dannieboiz]

A few factor on why I'm looking at this size furnace.

1. Based on my current system size 115k btu 20+ years old, assume 70% efficiency, that's 80,500 btu, so an 80k btu @ 96% or a 100k btu @ 80% will be in the ballpark of where I'm currently at.

2. An HVAC contractor also recommended this range when they were out here a few months ago, due to size, insulation etc...

3. I've been looking at furnaces in family member home similar size and age and they all seem to have similar size furnaces.


One of the contractor however said that since I have toddlers and the house is occupied 90% of the time, he felt I would benefit from a 96% efficiency unit as my furnace is being used all day all winter. He also pointed out that the 96% efficiency unit would require more labor since he can't reuse the metal vents and need to repipe with PVC.

 

[yuri]

At the end of the day there is a enormous amount of BS from salespeople and urban myths etc about furnace sizing. The professional way to do it is using a load calc and you can DIY cheaply with that link.

My salespeople have it on their laptop and use it at the house.

Furnaces were oversized in the old days because bigger was better and gas was cheaper. Not anymore.

Efficiency is confusing. It is actually combustion efficiency that we are talking about. Older furnaces were about 60% efficient and then we went to 80% and then 92% and higher. You need to know how many BTU's you need to heat your house and nothing else. If you want to look at the BTU output of your current furnace not input then you will know. Take the input and divide it by the output and you will get the combustion efficiency. However that does not factor in heat loss up the chimney as to running cost. Getting confused?

Point being we use a heat loss calc and match the furnace to the output of the models available. Has nothing to do with toddlers or elderly people.
It is more efficient running longer and more comfy as you get more even heat. Stopping/starting wastes NRG $$.

My 92% efficient furnace is rated as a 70,000 BTU input . If it lost 10% it would lose 7,000 BTU and become 63,000 BTU output. Mine is actually 64,400 = 8% loss

If it was a 80% then you would lose 20% of the 70,000 which is 14,000 BTUs

 

[roughneck]

Bigger isn't better.

www.loadcalc.net

 

[dannieboiz]

Based on the loadcalc, i need 55350 btu for heating and 32634 for cooling.

So I supposed an 80k btu @ 80% is good enough in my case?

The price between the 80 and 100 is only about $60 even so it's still not recommended to go with the bigger one?

 

[yuri]

I don't know the exact output but 20% off 80,000 = 64,000 which should be OK. The model #s listed are input not output.

On their site the GMVC 80 is listed as 80,000 input and 64,000 output.

Bigger is not better as the furnace will overheat and cycle on/off 4ever on the high temp limit control and damage the heat exchanger.

When they build houses the ductwork size matches the furnace size but the cheap builders sometimes undersize it and that is a huge problem in the US with AC and heating. More so with AC.