high efficiency furnaces

[AmberB]

I have a 3 year old house and ever since I moved in I've had an issue with the furnace. I've been told its normal for high efficiency furnaces to blow cooler air than an older furnace and also kick in more often. I can't imagine how this is more 'efficient'. When I stand near the vents the air is not very warm at all. Often the furnace has to be really cranked up though it does eventually warm the house up okay. How does this save energy?

I just got my enbridge bill.... last month it was about $250 and this month $50 so we are averaging about $150/month. Is this a normal range for a 1200 sq ft. house? We turn the furnace down to about 17 at night. Keep in mind the house is only 3 years old so the windows and doors are in good shape...

p.s. I make sure to change the filter regularly.

[leonk]

It doesn't matter if you have your thermostat set at 17 or 30 .. the temperature coming out of the registers will always be set the same. The only difference is how long the furnace runs for.

I checked mine using a laser digital thermometer, and it registered between 55 to 65 degrees C (depending on what register I tested). So you might want to check on that.

As far as why the air might feel cool. There could be multiple reasons:

1) leakage in the duct .. most of your heat escaping inside the walls
2) registers not set correctly. Too much heat escaping in open registers in the basement, and never make it up.
3) undersized furnace (this is very common with new homes).

My parents 3100 square feet house has a smaller furnace than my 90 year old 1200 square foot home. Smaller furnaces = cheaper cost for the builder.
Smaller furnace = smaller blower fan. Not as much pressure; also less burners. I have 4 burners in my 5 year old high eff furnace .. they have only 3.

You might want to get an HVAC pro to come and check your house. They have tools to test pressure and temperature.

[AmberB]

Great suggestions Leonk...

I am going to check the temperature from the vents like you suggested.... and read up on the furnace model that I have to confirm that its the appropriate size for my house. I may even consider taping up the duct joints in the basement to avoid heat loss. I make sure to keep the vents down there closed.

If all else fails I will consider getting a pro to look at it. I asked the builders about it when I first moved it but of course their answer was that it was just fine. It wouldn't surprise me if they put a sub-par furnace in the house....they are very cheap and skimped on alot of things.

thanks!

[fastlayne]

OP, state the make and model of the furnace. Perhaps other RFDers have the same model and can give their experiences.

I have a HE and would note that, with a variable gas valve, the heat output at the registers can be little more than current room temperature (based on my perception and without the aid of a thermometer).

Are you running the furnace fan 24/7 for circulation? Could this be the "coolness" that you are feeling, since the heat would not be on?

[Keelie]

We got one put in last year, and I notice a big difference in the heat that comes out of the vent compared to that of our old furnace. It definitely is not as hot, it is a bit cooler.

We were told that the older furnaces blow really hard, and most of the heat is escaping through the chimney. With the high efficiency, the heat is not being lost and its all staying in the house. So it does not need to blow really hot into the house.

Our heating bill has gone down quite a bit and the house stays toasty warm.

[Munchos]

We got one put in last year, and I notice a big difference in the heat that comes out of the vent compared to that of our old furnace. It definitely is not as hot, it is a bit cooler.

We were told that the older furnaces blow really hard, and most of the heat is escaping through the chimney. With the high efficiency, the heat is not being lost and its all staying in the house. So it does not need to blow really hot into the house.

Our heating bill has gone down quite a bit and the house stays toasty warm.

Thats what makes them "high efficiency". The closer to room temperature of the flue gases, the higher the efficiency.

If your furnace is starting up often, usually its a sign of an oversized unit as it will heat your house much faster than a smaller rated btu furnace. If it was undersized, you would notice that it would stay on for long periods of time due to the lower btu output. This is way more common than undersized units. For a size of a house that large I would guess a 60 000 btu furnace would be sufficient enough but that is solely based on square footage alone. If you have a lot of windows,doors, etc.. than this could easily change.

[leonk]

munchos.. thanks for your insight..

Any reason why a lot of old homes in my area (where I know the owners, and talked about their furnace) more than not have over sized furnaces .. some times by a LOT!?

My house is 1300 sq feet (w/o the finished basement) and my furnace is 76,000 BTU. A friend has a similar sized home 2 streets down with 110,000 BTU furnace!!!

Is it the recommended size for houses w/o insulation in the walls, or are bigger furnaces typically on sale? :D

[Munchos]

munchos.. thanks for your insight..

Any reason why a lot of old homes in my area (where I know the owners, and talked about their furnace) more than not have over sized furnaces .. some times by a LOT!?

My house is 1300 sq feet (w/o the finished basement) and my furnace is 76,000 BTU. A friend has a similar sized home 2 streets down with 110,000 BTU furnace!!!

Is it the recommended size for houses w/o insulation in the walls, or are bigger furnaces typically on sale? :D


Most likely its some sales guy who doesn't know what they are doing and are just matching the btu rating of the old furnace that they are replacing. I know I installed a 80 000 btu furnace in a house maybe 900 square feet. Way to big for the house but they were planning on an extension on it, so hopefully they actually do that otherwise money down the drain for not only the purchase of the furnace but future problems down the road.

