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Heat for new home build

Posted by bob4321 (My Page) on
Wed, Oct 24, 12 at 21:34

Question on heating system for a new home build. I am building a fairly large house approx 4500 sqft. I want to go with radiant heat in the house, but the quotes have been astronomical (close to 95K). The house is a mix of tile and wood floors. One contractor suggested that for the second floor, only put radiant in the baths - then use hydronic heat coils in the A/C handler in the attic to supply hot air heat for the bedrooms. This seems to be a fairly popular configuration for new builds in my area and saves quite a bit.

I am not a big fan of forced air heat, but maybe it makes sense given that the heat is only on upstairs a few hours a day (early AM and bedtime).
Has anyone done a combination system like that? Any drawbacks I'm missing?
Thanks


Follow-Up Postings:

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RE: Heat for new home build

"use hydronic heat coils in the A/C handler in the attic to supply hot air heat for the bedrooms"

I am not familiar with this set up. Can you explain how this works?

What is it that you don't like about a forced hot air system? Will this house have a basement?


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RE: Heat for new home build

My suggestion is high-end but you would have to crunch your own numbers to see what the cost differentials would be while taking into consideration life cycle, maintenance and operating costs.

I would install either a triple function geothermal heat pump (hot/cold forced air, full capacity hot water & DHW) with full hydronic radiant in-floor heating and forced air cooling/heating or go all hydronic geothermal with full capacity hot water and chilled water for cooling, full in-floor hydronic heating and in-ceiling hydronic fan coil cooling (or heating). This method requires NO ductwork at all (unless you install an HRV or ERV which may be advisable)!

I would not install anything in the attic on new construction if it can be avoided.

Consult with those that have proven expertise in this particular field, others in the HVAC, building contractors and architects may try to discourage any such approach, often because of their own lack of knowledge.

One integrated system such as this can also be expanded to simultaneously incorporate pool heating and snow melt.

I belief what you would invest up front you will more than get back in energy savings, resale value, reduced maintenance and life-cycle costs. Others on this site and elsewhere would challenge this analysis - run the numbers yourself to decide!

SR


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RE: Heat for new home build

The system would pipe hot water from the boiler to a set of coils in the airstream from the air handler. So you would use the existing AC unit and ducts to supply hot air for heat.

The house will have a full basement and is 2 stories. I would much rather have radiant heat over forced air for a variety of reasons including comfort, noise and efficiency of low temperature radiant.

Has not considered geothermal. Am trying to save a bit on the cost, and my total heating costs with gas are not that steep to justify the cost. The house is energy star compliant and will use a very efficient boiler.

On a differing topic, I was reviewing the bid for the AC units. The house is 2 stories, 4500 sq ft, with high efficiency windows and insulation built to energy star compliance. I know I need to ask about the manual J calculations, but the units seem greatly oversized. One bid was for 4 units- 2.5 tons, 3 tons, 2 tons and 3 tons. That's over 10 tons for the house. Does that seem way oversized.?


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RE: Heat for new home build

Where is this house located? This seems oversized even for the hottest part of the country.

I would put all the HVAC equipment in the basement.

Baseboard heat is the most comfortable and quietest. However the newest modulating forced hot air furnaces come in a close second. It is a good alternative if you looking to save money.


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RE: Heat for new home build

Location location location.....As in where are you?

And then how tight is the house - and is that decided already?

Yes 10 tons is absurd and you have to wonder what else is being done so poorly. I have 7 tons in a larger house and I am well oversized in an area so warm that no one has radiant heat (NC)

If you have a tight budget at all, you really should rethink forced air heat. Radiant heat when you need a/c is a luxury for those that have nearly unlimited budgets but I suppose it depends where you live. You can put such a sweet forced air system in for $30k that you would never know it is on. You would have full humidity control. Good air filtration.

I would do radiant if I didn't need a/c partly because you get rid of the ugly vents. Also the incremental cost is so much lower.

But if you are in an area of the country that uses both a/c and radiant heat, you should put your money into insulation. A r-30+ wall with proper windows doesn't require much heat and that is where the money should go....

People have lived with such garbage forced air heating systems that it biases them unfairly. It is like diesel cars - comparing today's models to some filthy thing from the 70s just isn't fair.

Radiant is still nice to keep your feet toasty....


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RE: Heat for new home build

The house in in Long Island. Bit north of you, but still have 2 months of humid summers. The house is being built to energy star compliance - sealed tight with blowback testing for certification. Walls are all R19 and ceilings are all R30. Windows all high efficiency.

There is a full basement for equipment.

My current house has radiant heat in my bath and kitchen now, with baseboards for remainder of house. Really like the radiant and the baseboard is quiet and effective but obtrusive.

