Radiant Heat PLUS Forced Air Backup?

Mike T., Swampeast MO

The one HVAC contractor [seems] DEAD on track. Even without lots of solar gain from lots of glass the "shoulder seasons" can be difficult with radiant heat. Add lots of glass and even the "meat" of the heating season can become problematic. You either loose too much or gain too much via that glass.

You have a great advantage with a private "free" source of gas. Use the funds you save for supply to build a fine and efficient system (that may involve the unusual luxury of two distinct system used for both comfort and efficiency). That way there's more gas for you to sell...

Moissy

Radiant Heat PLUS Forced Air?

We are building a 2800 sq. ft. ranch house in southwestern Pennsylvania and would like to have gas hot water radiant heat. Lots of glass in some rooms and one cathedral ceiling.

One HVAC contractor is telling us that we should install a supplemental forced air system because for one month in the spring and one month in the fall the radiant heat won't keep it comfortable enough...they're saying to keep it warm enough at night will make it too hot during the day and we'll need to open the windows during the day.

We also want an AC system so we know we'll need to install ducts, but wondering if we really need to consider a forced air furnace since we don't want to spend the extra $$.

I should also mention that in the future we are going to have "free" gas because of some mineral rights that are reverting to us on the property, so cost of gas is not the biggest consideration here. Any thoughts? Thanks!!!

Unknown

Mike, what are you saying?

Solar gain is an issue. Look at that; mass is mass and it can only heat up or cool down so fast, for sure.

But, if the solar gain itself is not too severe, a good control strategy can make the slab stay comfortable throughout the heating season. Nice outdoor reset, indoor feedback controls like Teknet 4, for example. It's a rare building indeed that Tn4 cannot manage comfortably. It happens, but it is definitely not common.

Gah.. no need to jump right to FHA as the answer!

Kevin__Flynn

If the issue is the shoulder seasons, ie. spring & fall you might consider a heat pump system.

There shouldn't be much of an up-charge to go to a heat pump condenser outside & a heat pump coil instead of a cooling only coil in the air-handler.

Not only will it be just a minor increase in install cost over your A/C only system but the months that you would be using it for heat would be the months that a heat pump would be at its most efficient.

Just a thought.

Kevin Flynn

WaterHeaterGuy

I love the dual system. Let me give you another scenerio that this system really shines.

Bringing in the groceries. You leave the door open for a while and all of your air temperature drops. You can close the door and wait for the mass to heat the air back up again, or help it along with an air to air exchange.

Unknown

I am sick of this "example".

Leave a door open for awhile and you CAN NOT cool down the mass fast enough to cause an issue. If the radiant is installed properly and running properly, it should be back to regular room temperature very quickly indeed once the door is closed.

With good radiant systems, I hear comments all the time from garage and shop owners who open huge overhead doors all the time about how fast they are comfortable again once the door closes in the middle of winter.

WaterHeaterGuy

The mass DOES NOT cool down... the air temperature does.

As for it comming back quickly to a comfortable level, well that does depend on a properly designed and installed system.

RadPro

We need to know about the radiant method you are using.

A low mass "Dry" system such as Roth Panel or Warmboard, react to sudden load changes with ease.

I agree with NRT.Rob, dont jump to warm air to hastily. It may not be a "must have".

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Unknown

And air does not take long to heat when you have it surrounded by heated mass. You aren't waiting for the slab to recover, you are just waiting a very short period of time for some air to heat back up. Unless the system was caught in a cooled down off-cycle due to some poorly planned bang-bang operation, or perhaps if the slab has been off for awhile due to solar gain or something like that.

Mike T., Swampeast MO

Sorry for being too hasty in my original recommendation. I did however assume (arggh) that the person making the "dual system" recommendation was basing such on both the plans and his experience.

To the homeowner: check references for the contractor suggesting the dual system. Combine that with your own research and personal feelings about what the contractor says and, most importantly, WHY he says such is needed and justified. Also I UTTERLY applaud you for building a reasonably sized home when you have access to "free" energy plus a surplus to sell. In such situation I could NEVER fault you for splurging on glass and views...

Air-air heat pumps are certainly useful in some conditions, but it's hard to recommend such to someone who has access to natural gas on their own property.

Christian Egli_2

Free natural gas?

He he he, set the floor temperature on sizzle and open the windows wide, year round -why waste? This would seem to be the natural urge, too many people who don't pay for their utilities think this way

The true beauty of radiant (and floor) heat is that it has not much to do with air temperature. You can heat very drafty places quite efficiently and quite comfortably because you have nice cool wintery and humid air to breathe and yet you feel nice and cozy because of the radiation. It's like enjoying the sun on an outdoor terrace in the winter. To maximize the radiation power, either go for large radiator panels (the floor would be the largest possible) or go with a powerful heating fluid like steam. Then sit back, relax and enjoy.

You're thinking of redundancy, and I think it makes complete sense to add gas heat (at a very minimal additional cost) to a combined heat and AC system. You can always hope both systems won't brake at the same time. But for comfort purposes, I don't think you'll be using the hot air all that much, you've got no reason either to use the electric heat pump for fuel cost purposes.

With this in mind, make sure to design the air ducting around the most efficient AC operation possible. Indeed, what's good for AC design is not for hot air, and vice versa. Usually some compromise is found (in PA, usually to favor the hot air operation), but you clearly need the air pipes to work best for AC.

Your contractor is correct in mentioning the overheating problems, floor heat is slow to react and this is a problem with rapidly changing weather, -but it isn't anything that can't be fixed with lots of electronic control and complex pumping.

Free gas you said? You must just hate paying an electric bill.

You can install a natural gas powered cooling system, either engine driven or an absorption system. Free AC.

Free gas, wow!

Have you converted your cars to run on compressed natural gas? Free rides.

Lastly, here is my favorite thought so far. It seems you must live in a rural area with perhaps frequent winter power failures. Of course, you'll surely have a natural gas driven generator, but there is a very simple way to have a central heating system that operates without any electricity, it provides wonderfully powerful radiance, it is very even, it is very quick to adapt to wild Midwest weather, it burns natural gas (which you like), and it's called steam heat.

It may seem old fashioned but there is nothing out dated about it. Hopefully you'll consider some of these ideas.

Enjoy your gas.

nick_7

I don't think a forced air furnace for the forced air heat portion is called for. If you have hot water available you can put a hydrocoil on the duct system at minimal expense. Else, you might consider an electric coil. An AC sized duct system should provide adequate forced air for shoulder seasons, with added benefit of dehumidifiying on damp, slightly cool days when only a touch of heat is called for.

joel_19

Ureka!!!!

I can't believe that it took somebody so long to say hydro air!! just do it . These guys arguing about the slab cooling off are missing the point . your putting in all the ducts anyhow and putting in an airhandler , just upgrade that and your done . Simple , effctive and cost effective

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