[leonk]

What kind of problems would one see if they have a severely oversized furnace??

[Detox99]

I saw this thread and thought I would ask a question............

We live in a 100 year old house in Toronto. Our current furnance is abour 20 years old and we are looking to buy a new high or mid efficiency furnance.

Will a high efficiency furnance be wasted in a house that is already so drafty? The house is traditional double brick construction with lath and plaster walls. We did have the windows replaced this year.

Many thanks,

Detox

[Tjalfe]

It doesn't matter if you have your thermostat set at 17 or 30 .. the temperature coming out of the registers will always be set the same. The only difference is how long the furnace runs for.

This is assuming it is a single stage furnace. Dual or variable stage furnaces do indeed output less heat on stage 1, and will slowly ramp up till it hits the target temperature.

[speedway84]

I saw this thread and thought I would ask a question............

We live in a 100 year old house in Toronto. Our current furnance is abour 20 years old and we are looking to buy a new high or mid efficiency furnance.

Will a high efficiency furnance be wasted in a house that is already so drafty? The house is traditional double brick construction with lath and plaster walls. We did have the windows replaced this year.

Many thanks,

Detox

Hey, I'm in the same scenario (100+ yr old home, ~20 year old furnace, double brick, plaster&lath).

A high efficiency furnace would likely have a higher payback in this type of home, vs if you installed a high efficiency unit in a well insulated home.

If you are using a higher efficiency furnace you are converting more of that gas into heat (regardless if it is leaving through the walls :( )

[whodaphucru]

I posted this elsewhere on RFD with no response so hopefully some insights here.

I am doing a number of energy upgrades through the eco energy program (mostly insulation related) and I am trying to decide about whether I should get and ERV/HRV and whether I should get a new furnace.

First off, my furnace is not that old, coming up on 6 years in service, it is a Carrier 58MSA which is rated as 90% AFUE. I believe this unit is only a single stage unit with only a single fan speed (AC unit). What I am trying to figure out is since I already have done the energy audit (that is already a sunk cost) is there any value in taking advantage of the rebates/ tax credits to get a new furnace. Here is my math:

$1300 (ecoenergy rebate) + $100 (enbridge) + $500 home reno tax credit = $1900 towards a new furnace.

I am guessing that a new furnace of 94% efficiency or better with a variable speed DC motor is likely $3000-$3500 installed. So can I recoupe the $1100-$1600 in energy savings (gas/ electricty) and over what time? I can't believe it'll be more that $100-$150/ year at the high end. Also when would I start to expect repair issues on the existing furnace to factor into the payback formula?

Would I see any other non energy related benefits like better heat circulation in the house, noise reduction, etc.? Are 96 or 97% AFUE units significantly more than 94% units?

Secondly, I want to get an ERV/ HRV not for energy savings but for general comfort in the house. However given the fact the you get $750 from ecoenergy this seems like the time to buy one. Does this require a new furnace or can mine be retrofitted? Is there any advantage to doing this at the same time as a furnace? What is a good name brand and what should I expect to see in terms of installation costs?

So in a nut shell if you were in my place and planning to stay in the same place for long while would you get a new furnace because of the rebates/ tax credits above or stick with the builder furnace?

Thanks,

[JWL]

Secondly, I want to get an ERV/ HRV not for energy savings but for general comfort in the house. However given the fact the you get $750 from ecoenergy this seems like the time to buy one. Does this require a new furnace or can mine be retrofitted? Is there any advantage to doing this at the same time as a furnace? What is a good name brand and what should I expect to see in terms of installation costs?

Good call on the HRV. With today's airtight homes it significantly increases the air quality/freshness.

They can be retrofitted as they are independent functions (other than the fact that you will have the furnace fan "ON" rather than "AUTO". I don't think there is a particular advantage to having it done at the same time as the furnace.

[tallAJ]

note that with HRV's and houses being air tight, it drastically reduces your humidity level in your home so a humidifier is needed. i have one and a HE furnace (95.6%) and we are sitting at 30% humidity. its a green home tested by LEED

[whodaphucru]

note that with HRV's and houses being air tight, it drastically reduces your humidity level in your home so a humidifier is needed. i have one and a HE furnace (95.6%) and we are sitting at 30% humidity. its a green home tested by LEED

WIthout a humidifier in past years I would get into the high 20's, this year mid to upper 30's all winter long with a built in humidifier. I guess the humidifier would run all the time with the ERV/ HRV? Will an ERV help some of that humidity transfer?

Any ideas on the cost of an ERV/ HRV and is this something that could be done DIY?

[tallAJ]

not sure of the cost but i think install is not to difficult. it might be hard to run lines to furnace and outside exhaust.