The idea is to put radiant on the entire first floor (wood and tile) and put radiant on 2nd floor for tiled areas only. The air handler for 2nd floor AC is usually placed in the attic to limit duct runs from the basement - but it could be located in basement. Then use the boiler to send hot water to exchanger in front of the AC handler for general 2nd floor heat.

Going full radiant for the remainder of the 2nd floor would probably be 10K additional.

My only experience with forced air was my parents old house - noisy, dusty, dry. But it was instant gratification when you wanted heat. With what the contractor is proposing, however the AC ducts are layed out and perform would be how my heat would sound. He also specified humidifier and effective filters.


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RE: Heat for new home build

Ducted air gives you better options for dehumidifying which is key in a damp area like yours. If you don't want to go geothermal, you should consider a heat pump, which will cost only a little more than conventional air conditioning, and is very efficient. Your gas furnace becomes just a back-up, or for when/if temperatures dip too low.

The hydronic option for upstairs is interesting.


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RE: Heat for new home build

"My only experience with forced air was my parents old house - noisy, dusty, dry."

Forced air systems no longer suffer from these problems.

How are you going to humdify the air when using the radiant heat?


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RE: Heat for new home build

R19 and R30 would be low in my area for new construction. I"d be doing R25 and R50. And I'm 400mi farther south.


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RE: Heat for new home build

R19 and R30 were speced by the architect and the energy rater.
Is R19 the limit for fiberglass in 2x6 walls?


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RE: Heat for new home build

What I've heard is that in a well sealed house humidity should not be a problem. But, I think you are correct that if I use forced air for heat in at least part of the house I can add humidity during heating season.


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RE: Heat for new home build

Walls can/should be sheathed with rigid foam - stops the thermal bridging and can bump you up in r-value. If you have an energy rater and architect, they really should mention it. It is actually cheaper and more effective to do 2x4 walls and sheath with rigid foam. Foam is forever also or close to it.

I grew up in LI - it really isn't that cold.

I personally think most houses in LI are baseboard/radiant is because they are too old to have central a/c - not for comfort reasons. But then again - I was there awhile ago.

Modern forced air of a certain quality is not noticeable when running, not dusty and has a humidifier so isn't dry.


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RE: Heat for new home build

Rigid Foam - do you mean the solid foam boards under the siding?
Many of the LI homes have the in-wall convectors - units under the windows embedded in the walls. Not very good heating units. After that, houses started to migrate to baseboards.
Question forced air heat - I know that the newer modulating furnaces and multiple speed air handlers are very efficient and quiet. If I was doing the hydronic coils in an A/C air handler, would that be just as effective?


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RE: Heat for new home build

The hydronic coils in an a/c air handler is a unique thing that doesn't dry the air as much as a typical furnace. It certainly costs more than a furnace and humdifier so I've never understood the advantage. But otherwise, it has the same effect.


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RE: Heat for new home build

I think it becomes economical when you are doing some radiant and some forced air. You require a boiler for the hot water radiant, so rather than getting a boiler and a furnace, the existing air handlers can be used with the boilers hot water.


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RE: Heat for new home build

"The hydronic coils in an a/c air handler is a unique thing that doesn't dry the air as much as a typical furnace. It certainly costs more than a furnace and humdifier so I've never understood the advantage. But otherwise, it has the same effect."

Wait a minute, David, I think the only thing changing the air's relative humidity is the temperature rise, not the method used to warm the air. Whether the rise is caused by a warm air furnace, a hydronic furnace, a radiator, sunlight shining into the room or a space heater, if the air temp increases from (say) 50 degrees to 70 degrees and the air volume is otherwise sealed off from outside, the ending relative humidity is going to be the same.

This is not like warm humid air passing over a cool surface as in AC, with water vapor coming out of the air. With heat, no water vapor is leaving OR being added to the air.

Maybe there's a pro who can shed light?


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RE: Heat for new home build

A well-sealed house will be more humid in the heating season because the moisture does not escape. Whether you need a humidifier or not depends on how much moisture you generate with your activities.

A hydronic coil/force air will not affect humidity any differently than a furnace/forced air on a theoretical basis. The only difference that might come is is if ducts external to the house envelope leak it will cause a loss of humidity.


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RE: Heat for new home build

That insulation level is ridiculously low for a modern build concerned with energy efficiency. Put more money into the shell and you can put less into the HVAC and be dollars ahead. If costs are a concern, I would only do electric radiant heating mats in the bathrooms and do a standard forced air heating system. The radiant mats are only designed to take the chill off of the cold floor and you will still need to actually heat the bathrooms with the home's main heating system, but they are really nice little luxuries on cold mornings.


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RE: Heat for new home build

The insulation levels were chosen by the architect and the energy rater said were more than sufficient. They seem to be more concerned with sealing the ducts/walls/house for the pressure testing. I may discuss adding a layer of rigid foam on the exterior (R8) on top of the wall insulation and what additional ceiling insulation would cost.


