Gas Furnace vs Hot Water "A" Coil

[steve cornell]

I'm building a new home and about ready for the HVAC, I have quotes for the system and am about ready to decide but thought I'd through out one more option..........

I have hot water radiant heat in the basement and garage floors and will use radiant heat under the ceramic tile in the kitchen \ breakfast area and I am installing a 3 zone F\A gas furnace with A\C and I'm planning on heating the radiant floors with the hot water heater but before I commit I thought I'd ask, would I be any better off going with a boiler and a hot water coil with a heat exchanger instead of the natural gas furnace?

The heat calculations for the home call for 3.5 tons of air and 40,000 btu heat loss, the home is a 2 story with 2 bedrooms and bath upstais with open balcony and a bonus room over the garage.

Thanks in advance for any opinions!

[BaldLoonie]

You won't find small furnaces that can move 3.5 tons of air. Probably would make sense to get an air handler with a hot water coil in this case. You're going to need a boiler for the radiant. Water heaters aren't meant for that purpose. The boiler could do your domestic hot water and the heat for the rest of the house.

[aircooled53]

Heat the hot water with gas or heat the heat exchanger with gas with forced air?
Heat from hot water through coil would be some what cheaper to operate, but the force air furnace would heat the conditioned space with warmer air faster.

[steve cornell]

Thanks for the replies....

If we go with a furnace we are planning on a 2 stage 80K - 100K btu with a 4 ton a\c unit.
The house is about 2800 sq\ft (1650 first floor, 650 second floor and 500 sq ft bonus room) the house is very well insulated and I believe the manual J calculation I have to be fairly accurate.

I guess my question is would I be any better off going with a boiler (instead of using a hot water heater for the radiant in the concrete)and using a heat exchanger with hot water for the forced air? either way natural gas will be the fuel whether we use the furnace or hot water exchanger.
Which would be more energy efficient?

Thanks again!

[smadave]

First: Your system is rather complex, more complex than most (notice I said most guys, before you get offended I am sure there are a few of you who are very capable of answering this man's question) people on here are used to working on. Probabally too complex to answer on the web. You should get an expert on radiant heat to look at your system and answer your questions.

Second: By the sound of it...you arent going to seriously take anyone's advice anyway. You are just looking for someone to agree with your ideas

Last: Sorry Baldloonie, but you can get a small furnace to move that much air. Carrier Model #58MVP040-F-1-14
#58MVP060-F-1-14

Just an observation

Dave in NJ

[BaldLoonie]

I stand corrected and if my worn out memory holds, will remember that

[steve cornell]

"Second: By the sound of it...you arent going to seriously take anyone's advice anyway. You are just looking for someone to agree with your ideas"


?????????? sorry if you think I'm just waisting bandwith here but I have been reading this forum for months and thought I would ask for an "expert" opinion, I have had several local "experts" give me quotes and these guys are so good all they have to do is walk in the house and ask "how many sq ft you got" and they know exactaly what size hvac I need.

Again thanks for the replies, I'll just continue reading and hopefully learn more.

[jrbenny]

I'm in the research phase of building a home, and I'm curious about your decision. Why you aren't putting radiant floor heat in the entire first floor?

I'm looking at a 1200 to 1800 SF ranch with walkout basement. My intentions are a 90+ boiler and in-floor radiant on both levels. I don't plan to use a gypsum floor, but rather a reflector under the pipe for the main floor. This will keep the cost down somewhat.

My air conditioning will be a two-stage a/c with air handler. The duct work will be in the attic for ceiling registers since it will be cooling only.

Anyhow, why the decision for a gas furnace instead of complete radiant heat? Definitely a sacrifice in comfort.

[steve cornell]

I had originally planned to install radiant heat in the entire house but since I'm using several different floor coverings which would require different temps. and installation methods and since I'm going to have to install ductwork for the A/C anyway it is much less money to go with F\A.

[jrbenny]

That makes sense. The multiple floor coverings do pose a problem when it comes to the design requirements of radiant heat.

As for your original question, I'd stick with the gas furnace. Most residential air handlers aren't designed to handle the static pressure drop of a hot water coil.

However, as a caution, you indicate that you plan to use a water heater to do the radiant. As BL noted, water heaters aren't approved for radiant applications. If you've found one that is approved, please let us know. Most of us are eager to learn new information.

[rich pickering]

Water heaters have an afue of about 40%. Boilers start at 80%. No brainer there.
Are you going to live in this house long? Check out tekmarcontrols.com and look at the tn4 system. Multiple temps for heating, along with hrv and cooling control all in one package. If you are going to the expense of radiant, why not control it properly.

[sadlier]

I would go with the gas furnace. The water coil and controls will likely be more problematic than a gas furnace. However the complete house should be taken into consideration, such as the venting of the furnace, the efficiency of the boiler, etc.

[simpleman]

All tho we hear you when you say three or more mixing station sound overprice we still don't understand why would you mix force air and radiant.

Just puts your thinking cap on just a second and wonder how
radiant and force air will ever be compatible.

If the house is only seeing a 40.000 btu lost..then there is
no reason why panel rad or basboard would not match the infloor more closely in the way it reject its heat.

Look into the term Mean Radiant Temperature and then make
your mind up to rather you still would not be better off as
Jr said with radiant thru out.

Lots of option with H20...think wall panels as well.


If I may add...everytime we have done radiant and forceair
together..the customer and myself were not happy with the results.

[Edited by simpleman on 12-04-2005 at 06:17 AM]

[steve cornell]

Thanks again for the replies!!!

You have me thinking, as I said my original plans were for radiant heat throughout and I could go with baseboards instead of infloor (which at this point would be "under floor") for the carpeted and hardwood areas.
I guess what really swayed me away from all radiant was A/C, here is a link to my website with pictures of the home under construction http://www.rtol.net/scornell/newhome.htm
I have plenty of room in the attic for an air handler, any suggestions on the proper way to cool this home if I do go all radiant?

[beenthere]

Not sure what you mean by proper way to cool.

Do you mean zoned?

[johnsp]

Are your interior walls all done? If you want a zoned AC system you have do the ductwork first before walls are done to bring duct work down to 1st flr and basement. Else 2 AC systems will be needed.

You seem to have a big investment in radiant already, and should look to get a high efficency modulating and condensing boiler. If your house is well insulated, put extra baseboard in so you can run the whole system at a lower temp. Get a reverse indirect WH like ErgoMax, Turbomax that can also act as a buffer tank for your heating system.