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Ask me anything about HVAC heating air conditioning air quality control

  • Last Updated:
  • Dec 15th, 2019 2:00 pm
Deal Fanatic
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Aug 10, 2011
9348 posts
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Somewhere
The general consensus is to not replace a working furnace (for the most part).

My question is if I wait until mine dies (I assume I'll know during middle of winter since that's the only time furnace is on), how long does it take for a contractor to be contacted and a new one installed?

I don't want to freeze to death.

Would best practice to do all research and find a contractor beforehand, then contact that company the second your existing dies?
:confused:
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Oct 29, 2004
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1chinaman wrote:
Mar 15th, 2019 12:42 am
Likely can use your existing single stage furnace if has different speed taps on motor.
Have a competent installer check air flow on the different speeds.
Have first stage call goto board normally
Install a relay for 2nd stage cool to switch from low cool airflow to hi cool airflow on blower motor.
I might need to replace my single stage furnace. Can all dual stage furnaces run single stage AC?
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Oct 9, 2011
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spyhero wrote:
Mar 18th, 2019 12:59 pm
I might need to replace my single stage furnace. Can all dual stage furnaces run single stage AC?
I have a 2 stage furnace and it has no issues running my single stage AC
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dpw198 wrote:
Mar 18th, 2019 1:37 pm
I have a 2 stage furnace and it has no issues running my single stage AC
That's good to know.
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Jul 15, 2003
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Montreal
Ok, I'll dip my toe in the water, even though I don't know what half of the terms thrown around in her mean.

I have a keeprite bi-energy (oil/electric) furnace, which takes two air filters, a 20x10 and a 20x15 or 16. I've been looking at getting more filters for when I change them, but I'm usure what MERV rating filters to get, I read that for HEPA standards I should get something 13 or over, but I read somewhere else that I should check the furnace's manual and get what they recommend (I don't know where the manual is, and was unable to even find a bienergy keeprite furnace online). Am I going to mess anything up of I get merv 13 filters? I don't mind replacing them a little more often, but I don't want to put extra stress on my furnace or anything. (The furnace is 5-10 years old)
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Newbie
Mar 21, 2019
4 posts
Hi,
Need help here urgently since I need to sign a contract before April 1st to receive the QC government grants. I have a 2 story townhouse with approximately 1600 sf of living space on two floors without a basement (just a garage below). I am replacing an existing 2.5 ton heat pump with electric furnace. I have received quotes from different HVAC contractors some recommending 2-ton system and some 2.5 tons. The old heat pump was never very good in the winter, often switching to auxiliary heat quite early. In the summer it seemed to run fine, but I do recall the cycles being relatively short when the weather was more mild (most of the summer). I do recall it running almost all day last summer during the heat waves, but then again it may have been on its last legs since it leaked out all refrigerant buy the end of the summer. Note sure what to do! Going with a 2-ton will probably make the summer more comfortable, but make winter performance even worse. Opposite is true if I choose the 2.5 ton. Anyone who can offer help would be much appreciated!
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Nov 14, 2006
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DavidM94216 wrote:
Mar 22nd, 2019 5:09 pm
Hi,
Need help here urgently since I need to sign a contract before April 1st to receive the QC government grants. I have a 2 story townhouse with approximately 1600 sf of living space on two floors without a basement (just a garage below). I am replacing an existing 2.5 ton heat pump with electric furnace. I have received quotes from different HVAC contractors some recommending 2-ton system and some 2.5 tons. The old heat pump was never very good in the winter, often switching to auxiliary heat quite early. In the summer it seemed to run fine, but I do recall the cycles being relatively short when the weather was more mild (most of the summer). I do recall it running almost all day last summer during the heat waves, but then again it may have been on its last legs since it leaked out all refrigerant buy the end of the summer. Note sure what to do! Going with a 2-ton will probably make the summer more comfortable, but make winter performance even worse. Opposite is true if I choose the 2.5 ton. Anyone who can offer help would be much appreciated!
Little bit more info needed , what year was it built ? How's insulation? Windows ? Doors ?

