What to do with old hydronic air handler?

clueless_in_chicago

Hi all,

I bought my first house a few months ago, and it has a peculiar setup, from what I can tell. There is a ~30 year old downflow air handler with a heating coil fed by my hot water heater in an open loop configuration. The heating coil has significant corrosion on it, and we expected we would need to replace that. However, I think given its age, we need to replace the whole air handler, which also mean replacing the cooling system as well.

I have one quote to install another hydronic unit, one quote for an electric furnace, and one quote to do a gas furnace. The hydronic and gas systems are roughly the same cost and the electric system is maybe 30% less, though hydronic option will take 10 weeks to arrive.

I feel like the hydronic system should be cheaper than it is, as a more readily available hydronic air handler must be an option, but I can't find another HVAC specialist who does that.

In the event that I can't find a cheaper hydronic system, which route should I take? The house is insulated well (2x6 walls), if that matters.

delta T

My .02:

The higher cost of running the electric furnace will likely mean that unit is more expensive in the long run. I would say (as much as I hate to, being a hydronics guy) that a gas furnace (preferably a condensing model) is probably your best bet. I am not a fan of using water heaters as a space heating source unless it is actually designed for it (some are, most aren't) and then only grudgingly. Tank style water heaters are not terribly efficient, a new furnace will be more efficient.

You need to factor into your cost equation the cost of the water heater as well as the hydronic coil as unless the water heater is designed for space heating, it likely has a shortened life and it will need to be replaced soon enough as well.

clueless_in_chicago

Thanks for that, Delta.

If I wanted to keep hydronics, what would you recommend? And are there good options for a down flow system that can add an A coil for cooling?

I may go for the furnace, but I perceive the hydronic system to be more efficient and that makes me biased towards preserving it.

SWEI

What are your gas & electricity costs like?

clueless_in_chicago

The house was being completely renovated and we only moved in a couple weeks ago, so I can't give you a representative monthly cost.

SWEI

What are the rates for gas (per therm) and electricity (per kWH) there?

clueless_in_chicago

I don't know (my wife pays the bills), but I have been told by a coworker that electricty would cost 3-4x as much. I'm not sure of the context of that (e.g. rates vs effective heating bills), but seems straightforward enough to not entertain an electric furnace.

SWEI

A modern VRF heatpump might be another option. It will consume about 1/3rd (possibly less, depends on the specific unit and your climate) of what a resistance heater will. Bonus: A/C comes for free.

For either option, a truly qualified contractor is critical. A heat loss calc and an evaluation of your existing ductwork are required for proper sizing. Improper sizing will:

• Cost more to purchase
  
• Cost more to operate
  
• Have a shorter life
  
• Deliver less comfort
  

clueless_in_chicago

I have had a couple solid quotes come in accounting for duct sizing and the like to figure out the right equipment, so I feel ok there.

I certainly don't know much about the merits of heat pump outside of some quick googling following your suggestion, SWEI. Is there anything about my situation that prompted that?

FWIW, I'm in the Chicago area, so winters are cold and summers are fairly hot.

SWEI

The prompt was the ratio of electricity cost to gas cost. Heatpumps multiply the electricity they consume by a factor (ranging from about two to about seven) as they do their thing. At 3-4X you're close to a trade-off on net cost of heatpump versus NG. Modern inverter-driven compressors produce meaningful output in ambient temps as low as -15°F, and are quite efficient. COP (that multiplier) on a Fujitsu we recently installed is 3.4 at 50°F and only falls to 2.5X at 5°F. I'd say 3X is a good average number for a reasonably cold climate. The manufacturers have modeling programs that can estimate your monthly and annual electricity use based on detailed climate data.

Every region is different. Electricity here runs 8-9X what NG does, and ~1.3X what LPG does. Don't just look at the price listed on the bill. You need to subtract the fixed costs (monthly service, customer, or meter fee) and then divide the remaining number by the kWH used during the period. Rates may also vary by season, so be sure you pick a bill from a winter month.

Snowmelt

I have a suggestion a Bradford white with side loops and a comfort air air handler

John Mills_5

Your average water heater is not very efficient. So if you stay hydro air, you probably won't note a change in gas bills. Going with an 80% gas furnace would likely be a decent improvement and a small 96% furnace even more. As they've said, likely straight electric would be really steep in operating cost and could require a larger main panel.

High end heat pump as mentioned would cost you a bundle. Have your nitro tablet and be sitting down if you get a quote on one of them

ChrisJ

If I may ask the pros,

What's the point in hydro air over a standard gas furnace?

clueless_in_chicago

I think it makes the most sense to go with a gas furnace, given the lead time for the hydronic unit and the likelihood of limited service options down the road. My current water heater is supposed to be good (Bradford White), but the guy who quoted me that system agreed with Snowmelt that a separate loop is recommended for heating.

I found a good HVAC guy who did the heating and cooling calcs for a gas system, so I will go with him. He quoted a few configurations, all with variable speed fans, but both 1 and 2 stage condensers and furnaces.

Are 2-stage units worth it for comfort over a 1-stage with a variable speed fan? My HVAC guy did say that there shouldn't be any energy savings, it's strictly about comfort/noise. I know a 2-stage is going to have less temp swings than a 1-stage, but i don't understand how different it will be with the variable speed fan.

SWEI

A two stage will provide increased comfort, but proper sizing becomes even more critical. A couple years ago we replaced an 80k (80% induced draft) furnace for a customer. The 42k (96% two-stage variable speed) model dictated by my calcs was on the edge but I didn't know enough about the existing ductwork to be 100% confident with that choice so I let the customer talk me into using the 56k model instead. After two winters of use, the furnace reports that it ran less than six hours on high fire.

clueless_in_chicago

Thanks for that. I have further questions, but I will start a new post instead.