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RE: Heat for new home build

There is no question, the low lying fruit is in air sealing but there is also no question that more insulation is helpful.

There are people recommending R-40 for walls - I think that is a bit of overkill in your climate. I personally have r-40 in our attic in NC which has a much milder winter than you. Your recs for attic goes as high as r-60.

It is surprising to me that your attic can be r-30. I think NC just upped our requirements to R-38.

We did Energy Star and they don't actually require any additional r-value over code. Your energy rater stating that r-30 is "more than sufficient" is questionable. The DOE puts your recommended attic insulation at R38 to R60. You have to be in Southern NC to get down to R30. That is DOE based on cost effectiveness. Many codes go well beyond cost effectiveness.


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RE: Heat for new home build

What I'm discovering in this thread is that there are many different requirements for insulation - the DOE has recommendations for much higher R values than is required for Energy Star Compliance, and the local town has different requirements.

At this point I seem to be at the bare minimum and will do work to see what it takes to come up to a reasonable level.


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RE: Heat for new home build

Don't forget that the Code, or standard, is the WORST you can build to, the very bare minimum.

Better insulation is worth doing, and now's the time.


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RE: Heat for new home build

"Don't forget that the Code, or standard, is the WORST you can build to, the very bare minimum."

If you lived in NJ you wouldn't be saying that. You would be surprised by the codes we have to follow.


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RE: Heat for new home build

"Wait a minute, David, I think the only thing changing the air's relative humidity is the temperature rise, not the method used to warm the air. Whether the rise is caused by a warm air furnace, a hydronic furnace, a radiator, sunlight shining into the room or a space heater, if the air temp increases from (say) 50 degrees to 70 degrees and the air volume is otherwise sealed off from outside, the ending relative humidity is going to be the same. "

When you heat (or cool) a small quantity of air that is then dispersed into a larger volume the RH changes tend to get exaggerated by the extra heating (and cooling) in the small quantity of air the system operate on compared to the total volume of the space being conditioned.

Add to that that the outside RH is usually lower during heating season, heating the air up further lowers the RH, and the higher temp air from the vents is even lower RH until it mixes.

You have to keep in mind the difference between RH and absolute moisture content also.


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RE: Heat for new home build

Brick, I was simply explaining that the reduction in relative humidity (ie, dryness) comes from warming the air - it doesn't matter how it's warmed.

I don't agree with your small volume/large volume view unless you're standing in front of the supply vent. The air coming out of a forced air supply mixes quickly with what's in the interior space unless airflow is a problem.

I live in a mild climate where gas forced air furnaces are everywhere and indoor dryness in the heating season isn't an issue. No one has an indoor humidifier. The driest indoor living quarters I've experienced had hot water radiator heat, but that wasn't why it so dry. It was because it was a place with colder winter temps. No matter how tight a new house is, there's always air infiltration (whether intentional or not) and the dry outdoor air in cold winter places produce uncomfortably dry interior air.


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RE: Heat for new home build

Conventional wisdom is that forced air is drier - that doesn't mean CW is right....I suppose forced air with ducts in unconditioned space with leakage certainly pick up drier air. There is always an increase in infiltration from moving air around but I'm not sure how significant that is with a newer house.

Here in the South, houses are dry in the winter probably because infiltration is pretty high. Humidifiers are common. Infiltration is high because the climate is mild so the benefits of building tight are lessened. Our houses are also bigger - so human humidity and showers humidify the house less.


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RE: Heat for new home build

Houses built on a slab tend to be drier in the winter than those built with basements. The air in the basement tends to have more moisture since it is below grade. Some of this moisture finds its way into the living area of the house.


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RE: Heat for new home build

Even drier still are raised houses with open crawl spaces because they leak like all get-out.


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RE: Heat for new home build

Right - our dry houses in the mid-South are mostly on crawl spaces. Last time I lived in a crawl space house, I didn't think or understand about infiltration. But thoses houses were pretty leaky through the floor.


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RE: Heat for new home build

Sorry have not responded in a few days to all the posts, but have been sitting in the dark in LI with no heat. But I did learn an extremely important
lesson in the wake if Sandy- I will never install a superstor type tank off my boiler for domestic hot water ( it was part of my original plans).

My current house has a separate gas fired hot water tank. My family may not have heat, but we have ample hot water with no
power. Boilers require power, heaters with pilots do not.

Just thought I'd pass that along. I know the efficiency of a storage tank and condensing boiler can't be beat, but a week or 2 of not having hot water can change your thinking.


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RE: Heat for new home build

That is a big consideration in my part of the world, Gulf on Mexico coast. It tends to be hot here when we have big weather events. The water coming out of the mains is often around 80F so water heating is not as big a deal as energy for cooking.


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