If newer 2ton should be fine for cooling , if older and not good insulated 2.5 ton maybe better. You have to make sure the furnace they are installing can send enough cfm for the cooling its matched up with.
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Mar 21, 2019
4 posts
lilmikey wrote:
Mar 22nd, 2019 7:07 pm
Little bit more info needed , what year was it built ? How's insulation? Windows ? Doors ?

If newer 2ton should be fine for cooling , if older and not good insulated 2.5 ton maybe better. You have to make sure the furnace they are installing can send enough cfm for the cooling its matched up with.
House is recently built in 2006 in Montreal climate. Had it evaluated by one of the government agencies in order to obtain one of the grants. They said the leakage was 6.7 changes per hour for ACH 50.

Windows and doors are double pane but probably at the min required bldg code of 2006.

Thanks again!

Old unit failed after only after 13 years due to excessive corrosion on the inside coil.

Looking at either Daikin or Lennox btw. Lennox being more expensive.
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DavidM94216 wrote:
Mar 22nd, 2019 7:36 pm
House is recently built in 2006 in Montreal climate. Had it evaluated by one of the government agencies in order to obtain one of the grants. They said the leakage was 6.7 changes per hour for ACH 50.

Windows and doors are double pane but probably at the min required bldg code of 2006.

Thanks again!

Old unit failed after only after 13 years due to excessive corrosion on the inside coil.

Looking at either Daikin or Lennox btw. Lennox being more expensive.
Can I ask why not go natural gas furnace ? Your house should be fine with a 2 ton unit.
Newbie
Mar 21, 2019
4 posts
I considered it (gas furnace) but it would have been a hassle to install since it’s a twon house there really wasn’t a good exit for the exhaust where the furnace
Is located. Also the space where the furnace is located isn’t really large enough for a gas furnace. Here in Quebec electricity is much less expensive at .09$ /kwhr.

The idea behind a heat pump is that it is still cheaper to operate in the early and late parts of winter than agas or electric furnace. But with a 2-ton unit I don’t see it being capable of heating much below +5 or 0c.

So you think for a heat pump two tons is really the right size? How do you come to this number? Would you say that 2.5 tons is over kill or will it work too?

At least all contractors quoted the furnace with a 2.5 (with 2-ton hp) or 3 ton (with 2.5 ton hp) coil.
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Nov 14, 2006
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DavidM94216 wrote:
Mar 22nd, 2019 9:24 pm
I considered it (gas furnace) but it would have been a hassle to install since it’s a twon house there really wasn’t a good exit for the exhaust where the furnace
Is located. Also the space where the furnace is located isn’t really large enough for a gas furnace. Here in Quebec electricity is much less expensive at .09$ /kwhr.

The idea behind a heat pump is that it is still cheaper to operate in the early and late parts of winter than agas or electric furnace. But with a 2-ton unit I don’t see it being capable of heating much below +5 or 0c.

So you think for a heat pump two tons is really the right size? How do you come to this number? Would you say that 2.5 tons is over kill or will it work too?

At least all contractors quoted the furnace with a 2.5 (with 2-ton hp) or 3 ton (with 2.5 ton hp) coil.
Honestly I forgot your in QC where electricity is cheaper so makes sense. When installing AC you can go with bigger indoor coil ie. 2 T outdoor with 2.5 indoor coil but haven't seen it other way around. But since you are basing this more for a heating application then I would go with a 2.5 T as heating will need to go up.

Whatever you decide to get make sure they run a stat with an outdoor air sensor that will not let your HP run in heating when outside air temperature is below a certain setpoint ie. 0C This way when it cant run to produce anymore heating it will disable it and turn on your auxiliary heating (electric).

I have seen some newer HP units that are suppose to run efficiently all the way down to -20C which are made by Mitsubishi (Hyperheat) and another version by Daikin, maybe a better option if you want to get away from electric heating in general.
Newbie
Mar 21, 2019
4 posts
Yes the indoor coil is always bigger.

Typically they set the cutoff point at -12c since until that point there is still enough heat (3-4kw) coming from the heat pump. They can also run both at the same time (first 5kw of aux heat with hp). I think there are many options here and none wanted to go into it in detail during the sales phase.

