Question for the HVAC experts, from client with wall heat

In northern Arizona, some of the older homes have wall heat only. We inspected one recently and the client wanted to know what it would take to convert to central heat/AC, and if that is even possible. I recommended contacting a HVAC company or two for quotes. However, I would like to learn more about this.

This is a 1970s home built on a crawl space with an accessible attic over part of the home. The other part of the home is two story with limited attic. My thoughts were that it may be possible add ducting to the home from the crawl space, like with a manufactured home. Another option would be to run ducts through the accessible attic space and then external ducting (that “industrial look”) in the other part of the home. Another option might be radiant floor heat, but that doesn’t add AC.

The client really wants central heat and AC, not mini-splits in each room.

If temperature is a factor, this area averages lows of 19-20 degrees in winter and highs of 83-84 in summer.

Ideas and expertise are greatly appreciated. TIA. :slight_smile:

All the things you mention are possible, without seeing the place, and keeping in mind I don’t live in AZ, but in anti-AZ, I would use the crawlspace, I can’t think of a single good reason to use an unconditioned attic for duct work or heating cooling appliances, given that attic temps are going to be well over 100 F when the sun is shining on the roof. A crawl would probably always be cool but not very because ground temps are more stable, so that helps with AC, which you would probably use more than heat anyway.

If anyone ever asks me questions like these I always say: “Anything can be done with time and money.” FWIW, as Erik mentioned, it sounds like a very feasible undertaking.

Go with a packaged unit through the crawlspace.

Too much heat in the attic.

Too much work installing a split unit:
two electrical circuits required.
refrigerant line set required.

Pkg unit you just hook up duct and electrical after you knock a hole in the foundation wall.
Only one electrical circuit.
No refrigerant line.

I hate package units for crawls after the duct is installed there is no room to get to the plumbing we all know plumbing never fails and never ever leaks so just go ahead and fill the crawl with ducts:p

If it was my home located in the devil’s kitchen I would use a downflow furnace with the supply air duct in the crawl space and use a central location for the furnace and plenum. I would use round metal duct and keep it close to the floor joist to allow room to crawl beneath the duct to have access to the plumbing. If the crawl space height was limited I would use a upflow to the attic and with lots of insulation. We have attic temps in Okla up to about 140 degrees with supply air ducts operating just fine. (well Insulated)

Well Flagstaff being at roughly 7,000 feet above Sea Level it does not really get hot there.

Putting the ducts/equipment in either the crawl of attic is fine, but floor registers would be the most efficient IMO. Consult a local HVAC Contractor.


As suggested above, a package unit would the be least costly install.
After that a standard split system would be a great option. If the crawlspace is deep enough and duct work can be kept tight to the bottom of the joists, clearance shouldn’t be an issue. Typically duct height is 8" plus insulation.

Getting adequate supply AND return ducts to the upper level is going to be the challenge. I’m seeing more older houses where there are supply runs to an upper level and no returns. Bedrooms especially will not be comfortable without a way to get a return installed.

I didn’t catch that 2 story issue.

Reminder; you can not condition two floors with one hvac system without a zoning system installed with returns al all levels.

Like David said, a zoned system would work. More than one system would work, mini split systems would work. Heat only system and room ac units would work…

Talking to a local HVAC Contractor would probably work best. :wink:

If the loads are similar you can condition a two story home with a single central system, with a properly designed duct system. No zoning needed.

Where I see a lot of questions are a single or two story home over a basement. The thermostat is on the main floor set at 70 degrees and the basement is always around 5 degrees cooler. Two very different loads.

Bull ****.

I won’t waste my time explaining why either…

David Andersen meet Scott Frakes. Scott meet David. I have enjoyed both of you in person. You both have backgrounds in HVAC albeit by a little different avenue. You may enjoy getting to know each other. Try it out…or not. :mrgreen:

That’s the way it works here as well.

Thank you for all the replies. Great information here! This will assist me in being able to tell clients about various options that could work for the home.

This home, being northern AZ, AC cooling is optional. However it is often added for convenience for those hot and sometimes humid days during the summer monsoon (when evap coolers don’t help much). It’s not the devil’s kitchen up there. Northern AZ is more like Colorado but with the monsoon effect.

Now where I live, this is the devil’s kitchen. Most air handlers are in the attic with ducts that have a lot of insulation. Yes, it’s a real treat going in those attics in the summer. Least favorite part of my job. I’d prefer a crawl space to an attic, :shock: for any inspection in the summer.

Yea, OK.

But I ain’t going to sit here and discuss ‘opinions’, just fact.

#1 You can’t have the same load on the 1st and 2nd floor.
a. Conduction: the first floor is sandwiched between the basement/crawl space/ slab and a conditioned space above. The 2nd floor is between the 1st floor (conditioned space) and the attic. Q=UADelta T. Heat transfer can never be the same.
b. Radiation: equipment load consists of: conduction + convection + radiation = 100%
The 2nd floor is much more susceptible to amount of radiation load than the 1st which only has one to two walls exposed to the sun at any given time.
c. Convection: Hot air rises and cooler air falls. Depending on operation mode, heat will move from one floor to the other because of it’s design. In the cooling mode, the conditioned air on the first floor pushes the warmer air up to the 2nd floor, increasing it’s load. In heat, the reverse happens.

2# Duct design: you can not optimally design an HVAC system to operate in both the heating and cooling mode without the use of other controllers. Location of duct (supply & mainly return) must be in a different location for proper operation. Air Stratification can not be avoided. You may get 68F air in the room, but you have to be sitting on the ceiling to experience it.

70% of the time when I get a call for ‘uncomfortable’ conditions, I find it related to duct design. I will not argue that a properly designed and balanced duct system will help. Pic here are in the heat mode. The duct is designed for cooling (because of regional location). This is how it works in the heat mode.

People complain more when they are cold than when they are hot.
When we are hot, it’s because it is hot outside. When we are cold, there is something wrong with the HVAC.
Not always so…

Thanks, David.

You still doing good after the prayer chain outcome?..I hope so. :smiley:

Had five visits to doctor/hospital on Wed. Brought home strep throat!

Other than that… Things are good! Thanks.

Was cutting grass yesterday. You ready to put the snow shovel away up there yet? :wink:

Bummer on the strep throat. I’m praying for you, my friend, all the way around.

Hoping to get rid of the shovels soon, although the last 4-6" fell on may 1st a while back…:slight_smile:

Thanks Larry!
Don’t put away that shovel just yet. However, I think the snowfall is coming to an end.

It looks like you have a lot of HVAC experience. Your contributions here are certainly appreciated and we can all learn from you.

In my experience, specifically with forced air systems, is that a properly designed non zoned duct system on a two story home will work great. Obviously a zoned system gives the homeowner greater control.
The location of a properly placed cold air return(s) can really make a difference.