replacing 2 furnaces with 1 boiler and 2 air handlers

Wayco Wayne_2

I am doing this more and more. I am installing Trane high efficiency Heat Pumps and installing hot water coils heated by a boiler as back up heat. It is important to locate the hot water coils downstream of the evaporator coil so the heat pump can continue to operate and save money, even when being backed up by the boiler. In my area electricity prices are more stable than the rising fossel fuels, and heat pumps are more efficient operating price wise. However heat pumps lose comfort when the outside temps go below the balance point, so that's when the boiler back up turns on. I'm doing the same to my house and will be installing a Taco 00 variable speed circulator that will vary it's speed to maintain a certain supply duct temperature, so as the Heat Pump loses it capacity due to colder outside temps the circulator will maintain the comfort of warm air. I tell customers it's my hvac version of a hybrid, elec and fossel fuel combined. The old name for it is dual fuel. :) WW

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Bill T_2

General HVAC question

I now have 1 30 gallon oil fired water heater and 2 oil furnaces, each 105,000 btu's. One for each floor of my house. With these units I need 3 service contracts PLUS 2 contracts for the a/c units. The annual service contracts are killing me. I want to replace them all with one boiler for domestic hot water and 2 air handlers for heat and a/c. My reasoning is I would only have one burner to maintain, and this system would give me the option of adding hydronic zones for radient heat under hard floors if I wanted to later. Does this make sense?

Brad White_67

Yes it does. Done all the time.

Because of the disparate loads (domestic as one and air heating in two big chunks) get a staged pair (and if gas-fired) modulating boiler which can rise to the occassion but coast when average weather occurs.

There is another thread on the oil fired Pinnacle boiler just out in an 85 MBH capacity. If you are limited to oil this may be worth looking into.

With a load that size (and assuming a proper heat loss was conducted!) you may consider two or more oil boilers with staged firing.

These could be 50%-50% each or 67% each depending on your weather and heating profile.

Key is to set it up for domestic HW priority.

More cost up-front, but I would guess that one boiler will take care of about half your hours of heating alone and the other will fill in on cold snaps. You would also have some redundancy.

With hydronic air handlers, see if you can get the coils selected to accept 140*F or lower water temperatures so that you stay in condensing (if gas is available) or at least use P/S piping in order to protect the boiler but enjoy the efficiencies of lower temperature supply water.

Bill T_2

Brad. Thank you for your reply. I'm not going to do this job myself but I was looking for some advice to be an informed buyer. Now I know what I'm looking for at least. Hydronic air handlers. Thanks again.

Bill