Energy audit and new Furnace Question

[ootyboy]

I am new to the forum -- but have spent a lot of time reading posts on this amazing resource.

I have a question about an HVAC replacement. I got an energy audit last year and implemented a number of their suggestions (except the HVAC ones, since I was planning on replacing the unit and the ducts). In the audit they recommended heating output BTU's for the house. Currently, we have 2 furnaces, the first is 60,000 BTU (80%) and the second is 40,000 BTU (80%). The reports suggests an "Actual Heating Load" of 18,600 and 21,500 respectively.

Does that mean that I can get away with a single 40,000 BTU unit for the entire house? The house is 3100 SF, with a split level. Most of the ceilings are at 8 feet with one room having high ceiling.

I've had multiple HVAC contractors come by the house and each one has recommended a single 5 Ton (120,000 BTU) unit for the whole house. Given the numbers from the report this seems like over kill. To me it looks like they are just taking the current BTU and adding it all up to come up with a new unit.

I have been looking at York/Rheem super efficient models that come with modulating furnaces and variable fans.

Any thoughts/suggestions would really be appreciated.

BTW: I live in Northern California near Sacramento. So the weather is pretty mild.

[jimj]

Have any of them done a manual J? I would guess not. If not why not?:whistle:

[comfortdoc]

Will there be central A/C with these units? If so what size?

What will the duct modifications be to combine into one system?

[second opinion]

I am new to the forum -- but have spent a lot of time reading posts on this amazing resource.

I have a question about an HVAC replacement. I got an energy audit last year and implemented a number of their suggestions (except the HVAC ones, since I was planning on replacing the unit and the ducts). In the audit they recommended heating output BTU's for the house. Currently, we have 2 furnaces, the first is 60,000 BTU (80%) and the second is 40,000 BTU (80%). The reports suggests an "Actual Heating Load" of 18,600 and 21,500 respectively.

Does that mean that I can get away with a single 40,000 BTU unit for the entire house? The house is 3100 SF, with a split level. Most of the ceilings are at 8 feet with one room having high ceiling.

I've had multiple HVAC contractors come by the house and each one has recommended a single 5 Ton (120,000 BTU) unit for the whole house. Given the numbers from the report this seems like over kill. To me it looks like they are just taking the current BTU and adding it all up to come up with a new unit.

I have been looking at York/Rheem super efficient models that come with modulating furnaces and variable fans.

Any thoughts/suggestions would really be appreciated.

BTW: I live in Northern California near Sacramento. So the weather is pretty mild.

I would go with your audit numbers

[ootyboy]

jimj, the Energy Audit company did Manual J. Here is the sentence from their report: "Each room’s airflow requirements are calculated using ACCA Manual J." they provided some nice graphs showing CFM usage per room in the house.

Comfortdoc, yes there will be an A/C unit that the HVAC contractors says should match the Furnace and be 5 tons 16 seer unit (if I go with that size) The plan is to completely redo the duct system. The current one is old and poorly installed and leaks a ton of air. The plan it also to add a few new registers to improve airflow to certain dead spots, and use 2 returns for the single unit.

As far as connecting the 2 duct, there really is no need since the entire thing will be replaced and be sized for the house.

The other thing is I am leaning towards a single Zone system with the Variable Speed/Modulating furnace and 2 stage A/C.

[jimj]

But the contractors that you have contacted have not done a load. You need to look for a contractor that will and does a manual J, not because you ask but because it's the rite thing to do!

[ootyboy]

Jimj, I did not insist since the energy audit company did a great job -- they had all the right equipment and software to calculate load. None of our local HVAC contractors I've talked to have the type of equipment and computer software that the energy audit company does. I think they did an amazing job and provided a detailed report -- so i decided not to do it again.

[jimj]

Jimj, I did not insist since the energy audit company did a great job -- they had all the right equipment and software to calculate load. None of our local HVAC contractors I've talked to have the type of equipment and computer software that the energy audit company does. I think they did an amazing job and provided a detailed report -- so i decided not to do it again.

Well........... If you listen to the HVAC contractors that you have that detailed load that you have is useless!:gah:

[ootyboy]

Any other feedback on this -- aside from running the manual J process again? I really want to right size this system.

I am strongly leaning towards the York YP9C, which has a modulating/variable furnace. In this case would it be safe to go up to say 80,000 BTU furnace and a 4 Ton Unit given the Manual J numbers? Or should I stay with the 40-60K BTU recommendations of the audit?

Thanks in advance for any help.

[motoguy128]

With a 2 story home you want 2 zones... either with one systm or 2 indepedant systems. You heating and cooling loads are not the same on each level year round. THe upstairs will need proportionally more cooling CFM in summer and less CFM in winter than the downstairs. SO still go with a modulting furnace and a 2 stage AC unit... but look at zoning.

If you have the money to spend, consider a carrier infinity system and maybe doing 3 or 4 zones depending on your homes layout. For example a kitchen and formal dining room may have very high heat loads when there's guests or your cooking. Same with a Living room when you have the TV on and whole family in there. Upstairs you can keep a master bedroom a diffrent temperature than the other bedrooms as well as better manage shifts in heat loading during the day from solar heat gain.

Just a suggestiong. But I would definitely install a zone system, especially if your redoing the ductwork. IF you heat gain calculation place you closer to a 3 ton system (<38k BTU), if you zone it, you can often use a slightly undersized system because both zones are typically not needing peak capacity at the same time sicne you may not be at deigns temperture through the house during design outdoor conditions. FOr example in the afternoon when you come home you might keep the upstairs a little warmer sice yu're goign ot be spending all you time downstairs, the nin teh evening, it's now below design condtions and you cna then cool the upstairs off for sleeping and let hte downstairs warm-up= overnight. With a single zone you have to heat and cool the WHOLE HOUSE all together during and programmed periods. Same with the furnace. Evne with a mod, you don't want to oversize it... or you defeat the point of having a mod furnace... to have very long run times. Plus mod furnaces get a littel elss efficient at low fire. With a oversized furnace, it will spend more time at low fire as well as cycle on and off more.

In my house, I can set the downstairs to 60F overnight but leave the upstairs 64F. When I'm at work in the afternoon, I set the upstairs to 61F (which it rarely reaches until its' really cold out) and downstairs I keep at 64F because my wife usually comes home for lunch. My setbacks are a little xtreme because my equipment was well oversized by the previous owner's installer. With a properly sized system the setbacks will only be a few degrees.

[ootyboy]

Thanks Motoguy -- great advice.

Our house is more of a split level, than a 2 story. The only part of the house that is on the second floor is the master bedroom. I had originally thought about going with 2 zones, but after reading some of the posts about modulating furnaces and Zoning problems decided to stay with a single zone system. From what I understand if you Zone a modulating furance it essentially becomes a 2 or 3 stage system?

The concern I had is the first Zone would be 2000 SF, and the second would be 1000 SF. So if I turn off Zone 1 and only do Zone 2 with say a 4 ton modulating/variable unit I am either getting a lot of airflow or as you mention the furnace would be running at "low fire" for extended period of time.

I am certainly leaning towards a 2 stage A/C as well -- but the I am a bit concerned about the Zoning of of the modulating furnace.