I've done quit a bit of work sealing air leaks, dual pane vinyl windows, re-sealing ducts ,etc. to my 2100 sq ft 2- story house in San Diego. My house was built in 1987 and has one of the first 82% carriers, 95,000 btu/hr input. Even without all the upgrades the furnace was a bit too large for this house. Now with the upgrades on about the worst case day in my location (41 outside, 68 inside, call it 30 deg delta) the furnace only runs for maybe 15-18 minutes max out of every hr. My many heat load calcs, manual, program and furnace run times lead me to believe that my max heat load is just a bit less than 30 K btu/hr. All of the local installers I've talked to want to install 60-70 kbtu/hr furnaces (input and 90+%).

I thought I wanted modulating or 2-stage also for comfort and before visiting this site I thought this oversizing would be OK. The installers also wanted to install another 4 ton AC. Given a 4 ton AC I can understand the need for a larger furnace to provide enough air flow in cooling. My calc also said less than 3 tons would be more than adequate. So it seems I've done too good of a job making my house more efficient. Combine that with our light heating loads in San Diego and it seems there isn't a small enough furnace to fill the bill for me. Even the smaller 45 Kbtu/hr furnaces seem to be too large. Unless I add more rooms, increase the winter indoor themperature, or the winters get a lot worse here I'm not sure what to do.

Any thoughts or suggestions? Thanks

I would listen to the installers. Especially since they all seem to agree. You can do all the calculations in the world, but these guys have been installing them for years and years, thus learning what will make you happy and warm or cool, with the best efficiency. Nothing worse than a homeowner trying to tell the pro what to do. I understand that you want what you want, but the installers know what they are doing. They do it for a living and if they do as you want, then when you call back with a problem, they will say, hey we just did it the way you wanted it. I really recommend taking the installers advice.

Would you rather put in an undersized unit and not have enough heat, or over size a little to make up for future additions, and possible extreme cold spells. Maybe talk to some friends that could recommend a certain heating contractor. See what they have to say. If they say the same thing as the other contractors, then just pic the contractor that seems most reputable, and cost efficient.

Do a full manual J for a accurate estimate of your HVAC requirements. With all the changes you have made I am sure the requirements for your home have changed.

On the A/C end I would rather have a unit a bit to small and have it run all the time to keep removing the moisture than one a bit to large that cycles on and off to often leaving the air cold but clammy.

BTW not all variable speed systems are problem prone. I know this owner personally and his stuff is great. It has been made and used with no problems for over 25 years. I run 3 of them in my different airhandlers at home.


FanHandler.com

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Originally Posted by mygirlsdad77

I would listen to the installers. Especially since they all seem to agree. .

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Yeah but what concerns me is that none of them have offered or suggested a manual j calc. I've done a manual calc and a follow-up online with HVAC-CALC as well as another reference that is based on delt-t and furnace run times. My furnace will typically only run for about 8-9 minutes which indicates it is way oversized and confirms all the calcs.

Oh and they all just use the "rule of thumb" to size the AC. I thought that sort of approach was gone by now but given our mild climate here they get away with it. And it was one of these same pros that very badly mis-diagnosed my a furnace issue I had last year. I don't think all pros are in fact pros and it's tough figuring that out.

But most pros agree that if a manual J isn't mentioned to say thank you and look for someone else. And oversized AC's are just asking for cold clammy house.

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Originally Posted by hvac1000

Do a full manual J for a accurate estimate of your HVAC requirements. With all the changes you have made I am sure the requirements for your home have changed.

On the A/C end I would rather have a unit a bit to small and have it run all the time to keep removing the moisture than one a bit to large that cycles on and off to often leaving the air cold but clammy.

BTW not all variable speed systems are problem prone. I know this owner personally and his stuff is great. It has been made and used with no problems for over 25 years. I run 3 of them in my different airhandlers at home.

FanHandler.com

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I agree with you 100%. The motor control reference looks interesting. What about the higher temperature rise with the lower air flow? I guess you just can't go too low with it and have to verify that?

Sounds like you have it all figured out. Just go buy the furnace you want. Install it, and call yourself when it doenst satisfy you. LOl. Actually, it sounds like you are doing a better job calculating your house needs than the available contractors in your area. Stick to your guns. Seems you know what you need, and want. I still think there has got to be a contractor in your area that will work with you, and warranty their work.

The motor control reference looks interesting. What about the higher temperature rise with the lower air flow

No problems the two sensors supply and return ramp up the motor speed automatically. When cool down is sensed the motor ramps back down to the original setting. Works just in the reverse in the A/C mode. At the university during testing almost got a full flow out of the 3/4 pipe in the A/C mode on a 5 ton unit. It removes the water right now then rtamps back up to do the colling part of the A/C's job.

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Originally Posted by mygirlsdad77

sounds like you have it all figured out. Just go buy the furnace you want. Install it, and call yourself when it doenst satisfy you. lOl. Actually, it sounds like you are doing a better job calculating your house needs than the available contractors in your area. Stick to your guns. Seems you know what you need, and want. I still think there has got to be a contractor in your area that will work with you, and warranty their work.

