Question on bid for replacement furnace

[drbenjamin]

Guys

I am looking to replace the 22 yr old gas furnace in our home and I am concerned about the bid I received. I called up the company who had installed the original unit (when the home was built), and the person who showed up walked through the house, counted the registers, and wrote up an estimate. I was at work so didn't get to talk to him. Having learned here that a heat load calculation is needed to properly size a furnace, I called an asked if he intended to do one. He left me a voicemail claiming that
1) They had done the calculation when the house was built, and nothing had changed
2) He needed to get a minimum of 100cfm at each register, and he only had one unit that could deliver that airflow; if a heat load calc indicated that a smaller unit was needed he didn't have one that could deliver 100 cfm
3) It's a 2 stage unit he proposed so there's not as much danger of oversizing as the unit will spend most of it's time at the lower setting

The price is reasonable, and we've been happy with the service this company has provided during the 4 years we've owned our home. On the one hand I feel like the company has failed to demonstrate their competence in HVAC by giving a proper, calculated estimate, on the other I feel like the furnace they propose to install is probably just fine and I don't want to get hung up on formalities. What do you all think?
Thanks!

[coolwhip]

Me thinks that a 50ton/80ton system is waaaaaay to large for the house.

[drbenjamin]

Me thinks that a 50ton/80ton system is waaaaaay to large for the house.

OK, sounds like I'm misremembering his exact words. it was 50 (somethings) / 80 (somethings)

I'll check the voicemail and update my original post.

[m kilgore]

Ask them to produce the original load calc. If every register needs 100 CFM I would be very suprised. Bathrooms usually take very little. Other rooms should differ in CFM also.

With a variable speed two stage unit you need to be sized right in order to heat your house right. A 2 stage unit is for comfort and needs to be sized properly. You can't size off of each register needing to be 100 CFM.

Get another estimate.

[beenthere]

Doubtful that you need 100 CFM in the bathroom, and all the other rooms need the same CFM also.

As far as not being concerned about a 2 stage being over sized. You should be.

Get other estimates.

Since he said he needs 100 CFM for every register.
How many registers do you have.

A 40,000 BTU furnace comes with a 3 ton blower, which would be 1200 CFM, or 12 registers.

There is a chance, you being fed some BS.

What size is your home. And what area do you live in.

[drbenjamin]

THanks for the helpful replies guys. I double checked the voicemail, he is claiming that a 3.5 ton blower is needed based on the register, the smallest furnace he has w/ that sized blower is a 2 stage 60K input/88k input. We have a 2300 sq ft home in Redmond WA. I will definitely ask for the heat calc, but how do I evaluate it? Am I making sure that the furnace has the capacity for the coldest anticipated day? Or do I want to match the average expected requirement?
Thanks!

[beenthere]

The calc is done at the coldest temp for 97½% of time.

So you have 14 supply registers. LOL

That is not how you size a system for heating or cooling.

If you want, you can do you own.

Its a 50 dollar fee., Here is a link to it.
http://hvaccomputer.com/talkref.asp

[Mr Bill]

I guess if we took up for our tradesmen as much as we try and found something wrong in everything they do all the time there would not be so much paranoia with the public, of course some here would have to go into detox and we probably would not need this forum anymore. The guys changing out and existing furnace that has moved a certain amount of air for 22 years and the price is reasonable, and he has been happy with the service this company has provided during the 4 years he has owned his home and now we need to get NASA involved?

on the other I feel like the furnace they propose to install is probably just fine and I don't want to get hung up on formalities. What do you all think?
Thanks!

I think sir you already have your answer above.

[beenthere]

He's happy with their service.

So how does that determine if the furnace is oversized and using more fuel then it needs to or not.

[Mr Bill]

He's happy with their service.

So how does that determine if the furnace is oversized and using more fuel then it needs to or not.

O God! carry on soldier. I would be more concerned about CFM's or air flow than fuel usage that would tell you if it's oversized, anyway I did not want any pissing contest, I was really just making a remark that it would be good sometimes to stand behind some of our tradesman because..... we all can find "something" wrong with anyone's job trust me.

[Alden_Sloe]

We have a 2300 sq ft home in Redmond WA. I will definitely ask for the heat calc, but how do I evaluate it?

You can email me by bringing up my profile and just under the screen name is download vcard. I had a number of estimates done and can tell you who did/didn't do load calcs as part of the bid process.

[DanW13]

2) He needed to get a minimum of 100cfm at each register, and he only had one unit that could deliver that airflow; if a heat load calc indicated that a smaller unit was needed he didn't have one that could deliver 100 cfm

Sounds to me like your service guys only had one in his warehouse or shop that was enough BTUS to sell you with out having to go get the right size furnace for your home, so it seems to me like he is just trying to unload a furnace that he can't sell to other home owners, but thats just my opinion.

[beachtech]

2) He needed to get a minimum of 100cfm at each register, and he only had one unit that could deliver that airflow; if a heat load calc indicated that a smaller unit was needed he didn't have one that could deliver 100 cfm

Sounds to me like your service guys only had one in his warehouse or shop that was enough BTUS to sell you with out having to go get the right size furnace for your home, so it seems to me like he is just trying to unload a furnace that he can't sell to other home owners, but thats just my opinion.

you hae no idea what your talking about, do you?