My main concern is that I know the AC will work better with a 2-ton unit. But I know the winter performance will be worse then before. Hence i will just ask them to force it to switch to the furnace heat at like 0 or -5 like you said. The problem with this is that then there is almost no savings, and I’m wondering why bother with the heat pump alltogether.

On the reverse side the unit will probably give enough to heat so that it can be used with only 5kw (1stage aux heat) most of the time. It ac dehumidification won’t be great. And I wonder if that was the reason why old unit failed so early since it was the coil that corroded.
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Nov 14, 2006
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DavidM94216 wrote:
Mar 23rd, 2019 11:29 am
Yes the indoor coil is always bigger.

Typically they set the cutoff point at -12c since until that point there is still enough heat (3-4kw) coming from the heat pump. They can also run both at the same time (first 5kw of aux heat with hp). I think there are many options here and none wanted to go into it in detail during the sales phase.

My main concern is that I know the AC will work better with a 2-ton unit. But I know the winter performance will be worse then before. Hence i will just ask them to force it to switch to the furnace heat at like 0 or -5 like you said. The problem with this is that then there is almost no savings, and I’m wondering why bother with the heat pump alltogether.

On the reverse side the unit will probably give enough to heat so that it can be used with only 5kw (1stage aux heat) most of the time. It ac dehumidification won’t be great. And I wonder if that was the reason why old unit failed so early since it was the coil that corroded.
You got all your options, you know what you are dealing with so you can make the right decision. Would be good to have the electric reheats after the coil which it doesnt seem you do in your case? In Ontario i've seen more and more townhomes with water heated (water coil) furnaces from their hot water tanks. I dont prefer that option as if you lose your tank you lose water and heating.

I installed a geothermal ground source system in my parents home which is around 3000 sq ft, the system required a 7 ton as you always need to calculate heating first in HP system. If it was just an AC system they would need a 3/3.5 ton system. Electric heating is the worse as it dries the hell out of the air when its running, but where you live its cheaper than gas so I get it.

If you want the HP to run all winter Id looking into those low ambient systems I mentioned in the earlier post, regardless make sure your humidifier is working right if staying with electric reheats. Good luck.
Jr. Member
Oct 29, 2007
159 posts
7 upvotes
Toronto
I recently received a quote which for a 1500sqft detached 2 story house built in 2001 wanted to do the following -

60,000BTU 2 stage furnace
1.5ton AC

They cited "2 stage has a low fire of 40000 BTU and a high fire of 60000 btu so it uses as much gas as it needs. Typically for a 2 stage furnace we like to go a size up so the furnace will run on low fire most of the time. This is the goal if this technology where as if we install a 45000 btu it may run on high fire/2nd stage 90% of the time. "

This does not seem right. If the house only needs 45,000, why would I want my low fire stage to be so high? Would it not be beneficial for that to be a lower BTU while the high stage is 45,000?
Sr. Member
Oct 9, 2011
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SugarySnack wrote:
Mar 26th, 2019 11:05 am
I recently received a quote which for a 1500sqft detached 2 story house built in 2001 wanted to do the following -

60,000BTU 2 stage furnace
1.5ton AC

They cited "2 stage has a low fire of 40000 BTU and a high fire of 60000 btu so it uses as much gas as it needs. Typically for a 2 stage furnace we like to go a size up so the furnace will run on low fire most of the time. This is the goal if this technology where as if we install a 45000 btu it may run on high fire/2nd stage 90% of the time. "

This does not seem right. If the house only needs 45,000, why would I want my low fire stage to be so high? Would it not be beneficial for that to be a lower BTU while the high stage is 45,000?
I think your instincts are correct.

How many BTUs is your current furnace and does it keep your house warm during the coldest days this winter? Take the BTUs of your current furnace and multiple it by the efficiency rating and compare it against the math for the 60k BTU unit. The numbers should be close and not vary by 10k or more BTUs which is probably what you will find as the guy said he is going to put you up one size.

My 3000+ sqft house has an 80k btu 2 stage furnace. During one of the coldest days this winter, my furnace ran on stage one for about 90% of the time when the total furnace run time was around 12 hours on that particular day.

You don't want to over size the new furnace otherwise your stage one will short cycle and stage two may only run for minutes a day.
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