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Well not all of it really, that's why this site is so good. There's a lot to be learned and I'm hoping to put off this purchase for another season while I search for an installer here. The Lennox guy here seems to be the most knowledgeable but I'm not sure I really like the brand that much and it does seem to be pricey compared to others.

My co-worker, an electrical engineer installed his own Goodman furnace, ac and zone control. He found someone to help with the AC charging and hookup and the guy looked at his system and replied with a daffled look "I don't do commercial". He had to have a lot of custom sheet metal made and I don't think he could have bought his system for under $20K, it's pretty complicated. One issue he still has is his vent pipe is tuned to play some weird harmonics that he hears every time it shutsdown. I think I'll probably pay someone to do it right rather that go that route. Fixing the one I have is tough enough without all the help I've had here.

I agree about lennox. The cost of equiptment alone will most likely be more expensive than the price of most other furnaces (equiptment and install) I have found that most lennox installers do come across as very knowledgeable. The thing is, they are only knowledgeable about lennox. They are more interested in selling you an expensive lennox than really trying to help you find the most efficient, cost effective install. Lennox dealers are almost in a different world. The price of their equiptment alone makes me think that the units are made of pure gold, with diamond heat exchangers.

I am not fan of the Lennox equipment at all. I haven't been impressed with their quality or availability of parts.

It is kind of out of character for me to suggest this but have you considered a heat pump system?

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Originally Posted by MarkwithaK

I am not fan of the Lennox equipment at all. I haven't been impressed with their quality or availability of parts.

It is kind of out of character for me to suggest this but have you considered a heat pump system?

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I'm not sure but the price of electricity might make the heat pump a tough sell. I have a PV array that completely zeros out my yearly bill of about 2700 kw-hr per year. If I had a heat pump at the time I might have put a larger PV arrray in .

We have tiered billing so that the first say 378 kw-hr costs you about $.13 per kw-hr but if you use around 1000 a month that puts you in tier 5 and the cost almost $.30 per kw-hr. A bill of over $300 for 1400 kw-hr is typical here. Gas isn't quit so bad.

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Originally Posted by hvac1000

FanHandler.com

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So this fanhandler looks very interesting. Do you know how much it costs. What kinds of issues are there with the lower speeds. I see it recommends using one of the slower speed taps as the max heating speed. Will this produce to high of a temp increase? How low have you run a std motor with one of these? Can it be set up to actually turn off say during the night? Do you use a special thermostat? If it's not too expensive I could get one and then just move it to the next furnace when this one quits. Thanks for the suggestion. And it avoids all those issues with expensive variable motor replacements.

Do you know how much it costs

For the exact cost you will probably need to talk to a contractor that installs them since usually it only sells to the trade. (and that is done for a reason).

What kinds of issues are there with the lower speeds. I see it recommends using one of the slower speed taps as the max heating speed. Will this produce to high of a temp increase?

Actually there are no issues with these units unless you have a really cheap made blower motor. Since a professional does the install all issues as far as temp rise across the heat exchanger are taken care of by them.

How low have you run a std motor with one of these?

I have run a standard motor so low that you could count the fins on the blower wheel as they went by but that type of operation is not that these units are set up to do since running at that slow a speed can be harmful to a standard sleeve bearing motor over time. Now a ball bearing motor will take the abuse..

Can it be set up to actually turn off say during the night?

Yes but I cannot see the advantage of that. When running at low speed the motor draws very little current and it is extremely quiet so quiet that it cannot be heard.

Do you use a special thermostat?

No not unless you want to run a hot deck/cold deck system in whick both the heating and cooling run at the same time to provide a absloutely perfect balance temperature and humidity during different times of the year. My home was set up 30 years ago to use the hot deck/cold deck system but over they years as utility costs went up it became uneconomical to operate as such. The program is still in the main operating computer as a carry over but has not been used in years.

If it's not too expensive I could get one and then just move it to the next furnace when this one quits

The nice part of this device is it is a stand alone device and can be added or removed at any time.

While I am sure you have some talent the owner of Fan Handler likes to see his devices installed by a professional who really knows what they are doing. There are many reasons for this but I will mention a few.

If a unit is installed by a professional any problems that could pop up are eliminated before they become a problem.

Amprobe/watt meter,air speed tester, accurate capacitor tester,professional grade probe temp tester and other tools along with the knowledge to use them are needed to really do the job correctly.

Some times a run motor capacitor will need a value change to stiffen the response with the use of this device and other items may need adjustments. For these and other reasons is why the owner of the Fan Handler company wants them professionally installed since his reputation is at stake on every install.

The owner is not some young guy who is into China's mass imports of junk. Each one of these units is made by hand in his shop and tested completely before being released. Nothing has been cheapened by a bean counter since the owner is the bean counter and every electronic item that goes into building these units is rated at way over the standard duty cycle. In other words if these units are installed correctly you will never have to buy another unit since they just do not fail and they are not a cheap built piece of crap from China.