Dealer Switching from 60,000 to 80,000 btu

[jim15102]

My dealer is replacing my 60,000 btu Carrier 58MVP furnace to a 80,000 btu Carrier 58MVP furnace. This is due to the furnace not heating the house efficiently.

My question is does anything else need replaced for the new furnace or existing 3 ton Carrier 38TDB air conditioner to work correctly?

Thanks in advance for the help!

[hvacprodmgr]

I would verify that a load calculation was done to confirm that the 80K is needed.

[jim15102]

They did a load calc and stand by the fact that a 60k furnace is what the house needs but the problem is with the fact that I keep the thermostat set on 71 but the furnace runs constantly on low speed and the low speed does not keep the house warm. High speed is great and does a great job heating the house. There is about 1600 sqft of space to heat.

At the install they wanted to put in a 2 ton air and I asked for the 3 ton which does a great job of cooling the house.

[air of honesty]

As teddybear is fond of pointing out, the problem is frequently more to do with caulking, sealing and insulation than sizing. Most go the easier but more expensive route of replacing the equipment than doing the painstaking labor to deal with the real issue. One creates a higher bill, the other permanently lowers it.

Have they tried something as simple as raising the fan speed for the heating mode? Are you trying to close off rooms to save/waste money?

[jim15102]

First thanks for all the insight..

My windows are also brand new and were installed right before the new furnace and air conditioner. I have checked the seal and perimeter of the windows with a lighter on windy nights and there seems to be no leaks what so ever. I also just blew 6 additional inches of insulation in the attic.

I had 5 estimates and all were for 75 to 80k units. This guy assured me this was correct and gave me a swap out warranty.

One last thing.. Most of the vents in my house are closed so the heat only goes to rooms that I use. He has adjusted the fan twice now.

[Edited by jim15102 on 01-31-2005 at 07:53 PM]

[Gunnery Sergeant Hartman]

Good luck with your mold problems in the future...

[jim15102]

Why would I have mold? There was only 3 inches of insulation in the attic in the first place.

[Gunnery Sergeant Hartman]

Oversized air conditioner does not remove humidity.

Sounds like you hired some hacks if they tell you that you need a 2 ton A/C then you tell them you want a 3 ton and they do it.

[Freezeking2000]

Are you saying the 60,000 btu unit heated properly, ran constantly and cycled between high and low fire when under design conditions?

If this is what you are saying i think you have the correct furnace installed already. The low fire should run all the time and go to high fire as neeeded to maintain temp. Maybe all you needed was a thermostat with a closer differential setting!

I would never put in an oversized heating system in your home due to lack of customer understanding.

[Freezeking2000]

You cant close off vents in your home. A heating system designed to heat a home cant be used to heat just selected rooms unless designed with a zone controll system. You will see higher bills after you change the unit. You will also crack the heat exchanger unless you OPEN the damn vents!

[Gunnery Sergeant Hartman]

My guess is the guy wouldn't accept that this is how his new 2 stage furnace works and they put in one that would "cycle" more frequently to shut him up.

[mayguy]

A two stage system will run longer on first stage, and the temp is a little cooler too..

Ideal thing is have the furnace run longer..

Also agree with the guys, over sizing the A/C is not going to help..

[jim15102]

I have browsed this site for a while now (great information) never had a question and the one time I do these are the reponses I get??? No one even attempted to answer my question!!!

Just for the heck of it I will respond so hopefully everyone does not think I am an idiot...

The house called for a 2 1/2 ton ac the 38TDB came in only 2 and 3 ton units. Since I had other estimates for 2 1/2 and 3 ton units I asked for the 3 ton.

I did not close the vents the installer did to force air to the rooms I was complaining about! I did not know this would cause a problem.

I also understand the two stage furnances, the problem like I said before its that on the first stage (which is most of the time) the house is cold even with the thermostat set at 71. On high fire the house is very comfortable.

The reason I do not think this furnace is correct for my house is that I used 16 MCF's (bills are always actual) to heat my house last month. That is more than my 32 year old 130,00 btu furnace ever used in a single month. And the fact that most other estimates were between 70k and 80k furnaces.

