Trying to decide: Gas or Geo in a weird home.

[bobequus]

I would like to replace my ancient gas hot air furnace. The problem is that my home is weird. Originally it was a stone barn built in the

18th century (SE PA) and converted in 1949 by one guy, a school teacher. The ductwork for the second floor is typical, albeit old. It's the first floor that makes you crazy. The ductwork is a labyrinth built from brick that runs in a continuous maze throughout the first floor. On top is a slate floor. (You can see original photos at my website: ; look at photos 11,14, and 15). When we bought the house we were told that it was radiant heat. However, there are four registers to expel hot air into the first floor. The house is very cold in the winter. I use a wood burning insert on very cold days as auxilliary heat. (The house is very easy to cool, however.) One reason is the furnace, an oil converted to gas, is incredibly inefficient and really beat. I held off in replacing the unit as we were doing a massive renovation which includes a lot of new insulation. However, that project is 4 months behind and winter is coming. One of the ways this furnace is so bad is that the air coming out into the ductwork immediately above the furnace is only about 100 to 105 degrees. By the time it gets to the registers on the ground floor, it is down to about the mid to upper 70's. We were ready to install a geothermal unit, but after some research, I got to thinking. A geo unit will put out about the same temperature as our current furnace. Will we end up in the same boat? Do I need a gas furnace that will put out temperatures that are higher to utilize the stone as a radiant source? The installers that I have talked to either ignore or dismiss or shrug when I ask. I'm trying to find a real HVAC engineer to help figure out what will work best, but have as yet not gotten a reply from any. I don't think that they have much interest in residential. At this point, I'm looking for ideas, suggestions, comments; anything that will help me make an informed decision. Thanks.

[.p.jm.]

When the going gets weird, the weird get going. Sounds like your'e going pretty good ;-)

No, it's the drugs I took in the late 60's / early 70's that did that.

Mis-design of the gas conversion. Too much airflow for the burners.

Yep.

Yes.

I guess they don't want your business. Oh well.

If you want to heat mass as a radiant source, you do need a high enough supply temp to do it. A HP, geo or otherwise, will not do it for you.

You can either go with combustion-source hot air ( gas fired, etc ), at ~ 140 F discharge temp, or radiant water loop ( controlled as needed at temps up to ~ 180 ( based on outdoor temp and setpoint ).

Looking at the pictures, it's too bad you didn't put in radiant HW loop before the slate went down. That brickwork maze is NEVER going to be right - it will ALWAYS be overheated at the beginning of the journey, and cooled to ambient temp by the end of it.

To do radiant loop, you'd need to take up the slate and use that 'duct' space to run the PEX.

You might look at putting in a gas-fired boiler, with hi-eff storage tanks for both heating and potable HW. Find some room to run PEX tubing loops ( continuous loops of 3/4" pex, effectively needing a ~ 2 " transit space - easier than finding room for ducts ! ) to distributed / zoned radiators or small zone AHU's.

If you can get a snake through that 'duct' space, you coudl use that.

Or perimeter radiators, maybe.

Then you could control zoning via a manifold etc.

[ilbebauck]

Generally speaking, Geothermal is an expensive installation compared to conventional hvac designs and youve got to plan on staying in the house quite awhile to break even. However, it may add to the value of your home . Youll need to get some quotes both ways from local Contractors with a highly detailed proposal so you can compare apples to apples .

[.p.jm.]

Which kind of misses the point that geo can not be applied to this installation.

[Jon Elson]

On 09/17/2011 07:53 AM, bobequus wrote: One of the ways this furnace is so bad

Why is this? What is wrong with the furnace?

Jon

[Ken]

Davie Boi usually misses the point

[j]

What is the downside of that? Other than a cold floor, that would seem to be the way to go.

Otherwise the slate floor would have to come up to fix that "labyrinth" of ducting.

[.p.jm.]

Cold floors. it would be ideal to insulate the pex underfloor, but if that's not possible, you can get away with it. The heat to the under-floor will not be wasted, exactly, as it will warm the slate up a TINY bit. yOU'LL WNAT HIGHER FLWO RATES AND LOOP TEMPERATURE TO MAKE UP FOR UNDER-FLOOR LOSS.

And I'll be needing a new caps lock key, it seems.

It will still be cold to the feet. Walmart has some nice area rugs on sale :-)

But at least if you can get a pull-rope AKA snake around the points / labyrinth as needed, enough to pull a PEX loop, or even over it around the perimeter, you can have something resembling even heat, and for not too much $$, as DIY project, really.

Don't skimp on the zoning, you'll need it to make up for uneveness of distribution etc. Think 'more smaller zones', each on it's own stat. Pull the stat wire at the same time as the Pex, as appropriate for the pull.

Design for 'maximum worst case cold minus 10 degrees colder', you can always adjust loop temps, on / off cycle times, etc, as needed. Too much heat is easy - turn the fuckign thing off. Too little heat when it's running flat out is a problem.

An outdoor reverse reset stat on the boiler will be a good investment. As the weather gets colder, the boiler temp increases, etc.

Learn about loop sizing first. Headers, manifolds, etc.

3/4" Pex IS always BETTER THAN 1/2". IMO, you have no use for ANY 1/2" at all. Headers should be 1".

Yep.

[j]

Thanks.

Snaking the pex through and using a higher line temperature to compensate for the poor coupling to the floor sounds like a plan.

What I wondered was the loss through the ground. I know that in crawl spaces often just the perimeter is insulated (walls and below grade on the slab edge). It seems to me that this same effect applies here, the thermal time lag would, I think, be horrible though.

Speaking of which, I have a rental that has a crawl space that needs insulating. Cement block foundation. Would you care to offer an opinion on whether I should insulate under the floor or the walls? Before I fixed all the duct leaks it was a toasty floor!

Cheers, j

[.p.jm.]

Don't get me wrong - you're running the PEX to feed radiators, NOT to heat the slate. You will NOT heat the slate to any appreciable degree without good coupling.

Yeh, you're going to loose a lot to the ground / slab. And the lag will be measured in weeks or months, not hours or even days, as far as THAT portion of the heat is concerned. Think of it a simple 'loss'.

Depends - you want the heat you buy to go where you say it should, or WTF it feels like ?

[j]

OK.

Thanks, that settles that.

I've wanted to do staple up here (full uninsulated basement, ~ R26 batts in joists) and feed it with my solar. I've got a jig for the plates and much of the material but it seems like a lot of work and adding backup gas heater/boiler would be in the mix. I suspect it is a project too much for this year...

Cheers, j

[PaxPerPoten]

After carefully considering your many problems with this property, I am inclined to suggest doubling the fire insurance and renting it to a not altogether recovered Pyromaniac.

[.p.jm.]

Wassup, your landlord kicking you out ?

[PaxPerPoten]

Naw..Just bored with"j's" constant whining. Been watching politics lately, Paul? A couple of more Republican Primary runners and we can have a full football team.. ;-p That Governor Chris Christy would make a Helluva a center, or lineman.

[.p.jm.]

Christy / Rubio ticket could not lose.