[travisfl]

Originally posted by jim15102
I did not close the vents the installer did to force air to the rooms I was complaining about! I did not know this would cause a problem.

Now you do, so you should open them.

Originally posted by jim15102
I also understand the two stage furnances, the problem like I said before its that on the first stage (which is most of the time) the house is cold even with the thermostat set at 71. On high fire the house is very comfortable.[/i]

This isn't an indication that the furnace is undersized. In fact, it may be that the furnace is sized correctly, perhaps even a little oversized, and that your thermostat just needs to either be set higher and/or be set with a smaller deadband.

Originally posted by jim15102
The reason I do not think this furnace is correct for my house is that I used 16 MCF's (bills are always actual) to heat my house last month. That is more than my 32 year old 130,00 btu furnace ever used in a single month. And the fact that most other estimates were between 70k and 80k furnaces.[/i]

It has been a cold winter in most of the country. How do your heating degree days for this billing period compare to last years? Also, are your new windows more energy efficient than your old ones, or the other way around?

[garry b]

Jim: I wouldn't take any comments here too personally. I doubt anyone is being rude or ignorant with you. More like just quick and to the point. So many of these questions have been answered a multitude of times it's almost unbelieveable.

Anyway...here's my 2 cents...and fyi, I'm a home owner and not an HVAC tech.

The load calc says 60K is the right size for your home? Then 80K isn't the answer. The right size is the right size. Putting in a bigger unit for naught will potentially cause you more problems like short cycling. If they are suggesting a two stage 80k unit, then what's really going to happen is the new unit will run on low fire the majority of the time if not always...but that's just because low fire on the 80k is not far off of high fire on the 60k.

You also say the furnace won't heat the house up on low but does fine on high. That alone almost verifies (almost) you have the right sized furnace (house heats okay on high). What's also fine is that if it is colder outside, low is not expected to be able to handle the task...that's why there's a "high". Not sure how much you know about the mvp but it should start on low fire and if the temp rise is too slow, it will automatically change up to high fire. When it gets close to the set temp cut off, it will roll back to low fire and finish off the heating cycle. Does your furnace do this? Maybe your unit was set to run on "low fire" only and now someone has set it to run on "high fire" only. If it was set to "low fire" only, it would take forever if ever to heat your house up properly. If someone has set it to "high fire" only, then it will always be up to the task but them what's the point of having a two stage furnace?

Also, if you don't have a two stage thermostat, you might want to consider one. It works better than the single stage thermostat using the logic of the furnace. Maybe an Infinity Control should be hanging on your wall if it isn't already.

Let us know what's what.

[travisfl]

Originally posted by jim15102
The reason I do not think this furnace is correct for my house is that I used 16 MCF's (bills are always actual) to heat my house last month. That is more than my 32 year old 130,00 btu furnace ever used in a single month.

Gas consumption has very little to do with the size of the furnace. 1000 CF of natural gas = about 1.027 million BTU at 100% efficiency. Derate by the efficiency of your furnace.

[Edited by travisfl on 02-01-2005 at 02:40 PM]

[Freezeking2000]

Hey Jim,

I think you may have other issues with you gas consumption other than too small of a furnace. You can set a 2 stage unit to cycle with just the high fire rate and see if you like it better. I suspect you have a major duct problem or an air distribution problem. I would double check for gaps in your ductwork to make sure you are not sucking return air from unconditioned space. Also the temps and wind have been a bit more extreme this yaer than many past years in Connecticut any ways.

As to sizing your unit if high fire does not run constantly you have the correct size unit.

[jim15102]

I do have the infinity control. Also high fire normally takes about 10 minutes to get the house back to temp.

Let me explain my problem:
The themostat reads 71. Every room except where the thermostat is (hallway no vents) is atleast 4 degrees less. I bought a thermometer and put it next to the thermostat to verify it was working correctly then tested all the rooms. I even moved the thermostat to a different room and got the same results.

If I turn the thermostat to 75 degrees the house is warm but then my bills will be huge. I didn't have this problem with my old furnace.

Again thanks for all of your help.

[johnl45]

If your dealer can't figure this out it's no wonder your having problems.

[beenthere]

JMO, you have an air distribution problem, not a furnace size problem.